Posts tagged with: solar installation

Solar PV installation, Harpenden, Herts. 2.22kWp system

Having been interested in domestic energy generation for several years, we’ve been watching developments in the various technologies over this time. The wind technologies for the domestic market never lived up to expectations. Our hot water is obtained through a gas combi boiler so solar hot water wouldn’t be financially viable. As for PV, the recent government FiT scheme suddenly made it very attractive. So we started looking into it. We did our research on systems, manufacturers, technologies, searched websites for indicative prices and contacted several installation companies for a chat.

At this point I must warn prospective PV clients about the selling techniques some companies employ. As knowledge grows about domestic PV and the government’s incentives, companies are springing up at a very swift rate to jump on the band wagon. There’s companies sending out reps with little or no knowledge of the technicals, and operating the ‘double glazing’ sales/marketing techniques whereby the price drops 40% over the course of their visit! If you come across one of these techniques, DON’T sign up!! The reputable companies will provide an indicative quote by phone or email and if you’re interested in taking it further, they’ll send out a technical bod for a site visit. The site visit will confirm your property’s orientation, the roof construction, the cable routing, the siting of the electronic boxes, and confirm (or modify) the indicative figures of generation (units and cost benefits) that you’ll have received in your provisional quote. It’s worth bearing in mind that any indicative figures given to you should have been based on the government’s SAP figures, which are generally conservative.

The company we chose was Spirit Solar, based in Reading. They were professional, thorough, knowledgeable and above all fun to deal with. They shared the ‘buzz’ and excitement of ‘green’ energy, which made the whole experience even more pleasurable. The installation went without a hitch and we were generating juice by 4pm on the second day. We do, however, live in a bungalow which made the install relatively easy. There was no need for extra scaffolding and we had given thought ourselves to the cable routing to make things easier.

We’re now one week on from commissioning and all the facts and figures we worked out (and those we were quoted in quotes etc) appear to be on target as expected. And we can’t stop watching the Sunny Beam wireless generation meter!

We have 12 x 185kWp Yingli poly panels with a SMA Sunny Boy 2500 inverter, providing a 2.22kWp system. We face due south-west with no shading. The expected annual output is around 1,750kW – about half of our annual electricity usage. System cost was £10,500.

We anticipate an annual return of around £900 – a combination of Feed-in, export units and the saving on our electricity bill. Guaranteed for the next 25 years, and tax-free!

Steve Bryant. Aug 2010.

Announcements on earlier this month that the Spanish government was to reduce spending in another sector of the Spanish economy would hardly have made for happy reading on the pages of El Pais and El Mundo. Nevertheless the news was that huge spending cut backs would be made on solar energy with tariffs designed to attract uptake with reductions of up to 45 per cent.

Draft proposals from the Ministry of Industry announced that spending cuts would reflect those seen on feed-in tariffs in Germany and Italy where the tightening of purse strings has necessitated the removal of what are seen as non-essential expenses.

Indeed, Spain will be reducing tariff payments for roof-based systems by up to 25 per cent but for large ground based solar installations a much more eye watering 45 per cent, news not likely to impress installers or investors.

Feed-in tariffs work by offering producers of renewable energy fixed, premium rates for the energy they both use and feed back into the grid. The energy firms are obliged by legislation to purchase the renewable energy at the premium rates the costs of which are spread across Spanish energy consumers. The Spanish government has therefore been able to justify cut backs explaining that they are a means of controlling rising Spanish Energy Bills.

The problems of course is that while consumers may make some savings on their monthly electricity bills, cut backs at this period could cause serious long term harm to an area of the Spanish economy which has been booming over the last decade.

With news this week that growth of the UK solar market has finally over taken that of Spain, it highlights once again the essentiality of tariff mechanisms as a way of creating long term attractiveness for investors in the face of struggling economies.

When thinking about renewable electricity for your home, two options spring to mind; photovoltaic panels and small wind turbines. But which one should you choose? The government has introduced a feed-in-tariff that pays a subsidized amount for the electricity they produce and the amount paid for small wind turbines is similar to that paid for small PV systems (34p/kWh compared to 41p/kWh).

The key criteria to deciding which technology will be the most profitable is the cost of producing a unit of energy from each one. For this you need to factor in the up front costs such as equipment and installation, and then look at how much energy they will produce once out there over an average year. Without going too heavily into numbers my argument is that in some instances, micro-wind turbines will have a lower cost of energy than solar panels, but for the majority of cases solar panels will be better and this can be explained by some basic science.

Without a doubt, on a large scale, wind energy is cheaper than solar. The cost of energy from large-scale wind farms is somewhere around 10p/kWh whereas the cost of energy from large-scale solar is three to four times greater at present. Big wind turbines are now very well designed products and many years of industry development means that the costs have fallen dramatically and continue to do so. Big solar farms are also rapidly reducing in cost and make a lot of sense in some locations, particularly in the many regions where wind farms are not suitable, but for now they do not compete.

On the small scale however, the economics are drastically different. As the size of a solar installation decreases, the performance falls linearly with the amount of area used, and therefore the cost of energy does not change so dramatically. In contrast, as wind turbines get smaller their performance gets disproportionately worse. This is for two mains reasons:

The first reason is that as the turbine blade length gets shorter, the ‘swept-area’ decreases quadratically. This means that if you decrease the length of a blade from 80 meters to 40 meters, the area covered by the blade decreases from 20 thousand square meters to just 5 thousand. The ‘swept-area’ determines how much wind energy the turbine can use. So when you decrease the blade length you still need all the expensive moving parts like the generator, but you get disproportionally less energy – for one big wind turbine you would need thousands of smaller ones to cover the same area. The second reason is that where you use micro-wind turbines the wind speed is generally slower. This is because most of us live in built up areas where there are other buildings nearby. These buildings disrupt the wind, making it irregular and slow. Wind speed is crucial to the effectiveness of a wind turbine, again because the energy contained in the wind is disproportional to its speed. If the wind speed drops by a factor of 2, the energy produced by a wind turbine decreases by a factor of 4. Comparing most built up areas, the average wind speed is much lower than half the wind speed found high-up in open spaces where you find most wind farms.

These two factors combine to mean that for most homeowners solar panels are the most sensible and safest option. Of course, if you live near an open space and get a lot of wind then a micro-wind turbine could be a great investment. However, if you do live near a windy open space, I would suggest trying to build as big a wind turbine as possible, as their cost effectiveness increases dramatically with size.

Solar panels fall into two main technological categories. The incubant, established tyoe are called crystalline silicon solar panels and the exciting but unproven type are known as ‘thin-film’ solar panels. To understand the advantages and disadvantage of each technology I’ll briefly explain how each type of solar panel is made. Crystalline silicon solar panels are made from 50 or so ‘solar cells’ connected together and encased in glass. Each solar cell is in fact a thin slice of large crystal of pure silicon (called an ingot). These large crystals are grown from a seed crystal surrounded by molten silicon at very high temperatures. The silicon used must first be extracted from silicon dioxide (also known as sand) and then purified to a very high level. Once the crystal is formed it can be sliced into wafers. The wafers are then specially treated to make a junction between a positive and negative type semiconductor, and then other layers such as the conductive contacts are added to make a working solar cell. This process has many steps and consumes a lot of energy. However, many companies have spent a lot of time refining the process to make it as efficient as possible so almost all parts of the process are now automated.

Thin film solar panels are made using a radically different process. The underlying physics is similar in that they still use a junction between a positive and negative doped semiconductor, however thin film solar panels have the potential to be made in much fewer steps than crystalline silicon. The idea is to take glass (or sometimes foil or plastic) and coat it directly with a series of layers, including the active semiconductor layers to produce a working solar cell. The glass is then encapsulated with a protective plastic and a second sheet of glass as protection. This process saves having to make lots of small cells and connect them together. The other advantage is that the layers are very thin, hence thin film solar cells. The active layers of the cell are only a few nanometers (billionths of a meter) compared to 0.2mm for each silicon wafer.

The important point of all this is that the manufacturing cost of thin film solar cells has the potential to be significantly lower than crystalline silicon. Unfortunately, there are some catches. Firstly, they are not as efficient as crystalline silicon. Crystalline silicon reaches 16 – 18% efficiency in modern solar panels, whereas the most efficient thin film solar panels on the market today  are under 11%. The next drawback is reliability. Thin film solar panels have had less time to prove themselves and have been known to suffer from degradation meaning that their performance gets significantly worse over time.

Despite these drawbacks, several companies have managed to become very successful in manufacturing thin film solar cells. The most notable is called First Solar who are now one of the top two largest solar panels manufacturers in the world and have a significant advantage over rivals due to their low manufacturing costs. First solar make thin film solar cells made from cadmium telluride, one of a number of semiconductor materials that can be used for thin films. First Solar’s panels are less efficient but are very popular for large scale solar installations because of their low cost.

Before the financial crisis, when silicon was in short supply and very expensive, all thin film solar panels were a good idea. First Solar could not produce enough and billions were invested in a large number of thin film solar companies aiming to follow in their footsteps. Now that the silicon shortage is over and the price of crystalline silicon solar panels has fallen, the environment for thin film solar cells is more challenging. First Solar will remain a strong player as they have managed to get to high volume and have a reliable production process. Many of the 200+ start-ups hoping to replicate their success will struggle however. For thin film solar cells there are a wide range of different manufacturing processes and materials that can be used, and there is still a lot of research being done to improve our understanding of the underlying physics. This means that there is a lot of opportunity to invent a ‘unique’ technology and start a company but only the best thin film solar companies will make it however. They have to show not only that their technology is efficient and reliable, but also demonstrate that large scale production is feasible and low-cost. Many ideas that look good on paper or in the lab turn out to be impractical when it comes to volume manufacturing.

At present, it seems like crystalline silicon will retain a strong market share for the foreseeable future (it current represents 80-90% of the market) but I believe that eventually certain thin film technologies will begin to displace crystalline silicon. There is a lot of potential for efficiency improvement in thin film, as well as lower manufacturing cost. Some technologies, particularly that usce solution processing are really very exciting.

What does this mean for the UK solar industry? Very little actually. I would expect over 90% of the UK market will be crystalline silicon for a long time. The reason is that the UK market will be dominated by smaller rooftop applications (partly due to the structure of the tariff as discussed last week). In such space-constrained applications you want to use the most efficient technology to maximize the energy generated from the available area. For now, this means always choosing crystalline silicon as it’s efficiency is significantly above any thin film solar panel out there.

Keep an eye out for breakthroughs in solar technology as some are surely bound to occur, but beating high quality crystalline silicon solar panels made in China for cost, efficiency and reliability is not easy.