Higher Standards for Housebuilders Do Not Slow Development

The Truth has Been Revealed by Scottish Developers

NOTE - a new blog with updated data is available here

Housing developers say that if you make them build more energy efficient homes, they'll cost more and less houses will be built.

Our politicians have swallowed this argument hook line and sinker time and again.

I've written about this before - the flaw in the argument is the assumption that the developers costs have to rise. They don't. This is because one of the main costs of building the house is what you pay for the land, and if everyone is faced with the same regulations, then the value of the land is driven down and the landowner makes a slightly smaller profit from the deal.

Developers have successfully held up tighter building regulations on numerous occasions.

• The update to building regulations in England in 2012 ended up as only a 7% reduction in carbon emissions (compared to the significant cut required in the original zero carbon homes policy)
• In Scotland in 2012 there was no energy efficiency improvement at all.
• The Housing Standards Review resulted in legislation in 2015 with the intent of limiting local authorities powers to require higher energy efficiency homes through planning (legislation that is still not in force).
• Finally, after 10 years of clear policy direction, one of George Osborne's last acts before disappearing off to take lucrative directorships, was to tear up the Zero Carbon Homes plan (the existence of which had been mendaciously used to justify the changes in the Housing Standards Review).

So it's very interesting to see what's been happening in Scotland. After many years of shadowing Westminster on building regulations (apart from the obvious requirement to go just a percentage point or two lower on carbon emissions to make a point), Scotland really pulled ahead with its changes to regulations in 2015.  The graph at the top of this piece shows the gap opening up.

If developers' claims that higher levels of regulation would stop housebuilding in its tracks were true, you'd expect housebuilding in Scotland to have gone off a cliff.  Has it?

Has it hell.

The Merton Rule is Not Dead, Long Live the Merton Rule!

Can Local Authorities Still Require Energy Efficiency Higher Than Building Regulations?

The largest housing developers would very much prefer it if they were able to build the same house in Aberdeen that they build in Abingdon. If they can do this, then the cost of the architect and engineers to design their standard properties can be spread across more units, and their buying power can be increased by using the same component parts in every house they build. This is one of the ways they out-compete smaller, more local building companies.

For this reason they dislike local rules and regulations that affect the houses they build.

In 2008 UK government enacted the Planning and Energy Act, which among other things clarified that local planning authorities had the legal right to require energy efficiency standards in new homes that exceeded the national building regulations. This approach to pushing developers to build housing with an energy performance beyond the national minimum had become known as the 'Merton Rule' after the local authority in London that had pioneered the approach.

Here's what the Act says:

1  Energy policies

(1)A local planning authority in England may in their development plan documents, and a local planning authority in Wales may in their local development plan, include policies imposing reasonable requirements for—
(a) a proportion of energy used in development in their area to be energy from renewable sources in the locality of the development;
(b) a proportion of energy used in development in their area to be low carbon energy from sources in the locality of the development;
(c) development in their area to comply with energy efficiency standards that exceed the energy requirements of building regulations.

It has been estimated that around 50% of local authorities took advantage of the new clarity to build such requirements into their local plans.

National builders didn't like it. They didn't like it at all. Different local authorities chose to ask for 10% renewable energy on site, 20% renewable energy on site, Code for Sustainable homes level 4.

The national developers were faced with different requirements up and down the country, a situation further complicated for them by the fact that different local authorities enforced their planning requirements with different levels of enthusiasm and competence. In some areas, particularly those areas that combine both high housing need and low house prices, developers might find a planning requirement for renewable energy on new developments to be highly negotiable. Other local authorities, notably in the south, with high house prices that means developers are queuing up to build new homes there, have been far more successful at holding the line on the aspirations of their development plans.

It could be argued that this is exactly as it should be. The UK has very high geographical differences in house prices. Local authorities could set their local planning regulations to achieve the highest energy performance that was consistent with the economics of housing development in their area, specifically whether the value of development land is sufficient to cover the additional costs of more efficient homes.

However, in 2015 things swung back towards the large developers. The government of Cameron and Osborne announced a 'bonfire of regulations' to free business from costly red tape. The Housing Standards Review was formed to look at red tape afflicting the house builders. Developers successfully argued that this patchwork of local planning requirements was 'red tape' and the review concluded that it should be swept away.



The government chose to add the changes to the Deregulation Act 2015. Section 43 of this Act amends the Planning and Energy Act as shown below.

43 Amendment of Planning and Energy Act 2008
In the Planning and Energy Act 2008, in section 1 (energy policies), after subsection (1) insert—
“(1A)Subsection (1)(c) does not apply to development in England that consists of the construction or adaptation of buildings to provide dwellings or the carrying out of any work on dwellings.”

This amendment would remove the ability of local authorities (in England only) to require developers to exceed the building regulations for energy efficiency. Note that sections 1(a) and 1(b) remain, allowing local authorities to continue to require that a percentage of the energy consumption of a new development to be met with renewable or low carbon energy.

The passing of the Deregulation Act is, however, not the last word in this story. If you work in a local authority in England and a housing developer is telling you that you can't impose higher standards than building regulations on a development, they're wrong. The fact is that section 43 has not yet been brought into force, so the original Planning and Energy Act text still applies.

If you look at the Commencement Section of the Deregulation Act, you'll see how the various elements of the Act are to be brought into force.

Some sections come into force on the day the Act is passed in parliament, others some set number of months later. No special mention is made of section 43, so it falls under this provision:

(7)Except as provided by subsections (1) to (6), the provisions of this Act come into force on such day as the Secretary of State may by order made by statutory instrument appoint.

A check of statutory instruments shows that this has not yet happened for Section 43, fully two years after the Act itself was passed by Parliament.

In fact, during a Lords debate on the Neighbourhood Planning Bill, in response to a question by Baroness Parminter, Lord Bourn confirmed that it was the case that local authorities still have powers to require higher building standards:

"The noble Baroness asked specifically whether local authorities are able to set higher standards than the national ones, and I can confirm that they are able to do just that."

So there you have it, the Merton Rule lives on!

 Local authorities still have powers to drive low carbon development in England, and it's just as well because our central government seems to have lost the will to do so. It's down to the sustainability officers and planning officers to enforce their local plans and they have the power to do so.

The Residual Valuation Model

Why Legislators Have Nothing to Fear from Tougher Building Standards

Simple isn't it? A chain of logic that seems irrefutable.

Legislate to make developers build better (low energy) homes and their build costs will rise.
These homes will not command a higher price, because the market is dominated by the price of existing homes for sale.
So the developer will make less profit.
Less homes will be built at a time when the country desperately needs them.

Our politicians have been buying this argument again and again from well-funded lobbyists working on behalf of housing developers.

The flaw in the logic is the assumption that the developers costs have to rise when you increase building standards. They don't. This is because one of the main costs of building the house is what you pay for the land, and if everyone is faced with the same regulations, then the value of the land is driven down and the landowner makes a slightly smaller profit from the deal.

The windfall from selling land to developers is so significant that a small decrease in the value is not going to slow down the market.

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 .

Shading

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.

References:

(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.

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.

thesolarblogger:

“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?

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!


Acknowledgements:

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

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.