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.