quote:I personally looked into it and was very shocked to learn all the solar panel companies output numbers are very optimistic to say the least.
Will have to dig up the numbers and specs but the output numbers these companies list are for direct sunlight at the equator. Once you start moving away from the equator the panel efficiency drops. As well time of year, weather conditions, etc etc.. And another factor was the panel being directly pointed at the sun.
I have a solar panel setup for my home where I monitor power production on a daily basis. What I have found that there are several main factors that determine optimum power output from the panels, assuming of course there is no cloud cover in the sky.
One is time of day. The output will be highest in a 4 to 8 hour span centered around high noon when the sun is at it's highest, and the panels will put out the most when the sun is highest in the sky.
Another thing that affects the output significantly is the temperature of the panels themselves. In summer, when it's warm, I rarely get the rated power capacity of the panels. In winter, when the panels are very cold (ie -10 to -45c) I sometimes get well over the rated capacity, even though the sun is much lower in the sky, than in summer. There are a couple of factors that offset the temperature of the panels, such as the much clearer skies in winter (less haze) and perhaps some increased light due to the snow that may reflect a bit of extra light into the panels. But the main effect is temperature.
The panel ratings are based on 1 kw of energy from the sun per square meter and at a panel temperature of 25 C. Panel temperatures in summer can go to in excess of 50C or even 75C. Panel efficiency drops by .25% for thin film and by .5% for crystalline cells per 1 C rise in temperature.
The tilt of the panels to the sun does not have too much effect on performance unless it's significantly off. That is why many install panels on a roof at a fixed angle (usually close to the latitude in degrees from horizontal).
Small areas of shade on the panel can also have a huge effect, but has not been a factor with my system.