More Solar for "Us"
Ok, I went off.the deep end? Bought 3 used 37watt uni-solar panels and a blue sky 2000e controller for the hefty price of $400, They were being listed as 75w panels, they are not The tested open...
Forum Discussion
Hi Mr Wizard,
See Mena's solar insolation site.
In winter time the radiation from the sun goes through many more miles of atmosphere which tends to absorb some of the energy. This happens every day, too as the sunlight must come through a lot of extra atmosphere at sunrise and sunset. Unisolar is better at low light levels because of the three different frequencies of light energy it produces power from.
Remember your high school science too, "The angle of incidence equals the angle of reflection". So when panels are flat mounted less energy is captured. Ideal angle is 90 degrees to the sun at every moment. Unisolar is better at this because there is no glass to absorb and reflect the energy, though some energy is reflected.
I'm too frightened of falling off the roof to even consider a tilting system--unless it were motorized with a remote control.
My foggy brain doesn't always remember to lower the TV antenna--which makes me glad I don't have a TV in my current RV. I would fear leaving my panels up by accident and I'm mistrustful of "automatic" systems.
The most efficient panels are now approach 22% over all efficiency based on square footage--but just like my favorite 2 volt cells--I can't afford them. They have essentially a "one way mirror" at the top layer, and mirror on the bottom--so light can get in--but can't get out--so there is more than one chance for a photon to hit a receptor and be turned into an electron.
Uni-solar is listed as 6.6% efficient, but again, are a great choice because of their shade and heat tolerant behavior. Typically 17 volt panels are rated at 25 C (77 f), make that 40 C (~104 F) and voltage drops by 3 to 5 volts. Even the best MPPT controllers can't deal with low voltage--so in the south where temperatures are high, series installations ought to be at least considered.
Uni-Solars output changes a little less than 0.1 volt per 1 degree C of temperature change. So, a Unisolar at 40 C is still putting out 15 volts--a nice usable difference for MPPT technology to get its teeth into. At 55 C (131 F) it is 13.5 and at 60 C (140 F) 13.0 volts. Of course, if the charge controller has a temperature sensor on it--charging may still happen.
I'm fairly sure that most RV's would be unbearably hot at 55 C. Time to skedaddle north!
Regular panels have glass which is a poor heat radiator, so it is entirely possible for them to be much warmer than the ambient temperature. Of course the substrate is a dark inky black or blue, and that absorbs infrared, heating up the whole panel. Uni-Solar have no glass and so radiate excess heat much more effectively. Panels, in an ideal world, would not be flush mounted--but have some space under them for air circulation for cooling.
See Mena's solar insolation site.
In winter time the radiation from the sun goes through many more miles of atmosphere which tends to absorb some of the energy. This happens every day, too as the sunlight must come through a lot of extra atmosphere at sunrise and sunset. Unisolar is better at low light levels because of the three different frequencies of light energy it produces power from.
Remember your high school science too, "The angle of incidence equals the angle of reflection". So when panels are flat mounted less energy is captured. Ideal angle is 90 degrees to the sun at every moment. Unisolar is better at this because there is no glass to absorb and reflect the energy, though some energy is reflected.
I'm too frightened of falling off the roof to even consider a tilting system--unless it were motorized with a remote control.
My foggy brain doesn't always remember to lower the TV antenna--which makes me glad I don't have a TV in my current RV. I would fear leaving my panels up by accident and I'm mistrustful of "automatic" systems.
The most efficient panels are now approach 22% over all efficiency based on square footage--but just like my favorite 2 volt cells--I can't afford them. They have essentially a "one way mirror" at the top layer, and mirror on the bottom--so light can get in--but can't get out--so there is more than one chance for a photon to hit a receptor and be turned into an electron.
Uni-solar is listed as 6.6% efficient, but again, are a great choice because of their shade and heat tolerant behavior. Typically 17 volt panels are rated at 25 C (77 f), make that 40 C (~104 F) and voltage drops by 3 to 5 volts. Even the best MPPT controllers can't deal with low voltage--so in the south where temperatures are high, series installations ought to be at least considered.
Uni-Solars output changes a little less than 0.1 volt per 1 degree C of temperature change. So, a Unisolar at 40 C is still putting out 15 volts--a nice usable difference for MPPT technology to get its teeth into. At 55 C (131 F) it is 13.5 and at 60 C (140 F) 13.0 volts. Of course, if the charge controller has a temperature sensor on it--charging may still happen.
I'm fairly sure that most RV's would be unbearably hot at 55 C. Time to skedaddle north!
Regular panels have glass which is a poor heat radiator, so it is entirely possible for them to be much warmer than the ambient temperature. Of course the substrate is a dark inky black or blue, and that absorbs infrared, heating up the whole panel. Uni-Solar have no glass and so radiate excess heat much more effectively. Panels, in an ideal world, would not be flush mounted--but have some space under them for air circulation for cooling.
