Solar panels are by far the most expensive item in a solar panel installation. Understanding the features that differentiate a good solar panel from a bad one is not so straightforward. In several instalments I’d like to give a guide to each of the key criteria to look out for. I will try keep it as simple as possible but it is something that many people ask me about so I think it isn’t a bad idea to discuss these issues in some depth.

First of all I’d like to discuss solar panel efficiency. This defines how effective a solar panel is in converting sunlight into electricity for a given surface area. The advantage of having a higher efficiency solar panel is that you can get more power out of a small available area. For this reason, high efficiency solar panels are normally priced at a premium and targeted at the domestic market where space is most constrained. High efficiency does not necessarily mean better quality or reliability however – these issues are covered later. Nor does higher efficiency mean better value; in many cases lower efficiency panels are used because they are more cost-effective in places where space utilisation is not so critical.

First of all, how do you find out the efficiency of a solar panel? It’s easy to find out this out for yourself. Remember that the power of a solar panel is given by the power you get out under ‘standard test conditions.’ This means the output is measure when the panel is exposed to a very bright light with an intensity of 1000 Watts per square meter (1000W/m2) at a temperature of 25oC. This is normally expressed in Watts (e.g. 185W or 230W etc) and is the power you will get when the sun is very strong. You can then multiply the module length and width (which is shown on the datasheet) to get the module area. By taking the module power in Watts and the standard test conditions of 1000W/m2 you can determine the module efficiency as follows;

Efficiency = power out / power in = module power / (width x length x 1000W/m2)

When evaluating solar panel efficiency its important to be aware that each solar cell has an efficiency higher than that of the whole solar panel (or module) due to empty space. Therefore make sure to find out which value you are looking at.

In general solar panels you will come across in the UK will be made of silicon (I have discussed thin film panels previously) so the discussion here will focus on these. The highest efficiency silicon solar panels on the market today are between 17% and 18% efficient. The efficiency of silicon solar panels is increasing due to R&D, but improvements are incremental and slow because there are a number of fundamental limitations to the efficiency of silicon solar cells which mean that any drastic improvements in the near future are unlikely. Perhaps I will describe those limitations in another article.

The main factor you will come across that affects module efficiency is whether the module is mono or multi-crystalline. In English this means that the solar cells can easy be made from mono or multi-crystalline silicon. Mono crystalline solar cells consist of a slice of a single, very pure silicon crystal and hence are very efficient due to few defects. Multi-crystalline solar cells, which comprise multiple crystals, are around 1-2% less efficient but are generally more cost-effective to produce. Personally I think it generally makes sense to use mono-crystalline cells for domestic installations where space is at a premium and multi-crystalline cells for larger installations.

Another factor that can affect efficiency is anti-reflective coatings. These are becoming more and more common. Nearly all solar cells have texturing directly on top of them that reduces reflection and now many solar panels come with anti-reflective glass. This generally consists of a textured glass that can be seen as a speckled pattern if you look closely. The improvement of anti-reflective coatings is hard to determine, although some manufacturers claim energy yield enhancements of over 5 percent.

When installing a solar panel system your ultimate goal should always be to get the best return on your investment, which means getting the most power for the lowest price without risking reliability and is dependent on many factors besides efficiency. Whilst there are a number of other technologies on the horizon that can be used to improve efficiency by small amounts, nothing will create a drastic change overnight. Prices of solar panels will continue to fall rapidly as production volume increases (in the same way as many other technology products such as computer memory) but these price falls will be matched by reductions in the feed-in tariff. Therefore don’t worry that installing today’s technology risks being superseded by a miracle solar panel tomorrow. Working in the industry gives you pretty good insight as to what is coming down the line.

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.

Following their announcement that they would be giving away free solar installations to households across the UK, it is perhaps unsurprising that energy firm, Homesun have received an unprecedented level of inquiries.

The offer will include both a technical survey to ensure that the property is suitable for solar panel installation and of course the actual installation, taking away the initial start up costs which often act as a deterrent to potential renewable installers.

100,000 systems will be given away to homeowners with south-facing roofs meeting the requirements of the survey, allowing them to enjoy all of the benefits of a solar panel system without having to outlay all of the initial costs associated with solar technology.

Solar panels could save homeowners up to 40 per cent on their electricity bills with estimates that a typical 3 bedroom semi could save up to £250 a year, with the added benefit that homes with solar panels installed fetch a higher price on the market than comparative properties without. A spokeswoman for Homesun commented,

“There’s real excitement about what we are doing. This just goes to show the latent demand for solar amongst the British public, they just needed to find a way to access it. Solar now makes perfect sense. I am proud HomeSun is leading the charge to take solar mainstream.”

Homesun have already announced that since the release of their offer, they have received 7,000 calls and have had 10,000 people log onto the Homesun website. Talking about the unprecedented level of interest, Chief Executive of Homesun David Green said,

“The phones have been absolutely mental and it’s put huge pressure on our website. We were not anticipating such enormous demand. It’s clear that for the first time, we have allowed renewable energy for residents to break through.”

Homesun’s offer has been made possible by the introduction of feed-in tariffs, government legislation introduced in April 2010 devised to increase the take up of renewable energy generation. The tariff works by offering premium, guaranteed rates for both the energy used and the units of energy fed-into the national grid from the renewable systems.

Homesun will therefore be able to recoup their initial investment and subsequently make a healthy profit on each installation. Homeowners will be given the opportunity to buy the tariff contracts from Homesun in the future but it is more likely that most will simply opt to make savings on their bills.

With offers such as Homesun’s making an impact in the media and the building of consciousness about the feed-in tariff, it is very likely that before long the market will be jam packed by suppliers offering very similar solutions

Market research and consulting firm, iSuppli has released a report showing the UK as the world’s fastest growing solar market in research looking at solar uptake since last year.

Good news indeed for UK solar and exactly the kind of market reaction which was expected following the announcement of the introduction of feed-in tariffs by the Department of Energy and Climate Change. While the cynics among you might point out that the UK was starting from the lowly figure of 6MW of output in 2009, it in no way detracts from growth figures of 1500 per cent, up to 96MW this year.

Feed-in tariffs, introduced in April 2010 work by offering fixed, guaranteed rates for small scale producers of renewable energy both for the energy they use and the surplus energy fed-back into the grid. The power companies are obliged by the legislation to buy the units of electricity at the top rates, the costs of which are passed onto the consumers.

In areas such as Germany, California and Spain, tariff systems have been an extremely effective way of generating investment interest in new renewable industries, traditionally perceived as unviable. Indeed, the annual Ernst & Young Investment Attractiveness Indices consistently ranks those countries with strong tariff legislation as the most attractive for renewable investors looking for good returns on their capital.

The UK growth is such that it has outstripped that of Spain, a mature solar market whose growth only tipped 730 per cent.

Dr Henning Wicht, Director of iSuppli commented that,

“Things definitely are looking brighter for the solar market in the United Kingdom in 2010, as the country has adopted attractive Feed-in-Tariffs to promote PV adoption. Furthermore, with leading solar country Germany cutting its FITs, the focus of the PV world is shifting to places with more favourable incentives, making the United Kingdom a solar hotspot this year.”

With tariff legislation now in place and growing consciousness of the viability of renewable energy, it is expected that the UK solar market will continue to grow albeit at the more steady rate of 50 per cent. The iSuppli study estimates that the UK market will reach 214MW by 2012 and 501MW by 2014 helping the UK to go along way to meeting its carbon reduction targets and building the foundations of a strong renewable energy industry capable of competing with the like of Spain and Germany.