Tuesday 4 October 2016

Thin Film Solar PV vs Silicon Wafer - Which is Better?

A guest article by Dr KT Tan cuts through the marketing to find out

Figure 1 (Source: Jethro Betcke, Oldenburg University, Germany)

Thin film solar PV was hailed as the next big thing in solar nearly a decade ago. Then, crystalline silicon wafer (c-Si) cells occupied more than 80% of the market share compared to thin film PV (1). There was a high anticipation in the industry for thin film PV to position itself for a run at c-Si and dominate the market for the near future. However, 10 years on, history shows that not only did thin film fail to conquer the market, but its market share has subsequently declined to only 7% (2).

Obviously, one major factor was due to the collapse of the price for c-Si cells, which quickly wiped off the cost advantages of thin film technologies. This blog is not going to discuss the reasons for this distorted market competition, caused mainly by the exponential expansion of production in c-Si cells, but to question and compare the technical merits of thin film PV versus c-Si.

Do thin film PV technologies have an arsenal of special features to outperform c-Si cells? 

Low Light Performance

The first common belief is that thin film solar PV performs better in low light conditions or diffuse sunlight (for example on a cloudy day). But is this true? The fact that this has been heavily promoted by the marketing guys is because these two technologies do have different spectrum responses to solar light. In other words, their ability to convert solar energy to electricity varies at different wavelengths. In general, the average wavelength in diffuse sunlight is shorter (i.e. more blue) that of direct sunlight – so if you have a spectral response peaking at short wavelengths, e.g. thin film amorphous silicon (a-Si), then you would perform better under diffuse conditions than clear sky conditions.

Figure 1 for shows the different spectrum responses of different solar technologies against the power of sunlight of different wavelengths at sea level at mid-lattitudes of Earth (called AM1.5).  Crystalline monocrystalline silicon (labelled m-Si) is compared against different thin film solar technologies based on amorphous silicon (a-Si), Copper Indium Gallium Selenide (CIGS) and Cadmium Telluride (CdTe).

If you look at Figure 1, you probably would have noticed that not all thin film technologies have the same performance response to differing light wavelengths. Thin film CIGS solar panels, for example, have a broad spectrum response akin to mono-crystalline wafer cells (m-Si), so based on this their performance in diffuse lighting conditions would be little different to m-Si.

Amorphous Silicon has a quite significantly different spectral response to crystalline silicon, with a greater response to low wavelength light.  So how do they compare in field trials? Figure 2 illustrates the results of a comparative study between a-Si and c-Si on a cloudy day. On average, the tests show an increase in energy generated of 15% for a-Si at low irradiance levels below 260 W/m2.  (Note: the tests were published by NexPower, a manufacturer of amorphous Silicon panels)
Figure 2 (Source: NexPower In-house test report)

However, performing better on cloudy days is of little benefit if it is combined with performing less well on sunny days (when more energy can be collected). If this were the case then the advantage of thin film PV under diffuse conditions might be a complete red-herring created by the marketing gurus.

A recent research project (3) supported by the Deutsche Bunderstiftung Umwelt (German Federal Foundation for the Environment) compared several solar module types (including thin film and c-Si) under North German Climatological conditions in a side by side trial for a year, and it turned out that no significant difference between the performances of the different type of modules could be found .


Let’s move on to the second common claim, that thin film PV are more immune to shading effects. There is no magic physics in thin film technologies that make them less tolerant to PV’s number one enemy – partial shading, except that the cells in thin film panels are usually very long and narrow (5 to 10mm wide and the whole length of the panel). In this case, the likelihood of total cell shading is diminished, provided that the installer has correctly oriented the solar modules. Most modern thin film solar modules have further split the narrow cell into multiple sections and incorporated by-pass diodes (4). Nevertheless, if they are not oriented wisely to avoid potential shadows, then it is back to square one (See figure 3).

Figure 3a: Correct orientation to shading           Figure 3b: Incorrect orientation to shading
(Source: Technical Note – Optimising Thin-Film Module PV Systems by SolarEdge)

High Temperature

Finally, how about the claims for superior heat resistance of thin film PV? This is perhaps the only undisputable advantage of thin film technologies – intrinsically, they all have a better temperature coefficient compared to s-Ci (5). In other words, their performance does not degrade as quickly as s-Ci when cell temperatures increase above 25oC.  However, as figure 4 shows, different thin film technologies display a wide variation in temperature response.  Amorphous Silicon (a-Si) is least affected by temperature, whereas CIGS solar panels are very similar in performance to crystalline Silicon.

Fig. 4 Variation of Power Output with Temperature for Different Solar Technologies
 Source: Virtuani. A, Pavanello. D and Friesen. G. Overview of Temperature Coefficient of Different Thin Film Photovoltaic Technologies, 25th European Photovoltaic Solar Energy Conference and Exhibition. 2010, Spain.

A comparative study between amorphous silicon and crystalline silicon suggests the benefit can be up to 20% more output on a hot day with an average ambient temperature of 34oC. See Figure 5. (Note: the tests were published by NexPower, a manufacturer of amorphous Silicon panels).

Figure 4 (Source: NexPower In-house test report)

Although the above result may sound impressive, you may be wondering which parts of the world regularly has an average ambient temperature above 30oC. Unsurprisingly, some research bodies in countries likes, Thailand (6) and India (7), have recommended thin film PV for precisely this reason.

In Summary

Bringing all these factors together, a collaborative research project carried out by Universities of Stuttgart and Cyprus compared thin film PV and c-Si by measuring actual performance over many years in Cyprus (8). The data has obviously taken into account all the differences in spectrum responses and temperature coefficients, the results are summarised in Figure 5.  Data for four years is presented from 2007 (labelled a) to 2010 (labelled d). The clear conclusion from this multi-year side by side test is that thin film modules do not outperform crystalline silicon modules.

Figure 5 Muli-Year Comparison of Solar Energy Yield from Different Technologies
(Source: Reference 8 – page 222)

There appears to be no clear technological advantage for thin-film PV against c-Si at present. In order for thin-film PV to experience a revival, there must be other factors involved which would make thin film PV more attractive than crystalline silicon solar PV. 

For example the homogenous appearance of thin film panels may make them look more appealing.
Thin film solar can be printed on any thickness of substrate and combine with other materials to form see-through graphics, stained glass, company logos, and blinds. With the ability of being semi-transparent, they could even mimic the appearance of natural materials, for example wood or marble.

Needless to say, apart from such niche applications, thin film PV also needs to gain more headroom in cost advantage against c-Si to offset a lower overall efficiency. Until then, it seems like c-Si will stay on top for now.


(1) http://www.marketsandmarkets.com/Market-Reports/thin-film-pv-31.html
Renewable Energy Sources and Climate Change Mitigation: Special Report of the Intergovernmental Panel on Climate Change
(2) Photovoltaics Report by Fraunhoher Institute for Solar Energy System. 6 June 2016www.ise.fraunhofer.de
(3) FLINS Project (www.flins-projekt.de) hosted by Universitat Oldenburg, Germany (http://www.uni-oldenburg.de/en/physics/research/ehf/energiemeteorology/research/former-projects/flins/).
(4) Correspondence with NexPower (www.nexpw.com )
(5) Overview of Temperature Coefficients of Different Thin Film Photovoltaics Technologies by Alessandro Virtuani, Diego Pavanello, Gabi Friesen at 5th World Conefrence on Photovoltaic Energy Conversion, Spain (https://www.researchgate.net/publication/256080289)
(6) Investigation on Temperature Coefficients of three types Photovoltaic Module Technologies under Thailand Operating Condition by P. Kamkird, N. Ketjoy, W. Rakwichian and S. Sukchai. Published on Procedia Engineering 32 (2012) 376 – 383.
(7) Variation of Temperature Coefficient of different technology Photovoltaic modules with respect to irradiance by P. Dash and N. Gupta. Published on International Journal of Current Engineering and Technology, Vol. 5, No. 1 (Feb 2015).
(8) Performance of Photovoltaics under Actual Operating Conditions by G. Makrides, B. Zinsser, M. Norton and G. Georghiou (pages 201 to 232). Third Generation Photovoltaics ISBN 978-953-51-0304-2. March 2012.

Tuesday 30 August 2016

Bird Proofing for Solar Panels

Bird Mess

I was surprised when posts about ‘bird-proofing’ solar panels popped up in my Linked-in Feed the other day.  “Is this really a thing?” I wondered.  So I contacted the guy from the pest control company that was offering the service to find out more.


“What damage do birds cause to above-roof solar systems like this? Why don't we see more of this kind of thing? Are birds a problem in only some circumstances or places?”

Kelly Farrant, pest control specialist:

“There are several reasons I get asked to carry out this type of work. Pigeons love solar panels as a place to build their nest as they protect them from the elements and is a safe environment for them from predators and humans. The two biggest complaints I get is first of all the noise, with the pigeons waking the home occupants around 3 or 4 in the morning every day with the bird noises echoing through the loft. The second is the mess they make. A heavy infestation can cause a blocked gutter in a week and over flow of bird mess down the side of the house, not nice if you have a white exterior. It also causes a lot of mess around the outside of the house which can also be very slippery when wet. Another concern is the constant collection of broken eggs and dead chick on the floor where they have fallen from the nest. The final reason although I have not heard it happening yet is a concern that the birds will cause damage to the cables. I have lost count of how many solar panel jobs I have completed this year but I would say it is over 40 with my best month being April when we completed 12 in one month. I hope this helps.”

Other LinkedIn-ers from the Pest Control Industry provided more background.

Mark Porter, Area Surveyor at Servest Pest Control:

“agree with the above. The guano deposited tends to build up & blocks up guttering. They also provide ample nesting sites to female birds looking to shelter the young from the cold & wet. with this comes biting insect activity that feed on the young while in the nest. Bird mite soon then become a problem for the resident when the chicks are strong enough to leave.… “

Barry D Phillips, a Pest Control Training Supplier:

"Everything Kelly just said plus the main issue with Gulls is they are attracted to solar panels as they see the reflection of the sky and mistake them for a pond , lake or other water source. They and Pigeons cause additional damage from via their fouling which is highly acidic and can cause erosion to certain materials and paint / or protective coatings. Gulls also like to drop items onto the ground from height so this explains a lot of the bones etc you may have found on some jobs."

So there you have it, yes bird-proofing solar panels really is a thing.

As if rack-mounted solar panels were not ugly enough already, you now need to cover the edges with a metal mesh to protect yourself from an infestation of pigeons or gulls that will keep you up all night with their noisy parties, fill up your gutters and damage your paintwork with all their poop, leave dangerous slip hazards on your garden path and infect you blood-sucking parasites....

Yet more reason to do the right thing and go for good looking roof integrated solar?

Friday 8 July 2016

Nailed Down

Clearline Fusion integrated solar installed by Go Green Systems.  Image (C) Go Green Systems

Change to UK Roofing Standards with Consequences for Solar

The British Standard for slating and tiling (BS 5534:2014) was updated in August 2014, and after a period of overlap to allow industry to finish jobs already started the previous version was withdrawn in February 2015.

Although the building regulations do not specifically call it up, most manufacturers of tiles and slates make sure that their installation guidelines closely follow the standard.  In addition, architects and designers will use it in their specifications and providers of insurance warranties to housebuilders such as NHBC require that tiles and slates are installed in accordance with the standard (for example, see section 7 of the NHBC technical document). 

The bottom line is that most new roofs in the UK will now be installed to this standard and the changes have some impact on the installation of solar on these roofs.

Fixing of Underlay

The underlay resists a proportion of the pressure difference created across the roof by wind.  If it is insufficiently well secured, it can balloon up and press on the underside of the tiles or slates.  New guidance in the standard describes how the laps strips of underlay should be secured - either by covering the bottom edge of the lap with a batten or sealing between the laps with double sided adhesive tape.

Solar wiring is often passed through into the building by passing the cables up between the laps in the underlay.  However, the double sided tape used to  stick down the laps is so effective it can't be peeled without tearing the underlay.  Installers might be tempted to cut through the underlay to pass cables through instead of taking the more time-consuming option of running them up to the top of the roof and into the building through the ridge vent.

No Tile Without a Nail

BS5534:2014 has an updated wind speed map, in which the wind speeds have increased compared to the previous version. This apparently reflects the greater likelihood of extreme weather events in a warming planet, and aligns more closely with European standards. 

Whatever the reason for this change, the outcome is that where previously only single-lapped tile roofs in highly exposed locations would need to mechanically fix every tile, now pretty much every roof is going to have every single tile nailed, screwed or clipped down to the tile battens.

For a roof that has been laid in this way, the task of retro-fitting an above-roof solar system has just got much more difficult. 

With a loose-laid roof (perhaps with only every fourth course of tiles fixed) you could simply slide tiles up and under the row above to fix brackets to the roof structure below.  This trick is also often used to provide foot-holds on the roof and avoid the risk of cracking tiles by walking around on top of them. 

For a roof built to the new standard, this option isn't available.  Real care is going to have to be taken to avoid the risk of damaging the roof covering so access to the roof is likely to need to be on boards or roof ladders.  Removing and replacing tiles for fixing roof hooks is going to be significantly more time-consuming, perhaps involving ripping nails to remove  a patch of tiles for each roof hook and using adhesive to replace that final tile (since it's impossible to nail).  Installers  may find that removing a large area of tiles and replacing them with a roof integrated solar system is far less trouble.

As the years go by, to stock of homes in the UK that have been built or had their roofs re-laid since the standard was updated will slowly increase.  It will become less and less of a sure thing to assume that the roof of the building you are quoting to install on will have loose laid tiles.  Solar installers should be particularly wary when pricing jobs on homes that have clearly been built in the last couple of years.

Of course for those solar installers that operate in the new build market the impact of the change is immediate.  With a loose-laid roof it was previously possible to install an above-roof solar system on a new home just like a retrofit on an existing one.  Occasionally the roofing contractor would refuse to provide a warranty on a roof if a solar installer had been tramping round on top of it lifting and notching tiles to fix roof hooks behind them.  Then it might be necessary for the build programme to allow time for the solar installer to fix roof hooks after the roofer had battened the roof but before they had tiled it.  This now becomes the only way to work with a nailed roof and clearly requires an additional visit to site for the installer. 

Even then, when you come back to fit the rails and modules above the tiles you need to figure out a way to get the cables through  into the building.  The cheapest option is push the cable up through a notch cut in the back of the tile (hopefully with some protection against abrasion of the insulation such as a flexible plastic conduit).  Alternatives include a flashing with cable glands or a similar cable entry created with lead.  All these options are extremely awkward to install without being able to easily remove the tiles fixed down by the roofer.

Little wonder that with the advent of cost-effective roof integrated solar that has closed the gap in cost with above-roof kits, most solar installers working in the new build sector have decided that roof integration is the only way forward.  Not only are the aesthetics more acceptable to customers it's now just so much less hassle to install.  It needs only a single site visit to fit the system after which the roofer can fit the slates or tiles all around using as many nails as they like!


Thanks to Etienne Hilaire  Avonside Renewables for their advice on the practical impact of the new standard.

Friday 24 June 2016

Solar for Housebuilders

New homes with integrated solar.  Image: Viridian Solar

Solar is a fast-paced, innovative sector.  Even those of us who work in the industry sometimes struggle to keep up with the pace of change.  Most house builders have now experienced the use solar PV on at least some of the developments, however with the advent of stretching new building regulations in Scotland and Zero Carbon Homes for London arriving in October, it seems like a good time to provide an update for house builders on how this technology has rapidly matured in recent years.

Costs Keep on Falling

The reduction in the cost of solar PV in recent years has been breathtaking.  As global production capacity for the manufacture of solar PV panels has grown, the cost have fallen dramatically.

Economies of scale have also driven down the cost of  so-called ‘balance of system’ components like dc connectors, dc isolators and electrical inverters.  Innovation in roof fixing systems has lowered costs and different products to work with roof coverings of all kinds have increased the speed of installation.  For flat roofing, the emergence and certification of low-ballast flat systems reduce the imposed loads and the need to reinforce the roof structure.  A skilled workforce has achieved significant efficiencies in installation times.

If it’s more than a year since you last looked at solar for a housing development, you should look again at the costs. 

Aesthetic Solar Roofing Systems have Grown in Popularity

Image: Viridian Solar

Roof integrated solar systems replace the tiles or slates on the roof rather than sitting above the roof covering on metal rails.  When these employ  a ’black-black’ panel (one that has a black frame and a black backing sheet behind the solar cells), the panels look more like an intended and sympathetic part of the building design and less like a bolt-on afterthought.

Developers should take care when specifying roof integrated solar to make sure they get the aesthetics they’re looking for.  Since the silver framed panels are of fractionally lower cost, a specification that simply asks for ‘roof integrated solar’ could result in installers (driven by an enthusiastic Quantity Surveyor) pricing silver panels above a plastic sheet, which looks little better than the rack-mounted above roof systems.

A booklet published by the Solar Trade Association – Stunning Solar – showcases solar design and features many excellent examples of roof integrated solar, also check out this gallery of fabulous photographs of homes with integrated solar.

The UK solar industry has developed MCS012 testing to ensure that roof integrated solar systems comply with building regulations on wind resistance, weather tightness and external spread of flame.

New Approaches to Cost-Optimisation Have Emerged

House builders, architects and energy consultants have taken some time to figure out how to use solar in cost-optimised designs for homes.  Clearly the rapid cost reductions the technology has achieved has made it difficult to keep up, but in addition the price-performance curve for solar is quite different from other energy saving options.  Insulation follows a law of diminishing returns - the next improvement in energy saving needs more and more insulation.  In contrast, the bigger a solar system gets, the lower is its cost per kWp and the lower the cost of the CO2 savings it produces.

What this means for those aiming to design cost-optimised new homes is:

  • A combination of solar and fabric (insulation) measures may be more cost effective than fabric alone.
  • If your energy assessor suggests that your homes need a small solar system (perhaps less than 1kWp) , you should also take a look at the total cost of a larger solar system coupled to less extensive use of alternative energy saving features.

At Viridian Solar, we see that  more and more house builders, energy assessors and architects are pricing for a range of different sizes of solar system for their homes, suggesting that some in the housebuilding industry have already understood the opportunity to use larger solar installations to optimise total construction costs.

I have written in more detail on this point in this blog.

Reliable Performance has been Demonstrated

In recent years concerns have arisen in the construction industry about the energy ‘performance gap’.  This is the difference in energy efficiency calculated for a house design and its actual energy performance once it’s built.  Unfortunately on building sites in the real world, things happen that don’t appear on the CAD drawings of the architect and energy assessor.  Small openings around pipes let in drafts, gaps are left between insulation and windows are installed in a position to create a thermal bridge.

Solar has proven itself to deliver the energy savings predicted by the SAP calculations - and if anything to outperform the estimates.  An assessment of the energy yield of PV panels by Sheffield University found 98% of installed systems were working according to their specifications. 

Not only does solar PV deliver the saints it promises, it does so in an utterly reliable way.  When the Renewable Energy Consumer Code assessed the complaints received about solar between 2010 and 2014, it was less than 1% of all installations, and this covered a time period during which cuts to the Feed in Tariff had driven extraordinary levels of deployment in short bursts.

 You Need Less Roof Area for the Same Power

Solar cells have become more and more efficient, raising the power output of solar panels as they do so.  Consequently less and less of the roof is needed to provide a given annual energy yield.
In the last ten years the average power output of newly launched solar panels, measured in Watts-peak (Wp), has risen by between two and three percent every year.  In 2010 people were typically installing solar panels with a peak power of 220Wp.  In 2014 this had increased to 250Wp.  Solar panels with a power of 275Wp are now commonplace today and panels of 300Wp will soon be widely available.

Shading is Less of an Issue

Image: Viridian Solar

Shade is clearly not good for solar panel energy yields, but the availability of micro-inverter and power optimiser technologies means that the effect of partial shading on solar arrays can be minimised.  Power electronics is fitted at the level of the individual panel in such a way that if one panel is shaded it does not pull down the performance of the whole solar array.  Solar can now be fitted to roofs with complicated shapes that produce self-shading and into areas between dormer windows.

Customers Love Having it

According to Feed in Tariff statistics, there are now more than a 800,000 homes in the UK with solar, around 4% of all homes.  Most of which are people who have chosen to install solar as a home improvement.  Solar regularly comes out as the most popular form of energy in public attitude tracking surveys, with an approval rating over 80%.  Solar homeowners benefit from a ‘feel-good’ knowledge that a significant amount of their power use is provided from the solar panels on their own roof, visibly reducing their energy bills.

Evidence is also emerging that solar adds value to the homes that it is fitted to.  A survey by GoCompare found solar panels to be among the top ten home improvements in the UK.  Another recent survey by Barclays found solar was one of the top technologies that homebuyers want, increasing the value of a property by £2,000.  An authoritative study in the US discovered an average sales premium of $4,000 for homes for every kilo-watt peak of solar PV the house was fitted with.

Electric Vehicles and Battery Storage are on the Charge

Image: Tesla Motors

Electric vehicle registrations are growing at an extremely fast pace albeit from a low base currently.  Many manufacturers are now committing to develop and launch whole ranges of electric vehicles in the coming years.  Battery storage technologies for static applications are also coming to the fore with a number of high-profile global corporations (Mercedes-Benz, Panasonic, Tesla) launching products aimed at residential customers.

Solar and battery storage is a perfect match, with excess daytime energy held for use in the evening or to provide transportation when required.

The way people use and think about energy is going to change and the speed of this transition is already catching out government and energy companies alike.

The home of the (near) future is going to generate its own power, store it for evening use, and provide a power hook-up for electric vehicles.  The UK fleet of electric vehicles will store excess power from the grid during sunny or windy periods and release the power back into the grid at times of peak demand. It won’t be long before a home without its own power generation, battery storage and a charging point for an electric vehicle is going to be as outdated as a home with an outdoor toilet at the end of the garden.

This article is based on work to produce this technical briefing for housebuilders by the Solar Trade Association.

Monday 23 May 2016

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.

Wednesday 27 April 2016

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.

Wednesday 20 April 2016

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.

Friday 4 March 2016

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.

Monday 25 January 2016

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.


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.