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Solar Power Efficiency

By admin on August 31st, 2011

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Solar power efficiency is determined by a number of factors. In this article I look at some of the factors you need to consider when thinking about going green and slashing your home energy costs.

There are many different methods of harnessing solar energy. One of these methods is the use of solar collectors. Solar collectors do the job of converting solar energy into heat energy. This heat energy is used to support heating systems, heat water and swimming pools.

The solar energy efficiency factor, which is defined as the usable thermal energy versus the incoming solar energy, varies from collector to collector.

Every collector is fitted with an absorber. The absorbers are made from different materials. Copper and aluminum are typically used; however, absorbers used in swimming pools are made of plastic.

The level of absorption shows the amount of short-wave solar radiation being absorbed. The degree of emission shows the ratio of absorbed energy to emitted heat. To ensure that a good proportion of the solar radiation is converted into heat energy, selective surface coating is used in absorbers. More than 90% of the radiation can be absorbed with the help of usual coating materials.

All collectors lose energy in the form of thermal and optical loss. Percentage of transmitted rays and the percentage that are absorbed is represented by conversion factor or optical efficiency h0. Basically, it is the product of the rate of transmission of the cover of the collector and the absorption rate of the absorber.

The heat loss is given in watt per m of collector surface and the difference in temperature (in C) between absorber and its surroundings. Heat loss is directly proportional to the temperature difference. Its shown with the help of thermal loss factor or k-value. A high conversion factor and a low k-value are associated with a good collector.

The conversion factor and thermal loss factor depend on the type of collector being used. For instance, the conversion factor for flat-plate collector is 0.66 to 0.83. Its temperature range is between 20 to 80 degree centigrade and the thermal loss factor is 2.9 to 5.3.

10 Responses to “Solar Power Efficiency”

1. Josephine W says:

   August 31, 2011 at 7:55 AM

   What is efficiency of coal power stations and solar energy?
2. Lir says:

   August 31, 2011 at 9:03 AM

   At a certain location, the solar power per unit area reaching Earth’s surface is 200?
   At a certain location, the solar power per unit area reaching Earth’s surface is 200 W/ m^2, averaged over a 24-hour day. If the average power requirement in your home is 3 kW and you can convert solar power to electric power with 10 % efficiency, how large a collector area will you need to meet all your household energy requirements from solar energy? (Will a collector fit in your yard or on your roof?

   Please Help. It would be much appreciated. Thank so much!
3. Master Anarchy says:

   August 31, 2011 at 5:06 PM

   Solar Power vs Nuclear Power – Cost Efficiency No Consideration?
   Recently I read that Solar Power may be generated for 8-12cUS/kWh.

   Does this make for a competative production price, given retail electricity costs?

   Should environmental costs be factored in to current prices, as some suggest they must inevitably be, would it then be competative?

   Should the lack of fissionable by-products be taken into consideration, given the current suite of Wars (on Terror, on Drugs, under the Rugs, etc)?
4. fhapgood says:

   August 31, 2011 at 5:56 PM

   solar power efficiency?
   Just to make sure I understand this solar power thing:

   1. Peak solar constant on the earth’s surface = 1 kw/meter
   2. Photovoltaic efficiency = 20%
   3. Intermittency efficiency = 20%

   (this is the relation of the peak to the average unit time, totalling across day and night, good weather and bad, summer and winter)

   4. Storage efficiency = 25% (Storage efficiency comes in two parts: losses inflicted by putting your power in storage and losses inflicted when taking it out. I am assuming 50% in both cases.)

   So we end up with 1000 kw/m * .2 * .2 * .25 = 10 watts a sq meter.

   I’m not saying that’s good or bad. I’m just asking if it is right.
5. Robin the energy saver says:

   August 31, 2011 at 6:06 PM

   Coal-fired power stations are not very efficient. Most of them don’t reach more than 40% efficient. A few can reach 45%.

   There is a theoretical limit to the percentage of energy that can be converted from heat to mechanical energy in any heat engine, which is the first part of what a coal-fired power station does. This limit depends on the difference in temperature between the heat source (burning coal) and the heat sink (the steam coming out the end of the turbine). The higher the difference in temperature, the more efficient. Most coal fired plants are well below the theoretical limit for their temperature delta, and typical efficiencies are in the 30-40% range. Coal quality also has an impact on efficiency. For example, coal with a high moisture content will be less efficient, because some of the heat energy in the coal will be used up converting the water in the coal into steam, rather than into heat. (State change from liquid to gas uses energy without producing heat, which is why when you boil water, the thermometer rises steadily to the boiling point, stays there for a while, and then once boiling starts, it keeps rising.)

   There are two main types of solar electricity generation. Small-scale and most large-scale installations are photovoltaic systems, which capture the energy from the photons that make up light, in order to create an electron and its opposite, a ‘hole’, which then power a circuit. Again there is a theoretical limit to the efficiency of a photovoltaic cell, but most commercial solar photovoltaic panels fall well below this limit. Current efficiencies are in the low to high teens for the more affordable units. Much higher efficiencies are possible – as high as 40% or more – but these often cost as much as 100 times as much.

   The second common type of solar electricity is produced by concentrating sunlight, using mirrors, onto a small target containing a liquid; that liquid becomes very hot due to the concentration of light and its conversion to heat, and that heat is then used to boil the liquid in order to drive a turbine. What you might notice here is that that turbine is basically, once again, a heat engine, and so subject to the same theoretical efficiency limits as a coal fired power plant.

   The main difference, however, is that with coal we are looking at a non-renewable resource which costs money and causes environmental damage to extract, whereas with solar we are looking at a renewable resource that is basically free once the solar station is set up.
6. kirchwey says:

   August 31, 2011 at 6:41 PM

   It’s simple math.
   1 m^2 of solar panel generates an average 10%*200 W = 20 W.
   You need an average 3000 W, which is 150 times as much, so you need 150 m^2 of solar panel.
   An average power of 3000 W is pretty large for a typical house. Is there a sawmill hidden inside?
7. islander8181 says:

   August 31, 2011 at 8:34 PM

   I heard recently that solar panels pay for themselves in 8 years. And with the cost of fuel going up they may pay off in 4 years. They are guaranteed for about 10 years and the life expectancy is about 25-30 years. If government would subsidize the cost and more manufacturers began producing them their costs would go down. Plus they can be put on almost anyone’s roof and do not pollute and pose no danger (unlike nuclear). I think solar and wind turbines installed on single family homes is the way to go.
8. syrious says:

   August 31, 2011 at 11:08 PM

   What is 100% efficiency in ref to solar power? How is it measured or determined?
   I’m reading Sucatcher catches thermal energy at 31.25 % efficiency. So, if it could do it at 100%, how much energy would that be? Measured how? By what? Does anything pick up 100% and use it or make it useful?
9. Prof. Normal says:

   August 31, 2011 at 11:48 PM

   A solar cell’s efficiency is the percentage of incident light energy that is converted to electric energy. 31% is actually really good for a solar cell, most of them are under 20.
   As for a theoretical 100% cell, the Second Law of Thermodynamics forbids any process from being perfectly efficient, but we’ll keep getting closer and closer…