In Praise of Small Things

Are we too Quick to Criticise Housebuilders for Small Solar Installations?

Those crazy housebuilding companies!   Imagine deciding to install solar on a new home, then only fitting a measly one or two panels!  It’s tick-box solar, a pointless waste of time.  What a shame!  What a missed opportunity!  Boooooo!  So goes the usual reaction from the solar industry.

For sure it is driven by ticking a box, achieving a target carbon emission level for the property and perhaps also achieving a site-wide planning target for renewable energy.  But so what if its small?  Is bigger always better?  Why is 4kWp the gold standard for a domestic solar installation?

I already feel that I’ve set myself quite a challenge, but I’m going to have a go at convincing you that there is something truly magnificent about these small-but-perfectly-formed solar installations.

Let’s start with self-consumption.  As I discovered while researching this topic for a talk at SEUK last year, (and wrote up in a blog here), even houses where people are at home during the daytime don’t use that much electricity when the solar is at a peak.  If it’s sunny at lunch time, people are sitting outside eating sandwiches, not arc-welding in the basement.  

Yes, you can shift some consumption, but there’s only so many clothes to wash.  Yes, you can dump your excess in a hot water tank, but you’re only saving the cost of gas heating in most cases.  Yes, you can charge an electric vehicle (unless you’ve driven it off to work).  And yes, of course you could put the excess in a battery for later.  But if you put a small system on a home it simply meets the base load.  In the homes I looked at data for, the base load was between 25 and 75 Wh/10 minute period.  Around 150 to 450W.  With a small system, everything you generate, you use.

And another thing.  Aesthetics.  Some roofs can take a 4kWp system, no trouble and still look great.  But it is a really quite big area to accommodate.  Other attempts to fit as much solar as possible on a roof are less successful.  Smaller homes, buildings with dormers or roof windows, these often look much better if a more compact and bijou solar system is installed.

The drive to 4kWp came from the Feed in Tariff banding, encouraging people to size for the greatest amount of subsidy they could get.  In this new low-FIT and soon-to-be post-FIT world we need to re-think what a solar installation has to be.  Small solar systems and lots of them can add up to a great deal of emissions reduction without stressing the grid.  Manor Solar is about to start installing Clearline fusion on new homes near Peterborough - it might only be 500Wp per house but there's 3,000 homes in the development - I make that 1.5MWp from one development.

Have I convinced you that small is beautiful?  Let me know what you think leave a comment below!

Fundamentally, if the solar industry wants house-builders and construction companies to use more solar, it should make the case for it, and do so in terms that are meaningful to the people we hope to convince.

Fortunately, solar has a great deal to offer the construction industry.  My next blog will look at this.

Zero Carbon Homes for London

"Bojo vs Osbo" Rivalry Sets Scene for Solar Boom in Capital

I have written many times about this government's shameful record on driving higher energy efficiency standards in new buildings.  If you want a summary of the numerous ways they have watered down, delayed and undermined standards, take a look at this earlier blog.

The latest blow to the many people in the construction industry that had invested heavily in developing skills, technologies and products to deliver the government's long-held Zero Carbon Homes plan was the announcement in July 2015 that the allowable Solutions carbon offsetting scheme was scrapped, as were plans for on-site energy efficiency standards slated for 2016.  Instead a wooly commitment to 'keep standards under review' was made.

The fact that the announcement was made in a Treasury document "Fixing the Foundations" suggested that it was the Chancellor himself that had decided that Zero Carbon Homes needed to go.

Government appeared to have bought the line from house builders that if standards were raised, they wouldn't be able to "solve the nation's housing crisis for us".

In late 2015, Scotland pressed on and tightened building regulations in 2015 beyond those in the rest of the UK.  Guess what?

The sky hasn't fallen in.

Housebuilding is as strong as ever north of the border.

Now the London Assembly has announced that it is going further still.  Way, way further.  London will be implementing its own version of Zero Carbon Homes for major development applications received after 1 October 2016 (for residential developments this means those with more than 150 residential units) .

The policy requires that new homes achieve a carbon compliance standard on site that is 35% better than the 2013 building regulations.  This corresponds to a 54% reduction compared to the 2006 Building Regulations, and seems to be based on a simplification of the proposals from the Zero Carbon Hub.  Its recommendation was an onsite carbon compliance level corresponding to a reduction of 44% for flats, 56% for attached houses and 60% for detached houses.

I reckon that an 85m2 semi-detached house would need a solar system of 1.2kWp to bridge the gap from the backstop fabric (insulation)  requirements considered achievable by the Zero Carbon Hub to the onsite carbon emissions requirement in this policy.

The developer can choose to aim higher than the onsite requirement, but the remaining gap to achieving zero carbon must be provided off-site or through a cash in lieu contribution to the relevant borough.  This money received by the local borough is to be ring-fenced to secure delivery of carbon dioxide savings elsewhere.   There's no details on what constitutes an acceptable use of the money, for example whether it has to be in London, or the UK or anywhere in the world, or whether it has to be on buildings or can include paying South American farmers not to chop down trees.  Guidance will apparently follow.  The GLA suggests a value of £60 per tonne of CO2 emitted by the building in its first 30 years is an appropriate level for boroughs to set for the cash in lieu payment.

If solar saves 950kWh/kWp and the carbon intensity of electricity is 0.522kgCO2/kWh then it needs to cost £0.89/Wp to be more cost effective than paying the £60/tonne cash-in-lieu offset.  On larger buildings this kind of price for solar is coming into view.

However, even on smaller buildings like homes, if the developer has already committed to needing solar to meet the on-site compliance requirement, then the extra cost for increasing the size a system from e.g. 1kWp to 3kWp could well be low enough to beat paying the cash fee.

Whichever way it goes, this is excellent news for solar in the capital, and potentially beyond.  New homes in London represent about one sixth of all new homes in the UK.

The GLA has commissioned research that demonstrated that the prices commanded in the capital can easily support the extra costs of this policy.  London is surely not the only place with high house prices (pretty much the whole of the South East probably would find the same).  If the policy proves to be robust to legal challenges or central government interference, then other local authorities could follow suit.

The Conservatives have left a Zero Carbon Homes shaped policy gap in building standards.  Fortunately a long-distance urination competition between two leadership rivals means that the baton has been picked up by regional government, to the benefit of future home owners and those businesses that invested in the government's original intentions to deliver world-leading building regulations.

MCS012 Finally Comes into Force

Image: Viridian Solar Roof Integrated Clearline Fusion System

That the implementation of MCS012 has been a challenging process must be obvious to any outside observer.  The standard for assessing the performance of solar roof mounting kits for wind resistance, weather tightness and spread of flame performance was first published in 2012.   Indeed, it was written into the 2013 Guide to the Installation of PV Systems as a mandatory requirement, and 130 different certificates have now been issued to roof mounting kits and components.

However, a first delay was made necessary when so many manufacturers had left things until the last minute that a log-jam was created at the test laboratories.  MCS wrote out to installers to announce that the requirement would be suspended until further notice.

A subsequent hold up due to concerns raised about EU notification was followed by inconsistencies between certifying bodies in the treatment of ‘universal’ roof integration kits that needed to be ironed out.

After such a delay, it feels like old news that the use of mounting kits accredited to MCS012 will eventually become mandatory for MCS registered solar PV installations on pitched roofs from May 2nd 2016, but it brings some big changes for the industry.

Read more about what MCS012 means for installers here.

Above-Roof Systems

MCS012 mounting systems intended to mount the panels above a roof covering are tested only for wind resistance (where they can be shown not to affect the fire resistance and weather tightness of the roof covering beneath).

This test is important because the resistance of most roof hooks to pull-out forces is determined not by the strength of the roof hook itself, but by the strength of its fixing to the roof.  In sound timber, this strength is determined by a combination of the size and number of the wood screws and the gauge of the timber into which they have been screwed.

Because of this, resistance values from tests where the hook is fixed to larger timbers than those used in the UK cannot be used as they would over-state the strength.

Some manufacturers have not tested at all, but instead used EN1995-1-1 (or similar) to calculate a resistance force for their fixings.  Such calculated screw pull out forces only apply when the timber to which the screw is attached is wider than 12x the diameter of the screw.  Unfortunately with slender UK roof trusses, this is usually not the case, making calculated resistances invalid.

A roof hook tested to MCS012 will have a certified, tested resistance in kN to uplift forces, creating a level playing field.  Solar installers can use this resistance with confidence to calculate the number of  hooks required for their installation that would have a combined resistance higher than the design wind pressure multiplied by the installed panel area.

In-Roof Systems

Solar systems that replace the roof covering have more significant testing requirements under MCS012, including a deluge test for weather tightness, a pressure test for wind uplift resistance and a test of the spread of flame.

The spread of flame test is a requirement for all building materials used as a roof covering.  Building regulations, e.g. Approved Document B in England, impose  limitations (area and location limitations) on the use of materials that do not achieve a high enough performance rating.  To comply with building regulations without a fire rating is impossible (which raises questions about how some roof integration systems were compliant before MCS012 forced those manufacturers that had not already done so to perform these tests).

Read more about building regulations for fire and roof integrated solar here.

It was this test of the spread of flame that has caused the most recent delay to MCS012 coming into force.  The original version of the standard had not properly accounted for universal roof integrated mounting systems (those that can be used with pretty much any solar panel).

MCS012 was previously silent on how to interpret the fire performance test for universal roof integrated mounting systems when these relied on the presence of the solar panel to achieve the fire rating of the system as a whole.  As a consequence, certifying bodies (CBs) were left to develop their own interpretation, which they duly did, but inconsistently.  Some CBs issued an MCS012 certificate that limited the system to be used with only the module with which the system had been fire tested, others tested with only one panel but issued the MCS012 certificate to apply when the mounting kit was used with any module at all.

The first interpretation is incredibly limiting for systems that give the installer freedom to choose any solar panel, implying that manufacturers of such systems would need to repeat costly fire testing with every single type of panel that their customers might want to use.  In theory, the second interpretation is dangerous to public safety as it extends the tested fire performance to an installation using solar panels made from plastic, wood or, for that matter, chocolate.

Solar panels had rarely been fire tested before MCS012 made it mandatory.  Their design appears so undifferentiated that it seemed obvious that they would perform identically in such tests.  However as tests proceeded, reports emerged that outwardly identical-looking products were performing very differently in the fire test.

At the same time, regulators in the US had found a similar issue with fire rating of solar panels and published standards (UL 1703) categorising panels into 15 families that could be considered to have the same fire performance for the US fire tests. An international precedent exists.

The MCS012 working group decided that the responsible reaction to this new information was to choose the most restrictive (and therefore most safe) option - that a certificate can only be issued for the roof integration system with the panel(s) with which it has actually been tested.  This change was implemented in the latest version of the standard.

Roof integration systems that use a dedicated solar panel or solar tile are unaffected by this change, as they will have already been tested with the only panel type they use.

However, manufacturers of universal solar roof integration kits that work with many types of solar panels now have a number of options available to them for their products to remain in compliance with the requirements of the MCS scheme (and building regulations).  They can either:

(1) Re-test the system without the solar panel in place to achieve a certified fire rating that is independent of the fire performance of the panel;

(2) Re-test with a range of panels to achieve a certified fire rating.  Installers must then choose panels to pair with the mounting system from a more limited range; or

(3) Change installation instructions such that the system must be installed above a material that achieves an adequate fire rating in its own right (for example a fire board or fire-proof membrane).

Now this is sorted out, and the certification consistently applied, the standard has been made mandatory for PV installations.  Work to understand which features of a solar panel's design affects its fire performance is planned, with the goal of creating a similar set of product families to those in use in the US, but based on UK fire testing standards.  In future, this would allow a manufacturer of universal systems to be used with a much wider range of panels based on a much smaller number of tests.

Solar Thermal in the Crosshairs

Bullet Point Needed for DECC Action Plan

The Department of Energy and Climate Change (DECC) has released its consultation on reforms to the Renewable Heat Incentive (RHI), and this time it looks like it’s the turn of solar thermal to be under threat.  DECC's intention is to completely remove support for solar thermal by dropping it from the RHI while support for other renewable heat technologies such as heat pumps and wood chip boilers continues under the scheme.

As the solarblogger shows below, it's relatively straightforward to pick holes in the government's arguments for singling out solar thermal.  Whether DECC will be swayed from what is looking more and more like an ideological attack on solar is more open to question.

Busting The Arguments

DECC says:
Solar Thermal technologies account for 17% of total accreditations (7,445 out of a total of 45,111) but just 2% of heat (11TWh out of 598TWh).

Solarblogger says:
Solar thermal delivered 2% of all heat (11TWWh out of 598TWh), but accounts for only 1.4% of committed budget at the end of 2015 (£0.69m out of £49.3m).

So what?  So what if each solar thermal system contributes a small amount of energy?  It’s being unfairly compared to massive biomass boilers heating country piles, factories, and barns!  We already knew that solar thermal was more likely to be applied to domestic hot water in normal family homes where the small amount of energy each installation delivers still represents a significant proportion of household energy consumption (around 10%).

If affordability is the basis on which solar thermal is to be excluded from the RHI, then surely the relevant statistic isn’t to compare the proportion of all installations against the proportion of total heat, it’s to compare the cost against the heat delivered.  On this basis solar thermal looks much better value for money.


UPDATE (4.4.16) - figures should be treated with caution.  The committed budget is forward-looking and the delivered heat is backwards-looking, so it seems likely that large numbers of biomass boilers installed in the current year will be increasing committed budget but not contributing greatly to historic delivered heat.  Research into OFGEM figures by Mike Landy at the STA suggest that solar thermal represents 2.8% of payments made under RHI for 2% of delivered heat.



DECC says:
When asked, around half of all owner-occupier applicants said they would have installed it anyway.

Solarblogger says:
The DECC survey asked people to report their motivations for doing something after the event.  Such surveys are prone to a well-documented error called social desirability bias.  This is a tendency of respondents to answer questions in a way that paints them in a good light.

What DECC fails to mention is that the proportion of owner-occupier applicants saying that they would have installed other RHI technologies anyway was also extremely high.

Proportion of respondents saying they would have installed the same technology irrespective of the availability of the RHI:

Biomass         11%
ASHP 31%
GSHP 32%
Solar Thermal 49%

Installing renewable energy systems is seen as doing a social good.  People are less likely to admit that they only did it because of a government bribe.  The less expensive the system they have installed, the more ‘embarassing’ it would be to admit you wouldn’t have done it without the RHI.

The survey is flawed and to rely on it as a reason to take such a significant action against solar thermal is shocking.

DECC says:
We judge solar thermal to be a mature technology with a well-established global supply chain.  It is not clear that ongoing RHI support will serve to build this supply chain in the way that it can for other less mature technologies in the UK like heat pumps.

Solarblogger says:
Again solar thermal is being unfairly singled out.  A well-developed global supply chain for solar thermal is being compared with an immature domestic (UK) supply chain for heat pumps.

Heat pumps also have a well-established global supply chain, due to their high deployment in other European countries (27 million in operation across EU) according to Eurobserver and 1.7million heat pumps were sold in the EU in 2014.

Just like for heat pumps, solar thermal has a strong global supply chain but a nascent UK supply chain.  Just like for heat pumps, action to stimulate a strong UK supply chain has the prospect of reducing costs in the UK.  The Solar Trade Association estimates by as much as a 30% reduction in costs for a volume UK market of 200,000 systems a year.

Past Performance is not an Indicator of Future Success

DECC argues that deployment rates for solar thermal are too low to justify keeping solar thermal in the RHI, and that they can’t increase the subsidy levels as they are already set at the so-called ‘Value for money’ cap agreed with Treasury.

If the folks from DECC had been able to find an unconflicted solar thermal company to talk to (one that didn’t also make a living from PV), and asked them what was the one thing it could do to grow the market for solar thermal, the answer would have been “Reduce the subsidy for PV”.

The Feed in Tariff had four years’ head-start on the domestic RHI and domestic solar PV launched with tariff levels four times higher than the cap imposed on solar thermal.  Until the most recent shock reduction in the Feed in Tariff, support for PV was still higher than the cap (taking into account that the domestic RHI is for seven years, and the FIT is for 20).

Add in the loophole that pays owners of solar PV systems for exported electricity, even when they divert that power to heat water instead of exporting it and it’s obvious that the real reason for solar thermal underperformance is more linked to decisions made in the department at DECC that looks after the Feed in Tariff.

The Feed in Tariff has now been cut to a level that gives a much more level playing field with solar thermal, and many installers were starting to re-boot their solar thermal expertise and explore this option.  A recent survey of member companies by the Solar Trade Association found level of enquiry for solar thermal running at double the rate of the previous year.

The tragic mistake that the Heat team at DECC might be about to make is to have reached their conclusions about the performance of solar thermal based on a period during which a separate department at DECC was supporting PV much more generously.

Fixes Needed in RHI

Linking the domestic RHI to the Green Deal was a mistake, and the cost of having to get a Green Deal Assessment affected solar thermal disproportionately compared to more expensive technologies.  The decision to remove this requirement would boost solar thermal.

Solar thermal is an excellent companion to heat pumps, taking the strain on high temperature domestic hot water and allowing the heat pump to focus on working at lower temperatures, where its performance is more optimal.  The domestic RHI tried to reward people that installed both technologies together by allowing them to claim support for domestic hot water for both heat pump and solar.  Unfortunately the regulations were drafted in a way that ruled out the most popular implementation of a combined heat pump/solar system – a thermal store, see my earlier blog on this cock up here.  The Solar Trade Association has proposed a number of different ways that DECC could have fixed this problem to boost solar thermal deployment, suggestions that were sadly, ignored.

The proposal to remove solar thermal from the RHI is based on flawed logic.  The market has changed drastically since funding for PV was cut and early signs since then show indications of a return to growth.  Domestic hot water is the heat load that cannot be insulated away and solar thermal has an important part to play in decarbonisation our homes and addressing fuel poverty.

DECC should continue to support solar thermal and fix problems with the RHI that are holding it back rather than throwing it out of the RHI.

How to Save the MCS from Irrelevance

Too Many Cooks at the Microgeneration Certification Scheme

In 1964 a 28 year old woman called Kitty Genovese was brutally attacked in front of her apartment building as she returned from work.  According to accounts in newspapers, the attack lasted at least half an hour and, despite her repeated cries for help, 38 people who either heard or saw the attack did not intervene or even call the police until after the attacker had fled and Genovese was dead.

Why?

Although it later emerged that the number of witnesses was exaggerated in the newspaper reports, psychologists have now proven that the more people who are around, the less likely it is that someone will act to stop something bad happening.  They call it the ‘Bystander Effect'.

For example in a classic experiment by Latane and Darley, subjects were placed in a waiting room either on their own or with others present.  As they sat there, the researchers had organised for the room to start filling with smoke.

When the subjects were on their own in the room, 75% reported the smoke to the organiser.  When there was three subjects in the room, the smoke was reported only 38% of the time.

One of the explanations for the Bystander Effect is termed “Dilution of Responsibility”.  The more people there are around, the more likely you are to leave it to someone else to do the right thing.  Obviously if everyone thinks the same, then no one does anything.

Which brings me on to the Microgeneration Certification Scheme

As the recent Feed in Tariff review unfolded, I heard many people wonder what the purpose of MCS would be in a post-subsidy world.  “If there’s not a Feed in Tariff, why would anyone ever bother with MCS?” was a typical sentiment.

This completely sums up the failings of the scheme.  If it’s just seen a tick-box exercise, a gateway to government handouts then absent the subsidies and the scheme is worthless.  As a consumer protection scheme it’s hard to find anyone in the industry that believes it works.

The irony of this is that the MCS was created by the industry itself.  If you think the management of the scheme is bureaucratic to the point of paralysis, or that its police have no incentive to drive out poor practice (or even look for it) in the companies they audit.  If you think the installer audit focuses more on the accuracy of paperwork rather than the quality of the outcome for the consumers; or the way you have to demonstrate you meet the “competence” requirements are baffling and incomprehensible; then apparently you only have yourself to blame.

After all, the people running it are the representatives of trade associations, certifying bodies, training providers and government bodies that make up the steering group, and you can see who they are by looking here.  There are no less than thirty two bodies represented.   Thirty two bums on seats at meetings.  Thirty two people to have a say on any decision.  Can you imagine how those meetings must go?

And thirty two is plenty enough people to produce the dilution of responsibility for no one to act to put things right.  Our industry representatives have allowed the MCS to become what it is due to the Bystander Effect, and it’s time for industry to demand that our representatives start representing us at the MCS.

This time last year, the Solar Trade Association produced a manifesto for change at the MCS.  It called for improvements to its governance, rigorous enforcement (and expulsion of substandard companies), measurement and reporting of the quality of installations (and therefore the success of the scheme), and spending some of the vast accumulated reserves promoting the industry and accredited installers to the public.

The solarblogger has heard that against the reluctance of the‘Interim CEO and Chairman’ a small group of members of the Steering Group were able to push for changes based on the ideas in this manifesto.  A 100-day plan to enact the changes was agreed, but a year later and little has changed, the actions bogged down in a sticky morass of procedure and delay.  Instead of hearing that these urgently needed changes have been made, we’ve had the scheme sending out communications about moving to a new legal structure to become a charity.  It’s spent the year rearranging the deckchairs.

The MCS has been given a stay of execution.  The outcome of the Feed in Tariff review has given it a short window where people will still want to use it to access government support.  The industry wants a scheme that is responsive to its needs, cost-effective and delivers effective consumer protection, something MCS is not providing at present.  The team appointed to run the scheme in its new charitable status need to get on with making the changes necessary for MCS to become useful in a world without subsidies and our industry representatives should stand up and help make it happen.

Self-Consumption of Solar PV Generated Electricity

The Amount Customers can use Themselves now Matters More than Ever

When the UK Feed in Tariff (FIT) launched, people investing in solar were paid the equivalent of 48p/kWh in today’s money for solar energy they generated (irrespective of whether they used it themselves or exported to the grid).  With electricity savings worth around 15p/kWh and export paid at 4.8p/kWh in today’s money the only number that really mattered was how much energy you would generate with your solar panels. Fortunately, solar professionals have accurate tools to forecast the annual yield for a solar, even relatively simplistic approaches such as the MCS calculation get pretty close.

As solar costs have fallen since the start of the FIT, the generation tariff has fallen too.  Now the generation tariff is worth about a quarter of the starting value - 12.47p.  If the government presses ahead with its reckless cutbacks on the FIT, then the generation tariff would be only 1.63p for domestic customers.

As these changes have occurred, the economic basis for installation of solar panels has become more and more driven by the value of the energy savings the system produces.  With the generation tariff at only 1.63p, the energy savings dominate (see the graph below).

Most solar companies have been using a value of 50% to estimate the amount of energy generated by the solar that would be used in the property (and therefore offset energy bills), so called self-consumption.  The justification for doing so is that this is a ‘government figure’ because the amount the FIT pays for export has to be deemed rather than metered, and government set the value of export at 50%.  So logic says that if the export is 50%, then the self-consumption must be 50% too, right?

Wrong.

Just because the government says it is willing to pay the export tariff on 50% of the energy generated, this is not the same as saying that all houses will use 50%, irrespective of the size of the array and energy consumption patterns of the house during the day.

In the past, errors in the estimate of self-consumption have not really mattered to the presentation of the economics.  Right now they are starting to matter.  As the generation tariff is reduced further, they will really matter.

The industry is going to have to develop ways to more accurately assess and predict self-consumption.

So let’s start by having a look at a few examples of real homes with solar.  Thanks to RBeeSolar and 4Eco for allowing me access to anonymised data on their systems.

Each graph shows a full 24 hour period running from midnight to midnight, with mid-day in the centre.  The day is divided into 10 minute sections and the energy flows are shown in watt-hours per 10 minutes.


Blue is electricity pulled from the grid for consumption in the house.  Orange is energy consumed in the house and provided by the solar panels.  Yellow is energy that cannot be used in the house and that is therefore exported to the grid for others to use.  The electricity consumption of the house is the sum of the blue and the orange.

House One

House 1 has relatively low total annualised energy use 2,250 kWh per year.  This figure represents about three quarters of the electricity use of a typical UK home (often taken to be 3,100kWh/year).    The use pattern shows a small morning peak and a larger evening peak.  There is little use above the baseload during the daytime on week-days, but additional electricity use at weekends, indicating a household where occupants are out during the working week.

Data was only available for July, August and September for this house, but the self-consumption rate during this period was only 22%, with 78% of generated energy exported.  The solar system is not especially large at 2.5kWp.


House 1 Self Consumption: 22%

House 2

By contrast, house 2 shows a consistent pattern of electricity use during the working week and weekend, indicating a household that is occupied during daylight hours all week.    The base load is a little higher than for house 1, and there are regular peaks of electricity consumption throughout the day.  

The pattern of electricity use is similar in winter, perhaps with a higher evening consumption.  The graphs clearly illustrate how on a gloomy winter day (Thursday), most of the solar is used in the house, but that there are still sunny days in winter and plenty of export going on. 

Total electricity consumption over the year was 2664kWh, so still a little lower than typical (86%).  The solar system on this house is 4kWp.


House 2 Self Consumption: 24%

House 3

House three has an annual electricity demand of 5,030kWh, comfortably higher than the typical UK house.  It also has a use pattern that indicates people are at home during the working week. When coupled with a  4kWp solar system, this results in a higher self-consumption level, but still only 37%.

House 3 Self Consumption: 37%

Conclusions

The withdrawal of Feed in Tariffs (whether sudden or gradual) is the clear direction of travel.  The result of this trend is that self-consumption of solar electricity becomes the dominant economic justification for installing solar PV.  Any error in the predicted level of self-consumption will have a larger impact on the overall financial returns than has previously been the case.

Based on the small sample considered above, the industry-standard use of a value of 50% for self-consumption of solar generated electricity in domestic installations looks generous.  With increasing availability of monitoring equipment householders will be able to check the accuracy of figures that were used in the sales process. 

Products that divert excess solar electricity to water heating may have a role to play in increasing self-consumption, but the economic savings will depend on the replaced energy that would have been used to heat the water.  The government’s announced intention to retrospectively pay only metered export once smart meters are installed means that if the house has gas-heating, the value of the gas use avoided is similar to the income from exporting the electricity. 

Diversion of excess solar electricity to charge electric vehicles or to battery systems that can store energy for evening use will become more possible as the price point of these technologies continues to fall.  In the meantime it could be that the economic optimum moves away from the current goal of maximising subsidy yield (aiming for 4kWp or as much as will fit) and we begin to offer slightly smaller solar PV systems that produce less excess on sunny days and a higher proportion of self-consumption. 

This maturing market could involve the solar installer fitting monitoring equipment in the house for a short period before making a recommendation about a right-sized solar installation.  From my experience of looking through data on these houses and others, the good news is that people appear to be real creatures of habit.  One or two weeks' worth of monitoring should be enough to give a good indication of the timing of people's energy use.


The industry needs to do more work to understand the relationship between the proportion of self-consumption and the size of the solar installation relative to the size of the annual electricity demand.  It may be that predictive tools, or at least rules of thumb can be developed to allow solar installers to size the solar system to achieve a level of self-consumption knowing the annual energy use of the household.

Scotland Shows the Way on UK Building Regulations

New Rules will Boost Deployment of Solar on New Homes

Ideal for New Build - Roof Integrated PV.  Image:  Viridian Solar

This month, new building regulations came into force in Scotland.  Let’s have a look at what they might mean for solar.

The way the building regulations for energy performance of houses work is that the designers have to keep the calculated carbon dioxide emissions associated with heating the house, providing hot water to occupants and running lights and pumps (but not electrical appliances) below a certain set level.  

The calculated carbon dioxide emissions are assessed using a government approved method (SAP2012), which is available in software form.

The level the designer has to keep below is arrived at by calculating the emissions from a house of the same shape, but with energy performance features defined in the regulations, a so-called ‘notional dwelling’.  The thermal insulation performance (U-value ) for the walls, floor, roof and openings is defined for this notional dwelling as well as other features such as values for air-tightness, the type of heating system and other energy saving measures such as use of low energy light fittings.

The reason for taking this approach is that it is not prescriptive.  It allows the building industry to experiment with combinations of measures that achieve the overall goal (carbon emissions) in the best way for them (which almost always means the cheapest way).

The table below shows a few key features of the notional dwelling for the new Scottish regulations and compares them with the same requirements for the previous regulations and also the current regulations in England.

Regulators also worry that cold, leaky homes might be built with low levels of thermal insulation and lots of bolt-on electricity generation, so they also set minimum levels of performance beyond which it is not possible to go.  These are called backstop values.

Comparing the notional values for 2013 with those for 2015, you can see that the thermal insulation has been tightened up somewhat, but not excessively.  You can also see that Scotland 2015 is not significantly better than England 2013 in this regard.

Where the two countries diverge massively is that the notional house in Scotland includes a PV system on the roof for homes heated with gas, LPG or oil, whereas the English regulations include no renewables at all in the notional dwelling.

The Scottish regulations call for the notional house to have a PV system sized as follows:

kWp = smaller of total floor area x 0.01  --- or---   30% of the roof area based on 0.12kWp/m2

If we take an average semi-detached house as an example, with total floor area of 85 m2 over two floors and a roof pitch of 35 degrees, this equates to a total roof area of 49m2

So the solar installation on the notional house would be the smaller of 0.85kWp or 1.8kWp
But solar installations on notional houses don’t help the solar industry.  What does this mean for real houses that are going to be built in Scotland from now on?

A developer in Scotland seeking to build this 85m2 semi could aim for any of the following:

1. Match the insulation levels in the notional values and install a 0.85kWp solar system
2. Exceed the insulation levels in the notional values and have no solar
3. Relax the insulation levels below the notional values and put a larger solar system on

As I discussed in a previous blog, insulation suffers from a diminishing return which means you need to pay for ever more insulation to make the next improvement.

By contrast, solar PV benefits from a falling marginal cost as you increase the size of the installation.  If you’re going to use solar, it’s more cost effective to use a larger system.  

The feedback I am hearing from housebuilders in Scotland is that they are embracing solar as a big part of their strategy for delivering homes to the new regulations.   Schemes we have seen so far indicate that the solar systems will be closer in size to those installed by householders when retrofitting, perhaps in the range of 2-3 kWp.  This is great news for the solar industry and also for the energy bills of people buying these homes.


If only England and Wales would implement such ambitious targets for new homes too.