so what's so special about transforming sunlight into heat?    Actually the transformation of short wave UV and visible light into heat and IR radiation is a natural process. It's not rocket science. It happens every day. Without heat the chemical processes that occur within water would be impossible. Life itself would be impossible. The transformation of light into heat is so natural that we often take it for granted, yet if the generous supply of sunlight  that falls on our Earth suddenly disappeared none of us would be around very long. Did you know that more sunlight energy falls on our Earth in 24 hours than all of the recoverable oil energy we ever had or ever will have. Without clouds and an atmosphere almost all the heat gained during the day would be lost at night. This phenomena is made possible because of the greenhouse effect . Without sunlight, clouds and the greenhouse effect life itself would be impossible and there would  be no oil to squabble about.  Hundreds of millions of years were needed to create oil from tiny one celled organisms and it only took modern man about 100 years to consume half our planets non-renewable supply. 

What will happen if the rate of consumption continues to increase at its current rate?
What will happen if the supply of oil can no longer meet the current demands?

INCREASING PRODUCTION: An increased supply of oil would increase competition and according to the laws of supply and demand the price of oil would drop, but this scenario is improbable. All the major oil field discoveries occurred before 1973 and the remaining small oil fields may never be exploited because major producers consider them to be non-profitable. 

DECREASING DEMAND: If people would travel less and conserve more the demand for oil might stabilize for awhile, but this will never be a total solution to an oil shortage. Old habits die hard. Guided by Adam Smiths green hand of greed oil producers will continue to drain the liquid gold  in the name of capitalism and free enterprise. Research needed to make renewable energies profitable will take a back seat without the intervention of a concerned government. It would be nice to have respect for our tiny spaceship earth, but we've been raised on a diet of capitalism. This is all we know. A sustainable economy is low on the list of someone caught up in the game of day to day survival. Government leaders should be busy preparing us for a world without oil instead of accepting bribes and supporting our addiction to non-renewable resources.



HOW ABOUT HYDROGEN FUEL CELLS?  Specially constructed fuel cells combine Hydrogen with Oxygen to make water and electricity. Since the byproduct of power production is water there are no toxic emissions to worry about. The problem with fuel cells has to do with the manner of producing and containing Hydrogen. Hydrogen may be extracted from petroleum or water. If Hydrogen is extracted from petroleum we're right back where we started from with less energy to show for our troubles. Hydrogen may also be extracted from water by the process of electrolysis. PV panels may be used to make the electricity for the process, but let's not forget to compress the hydrogen in a storage tank. This takes energy. The entire process of converting PV solar energy into Hydrogen takes place at an efficiency of less than 1%.

HOW ABOUT SOLAR PV PANELS?    Solar Panels convert sunlight into electricity at an efficiency of about 10%. Some manufacturers claim efficiencies as high as 20% but this is a peak power situation in direct sunlight on a cold day. High temperatures decrease the efficiency of PV panels. In time the performance of PV panels also decreases. Nothing lasts forever. 

HOW ABOUT SOLAR SOLAR COLLECTORS?    Solar Collectors convert sunlight into heat at an efficiency of about 60% which is approximately the same efficiency that oil burners convert oil into heat. Since the efficiencies of converting oil or sunlight into heat are the same the value of heat produced is the same as energy received by the solar collector. 

If we compare the performance of a 1m2 collector with a  1m2 PV panel what can we say about the value of the energy harvest? To work out a problem like this we may have to express energy in terms of  fuel oil equivalent to understand their relative value.

1. SUNLIGHT    The energy available to one hour of direct sunlight on one square meter over the period of one hour is approximately 1KWH (one kilowatt hour) this is a good one to remember. National Solar Radiation Data Maps express solar energy in terms of average daily kilo watt hours per day.
2. PV PANEL    A 1mPV panel at an efficiency of 10% will harvest 0.1KW in one hour. If 1KWH of electricity is worth $.15 than 10% of 1KWH is worth 1.5 cents.
3. SOLAR COLLECTOR     Now let's take a look at the value of energy collected from our 1m2 solar collector. One hour of direct sunlight on one square meter has the energy equivalent of 1KWH, as we said before. Since collectors convert sunlight into heat at the same efficiency as oil burners convert oil into heat the amount of solar energy available to a collector is the same as the energy harvest of the collector which would be 1KWH. 
Now ask yourself what 1KWH of heat worth?
Since 1KWH contains 3,400 BTU's and one gallon of fuel oil contains 150,000 BTU's one KWH is the same as 3,400/150,000 gallons of heat or .02 fuel oil equivalents. We can't really have a gallon of heat, but we can express heat as a fuel oil equivalent. A good rule to remember is that 1KWH of electricity contains the fuel oil equivalent as .02 gallons of #2 fuel oil. If oil is worth $2.00/gallon .02 fuel oil equivalents would be worth
$2 x .02 = 4 cents.

A one square meter of PV panel harvest 1.5 cents worth of electrical energy in one hour.
A one square meter solar collector harvest     4 cents  worth of heat energy in one hour.  

This is not to say that solar thermal energy is better than PV power or hydrogen fuel cells or wind or geothermal any other source of energy. Every energy source has unique applications. I prefer solar thermal energy, flat-plate collectors because of their high efficiency and low cost. You don't need a PHD in rocket science to build a solar collector. The future belongs to those with a do it yourself attitude. The low tech nature of solar thermal energy facilitates a variety of low cost do-it-yourself-solar projects. Once a person learns how to build and install solar hot water systems he or she will gain the experience needed to build a solar thermal roof or Trombe Walls or solar thermal engines by understanding the basic principles of thermodynamics for transferring heat and for generating power. An entire energy independent house can be designed and built by anyone with basic construction skills and with a background in solar thermal energy. Our future is only limited by the laws of physics and by our own imagination. As we evolve the possibilities of entering a "solar age" or age of enlightenment become more real. Our social evolution depends on the decisions we make and the leaders we elect to represent those decisions. 

Best of luck with all your solar projects.

John Canivan

Strawberry Fields Solar Book Store
How to Build a Solar Hot Water System
Energy Independent Housing 

Solar Thermal Energy

Solar Energy Center