There are currently thousands of different solar panel models on the market which makes it difficult to compare like for like. It gets even more complicated when you take into consideration panel product model names can vary from country to country for the same panel. There is however advantages in choosing the best types of solar panel that is suited to your geographical location.
Making a like for like comparison is best done by looking at specific characteristic of each model. You can of course spend too much time comparing and up to a certain point doing more research is not going to bring any extra dividends. You should also take into consideration that if you are using a solar installer they may well already use specific panels that they have found to be the best performers in your part of the country. You should also consider that the installer is likely to be able to get the panels at a wholesale discount as they buy panels in larger quantities. These other factors should all be taken into consideration.
If you are looking at different makes and model of solar panels then you may be considering buying panels separately and getting an MCS accredited installer to fit the panels or you may ask a local installer if they would be able to use your choice of panels rather than the ones they usually install. If you are thinking of using one of the free solar panel installers then you will not be able to choose the type of panel that is installed.
All photovoltaic solar panels turn the suns light into electricity, the more light that reaches the panels the more electricity they will be able to produce up to their specified capacity. This means that a 240 watt solar panel is not going to be able to produce 500 watts just because it is a sunnier day. Conversely if the light intensity drops below a certain threshold then the amount of electricity the panel can produce will also drop.
You will notice that in the morning as the sun is rising the output of the panels will rise. As the sun sets and the light starts to fade then the panels power output reduces accordingly.
Every solar panel has an output rating measured in watts. For domestic solar panels that are installed on householder's roofs these tend to be in the region of 170 to 300 watts. You can get smaller panels but for the purposes of a home solar system the ranges mentioned are the most cost effective and mist practical. As the wattage of the panels get larger the panels themselves tend to get larger and heavier. This tends to be the reason that the commercial sized panels are not used on homes. They would be too heavy for the roof to support, it would not be practical for the installer to manually lift the panels into place and they may be too big to physically fit the panels onto the available roof area.
One popular metric for panel comparison is the solar panel efficiency which is usually measured using the module efficiency percentage. This is usually measured under test conditions rather than in field tests as it would only be practical to get a comparable measurement by testing each panel under the same conditions which would not be possible if done outside. Testing is usually done in a lab using a fixed amount of light to represent the sun. The amount of light for these tests is usually set at 1,000 watts per metre squared and at a room temperature of 25°C.
The module efficiency varies quite considerably form about 12% to 19%, at the time of writing the most efficient solar panel available in the UK is Sanyo's HIT-H240SE10 which has an output of 240 watts and an efficiency rating of 19%. As a rule of thumb the most efficient panels tend to be those with the largest capacity in the manufacturers range. For example Sanyo's H230SE10 which is exactly the same size but has a 10 watt lower capacity and is only 18.2% efficient.
After efficiency the next most important factor is probably price assuming there are no specific panel sizing requirements. It is difficult to compare prices as although you can compare the cost of a specific make and model from different suppliers you may also want to use the metric of cost per watt to get the lowest cost. This of course means having to research multiple prices across multiple models.
In this industry solar panel prices are continually changing, in particular the cost of solar in the UK has reduced dramatically over the last year or so and is expected to continue to fall as solar PV becomes more popular. Most people will want a solar installation company to do the work of buying and installing the panels and so comparing specific makes and models will not be as pertinent. However I would suggest that if you are getting quotes from various companies that you make sure you ask what panels they use. This is important as one quote may be cheaper because they use cheaper imports which may not stand up as well to other brand panels.
Solar is a long term investment and so you want your panels to last at least long enough to have paid back their initial cost and preferably longer. Manufacturers give a performance warranty that states how long and how well the panels will perform and last. The standard manufacturers warranty tend to guarantee that the panels will produce electricity at 90% of their maximum potential and 25 years at 80%. Unfortunately solar panels do lose performance over their lifetime but the manufacturers warranty will guarantee that they will perform to specification.
Not all manufacturers offer the same guarantee the same level of performance so it is important to take into account the potential longevity of the panels. Although most manufacturers limit their warranty to 25 years this does not necessarily mean they will fail at the 25 year point. There are systems that have been installed by Sharp that are still working after 45 years.
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A roof facing as far as a West-South-West (almost West facing) direction or East-South-East (almost East facing) can still potentially generate up to 90 percent of a roof facing South.
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