Air heat with solar energy, a new approach

At present, both efficiency and output of solar thermal power plants are quite low and it's a big reason behind the high cost of kWh electricity produced in present day solar thermal power

plants. The other reason is the high cost of maintenance of array of

reflectors. But, this cost can be reduced to less than 1/3rd of the present day

level. The way is using atmospheric or psychometric heat along with solar heat.

The way is very very simple. First, evaporate the water with the help of a

vacuum pump in such a way so that the latent heat of vaporization of water

comes from the atmospheric heat and then heating the vapor produced in this

manner with solar heat. It can be easily calculated that in a steam at temp

300ºC produced in the same manner as that of present day thermal and solar

thermal power plants; latent heat of vaporization of water is about 2/3rd of

the heat consumed by water in this process. By vacuum evaporation of water, the

latent heat of vaporization of water comes from the atmosphere and heating the

vapor by array of solar reflector would need 1/3rd of heat necessary before.

Therefore, with just 1/3rd of the amount of solar reflecting arrays, we can get

same efficiency and output. And in night too, less heat reserve will be

necessary to run the power plant.

Vacuum evaporation of water is well tested in the experiments of open cycle OTEC. The vacuum pump in my project acts as the premium heat pump. It does so by vaporizing the water

inside the Evaporator. On an experiment done by Prof. L.A.Vega, it was found

that out of 1838 kW of gross output from 26.1 kg of steam, only 80 kW is spent

on the compressor i.e. vacuum pump. From that experiment, it can be calculated

to produce 1 kg of steam; approx. 3 kW of electricity is needed. This

experiment proves that the c.o.p of the vacuum pump can be much higher; i.e.

more than 22, according to the above mentioned experiment on open-cycle OTEC by

Dr. Vega (resource: http://www.otecnews.org/articles/vega/07_landbased_OTEC.html).

While the amount of power embedded in the 1 kg/sec vapor flow is (1000X550X4.2)

W or 2.31 MW. In a conventional thermal power, all the heat necessary including

the latent heat of vaporization have to be supplied by burning fossil fuel. On

a steam of 300°C

temp, 2/3rd of the amount of energy embedded is the latent heat of

vaporization. If vapor can be produced in this way, then much less amount (in

fact 1/3rd of less amount) of fossil fuel will be needed to take the

vapor to its desired temperature. But with that vapor, we can produce same

level of electricity.

The latent heat of vaporization of water can be collected from atmosphere by means of heat conduction through the walls of the aluminum or aluminum alloy tubes attached to the Evaporator.

Heat conductivity of aluminum is 2.37 W/m/ºK i.e. through an aluminum sheet of

1 sq meter and 1 mm thickness, 2.37 kW of heat would be passed with just 1ºK or

1ºC temp difference. Therefore, for conduction of 2.31 MW of heat with a 2.5ºK

temp difference, just 4 sq meter of aluminum sheet is sufficient. Therefore,

the cost of aluminum tubing wouldn’t be much.

The next part of the technology is almost like any other conventional solar thermal power plant electricity generation part. Therefore, there should be no difficulty in making and

operating that part of this technology. Though, this technology have some

little differences with conventional solar thermal power plants, but that

difficulties can be overcome easily with available techniques. In short, there

is no technological problem regarding the implementation of this technological

idea.

Advantages of this technology are:-

1) As much less solar reflectors are needed, the electricity produced by this technology will be cheaper than that produced by other solar thermal

technologies available at present..

2) As much less solar reflectors are used, therefore it takes much less are to construct in comparison to the other existing solar thermal power technology

and also much less cost to operate.

3) It can be made with present state of technology. No engineering or scientific breakthrough is needed.

4) This technology uses the embedded heat that is stored in the lower part of the atmosphere. In effect it is a part of solar energy falling on

earth. That’s why basic source of energy is unlimited and there would be less

pressure on depleting reserves of fossil fuel like coal, oil, gas etc.

5) Salt and fresh water are added bonus to this technology, if seawater is used.

6) It can be source of low cost air conditioning for buildings of close proximity.

I am just giving here a short zest of the idea here. Anybody interested, who is willing to discuss this idea with me, can contact me at pranabjyoti_calcutta@rediffmail.com.

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