Friday 5 December 2014

Mono vs Polycrystalline Solar cells - Myths Busted

Customers often ask what's the difference, but the old certainties have gone. 

Monocrystalline have missing corners, polycrystalline cells are square : Myth

Monocrystalline solar cells are cut from a large single crystal of silicon. The process by which this crystal is grown is remarkable. It is drawn from a molten crucible of liquid silicon by dipping in a 'seed' crystal and then slowly pulling this away from the liquid surface and rotating it.  By carefully controlling the temperature gradient in the crucible and the speed of withdrawal it is possible to create a solidified single crystal with the same atomic orientation as the seed.

If this cylindrical crystal were sliced to produce silicon wafers, they would be round and this would leave gaps when you tried to assemble them together into a solar panel.  So the cylinder is first cut along its length on four sides to make its shape closer to a square in cross-section.

There's a compromise here. The more you slice off, the closer to a square shape you get, and the more working area you can squeeze into your monocrystalline PV panel. The less you slice off, the less material you waste and the cheaper are the cells to manufacture.  The compromise that most manufacturers have reached is to make a shape that was a square with rounded corners (pseudo-square).

By contrast, a polycrystalline silicon wafer is made by melting the silicon feed stock, pouring it into a cube shaped mould and letting it cool and solidify.  The resulting block of silicon is sliced into pillars and these are in turn sliced into perfectly square cells.

So one difference between mono and poly is the characteristic shape of each; Poly are square and mono have missing corners.

Not any more!

The trimmings from cutting and slicing the silicon are no longer wasted; they are re-cycled as a material input for polycrystalline cell production. Some manufacturers now offer mono crystalline panels with full square cells.

Monocrystalline cells have an even black colour, polycrystalline are patterned and blue: Myth

When the polycrystalline ingots solidify in their mould, crystals start to form in many, many different places (nucleation sites) and grow until they meet up with other crystals.  The orientation of the atomic structure in each crystal is random and is different from its neighbours. When you slice though the ingot to make the wafer this creates a characteristic pattern, a kind of metal flake effect, on the surface of the solar cell because each crystal reflects the light differently. The cells also have a bluish colour. By contrast, mono crystalline cells have a homogeneous atomic structure throughout and have an even black colour.

Not any more!

High performance solar cells are now treated during processing to create pyramidal micro structures on the surface which improves light absorption.  Anti-reflective coatings are added to reduce light reflection from the surface. Both polycrystalline and monocrystalline cells can be made to look matt black with an even colour.

Monocrystalline panels are more efficient : True - well, sort of

The boundaries between the crystals in a polycrystalline cell (grain boundaries) can impede the flow of electricity, so mono crystalline cells (which have no grain boundaries) have always had higher efficiency. However, polycrystalline  cells have been closing the gap in recent years and the point has  just about been reached where the additional active surface area from the square cell shape in a polycrystalline panel makes up for the lower efficiency in the cell itself.

Check out this table.

It shows the product range from one of the world’s largest manufacturers.  Power is given in Watt-peak (Wp), the power output under standard test conditions. 

If you compare the standard mono and poly products (code 6/60 models), you can see the range of peak power output runs from 250 to 270Wp for the mono panel and from 245 to 265Wp  for the poly panel.  The difference is 5Wp, or 2% less power for the polycrystalline.

Monocrystalline/Polycrystalline  panels work better in low light conditions : No evidence

I have read many claims that one type of panel works better than the other in low light conditions, and writers on other websites seem to be evenly split in whether it is monocrystalline or polycrystalline that is best (presumably depending on which they sell).

I have been unable to find evidence to support these claims (in either direction…).

Until I see some evidence, I’m going to mark this one down as a myth!  Please let me know in the comments below if you know about this.

Monocrystalline panels have better high temperature performance : True – though marginal

Looking again at the table, the right hand column shows the Power Temperature Coefficient.  This is the rate at which the panel power output falls as its temperature rises.

Polycrystalline panels do indeed lose their power output more quickly, by about 0.02% more per degree C.  But what does this mean in practice? 

If, for example, a Monocrystalline solar panel were operating at 70C on a hot and sunny day, it would be producing 0.41 x (70-20) = 20.5% less power than is measured under standard test conditions (20C).  By contrast a polycrystalline solar panel could be producing 0.43 x (70-20) = 21.5% less power.

All other things being equal, polycrystalline panels would produce 1% less power at the elevated temperature.  But that is a very different thing from saying it would produce 1% less energy over a year of operation.  It’s not hot and sunny all day every day; in fact conditions to produce a 70C operating temperature are rare.  The energy penalty from choosing polycrystalline solar panels over monocrystalline would depend on climate, but will be far less than 1%.   Although there would be a penalty, it’s pretty marginal.

Polycrystalline panels are cheaper, monocrystalline are more expensive  : True, on average

The argument often goes that because the process of producing monocrystalline cells is more complex and involves more wasted material, they’re more expensive to make.

However, just because something is more expensive to make, doesn’t make it worth more to the customer.  The reason that monocrystalline panels command a price premium is that more people prefer the way they look and the panels have a higher power.  Having a higher power panel means you save money on other costs like racking and fixings for the same total energy output.  It also means that you can squeeze more energy out of situations where the area to place the panels is limited or expensive.

The PHOTON module price index report for November 2014 has average spot market prices for solar panels in Europe as follows.  (Prices are always given per watt-peak, Wp, so you can compare based on the power output).

Monocrystalline solar panels   0.65 EUR/Wp           (Range 0.48 – 0.95)
Polycrystalline solar panels     0.55 EUR/Wp           (Range 0.40 – 0.82)

So yes, on average monocrystalline solar panels are 18% more expensive on a per-watt basis, but the range of prices show that it’s perfectly possible to buy polycrystalline panels at the higher end of the market for a much higher price than the monocrystalline panels at the lower end of the market.


The old certainties are disappearing.  At the high end of the market, monocrystalline and polycrystalline solar panels are becoming more and more alike in aesthetics and performance.  If this trend continues, with black polycrystalline cells and square monocrystalline cells of similar performance, then average prices will converge too.

In mature solar markets, the domestic rooftop market starts to demand good looking solar panels, and has settled on solar panels with black cells and black frames with improved aesthetics.  For this market, your choice of solar panel will be far more about choosing a quality brand that you trust than worrying about whether those panels followed a polycrystalline or monocrystalline manufacturing route.

Sunday 9 November 2014

Solar for Combi Boilers

How to combine solar water heating with a combi boiler

A combi boiler provides central heating and hot water.  Hot water is prepared instantaneously
and on demand as cold water flows through a heat exchanger in the boiler on its way to the outlets

Combination (combi) boilers that provide hot water on demand have become more and more prevalent in the UK.  Data from HHIC shows that 77% of all new boilers sold in the UK in the last 12 months were combis. According to the English Housing Survey 2012, 49% of all homes now have a combi boiler.

Housing developers love combis because they don't need to give up valuable space to a hot water cylinder in small (sorry, "executive starter") homes.  In addition, eliminating the cylinder means that the overall complexity and part count in the heating system is reduced which improves reliability and lowers costs.

Manufacturers of hot water cylinders argue that the flow rates that combi boilers can provide can be inadequate, especially in multi-bathroom homes, but judging by the combi’s dominance of new installations their reputation for producing only a trickle of hot water may now be undeserved.

Challenges of Combining Combi Boilers with Solar Heating

Given that combi boilers are so prevalent, you'd think that the heating industry would have sorted out how to use solar hot water with them.  However, until very recently there wasn't a good answer to the question of how to combine solar with combi boilers.  This is because combining the two raises some technical challenges.

Solar energy arrives over the course of the day, whereas domestic hot water use is intermittent and concentrated in the morning and evening.   Consequently solar heated water must be saved up for later use in a hot water cylinder or heat store.  Since the amount of solar energy that is available varies from day to day and through the year, it's also necessary to be able to bring the solar heated water to a hot enough temperature with the boiler on those days when the light levels are not high enough.

So one approach is to re-configure the combi boiler to behave like a conventional boiler.  A new heating 'zone' is added to the central heating system with separate timer control and controlled from a thermostat on the cylinder.

Solar energy (either from a solar thermal system or a PV array and excess energy diverter switch) is added to this cylinder and the cylinder thermostat tells the boiler when it's needed for a 'top up'.

(1) Reconfigure the heating system to use the combi boiler with a hot water cylinder

This approach to adding solar to a combi boiler can be difficult to implement in practice.  There's often nowhere to put the cylinder (since the house has a combi boiler).  Even when you can find a space for the cylinder, the intervention to reconfigure the heating system can be significant.

A second approach is to send solar pre-heated water to the combi boiler.  A hot water cylinder is still needed to accumulate the solar heat, but it can be a bit smaller because it doesn't need a separate boiler heated volume inside.

(2) Sending solar pre-heated water to the combi boiler
There are two issues that need to be addressed when taking this approach.

1. Combi Boiler Inlet Temperature

Some makes or models of combi boiler may not be able to accept water above a certain temperature, either because there is insufficient control of the flame or due to materials selection of components on the cold water inlet side.

A combi boiler that cannot regulate the flame down sufficiently would produce too-hot water when the inlet water arrives above a certain temperature.  This causes a safety cut out switch to activate, killing the flame.  The boiler would cycle on and off producing too-hot and then too-cool water.  Operating this way is not good for the boiler lifetime.

Some boilers have plastic components on the cold water inlet side and some of these will not be suitable for water above a certain temperature.  

A component called a combi-diverter valve is available to work with boilers that have such limitations.  One product consists of three thermostatic valves and produces the following logic:

  • Inlet temperature >45C, add cold water to 45C, by-pass boiler straight to taps
  • Inlet temperature 27C - 45C, add cold water to reduce to 27C, pass through boiler
  • Inlet temperature <27C, pass straight through boiler

It may seem crazy to produce solar heated water and add cold water to it only to heat it up again in the boiler (for the middle temperature range), but bear in mind that doing so means you're using less of the solar heated water and leaves more heat in the solar store for later use.

The combi diverter valve ensures that the hottest inlet temperature the boiler will see is 27C, so this can be a way to make solar preheated water work with any combi boiler, so long as you can check that this temperature is OK for the model in question.

Unfortunately, boiler manufacturers do not routinely put the maximum inlet temperature of their products on their data sheets, at least in the UK.  My own experience of calling the 'help' desks of the boiler manufacturers is that it's often a struggle to get a definitive (or consistent) answer to this question.  If pushed, the safest (and default) answer is to say that the boiler should not have water above 'ambient' as an input, push again and you will get told 20C max - after all why would the manufacturer put themselves out on a limb for this?

Thankfully, an initiative by the Solar Trade Association (STA) and the Hot Water and Heating Industry Council (HHIC) has resulted in an online database of combi boiler inlet temperatures.  This list is new, and currently not comprehensive enough (special mention to Ideal for their derisory contribution - boo!).  I hope that over time more manufacturers will see the benefits of publishing this information and join in, and that those who have published will add data on more of their older models.

The STA and HHIC are to be congratulated on this initiative as it removes a significant impediment to the deployment of solar water heating.

2. Legionella Control

Legionella is a bacterium that occurs naturally in drinking water.  It is present at very low levels in drinking water but can multiply if that water is held at warm temperatures (20C to 45C).  If droplets of water containing high levels of the bacterium are inhaled it can cause Legionnaire's disease.  People with suppressed immune systems, for example the ill or the elderly, are most at risk.

Legionella bacteria can be de-activated by heating the water to above 50C, with the time taken to disinfect the water falling rapidly as the temperature increases above this level. 

A combi-boiler takes a flow of cold water, raises it to a set temperature of around 55C and then it quickly passes on to the hot water outlet.  There is very limited risk of Legionella because the water has not spent any time at warm temperatures before passing through the boiler.

Legionella risk is normally controlled in a standard hot water cylinder by setting up the controls to heat the water to 60C at least once a day (called pasteurisation), to deactivate any bacteria that could have multiplied in warm water.

Because solar energy is variable with the weather and seasons, it is not possible to guarantee that deactivation temperatures are reached every day in a cylinder heated only with solar.  Indeed, at certain times of the year a cylinder heated only with solar could spend periods at the warm temperatures in which the bacteria grow.

A twin coil solar cylinder will normally adequately control Legionella risk if the boiler heated section of the cylinder is heated daily to 60C for 1 hour, and the water is resident in the boiler heated section for 24 hours (which happens if the boiler heated volume is greater than the daily hot water use).

Putting a solar heated cylinder upstream of a combi boiler introduces a risk that the water feeding the boiler could have spent time at temperatures that allows the Legionella to multiply.  A paper by the Water Regulations Advisory Scheme (WRAS) confirms that because the combi boiler will only heat the water passing through for a short period of time, it cannot be relied upon to deactivate any Legionella that may have multiplied while the water was resident in a solar heated cylinder.

If the combi boiler cannot be relied upon to control Legionella risk, then alternative means are necessary.

For a conventional cylinder, where the water in the cylinder goes to the combi boiler, the most common approach would be a thermal pasteurisation of the water.  In practice this would mean  fitting an immersion heater to the cylinder and running it for a couple of hours each night when water is unlikely to be taken from the cylinder during the pasteurisation.

Overnight pasteurisation is a problem for solar energy for two reasons:

(1) The solar cylinder then starts the day hot.  If there isn't a significant water use in the morning, then the cylinder's capacity to take in solar heat is greatly diminished, reducing yields.
(2) The electricity used overnight to raise the cylinder to 60C is high in carbon emissions and expensive - offsetting some of the benefits of solar.

An alternative Legionella control strategy, used in products such as Viridian Solar's Pod,  is shown in (b) and (c) in the diagram below - here the volume of water in the solar cylinder is static, and instead fresh cold water is heated as it flows through a heat exchanger.  The problem of water sitting at warm temperatures for extended periods is completely avoided, and thermal pasteurisation is unlikely to be necessary.

If the stored water passes through the combi boiler, then additional immersion heating
is likely to be required for control of Legionella risk

Installing solar water heating with combi boilers has been left in the 'too hard' box by the heating industry for too long.  It is my hope that the emergence of a new class of products to make this easier in combination with greater information from the boiler manufacturers will open up solar water heating to the benefit of even more people.

Thursday 18 September 2014

What Has the MCS Ever Done for Us?

How to fix the Microgeneration Certification Scheme (MCS)

You pay your registration fees each year. You research each and every change to the regulations and make sure to adjust your paperwork, your working practices and the products you offer to keep in line with the rules. You engage with the annual audit of your work and put right anything the auditor finds. You go further and make changes to your processes to ensure these issues never recur. 

You are, in short, an ideal MCS installation company. The kind that the folks sitting in London running the scheme like to think that they have produced. 

The problem is that there's another installation company across town. They also have an MCS accreditation, after all it's needed for customers to access government incentive schemes. Their workmanship is shoddy, they don’t seem to be in it for the long haul and cut corners to make a quicker buck. They have accumulated a string of non-conformances on their paperwork from the annual MCS inspections but nothing ever happens, so they don't waste their time making changes. The inspector comes once a year, takes a cursory look at an installation of the company's own choosing (inspecting the roof work from the ground). So long as the company has one half-decent installation to show the inspector, they're good for another year.  This company can undercut its more diligent neighbour because it doesn't have the expense of bothering with the requirements of the MCS scheme or spending the time and care to put in the "high quality installations" the scheme claims to ensure. 

Back among the glass towers of London where industry representatives meet to oversee the MCS this company simply doesn't exist, or is at worst a 'bad apple', an isolated case. 

Unfortunately, the second company and their like are a very real in the minds of people who work for companies like the first and have to compete with them every single day of the year.  I have heard numerous stories from colleagues in the industry about companies "getting away with it", about complaints to MCS not adequately investigated and annual audits of installations that amount to little more than checking there really is a solar installation on the roof.  

This, in short, is the crisis of confidence that the MCS must recognise and urgently work to fix.  If scheme officials knows that there isn't a problem, that it really is just a very few bad apples then they should publish the evidence that has led them to reach this conclusion thereby reassuring an increasingly sceptical industry. 

Many people believe that way the scheme is managed has had the perverse effect of creating ’Natural Selection’ for the least desirable traits in registered companies.  Without meaningful audits of installations and a credible threat of expulsion from the scheme, the scheme penalises the diligent by imposing higher costs, handing a competitive advantage to those that join the scheme but don't bother trying to meet the standards. 

It is a great frustration for those of us who have worked  in the MCS technology Working Groups to hear such views.  If the enforcement really is this poor, why bother writing rules?  If the only companies that are applying the standards are those that would have worked to a good standard anyway then what’s the point of all those hours donated free of charge to the scheme.

Unless MCS changes

As I revealed in an earlier blog, the MCS is sitting on a cash pile of £6.6m, growing at the rate of £1.3m last year. That kind of money would pay for a lot of surprise audits. Perhaps industry would even be willing to pay slightly higher fees and put up with more intrusive audits if proper enforcement levelled the playing field and drove the bad apples out of the industry.

My colleague at the Solar Trade Association (STA), Chris Roberts has written a draft White Paper: 'Is the MCS Fulfilling its Potential?' to stimulate debate and comment from STA members on the MCS. Having collectively contributed more than 90% of the scheme income the views of the solar industry deserves to be heard, and I urge everyone in the industry to join the debate by reading the paper and feeding in your ideas and evidence to Chris. 

Monday 15 September 2014

The MCS Hoard

So here's an interesting thing about the Microgeneration Certification Scheme  (MCS)

The MCS is supposed to be self-funding, with fees applied on a 'per-registration' basis with these fees currently set at £15 per registration.  MCS installation companies also pay £110 annual fee, collected through the Certifying Body that accredits the installer.

Gemserv administers the scheme, and its latest annual report show that MCS has a surplus of £6.6m at the end of March 2014.

Indeed, the surplus grew in the most recent financial year by £1.3m, so this is not purely an artefact of the dash for PV of late 2011.

Figures for the number of installations the registered on the scheme database are available from the MCS website and show this:

So there were 122 thousand installations in the same period that the scheme ran a £1.3m surplus, corresponding to £10.65 of surplus per installation.
All this begs the question, why?  Why is the scheme building up such a large surplus, when its terms of reference are to be no more than self-financing?  What's all this money for?  How does MCS anticipate spending it within its terms of reference?
I'm personally not against accumulating some money from each installation if it's spent for the good of the whole industry, but just saving it up for a rainy day?  What use is that to anyone?
How would you spend it if you were in charge of the MCS?  Would you just lower the registration fee, or would you be happy to keep paying the extra, were the money to be spent on something useful.  Write in the comments below...

Saturday 23 August 2014

Is RHI More Trouble than it’s Worth?

To get support from the domestic Renewable Heat Incentive (RHI), there are some hoops it’s necessary to go through, but how much do these add to the cost of a solar thermal installation?

If you install a solar thermal system in the UK you can receive financial help from the government’s Domestic Renewable Heat Incentive (RHI).  RHI payments vary depending on factors such as the size of the solar panels, their location and orientation and especially the hot water demand of the house (which is taken from the number of people who live there).  It can be worth between £1,500 and £3,500, paid out over the first seven years.  In addition to the payments householders also benefit from savings on energy bills, the value of which are much higher the RHI payments over the long life of the solar heating system.

In order to qualify for the RHI, the solar panels must be of a certain quality - achieving accreditation with the Microgeneration Certification Scheme (MCS) or SolarKeymark, the installation company must also be MCS accredited and the household needs to demonstrate that it has taken straightforward energy efficiency measures such as insulating the loft and filling cavity walls (where there are cavity walls to fill).  The way that this last requirement is proven is to produce a Green Deal Advice Report that doesn’t show loft insulation or cavity wall insulation as a recommended measure.

In recent weeks it has come to light that some solar installation companies are advising customers that there’s so much cost and bureaucracy associated with installing a solar thermal system that qualifies for the domestic RHI that they are better off avoiding the scheme.

Let’s have a look at whether this argument stacks up.

Extra Costs for the Installation

Let’s assume that the installation is of identical quality both with and without the RHI.  The installer cuts no corners on the installation standard and that the equipment that is used is registered with the MCS or Solarkeymark.

The installer must log the installation onto the online MCS database for the customer to be able to claim the RHI. There is a charge from MCS of £15 to do this.  Let’s add £20 to that to pay for the time for someone to fill out the online forms.  Total £35

In addition, the household needs to pay a Green Deal Assessor to visit and produce the Green Deal report.  You don’t need to undertake any of the recommended measures unless they include loft insulation or cavity wall insulation.  The report costs between £150 and £250. 

So the total Variable Costs (cost per installation) are between £185 and £285

Annual Costs for the Installer

For an installer to be MCS accredited, there are annual fees to pay and administrative time required.  Let’s take a look at the costs for a smaller company, as it is generally thought that the burden is highest for these.

The solar installer must pay a fee to join the scheme and be audited each year.  For a solar installer with less than 10 employees the MCS annual registration and audit fee comes in at around £470 (see NAPIT fee sheet). 

In addition there is an MCS requirement that the solar installation company must be a member of an approved renewable energy consumer protection code.  Joining RECC depends on the number of staff, but for 1-6 employees it’s £250/year

Let’s assume the company wouldn’t operate a formal quality system if it wasn’t going to be MCS accredited and add £1,000 of admin time to these figures to pay an office administrator to maintain the paperwork that the scheme requires each year and make sure the document handover packs and quotes remain compliant with the scheme.

Both the fees and overhead costs fall (per technology) if the company installs other MCS renewable energy technologies as well as solar thermal, but let’s assume it doesn’t.

For this small company then, the total annual Fixed Costs of maintaining an MCS solar installer registration is £1,720.   

Total Cost

The total additional cost per installation of being RHI compliant is found by dividing the Fixed Cost by the number of installations the company does each year and adding this to the Variable Cost per installation.

This is where the costs of accreditation can start to look very high – it depends enormously on how many installations the installer does each year.  See the table below.

How the admin costs of an RHI compliant solar system varies with the number of installations
the installation company does each year

If the installer does only one or two solar installations a year then, yes the costs of RHI compliance is high compared to the benefit in claiming the RHI, but even at only one system a month the extra costs start to become really quite small compared to the RHI payments. 

The more installations that the company can do each year, the more the costs trends down towards the cost of the Green Deal Report.   Nor will every customer see this as a valueless piece of paper; some may value the guidance on further measures they could take to improve their energy efficiency.

The problem for the RHI is that until the scheme starts to drive demand for a reasonable number of installations, then for small companies that perhaps combine general plumbing with a very occasional solar installation the barrier costs of being MCS registered don’t look worthwhile. 

An excellent time to encourage a customer to consider solar heating is at the same time that a hot water cylinder is being replaced, but the plumbing company standing in front of the customer won’t offer this option if it isn’t MCS registered  If they do offer solar they might encourage the customer to ignore the RHI.  This is, of course, a classic chicken/egg situation.  Unless this plumbing company starts to offer more customers solar under the RHI, they’ll never see enough demand to justify MCS accreditation.

It would be good if there was a way to encourage this plumber to promote solar thermal to customers, perhaps in cooperation with a local accredited solar installer.  For any installation company that’s doing more than a handful of solar thermal installations each year, the cost of the RHI requirements are small relative to the RHI payments.

However this is not to say that MCS couldn’t do something to reduce the burden on smaller installers to meet the ever-increasing demands of the scheme.

Friday 22 August 2014

May Cause Side Effects

Solar Anti-dumping's Unforeseen Consequences

The ineffective fudge that came too late for solar module manufacturers is now poised to kill off the European inverter manufacturing industry

As predicted by many, the antidumping measures on Chinese solar modules brought in by the European Union have proved rather too easily circumnavigated.  I've heard of a number of approaches to evasion since the minimum price agreement was reached, but the most recent I've heard about should have Brussels Eurocrats in a cold sweat.

A Flag of Convenience?

I guess the most obvious sign of AD avoidance is the flood of Malaysian solar panels that are now prevalent at the low end of the market.  Many, including myself, strongly suspect that there's far more Malaysian modules being sold than there is manufacturing capacity in Malaysia. The obvious conclusion is that product is being trans-shipped from China via Malaysia and arrives in Europe with  paperwork to prove it's not of Chinese origin.

Some companies try harder than others to maintain the pretence that they have a factory in Malaysia. One company that approached us has gone to the trouble of making a Malaysian website (suspiciously similar to a Chinese manufacturer's and with all the same photos). It was only when we asked to visit the Malaysian factory that we were told that it wasn't company policy to allow visits, and that it was a 'quiet time' anyway so there wasn't anything to see.

Others are less circumspect about what they're doing. Take a look at this email I received offering to illegally rebadge Chinese modules as Malaysian with "all paperwork":

Dear value customer,

Nice to meet you!

Yes, for said product, here we would like to provide the professional trading solution to avoid the high anti-dumping duty that imports from China.

The routine for the containers will be as:

CHINA ---> MALAYSIA(change the containers in the free zone or inland warehouse) ----> England

Document issued details:
a. Malaysia solar panels factory CO
b. Master bill of loading under Malaysia factory
c. Malaysia factory packing list
d. Malaysia factory invoice

And the cost is much favor, it will save a lot of the anti- dumping tax:
1. Ocean freight from China port to Port Klang (west): to be advised
2. All in fee in Malaysia:
a. Include all the local fee for changing containers in Malaysia;
b. Include the above Malaysia factory document fee;
3. Ocean freight from Port Klang to England: to be advised

If you are intrested in such trading solution, kindly pls feel free to contact us anytime.
We have many successful cases to England for this item and other items.

Tks a lot.

Marketing Support

Another ruse is for the Chinese supplier to charge you the full minimum price and then separately remit money back to you against an invoice for "Marketing Support" or "Consultancy". The first invoice less the marketing support is the true price for the modules, but the only paperwork customs and excise sees is the first invoice at the minimum price.

My company has been approached with this offer on numerous occasions.

While this clearly isn't in line with the spirit of the AD legislation, I'm also not sure whether it would be strictly illegal.  After all, what's wrong with a manufacturer offering to part fund marketing initiatives in an export market?  Perhaps we'll see a test case soon?  Then again, perhaps we won't. Having brought in the rules, we've seen little evidence that the Commission has the stomach for the hard graft of enforcement.

Inverter Cross-Subsidy

I only heard about this approach recently, but if it becomes widespread it has the potential to wreak havoc upon European inverter manufacturers.

The way it works is that a Chinese module manufacturer agrees a price below the price undertaking level with you.  It then invoices you at the price  undertaking level and transfers the difference as a payment to an inverter manufacturer up the road. This payment is obviously invisible to EU customs, which only sees the modules being bought at the right price. The inverter manufacturer then sells you a shipment of inverters at a knock-down price (but not too low to be suspicious), with the price subsidised by the 'overpayment' for the modules.

The Antidumping decision came too late for the many, many European manufacturers of modules already in liquidation after years of fierce competition from Chinese competitors, but at least the continent still has world leading inverter manufacturers.

But for how long under the current regime?  SMA is already laying off staff and issuing profit warnings to investors blaming a lessening demand for solar in Europe.   How ironic if the policy intended to protect European solar manufacturing ends up contributing to the destruction of its manufacturers of solar inverters and Chinese dominance of this product segment in addition to solar modules.

The commission should either crack on with enforcing their price undertaking agreement with gusto, or should put the whole thing out of its misery and let Europeans benefit from world pricing on PV modules.  The current situation helps no one.

Thursday 24 July 2014

Short of the Mark?

If you’re relying on a Solar Keymark wind resistance it turns out that there are large parts of the UK where you shouldn’t install

Viridian Solar has recently launched the latest version of its wind load calculator to partnered solar installers.  The calculator has been updated to take into account new guidance in the latest version of BRE digest DG 489 “Wind loads on roof –mounted photovoltaic and solar thermal systems”.

Read my blog on the changes to DG 489 here.

I thought I’d take the calculator for a test-drive, and decided to use it to try to answer the question “Is the Solar Keymark wind resistance test to 1,000 Pa adequate for the UK?”
The Keymark requires solar thermal panels to be tested for wind resistance, but historically it was a pass-fail test set at 1,000Pa (100 kg/ m2).    With the recent introduction of the new standard for solar thermal panels (ISO 9806), Keymark testing will require a pass-fail test at 2,400 Pa (putting it more in line with the level required for solar PV panels in EN61215).
However, the vast majority of solar panels currently on the Keymark and MCS database have been tested to the old standard EN12-975 at 1,000Pa.  While it is possible for the manufacturer to request that the test continues beyond the minimum, most are content to achieve the ‘gold standard’ of Keymark.

So how well does a single test to 1,000Pa cover us in the UK? 

In assessing that a structure has sufficient resistance to wind, Eurocode 1 requires you to apply a partial safety factor to the tested strength.  The safety factor you choose depends on how the solar panel fails.  For example a solar panel that has its failure in a metal component has a lower safety factor (divide by 1.1) than one where the failure is in wood (divide by 1.44).  This is to take into account the natural variability in the strength of wood and the consistency in the strength of steel. 

Since Keymark doesn’t require a test to find the failure level, there’s no way of knowing if the panel would have failed at 1,001Pa or would have gone on to 5,000Pa.  You also don’t know what the failure mode would have been.  Unless the manufacturer has tested beyond 1,000Pa the only safe assumption is to use 1,000Pa and, if they haven’t tested to confirm the failure mode, to reduce this by the highest partial safety factor of 1.44 for failure in a timber fixing.

Consequently, to be in compliance with UK Building Regulations and MCS, a panel tested to only 1,000Pa should not be used if the calculated wind pressure is higher than 694Pa, being 1,000Pa divided by 1.44.

I ran the wind calculator for the common situation of a two storey building with a duo-pitch roof at various wind speeds.  I assumed that flat plate solar panels are fixed above the roof in a position to avoid the edge-zones (which have higher wind loads), that the building location was 75m in altitude and relatively close to but not right on the sea (2-20km) and that there were no special topographical features (the building is not on a hillside).

It turns out that it’s really rather easy in the UK to achieve wind speeds that produce uplift pressures exceeding those for Keymark tested products.  The table below shows the calculated wind pressure (including partial safety factor) and the map summarises the results.

Some solar manufacturers will to tell you to just put a few extra fixings on if the winds are high.  A few moment's consideration reveal this is completely inadequate.  If you haven’t tested to failure, you cannot know that the fixings are the weakest part.  It could just as easily be the cover glass that comes away at 1,001 Pa.

The only installation that meets building regulations and therefore the requirements of the MCS installation standards is one that uses solar panels and fixing kits that have been tested to a level that exceeds the wind pressure.

It is a welcome development that the new test method in ISO9806 is to 2,400Pa, though it is regrettable that the authors of the standard did not take the opportunity to resolve other shortcomings of the wind pressure test that I have written about before.
I don't anticipate that many products will struggle to achieve this higher pressure level, after all people have been installing all over the UK for years.  The fact remains that until they’ve been re-tested to a higher wind pressure there will be many locations in the UK where the Keymark alone falls short of the mark as far as building regulations are concerned.  The responsibility is clearly with solar installers to use solar panels with a tested pressure resistance high enough for the location.

Thursday 10 July 2014

The Allowable Solutions Puppet Show

In a recent article Stephen Williams, a Lib Dem government minister at the Department of Communities and Local Government (DCLG), was reported to have protested that as far as the government's Zero Carbon Homes Policy was concerned:

"There is a view out there that we have "watered down" our ambitions, or that we are merely "puppets" of the development industry. These views are outdated and blinkered."

Unfortunately for Mr Williams, a recent consultation response published by his department seriously undermines these claims.

The Zero Carbon Hub is an independent body created by the government to help define and deliver the Zero Carbon Homes policy.  After gathering evidence and consulting with the construction industry the Hub proposed that Zero Carbon Homes policy should be broken down into three requirements for new homes and proposed levels for each:

1. A minimum level of thermal insulation (called Fabric Efficiency)
2. A maximum level of carbon dioxide emissions from the house itself (called Carbon Compliance)
3. The balance of carbon emissions to be 'offset' through carbon dioxide reducing measures paid for elsewhere (called Allowable Solutions)

Fabric efficiency means building cosy, draught-free homes, this level was set just a little beyond current (2013) building regulations.

Carbon compliance could be achieved by pushing the insulation further (towards passivhaus level), or by installing renewable energy equipment on the homes such as photovoltaic (PV) panels, solar water heating or heat pumps.

Allowable Solutions was intended to help get difficult buildings over the line, and could account for around 30% of the improvement.  It would involve the developer paying into a fund that delivered energy measures off-site (perhaps like building wind farms or energy upgrades of existing homes).  It was suggested that the price of the offsets should be set at a level that would encourage developers to achieve as much as possible through improvements to the actual homes being built.

DCLG's Allowable Solutions consultation contained a question (Question 1) asking whether the Zero Carbon Hub proposal should be taken forward, and the results were recently revealed in the consultation response.

Fully seventy percent of consultation respondents (93 responses) supported the Hub's proposal.  Of the thirty percent that did not, many argued that even higher levels of energy efficiency should be required due to advances in insulation and renewable energy technologies.

By contrast a majority of developers, (14 out of the 22 responses from developers) did not agree with the Hub's proposals and wanted lower standards of energy efficiency for new homes, and more of the carbon emissions to be deemed as 'offset' through the Allowable Solutions mechanism.

So what did DCLG decide? 

It went with the developers.  The current proposal completely drops the carbon compliance requirement and allows developers to build homes little improved over those built today. 

DCLG ignored a clear majority in the consultation and it ignored the advice of the independent organisation it had created to help it deliver this policy.

According to the Minister, it is outdated and blinkered to think him a mere "puppet" of the development industry. 

Make your own mind up.

Saturday 14 June 2014

Picking Through The Wreckage of Zero Carbon Homes

The policy that categorically does not do what it says on the tin

It all started out so well in those early years.  There was a sense of shared endeavour in the construction industry.  When, in 2006, the government announced that by 2016 all homes built in the UK would have zero net carbon emissions, no one thought it would be easy, but many in the industry were eager to rise to this inspirational challenge.

The concept was that we should stop building new homes that would only need to be upgraded later to be properly energy efficient. Building these homes fit for the future would stimulate a mass-market for energy efficiency measures and renewable energy technologies and result in tradespeople and designers developing skills that could be carried over into the upgrade of our existing stock of buildings.

Well, here we are in 2014 and how has it fared?

In the run up to the Queen’s Speech, Stephen Williams, a Liberal Democrat MP and minister at the Department of Communities and Local Government (DCLG), began briefing via the Lib Dem website that he’d ‘saved’ the Zero Carbon Homes (ZCH) policy from those nasty Tories.

From information in his article its possible to piece together how ZCH will work.  So let's peer through the smoke drifting around and have a look at the train wreck we’re left with.

It seems like all housing developers will have to build homes that are equivalent to the Code for Sustainable Homes level 4, which is only a 44% improvement on the so-called regulated carbon emissions of a 2006 home.

However, even this overstates the ‘achievement’.  As I have covered before in this blog, the definition of zero has been adjusted to include only regulated carbon emissions (those from heating and hard-wired lighting).  All energy used by plug in electrical appliances (white goods, gadgets, audio-visual) have been removed from consideration.

Add back in the average emissions from plug in electrical appliances and the picture is even less flattering.  The original vision of Zero Carbon Homes has been diluted to such an extent that the achievement of which Stephen Williams is so proud is that a home built in 2016 will be allowed to produce fully 71% of the carbon emissions of a home built in 2006.

The average energy bill for one of these ‘Zero Carbon’ homes will be similarly unimpressive.  I calculate that a 3 bed semi-detached ‘Zero Carbon’ home would have a combined energy bill of £800/year whereas one built to 2006 standards would have a combined energy bill of £1080/year.

The political sleight of hand that Mr Williams is using to justify his hyperbole was announced in the Queen’s Speech and is the creation of legislation to enable an element of ZCH called ‘Allowable Solutions’.   This could be better called ‘Buying Carbon Offsets’ because it means that instead of pushing the performance of the building itself from Code level 4 to Code level 5 (zero regulated carbon emissions), the developer can choose instead to pay into a government-managed fund.  What this fund will be used for is, as yet, undefined, but seems likely to be spent on upgrading existing buildings.

Allowable Solutions was first proposed as a means of helping more challenging homes (for example flats with limited roof area) make it over the line by allowing carbon offsetting for that difficult last little bit.  What was supposed to be the mint chocolate with the coffees has now become the main course of the meal, potentially accounting for 56% of the regulated emissions.

The circularity of this is mind-bending.  Instead of building efficient homes in the first place, we effectively collect a tax from the developer, leaving the house-buyer with largely unchanged energy bills and putting the money into a pot which may or may not at some unspecified future point be used to improve existing buildings.

The opportunities for double-counting the benefits are also clear.  It's hard to imagine ministers avoiding the temptation to take credit for both the new homes being zero carbon and for whatever measures the fund is spent on at the same time.

Furthermore, there is to be a provision for ‘small developments’ to be exempt from reaching Code 5.  Again, it is not yet clear what small means in this context, but Barbour ABI has estimated that if small means a development of 10 or more homes then around 10% of new homes would be exempted from the policy, whereas if developments of up to 50 homes were to be considered small, then this figure would be around a third of new homes.

Which Tin?

In his article, Stephen Williams says that Zero Carbon Homes “does exactly what it says on the tin”

This astonishing claim doesn’t even get close to passing the ‘reasonable person’ test.  Someone offered a home described as Zero Carbon would have a reasonable expectation that the carbon emissions from the home would be zero and energy bills would be extremely low.

After ten years of backtracking, what we’ve actually got is a policy where new homes will produce more than 70% of the emissions they started with, coupled to a carbon-tax that might apply to only 2/3 of new homes built, and energy bills for the house-holder reduced by only 30%.

This policy "does exactly what it says on the tin" only as long as the tin in question is labelled "Business as Usual for Property Developers"

DCLG has succumbed to the enticingly simple argument that a proper ZCH policy would impose higher costs on developers and slow the rate of new build, thus threatening the economic recovery. The reason this argument is bogus is that if build costs rise, then the price a property developer would be willing to pay for land will drop.  Building to higher standards simply reduces the wind-fall to the land owner.  The only time the burden of building to a higher performance falls to developers is when they have speculated that legislation will be watered down and over-paid for their land bank.

It is not clear that this “world-leading” policy even meets the wooly definition of the European Directive on the Energy Performance of Buildings that the UK must comply with by 2020.  This requires all housing to be ‘nearly zero carbon’.  It may be that this is tested in the European Commission, indeed a number of renewable energy associations are already considering just such a move.

All is not Lost

A properly designed structure for the Allowable Solutions might just get this train back on the rails.  The price per tonne of carbon should be set to encourage the use of now common on-site measures such as higher levels of thermal insulation, heat pumps, solar water heating and solar PV.

One opportunity would be to set the price per tonne in a tiered structure, with an increasing marginal cost.

Code 4 is a 44% reduction in the emissions compared to a 2006 home, leaving 56% emissions available to offset under Allowable Solutions.  What if the chunk from 44% to 72% was priced at £120 a tonne, and the chunk between 72% and 100% was priced at £30 a tonne. Developers would have a strong incentive to drive efficiency up towards the 72% level (broadly equivalent to the old 'carbon compliance' level) using improvements to the building.

A developer who built to business as usual (Code 4) and paid the entire carbon offset would have an average cost to bear of £75/tonne.  By contrast a developer that improved insulation levels or installed renewable energy on the homes to bring down emissions below 28% of 2006 levels could reduce their average cost of carbon offsets down to £30/tonne.

A policy designed like this would be responsive to a changing market. If the housing market continued to improve and government decided that landowners could bear more of the costs of the policy, then the relative width of the bands could be adjusted.

Come on Mr Williams, all is not yet lost. You've still got time to make the reality of Zero Carbon Homes match your rhetoric.

Tuesday 3 June 2014

Slow Burner - how will the Domestic RHI Take off?

How much can the first year of the Feed in Tariff tell us about uptake for the Domestic RHI

How it went for the Feed in Tariff

A number of people (including the solarblogger himself) tried to temper expectations for the domestic RHI with the argument that the Feed in Tariff (FIT) took a bit of time to get going. The logic goes that it takes time for the public to become aware, for installers to work out how to market it, and especially for housing associations to get organised. 

I thought I'd take a look at the numbers to check whether they supported this idea. 

I wanted to compare the take up of PV in domestic installations before and after the introduction of the FIT. There is a wealth of data available from the Department of Energy and Climate Change (DECC) on the levels of PV deployment  under the FIT, but much less for the years preceding it. I relied upon this report on the Low Carbon Building Programme (LCBP) to build a picture of deployment rates before the FIT. 

Under LCBP phase 1 (the domestic stream) there were 4,428 installations of PV. The average size was 2.18kWp, for a total capacity installed under the scheme of 9.7MWp. 

Since the report doesn't disclose the deployment in each period, I estimated PV deployment based on overall scheme expenditure.  I then combined this with FIT data for systems below 4kWp, most of which is likely to be domestic. 

The results are very interesting. 

When you look at the plot of the overall data, it sure does seem that all the action started in year two of the scheme. But this is a trick of exponential growth. Look at the lower plot, where I have shown the data only up to the end of year one. The first year was spectacular. 

The level of deployment grew from round 700 installations a quarter before the FIT to 11,000 a quarter at the end of the first year. Before the FIT subsidy, solar thermal systems were being installed at a rate around 10 times higher than solar PV. By the end of the first year, solar thermal had declined slightly, but solar PV installations outnumbered them by almost double. 

And so to the Domestic Renewable Heat Incentive

There are a number of reasons why the domestic Renewable Heat Incentive won't take off like the Feed in Tariff did. 

1.  The Feed in Tariff.  

When the FIT was launched it was the only show in town. The grant scheme for renewable heat was derisory by comparison. As the domestic RHI launches, people interested in investing in their homes to reduce energy bills have the choice of both FIT and (I suppose) the Green Deal. 

2.  Installation complexity. 

With the exception of solar thermal, all the domestic RHI technologies replace an existing heating system, rather than being an add-on. People will be more cautious about installing a new technology when they worry that the impact of it not working is a cold house and no hot water.

Renewable heating installations are generally more intrusive too. A heat pump may require the replacement of radiators to cope with lower heating temperatures, biomass boilers can require a lot of space. New products such as this one which simplifies the installation of solar thermal to levels approaching that for solar PV may help overcome this barrier, at least for solar thermal where there's always the backup heater. 

3. Off Grid Target Market

The domestic RHI tariff levels were intended to stimulate a market in the 20% of homes that are off the gas grid. For sure, the returns are better when heating with oil or electricity, but returns for solar thermal on gas can also be good, as this analysis has shown

4. World First

The UK feed in Tariff followed the implementation of similar schemes in other european countries. Businesses could see the rapid take up of markets that had resulted and anticipating a similar trajectory for the UK, were pumped and ready once the scheme launched. By contrast the RHI this a genuine worlds first. There's no equivalent to look at to predict uptake. The many, many false starts for the scheme also didn't help. Many installation companies I spoke to weren't even willing to spend time thinking about it until they were absolutely sure it had launched. 

5. The Feed in Tariff (again)

My final reason is perhaps the most important. The way the government managed the Feed in Tariff has led to the widespread belief that as soon as any renewable energy scheme is successful it will be ruthlessly hacked back. The shadow that the treatment of the FIT scheme casts is long and pervasive. 

For all this, the scheme offers a level of financial support beyond anything that renewable heating technologies have benefitted from before. My plea to the industry is to give it a while before judging the success or otherwise of the scheme. 

It may take time to take some time to warm up, but warm up it surely will.  

Thursday 29 May 2014

The Domestic RHI and Solar Thermal Stores

The Law of Unintended Consequences Strikes Again

The domestic RHI was structured with the intent that the complementary combination of solar thermal with other heating technologies would be actively encouraged by receiving double subsidy for the domestic hot water energy.  Unfortunately, the wording of the legislation has prevented installers using the simplest way to implement a combined system (the thermal store) because it rules out solar systems that can make even a theoretical contribution to space heating.

Thermal Stores in Hot Water

Solar thermal systems can make a contribution to space heating as well as domestic hot water (DHW) preparation, especially in spring and autumn where the days are still bright and there is a demand for space heating.  These systems are not yet as common in the UK as those for domestic hot water, but in more developed European markets such as Germany and Austria, so-called "solar combi systems" are popular.

In a thermal store the domestic hot water is heated in a heat exchanger
and the contents of the store pumped around the space heating circuit

A good way to combine solar thermal with space heating is to use a thermal store, essentially a large (typically 500 litre minimum to 1,000 litre) hot water cylinder with heat inputs from both solar and the backup heating system and with outputs to domestic hot water and space heating.  Typically the body of water in the thermal store is heating system fluid (primary water) and domestic hot water is heated on-demand in a heat exchanger as it flows to the hot tap.

Both heat pumps and biomass heaters operate well when running continuously rather than cycling on and off, so charging a thermal store is a good technical solution that improves the overall efficiency of the heat pump or biomass boiler.

Where the designer is seeking for the solar to make a reasonable contribution to the space heating, the solar panel array installed is large (around 12-18 m2 for a domestic property).   The coverage of domestic hot water of such systems can be very high, 70% and above.

Where the designer is aiming for solar to mainly cover domestic hot water the panel array is smaller (typically in the range of 3  - 6 m2).  In this case there is still a theoretical possibility that the solar energy will contribute to the space heating, though in practice the system is sized with the aim of supplying 60-70% of water heating.
The current domestic RHI legislation completely excludes systems that can contribute towards space heating.  

The text in the RHI regulations defines an eligible solar system as follows:

a)     is designed and installed to provide heating solely to a single eligible property and solely for an eligible purpose using liquid as a medium for delivering that heat;

(b) meets the requirements set out in whichever of the standards for solar thermal plants specified in paragraph 1(5)(a) and (b)“eligible purpose” means, in relation to heat generated by— […](b) a solar thermal plant, the purpose of domestic hot water heating for an eligible property;

An implementation of solar where there is even a theoretical possibility of the solar contributing towards space heating is completely excluded from the scheme.

The reasoning behind ruling out solar space heating was that the domestic RHI is “deemed” – the solar energy is not measured, instead it is estimated using an approved calculation and the calculation only works for domestic hot water.

However, by ruling out any solar installation that does not solely heat domestic hot water, the domestic RHI has made the combination of complementary renewable heating technologies such as solar and heat pumps less likely. Solar thermal has lower associated carbon emissions than any form of back up heater, so every unit of solar thermal heat that can be used, whether for space heating or domestic hot water reduces carbon emissions.

Configurations where the solar is offsetting a proportion of fossil fuel space heating are also disincentivised by their complete exclusion from the domestic RHI.

When installing biomass or heat pumps with a thermal store, the additional cost to add a solar coil into the store is very low, making the marginal cost of adding solar thermal more attractive.  The domestic RHI would provide greater value for money if it encouraged, rather than discouraged such systems.

So how could the domestic RHI be changed to include solar space heating?

Two Suggestions

Two options occur, though I’d be pleased to hear of any other suggestions (please use the comments section).

First, it would clearly be possible to use a heat meter to measure the solar input into the thermal store.  Solar space heating systems cost more than solar systems aimed only at domestic hot water.  A requirement to fit a heat meter would be a relatively smaller proportion of the total installed cost and energy benefits, and houses that can fit large thermal stores are relatively thin on the ground, so it wouldn’t be too much of a cost for the scheme administrators to deal with the meter readings.

A second approach would be to allow space heating systems onto the scheme but to give RHI payments only for the domestic hot water energy provided, and calculate this with the current deeming method.  I’ve looked at this with the help of two years'  of data from a solar space heating system provided by Geoff Miller of GreenLincs Energy.  Simulations have also confirmed that the solar energy generated by a system providing solar space heating and domestic hot water is always higher than the same sized system targeted at only domestic hot water.  The RHI wouldn't be over-paying for solar heat.

The best outcome would be for it to be the choice of the homeowner whether or not to go to the expense and hassle of having a heat meter.  If they wanted the extra payments for space heating, then they would need to install a heat meter, otherwise they could claim for only the solar heat in their domestic hot water.

This has formed the basis of a proposal submitted to the Department of Energy and Climate Change (DECC) yesterday outlining how the scheme could be improved by allowing solar space heating.

Monday 14 April 2014

The 100% Solar Powered National Grid?

Image: Viridian Solar

Is your Car the Star?

I was intrigued by a recent article in the Telegraph (of all places)  in which the writer predicted that solar will dominate global energy production.

The article extrapolated the falling costs of solar photovoltaic generation in recent years and combined this with a whistle-stop tour of technical innovations in the sector - perovskite solar cells, flow battery technology  and robotic cleaning of panels in solar farms.

The article predicted the end of the fossil-fuel era, and concluded that wind turbines would at best be a regional niche technology because their costs were static by comparison with the enormous technological strides that will continue to be made in solar.

As is common in such articles, the intermittent availability of solar power was mentioned only in passing along with the solution – energy storage technologies.

The article made me wonder about energy storage.  How much energy storage would be needed if solar were to win the race for global dominance of energy production?  Is it a realistic prospect? 

Solar power production is intermittent in three ways.  First there is the unpredictability of cloud cover and light levels during the daytime.  Second there is the more predictable effect of the sun travelling across the sky during the day and disappearing at night.  Finally there are the seasonal variations in day length and clear skies from summer through to winter.

One Helluva Battery

Let’s do some simple analysis to try to quantify the challenge.  To keep things simple, lets take a look at the following question:

‘How much energy storage would be required to hold the electricity generated during daylight hours for use overnight?”

The graph shows the half-hourly electricity demand from the UK national grid for 23rd April 2013.  I chose a day that was pretty sunny, but in spring rather than summer or winter.  The total electricity consumption that day was around 826,000 MWh.

On the same day in April 2013, the 44.5 kWp south-facing PV array on the roof of Viridian Solar’s factory and headquarters in Cambridge produced 233 kWh, or 0.233 MWh.

If we were to scale up the PV array to produce the same number of units of electricity as the UK demand that day, it would be:

44.5 x 826,000 / 0.233 = 158,000 MWp or 158 GWp

To put this figure in context, the UK government central forecast predicts installation totalling 10 GWp within a decade in its solar strategy, however the UK installed 1.1GWp in the first quarter of 2013.

If progress continues in the reduction of costs of solar modules, then it’s not so impossible to imagine that the deployment of this level of capacity over the coming decades might happen.

I've scaled up the output curve from the Viridian Solar PV array for that day as if it were 158 GWp and added it to the graph to show the timing of solar power generation compared to the timing of electricity demand.

The energy storage required for the solar output to keep the country going through the evening, night and until the solar output exceeded the demand the next morning would be 428,000 MWh or 428 GWh.

By using the current level of electricity demand we’ve ignored the possibility that energy efficiency gains might reduce total electricity demand significantly and thus drive down the amount of energy storage we would need. 

We've also ignored the new technologies emerging that intelligently move the timing of electricity use for applications that are not time critical (such as running air conditioning and refrigeration).  Such technology could change the demand curve to better fit the solar output, also reducing the amount of storage required.

However, some 40% of our energy use today is for heating and currently most of this does not use electricity but instead burns gas and oil.  This massive demand for energy will also need to be de-carbonised and it seems likely that it will require electricity to operate heat pumps.  Clearly heating demand can be reduced with better thermal insulation and solar heating panels on our buildings, but it seems that we’ll be doing well if we can hold our electricity demand flat relative to current levels.

So what does 428,000 MWh mean in the real world?

Consider Dinorwig pumped storage power station.  This massive civil engineering endeavour in Snowdonia National Park comprises 16km of tunnels, 1 million tonnes of concrete and 4,500 tonnes of steel. The turbine hall is Europe’s largest man-made cavern.  Cheap night-time electricity powers reversible turbines to pump water from a lower reservoir at the bottom of the mountain to a reservoir higher up the mountain.  At times of peak demand the water is allowed to run back down through the turbines and generates electricity.

It cost £425m, took ten years to build and was completed in 1984, that works out to around £2bn in today’s money.

It has a power output of 1,728 MW for six hours, a total of 8,640 MWh.

We’d need to build another 48 of these babies to store solar PV electricity through a 24-hour period to meet demand.  Assuming sites could be found, and that their costs were similar to Dinorwig, then the bill looks like it would be a cool £100bn.  That’s a very big number indeed, equivalent to around 2.5 times the estimated cost of the HS2 rail line.


EVs for PVs

But maybe there’s a cheaper way.  Maybe the answer to the intermittent nature of renewable energy is sitting in driveways and garages all over the country.

Would it be possible to use the batteries of electric vehicles to store energy from times of excess generation and release it at times of need?  What do the numbers look like?

One of the main thrusts of electric vehicle development is battery storage.  The challenge is that although most vehicles are used for relatively short journeys most of the time, occasionally we like to go away to visit family or friends further afield.  We want our vehicles to have enough range to cover these infrequent long journeys.

Here’s the capacity and estimated range of a few of the electric vehicles currently on sale.


Most manufacturers have settled on a battery size around 25kWh as the right compromise on range and cost.  It seems likely that for mass adoption the manufacturers will need to develop vehicles with higher ranges.  However, let’s use 25kWh as a median value for the battery size in a car.

The annual average mileage for a car in the UK is 8,200 miles, or 22.5 miles/day.

Taking the average miles/kWh from the table means that to meet the average mileage a battery of only 6.3kWh is required.  On most days, the car has 19kWh of excess capacity that is only needed for those unusual, longer journeys.  If, through smart metering and information technology, this excess storage could be made available (perhaps yielding a small income to the car owner), how much storage could it provide?

There were 29.1million cars on the road in the UK in 2013.

If we assume that the entire UK car fleet changes over to electric vehicles then the excess battery storage this would represent is 515,000 MWh, higher than the amount that I calculated would be needed to spread PV generation out through a 24-hour period.

Hold on a Minute

Before we get too carried away, there are holes in this rosy picture of the future that need to be mentioned. 

We’ve only thought about storing energy from one (sunny) day to the next, but we need to solve the problem of having energy available in winter too, or on days where the sunlight is lower. 

One option is to install a massive excess of solar PV – many times more to meet demand in winter, 90% of which would then be idle on sunny days.  Solar panel prices would have to drop spectacularly to make this approach viable.

Another concept, popularised by the Desertec Foundation is to locate the solar panels in a place where it’s sunny more of the time and day length doesn't vary so much.  We then build low-loss power cables to connect from the desert to population centres.
It seems to me that wind, wave and tidal power generation will have a prominent role to play, due to their complementarity to solar – the wind still blows at night and average wind speeds are higher in winter.

Whatever the future holds, its clear that energy storage has a significant part to play, and how ironic if the car, which did so much to drive the development of the global petrochemical industry, will play a central role in bringing our reliance on fossil fuels to an end.