Your Questions About Solar Panel Efficiency

Susan asks…

Why do glass covers improve the efficiency of solar panels?

I am learning all about heat radiation in Physics. There is a question I am doing about Solar panels. It asks, why do glass covers improve the efficient of solar panels? I dont really understand. How do they?? thanks 😀 x

ssadmin answers:

Clear glass will allow most of the electromagnetic energy of sunlight into the air-tight volume of the solar panel.

The light strikes the black coated metal tubes and the black coated backing, and is absorbed as heat.

Part of this heat will radiate as infrared radiation, and much of this will leave through the glass.

But a great deal of it will initially remain in the metal as heat.

This heat will be partially transferred to the surrounding air, but because the glass stops the mixing of this air with the rest of the atmosphere, this heat will stay mostly contained within the solar panel.

If the glass were not there, there would be a huge loss of heat into the surrounding air.

Paul asks…

How much energy in joules can the solar panel produce each day?

Suppose one square meter panel of solar cells has an efficiency of 30% and receives the equivalent of 4 hours of direct sunlight per day. How much energy in joules can it produce each day? What average power of watts does the panel produce? If the solar cells were efficient they would generate about 1000 watts of power per square meter of surface area when exposed to direct sunlight.

ssadmin answers:

4 hours = 14400 seconds

1000 watts of power per square meter

1000 watts = 1000 joules per second
1000 joules per second x 14400 seconds = 14400000 joules
30 % of that = 4320 000 joules.

Since this is joules per day per m², the answer is 4320 000 joules/meter/day
or 4.32 MJ/m/day


John asks…

Effect of temperature on efficiency of solar panels?

I've done some research on this topic and from what I've read it suggests that the higher the temperature the lower the voltage output and therefore lower efficiency but from what we've learned in class it should be the opposite as the electrons would be ‘excited' from the extra heat and would therefore be able to produce a higher voltage output.

So I was wondering which is correct and why?

ssadmin answers:

The higher the temperature, the lower the voltage. Solar panels actually output more instantaneous power on a cold bright winter day than in the summer. But obviously, the sun shines longer in the summer, so throughout the longer day, it totals more output.
Update: I just found out why. Temperature affects resistance (ohms), changes to resistance changes voltage.

Sandy asks…

In the future, will solar energy be the main source of our power?

I realize that current solar panels are not that efficient. However, is it possible that they will eventually (in 20-30 years) be efficient enough to provide most of America's energy needs (75% or more)? The reason why I ask is that I once saw an TV interview in which some researcher from MIT was questioned about solar panels. He basically said that solar panel efficiency will double every two years.

Is this true? If possible, could you please cite an article or a reliable source?

ssadmin answers:

Hey Forsight, good question. Baypoint is quite right on the various energy sources. I agree with his assessment that solar will not be the main player in grid electricity in the years to come, but for different reasons. In the United States alone, grid electricity generates over 100 billion dollars in revenue each year. I am a bid advocate of solar power, but what is more important to me is that as we move away from a fossil based energy economy, we move into something more diverse. Lots of people think solar is the answer, or wind, or nuclear. I believe all these things are the answer, and I would be excited to see solar get 10% of that 100 billion dollars in 15 years. Solar has two main advantages over traditional energy sources. The first is obvious, the fuel is free. The second is that solar energy is spread out pretty evenly over the middle half of our globe, so people in New Delhi can get as much power from a small solar array as people in New York, and you don't need to run a wire between them to do it. But it's important to note that wind is a fantastic compliment to solar, in most places where the sun is limited, such as the midwest in the winter, the artic and cloudy coastal areas such as the Pacific Northwest, wind resources are generally good. Seasonally, many places that have limited solar power during one season, such as winter, have their greatest average wind speeds during the same season. Geothermal is also a great energy source if it is used properly, but again, it is more readily available in Iceland than it is in Lakeland, Florida. So the key to utilizing our abundant renewable energy sources is to use them all in moderation and not concentrate on one source at the expense of another, and our planet.

Ten years ago we embarked on a project to convert our home over to wind and solar power. It's been very interesting, we made plenty of mistakes, and we learned a great deal. People ask me if I had it to do over again, would I bother. My answer is, “If I had it to do over again, I wouldn't have brought in the utility company 20 years ago in the first place.” It isn't because I don't like the grid, or the utility company, they have been pretty reliable over the years. But in the first 10 years after our home was built, we used over 60,000 kilowatthours of electricity. In the next 10 years, we used less than 8,000. If I had taken the money I spent on those 68,000 units and put it into a solar and wind system in the first place, I would have paid for it by now.

Most people involved in renewable energy feel this way as well, our energy source should be as diverse as our people, but you don't have to take my word for it, here are some good resources if you're interested in learning more. Take care, Rudydoo

Richard asks…

What is the efficiency of the panel that is what fraction of the energy in sunlight is converted into energy?

A solar panel (an assemblage of solar cells) measures 58 cm X 53 cm. When facing the Sun, this panel generates 2.7 A at 14V. Sunlight delivers an energy of 1.0 X 10^3 W/m^2 to an area facing it. What is the efficiency of this panel, that is, what fraction of the energy in sunlight is converted into electric energy?

ssadmin answers:

The area of the panel in square meters is 0.58 * 0.53, or 0.3074 sq. Meter
If the power of the sunlight is 1000 watts per sq.meter, the panel receives
307.4 watts from the sun.
The panel puts out 2.7 amperes with a voltage of 14. The output power in watts
is the product of the voltage and current, 14 times 2.7, or 37.8 watts.
The efficiency is the ratio of power output to power input, so it is 37.8 / 307.4
or 0.1229 which can be expressed as 12.29 percent.
Solar cells aren't all that efficient, unfortunately. Hope this answers your question.

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