Panel Size: panels commonly range in size from 180w up to 300w. Do not judge the panel on its size. The different sizes are used to allow the most efficient use of space on a roof to get the most power. More powerful panels may cost more, but they may be cost effective if they enable you to get more revenue from a limited area of roof.
Panel Quality: 70% of all panels are now made in China. The rest are made in Europe, Japan and the USA. Quality is king and varies hugely. There are good Chinese and there are bad. Examples of the good ones are CEEG, Sungrid, Suntech, Phonosolar and CNPV. The Chinese also manufacture for many other PV companies. Even some German and Australian companies brand Chinese panels such as Schuco and Sungrid. In Europe you will find the world’s best but more expensive panels from Solar World and REC Solar. The Japanese also have some premier brands such as Sanyo and Sharp.
Country of origin: As mentioned above there are many misnomers on where the panels are made. A good example is Sharp of Japan who assemble parts from the EU, China and other countries, in South Wales. The well known German brand Schuco is in fact a good quality Chinese panel made by Canadian Solar.
Quality of silicon cell: There are only seven silicon cell manufacturers of any size in the world. A few make cells that they then turn into panels such as Solar World, CEEG, Sanyo etc but most of the world production is sold on to companies who then assemble the panels. There are 3 grades of cells, A, B and C. C grade get used for lamp posts, toys, calculators etc and some very cheap panels. B grade find their way to a lot of the panel assembly companies. A grade cells end up in only the best and most expensive panels and the results are seen in long term tests as discussed below. The lower the grade of cell the lower initial power output but also the quicker the impurities and defects will degrade the output performance with time.
Cell type: For most situations Mono crystalline and Poly crystalline silicon cells are used. Until recently, in good light conditions Mono crystalline would produce a higher output. Recent improvements have made Poly crystalline have similar out puts from particular manufacturers and also give the best low light performance.
Panel efficiency: it is very difficult for a member of the public to judge the efficiency of a panel. The only information that you will find easily is the supposed panel efficiency which is a calculation based on the power output in watts divided by the square meter-age of the panel. The power output is measured in a flash test or burst of bright light which does not reflect what happens in natural daylight. Some manufactures’ do not even do flash tests. You will also find the measured output of the panels is guaranteed to be within a +/- range. The best panels will very carefully grade their panels and guarantee a + only variance in power output.
Test result power output: The real test for a panel is a long term test in actual daylight conditions in a country with similar climate to the one the installation is planned for. No manufacturers will provide this information. Some will give some examples of a year’s output from a large installation. However, the German independent magazine Photon has been doing long term tests since 2005.
Inverter efficiency: Inverters are the other main component in a system and can alter the electrical energy produced by up to 8% so it is best to go for the best possible as every point difference is worth a lot of money over the life of a system (30-50 years). The best inverters are made in Germany and Italy with (EU) efficiencies between 95-98%. Carbon Legacy only use SMA of Germany and Power One of Italy. Look for a minimum of 5 years warrantee on inverters. Some will offer extended warrantees’ up to 20 years for a reasonable extra cost.
Inverter test results: Photon magazine also do regular updates on inverters to show the results of existing and new models.
Quality of installation: MCS registration is a reasonable measure of the quality of an installation company but reports of rogue companies hiring poorly qualified teams after achieving registration are becoming more common. Look for companies with a good track record and a genuine interest in the industry and who are willing to show photos or provide visits to their installations.
Roof mounting system: roof mounting systems should be TUV approved and preferably of European origin.
Type and security of guarantees and warranties: The German PV market has driven the recent drive for longer product guarantees (5 years) and 25 year performance warranty on panels. The better European manufacturers often have offices in the UK for any problems and provide excellent back up service. Most manufacturers will offer a 5 year product guarantee and a 25 year performance warrantee. Be wary of the few who still only offer a 2 year product warranty.
Enjoy,
David Hill, Managing Director, Carbon Legacy Ltd
david@carbonlegacy.co.uk www.carbonlegacy.co.uk
Tel: 0845 6972419 Mobile: 07977 926033
