PV Gap

Bradley Said:

Why cant we use trees to capture solar energy from the sun and then recover the energy from the trees?

We Answered:

Photosynthesis generally takes light, CO2 & water and makes sugars. These sugars are chemically converted in to food, propane, methanol, ethanol, coal, oil, wood and all the other fossil fuels and orgnic compounds on the earth, through natural, geologic, and/or manmade processes. At every step of each process, energy is lost. To gain usable energy, other than in biologic processes, requires burning something, and using the expansion of heated gases to create physical force (motion), or then using physical force to drive a generator to create electrical current.

We do not currently have an effecient method of making electicity using incoming Solar radiation. Current solar cells convert a small percentage of one section of the electromagnetic spectrum into electric current.

Hope this helps.

Dwayne Said:

Wouldn't places like Alaska be great for Solar energy since they have constant sun for months?

We Answered:

what's the temperature in alaska in the middle of summer?

not all that high.
and with the sun shining 24 hours a day, that means that the sun's energy is quite dilute.

in other words, the sun is always visible, but it's not high in the sky.
kind of like 4-5 o'clock in the afternoon - that's not when you get a sunburn.

what you want is solar panels in the desert where there aren't any clouds, so you can take the best advantage of the energy available.

and you want that light to pass through the least amount of atmosphere possible, which is not the case in Alaska.

April Said:

How can we use solar energy on cloudy days when the sun is blocked?

We Answered:

You can store the energy. This can be done in one of two ways, depending on how you generate it. For solar photovoltaic (DC) systems, you can use what amounts to large batteries to store the energy for a later use. This is expensive and rather inefficient, however. For solar thermal systems, you can store the heat in a liquid metal (like molten salt) and draw off the heat at a later time to convert the energy to steam (and then on to electricity.) You can learn more at the national renewable energy labs site (www.nrel.gov) and also at sandia national labs site.

Marvin Said:

How does the sun angle influence the amount of solar energy received at a given location on earth?

We Answered:

It is a geometry problem. If the Sun is at the zenith, or directly overhead and shining directly down on the ground, you get maximum illumination. Imagine a solar panel laying flat on the ground. It is maybe a square panel one meter by one meter. It gets one square meter of sunlight. Hold it horizontally above the ground and it makes a 1 meter square shadow. That shadow is the sunlight that hits the panel instead of the ground. Now imagine another panel standing on edge. All the sunlight slips past it to hit the ground. It makes no shadow. There is no sunlight absorbed by the panel, it all just slips by and hits the ground. Now hold the panel at some angle, More that zero light will hit it, but less than 1 square meter of sunlight will. Maybe it makes a shadow 1 meter by half a meter, so it is catching only half as much light as it could if you held it the right way.

Now the Sun is usually not directly overhead. Even at noon, the Sun cannot be directly overhead unless you are in the tropics. You can see this with a globe and light source. Especially at the poles the Sun never gets anywhere near directly overhead, and in winter it never even rises. There is 6 months of night at the pole.

Annette Said:

how does the sun angle(altitude) influence the amount of solar energy received at a given location on earth?

We Answered:

The greater the angle between the sun and some point on Earth means that point receives less solar energy than if the angle was lower. In other words, the more directly overhead the sun is the more energy is received.

This is why winters in the Northern Hemisphere are cooler than summers; the sun rises and sets farther south and takes less time to move from horizon to horizon. The N. Hemisphere not only gets weaker radiation but it gets it for less time. In the summer it's just the opposite -- the sun rises and sets farther north and takes longer to move from horizon to horizon.

Claude Said:

What changes can solar energy cause to a person lying in the sun?

We Answered:

It's not solar energy, but certain wavelengths of light that come from the sun that affect a person who is sun bathing. Like UV rays that your sunscreen protects you from, most of these rays damage a persons skin.