A Concept for a solar power plant that utilizes a heat pump
This is only a concept design - one that came to me the other day. I don't know if it is feasible, or if it has been tried before, but I haven't heard of a power plant using this method. So - for what it's worth - here it is.
This design is based on the concept that a heat pump can put out more heat
energy than the electricity put in - from four to eight times as much. It's not
truly free energy, of course (though it is to you). The energy is normally drawn
from the outside air by the evaporator coil, and then transferred inside to a
condenser coil, to heat a building. It operates like an air conditioner, only in
reverse. Here is a sketch of the basic cycle:
The compressor (run by electricity) pressurizes a gas, which turns to a liquid.
Heat is removed from the high-pressure liquid by the condenser coil. The liquid
goes though a small opening (a capillary tube or expansion valve) into the
evaporator, where, under lower pressure, it turns back into a gas - absorbing
heat in the process. The low-pressure gas then returns to the compressor inlet.
The sun provides about 1000 watts of energy per square meter under ideal conditions. One of the problems with generating power (without going to photovoltaic cells), is that you really don't get enough heat to run a generator. To overcome that, you need to build a concentrator, like a parabolic reflector. That requires a complex design, a tracking mechanism for each reflector, and a way to change the heat into electricity.
The big problem, though, is that you still have to have enough surface area to intercept that 1000w/ sq. meter. When you go from a flat plate and shape it into a parabola, you lose area that the sun could be shining on. It would be great if you could keep that low-cost, flat shape, that doesn't require aiming, or any fancy technology. The flat plate collector only gets up to 150 degrees, or so. You can put it in a box with a glass cover and get 200 degrees, without much trouble, but it isn't hot enough to generate pressure to run a commercial turbine.
That's where the heat pump would come in. Instead of the usual 30-60 degree F air that a heat pump uses to heat a building in the winter, you would have incoming heat to the evaporator around 150-200 degrees F. The heat pump would be able to drive a boiler, using a heat exchanger, to generate high-pressure steam, which would run a steam turbine, driving an electric generator. The refrigerant would be different from a home heat pump, obviously, because it would operate at a higher refrigerant boiling point than the freon in a home unit. The technology would not have to be invented, or years of research done, because we already have it. The fact that the collectors are flat, and require none of the support technology of parabolic designs, should make this design much cheaper and more practical than the expensive solar power-generation projects currently being built or considered.
Here is a basic drawing of the whole concept:
High pressure refrigerant would change to low-pressure, after it leaves the
expansion valve. As it passes through the evaporator coil (mounted to the
collector plate), the liquid turns to a gas, absorbing energy. It leaves the
collector at 150-200 F. The refrigerant gas is compressed to a liquid, and the
condenser coil transfers heat to boil the water, creating steam. The
high-pressure steam spins the turbine, and comes out as much lower pressure
steam. The steam travels through a coil, which is mounted on the same flat-plate
collector as the evaporator. Heat from the steam is added (recycled) to the heat
from the sun, and the water turns back to a liquid. The hot water goes into a
reservoir tank, and some is periodically pumped back into the boiler, to keep
the boiler water at the proper level. Since the water is recycled, it would be
suitable for hot, dry areas, where the system would also work the best.
The system would be easily expandable by adding more collector plates.
The "S" would be the high-pressure supply line carrying refrigerant liquid in.
The "E" are expansion valves (one per collector coil). The "R" lines are return
lines (low-pressure gas) back to the compressor. The steam/water line that would
also be on each collector plate aren't shown.
I don't claim to be an expert at heat pumps. I've just done some reading on
how they work. Since the system just takes advantage of technology that we
already use, I don't see a reason why it couldn't work.
L.B.