Your Questions About Solar Panel Efficiency

Sandra asks…

What is the best solar panel?

In terms of efficiency and cost, what is the best solar panel.

I am limited in the number of panels I can put up (probably 6-8) so they must be efficient, but cost is important also.

What about these panels that can collect a wider range of light frequency?

ssadmin answers:

You have to decide which is more important to you, cost or efficiency.

The most efficient solar panels that are commercially available cost more than twice as much per square foot than the cheapest ones. Ultimately, I believe that the cost per watt was actually better on the cheaper, least efficient panels, but then you need a lot of square footage in order to generate any substantial power.

So it comes down to what you have more of, space or money.

The new panels that collect a wider range of light are not currently available commercially, and when they are I am sure that they will be expensive. I have read the research but have not heard of anyone mass producing them yet.

Helen asks…

At what angle do solar panels have to be positioned to get the most efficiency?

I want to build a house and put solar panels on my roof. What angle do I need to build my roof at so I can just place solar panels flat on my roof? Which direction does the solar panels need to be facing?

ssadmin answers:

This depends on your latitude and where you are. If you're in the northern hemisphere, it faces south, with a tilt direction at the sun with respect to the average tilt of the earth. If you're in the southern hemisphere, the solar panels (both photovoltaic and solar thermal) face north. If you're on the equator, then they may lie flat on your roof. In US at a latitude of 40 degrees, you may want a tilt of about 20 degrees (because of change of seasons). You can alway angel the panels easier than modifying an existing roof. Be sure NOT to shade any part of photovoltaic panels at ant time.

Richard asks…

1sq meter panel of solar cells has an efficiency of 50% & receives the equivalent of 8hrs per day sunlight…?

how much energy, in joules, can it produce each day? What average power of watts does the panel produce?
4.40 joules??? watts???? HELP PLEASE EXPLAIN!!

ssadmin answers:

This depends on what figure you use for the intensity of sunlight.

1000 watts / m^2 is a common figure used for bright sunlight at an optimal place on the surface of the earth, so if we used that, at 50% efficiency, that means the panel would be collecting 500 watts. Note that there is no photovoltaic panel with that collection efficiency today, so it must be a heating panel if this is a realistic question. That's somewhat confusing, as a heating panel would tend to be rated in different units than watts, like BTU's for example.

To get joules per day, Remember that one watt for one second is one joule. One watt for one hour is 3600 joules, since there are 3600 seconds in an hour. You can multiply it out the power of your panel, and by 8 hours, to get your answer.

George asks…

Need a chart for efficiency drop-off for solar panels when mirrors are used with them.?

Given that you have a 100W solar panel (rated with a 1000W/m^2 input), and you try to pump up the output with mirrors, is there a chart somewhere that shows the dropoff of efficiency with the increased illumination? Or an absolute maximum no matter how much W/m^2 is radiating them?

ssadmin answers:

As was said above, this depends on the cell manufacturer. Generally, the cell efficiency will increase with the insolation level (W/m^2) but decrease with the temperature of the cell. The trick to concentrated PV is really finding a way to passively cool the cell while pumping in lots of light.
Most CPV companies use special high-efficiency cells for this. Try Amonix, or the nice DOE folks at Sandia.

Mark asks…

Efficiency of solar panels?

How efficienent are solar panels? I mean, suppose we install a 1kw panel.. Wil it produce 5kw in 5 hours of good sun light?
Or like if its 80 percent efficient, wil it produce 4kw and so on.
Also, do the chinese solar panels give the same results as compared with panels from other countries?
I live in india, so we get plenty of sunlight during the day.

ssadmin answers:

Panels are labeled as to their nominal output. Efficiency can be viewed in two different ways.
First- conversion efficiency. The panels themselves are only about 15 ro 18 percent efficient at converting the suns energy to electricity currenlty. This according to manufactuers data sheets.

Second is your efficiency of mounting. Ideally you want the panels to be prependicular to the suns rays at all times. For various reasons this is not always the case. Compromises are made in the mounting that tries to optimize the panels for their location. This could be considered efficiency, but is difficult to measure accurately because you were limited in the manner of how could mount them, so compairing each installation to the ideal is at best a guess if you wanted to generate numbers.

Usually when a panel is mounted in a fixed position,
*you want to mount them at an angle that is the same as your lattitude plus 12 to 23 degrees
depending when you want your peak output.
*facing “Solar South”- which is not always ordinal south on your compass. It is the mid point of the period where the sun is unobstructed. In the southern hemisphere- Solar North.

In your question- the ony way to achieve 4 kilowatts is to find the same size panel with a conversion efficiency of 60 to 80 percent- shich does not yet exist.

The Chinese made panels compare comparably oor favorably to those made in Japan, Korea or the US, and most other countries. There is a Belgian company that has been boasting a 20 percent efficient panel, but they are not widely available.

With your location in India, you will see measurements higher than the nominal ratings, within certain liimits. At certain times of the day when the panel is in optimal or near optimal position, your 12 volt rated panel could output slightly more than 20 volts, and maybe more current than the nominal rating. So a 1 Kw panel could at times be actually producing 1250 Watts for short periods. Not much more than that though.

Yes, 1 Kw of panel will have produced 5KW/hrs after 5 hours have passed.

A website and a blog that may help some:

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