As with most things technical, calculating solar panel output and discovering which solar panel is the most efficient, is not quite as simple as adding two and two. There are several factors to consider when reaching an accurate figure, not only with regards calculation but also with regards where your solar panel is located and, indeed, where you are living.
The fact is that exact science is rarely an exact science, so when it comes to real life (PTC rating), the results can be very different to those calculated in a laboratory. For example, it is practically impossible to foresee how overcast a day can be in your area or, for that matter, how many overcast days there can be. How often will a cloud obscure the sun, and how long will it be obscured for? Since the output of your solar panel depends completely on the amount of direct sunlight that hits your panel, the answers to the questions listed above can have a real effect on the output of your solar array.
Some of the best brand names will boast a certain efficiency rating per square foot of panel but usually this rating is calculated in a lab. In reality the figures can vary drastically, though for some they are better than the lab results. In PTC tests carried out in California in July 2009, Sanyo and SunPower were found to produce the greatest output of the popular brands in the market. All of the tests were on 200w panels with Sanyo’s HIP-200BA19 panel producing 14.97w per square foot. Sanyo’s HIP-200BA3,5 produced 14.87w, while SunPower’s PL-SY-HIP-200CA18 produced 14.71w. Kyocera came seventh in tests with their KC200GT panel producing 12.13w per square foot of panel. However, the results may not be the same where you live.
So, how do we calculate your solar panel’s output per day given that it is needed to power your electrical appliances each day? Well, first of all we must bear in mind that output is measured in ‘sun hours’. This is one hour of full midday sun exposure, so one sun hour may be attained after three hours sunshine in the morning, since the sun is not as strong in the morning. The average number of sun hours per day is around 4, despite your panel being exposed to sunlight for perhaps 8 hours. Therefore, a 200w panel may produce only 800w output in one day.
Bear in mind that, per square foot, a typical photovoltaic panel can produce around 10w of power per hour, so 250sqft (25ft x 10ft) of panels can produce an output of around 2.5kW of power. If you have 4 ‘sun hours’ per day then that makes 10kW of power per day, or 300kW per month. Now compare that to the typical monthly electricity bill from your on-grid suppliers to see what your normal per-month usage is.
If your panel’s output is falling short of the calculated figure, how can you improve your solar panel’s output? Actually, it is rather simple to do this. First of all, check to make sure that the panel is clean as even the thinnest film of grit or sprinkling of dust can drastically reduce the panel’s performance.
Secondly, check the location of your panels. Is it caught by the shade of a tree for a couple of hours a day, or is it sheltered by a building or fence for too long? Being ‘out of the sun’ for even an hour can also affect the output figure of the panel, slashing efficiency by as much as 50%. There is no such thing as a panel that is completely ‘shade tolerant’!
Know the right tilt angle of your panel. Although this is not the most important factor, it can make a difference. It is reckoned the best tilt angle for your panel is the same as your latitude from the equator. For example, if your live 25 degrees north or south of the equator, then your tilt should be at 25 degrees (towards the equator, of course). The reason for this is that ‘full on’ sunshine is the best to receive, and getting sunshine at an angle does reduce the power farmed from it.
Each of these steps will improve your solar panel’s output – though don’t forget that the size of your solar array (number of panels) should be taken into account also. If your array covers enough square feet then you can power your home or business with plenty left over – just keep you array away from trees!
Solar Panel Output Video
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