Your Questions About Solar Panel Efficiency

Sandra asks…

Would mounting solar panels on windmills increase their efficiency?

Now I'm not sure how effective a solar panel that's constantly moving is, but you could at least put some at the top and on the main body, right?

Am I just plain crazy, or would it work?

ssadmin answers:

Why would you do such a thing. To collect the solar energy you will have to transport the power to a central location. This is much more difficult when the collector is rotating on a hub. The top of the windmill is very small for a collection point and the amount of power would be relatively small. Enough to run the computers in the windmill maybe but not enough to provide large scale power.

Chris asks…

Why does heat negatively affect a photovoltaic cell's efficiency in solar panels?

Can someone please explain why higher temperatures lower the efficiency of photovoltaic cells to produce electricity? I initially thought heat would play no part in a photovoltaic cell but have recently read that it adversely affects it. Does anyone know why?

ssadmin answers:

What makes photovoltaic cells produce electricity is light (especially in the ultra violet spectrum), not heat.
Where you use heat are so-called solar water heaters, where water is actually pumped through (black) panels and thus heats up by the absorption of the sunlight's energy by the metal panels.
Most electronic components work less efficient in higher temperatures than lower ones. Something to do with electrical resistance increasing with heat. Super-computers are cooled with some liquid gas, in order to avoid loss of processing speed.

Mary asks…

How to determine solar panel output?

Let's say I'm in a sunny climate with an instantaneous incoming radiation of 1000 W/m2 (I understand that radiation can also be expressed as power or W*h, but I'm looking at instantaneous power output). If I have a solar panel rated at 150W, does my solar panel efficiency need to be 15% (.15*1000) in order to obtain the maximum output level of 150W? Say, later in the day the radiation level is 800 W/m2. Does that same panel, with the same efficiency, only outputs 120W (.15*800) at this time?

Or am I going about this wrong. Is there some other means to determine output?

ssadmin answers:

Your thinking is absolutely correct. To the first order, the efficiency of a solar panel is fixed, and the power output is directly proportional to the insolation (intensity of light falling on it).

Mandy asks…

Can i improve significantly solar panels efficiency with mirrors?

we have some solar panel on our roof. My neighbor has a redwood that i causing some shading on my panels from september to march. if i placed some mirrors to light the shaded area, would it make my panel produce as much as if it were in full sunlight?
I understand it would not be very practical as the mirror would need to track the sun during the day.
just curious.
Where can i find info on effect on stringing the panels. i have 3 strings of 5 panels. i am better off if the shade is on panels in the same string leaving the other 2 strings alone, or if they affect one panel of each string so they all have a decrease output?

ssadmin answers:

They're like batteries, either wired in series in which case shade on one means a loss of voltage and perhaps an added resistance if wired in series or a short if wired in parallel. Diodes can be used to prevent the shorts resulting in just a loss of current but each diode represents not only a cost but a 0.6V voltage drop as well as energy loss so it's a tradeoff as to how you want to wire the cells to account for shade and for both economy and efficiency.

Mirrors that track the sun are called heliostats and are used to concentrate light on photovoltaic cells when the cost of such cells warrant it but these days the price of cells have come down enough to obfuscate such measures. You may be able to get away with the right curved mirror so that a different portion of the mirror comes into play as the day goes on, of course there's not just the different angles through the day but the different angles through the months as you've already noticed. It won't take much before the mirrors become more expensive and difficult to mount than the solar panels.

This is where solar thermal collectors really shine (pun intended). Vacuum tube solar thermal collectors work in partial shade and cloudy conditions and the majority of a houses energy consumption is for heating, air-conditioning and hot water, all of which can be provided for by solar thermal (air-conditioning can be powered by a thermal source if a lithium bromide water absorption chiller unit is used).

John asks…

What is the efficiency of solar panels and How dependable are solar panels, why is this?

ssadmin answers:

There is not room enough here to write everything about the research being done on solar cell efficiency. There are reports of cells that use 40 – 41 per cent of energy from the sun. Boeing and Honda are but a few. Different methods and technologies that are used have brought the % rate over the 40% barrier and more to come. By increasing the total concentration of sunlight on the solar cell it mutiplies the cell area for greater effeciency. Sorry can't go on, but try CNET news.

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