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How Useful is Solar Energy?

Why has solar energy not found widespread application, ever since the first oil crisis around 35 years ago? Is it the "oil mafia" and politicians working against it, or could it just be that there is no economy in it? How important is economy, when it comes to our planet's ecological survival? This article highlights a few of those questions.

When considering environment and solar energy, or energy at all, the first question would be what energy actually is. The answer is very simple - nobody knows! What we do know however, is how energy behaves. It has two main characteristics:

  1. It can not disappear into, nor be created from nothing (first law of thermo).
  2. It flows all the time and tends to disperse, if it is not hindered to do so (second law of thermo).

Our energy technology is about converting energy from one form into another - there is no "energy production", nor "energy consumption" (first law). While doing so, the thus converted energy spreads out and finally decays to heat at ambient temperature (second law). This means that it has become unrecoverable, but it is still there, not "consumed".  We can and do consume fuels and that is what we pay for, but not the energy that we freed from it in a conversion process.

Matter is the highest concentration of energy we know - one gram of it equals 25 million kWh (E = m.c^2). This is what we use in nuclear power stations, converting matter into pure energy. Chemical energy is the next highest concentration of energy. One gram of water has a bond energy of 120 kJ, the highest known and around three times more than fossil fuels. As 1 kWh is 3600 kJ, fossil fuels just contain around 0.01 kWh per gram. If this all doesn't say much to you, you may read my article about energy units.

The intensity of the solar radiation on the Earth's atmosphere is around 1400 Watt/sqm. Part of it is reflected, part absorbed by the atmosphere and what is left at sea level, varies around 500 Watt/sqm, plus-minus a few hundred watts, depending on the location on Earth. if we assume 500 Watt/sqm as average and compare this with fossil fuels, then one square meter of solar power during one hour equals around 50 gram of fossil fuels, giving 0.5 kWh in energy.

A volume of one liter contains around 800 gram of gasoline, diesel, etc, thus roughly equals 16 sqm of solar power during one hour. Say you drive you car for one hour at a speed of 100 km/hr, you may use 10 liter for that, thus, if it was powered by solar energy instead, it would have to carry a collector area of 160 sqm for the same efficiency as with the liquid fuel (around 20%). As we cannot do that, it's obvious that we need the solar collector to be somewhere else, where it can charge a battery, that we can have in the car instead. How big would that battery have to be?

A normal starter battery in a car, you know how big that one is, contains say 80 AH (Ampere-Hour) at 12 Volt, equals 80 x12 x 1, is roughly one kWh. In the car trip above, you needed a supply of 80 kWh, thus your battery for that would have to be 80 times bigger than the regular starter battery in your gasoline, or diesel car. Not quite, because an electrical motor has a much higher efficiency than a combustion engine, roughly 4 times higher, so your required battery size reduces to 20 times that of a normal starter battery - "small" enough? Well, you now have the equivalent of 10 liters of liquid fuel, so if your fuel tank contains 60 liters (around 15 gallons), your equivalent battery would have to be 120 times larger than a normal starter battery.  Because we are talking about the same car here, only with a different drive source, you may understand that your car is "somewhat" too small for carrying those batteries, right?

Never mind, you may say, I just have to charge a lesser number of batteries more often. True, but charging takes time. No problem, I can change batteries at a "gas" station, don't have to wait for charging them. Instead of fueling up the tank, I just change batteries. True again, but we still are faced with the volume problem.

For every say 100 liter of liquid fuel, the "gas" station needs to have 120 x 100 = 12,000 liter of batteries in stock (12 qbm) - it's gonna get a kind of BIG, doesn't it? Alas, not big enough, cause it also needs a solar power plant to charge all the empty batteries that come in, 1600 sqm for every replacement of 100 liter fuel. Not true, because this solar power plant may have an efficiency of just 20%, as we assumed before, so the real figure becomes 5 times bigger, 8000 sqm to replace every 100 liter of liquid fuel. This "gas" station will become the size of a small city! Of course it then needs an infra-structure, transport systems, etc, etc and who has to pay for all that nice stuff? Yes, YOU have to!

On top of it, your solar energy powered battery car will not be as convenient in use, as your gasoline or diesel driven car was. Because of the limited number of batteries it can carry, you will have to make many more stops at "exchange battery cities", than at regular gas stations before.

You may say that all this can be solved by using hydrogen as a fuel instead. Read my article on that subject and you may realize it is just moving the problem to another place, but not solving it!

The other day I was talking with some guys, if they would be willing to pay say 20% more for a "clean" car, that is equivalent to a "dirty" car. No way, was the unanimous answer. What would your answer be?

Btw, do you want to raise your voice over Climate ChangeArticle Submission, Global Warming?  Read this about Spaceship Earth first!

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Rudolph N. J. Draaisma  is a double graduated engineer in electrics and mechanics, specialized in energy conversion, refrigeration, waste-heat recovery and alternative energy systems.  The Alternative Energy and Engineering Site

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