Electricity from heat pumps

Hi,
I was talking to my mate in Spain yesterday, and he was interested in alternative energy. Electric solar panels, and batteries in particular.

As it is warm for a lot of time over there, I wondered about heat pumps, compared to solar panels. Having read that heat pumps can generate, something like 4 times what is put in. Could the 3x times 'profit' be used to power an electric generator. I understand there would be losses.

Any ideas?
Cheers, Camerart

camerart said:

Could the 3x times 'profit' be used to power an electric generator

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The "excess" is in the form of heat so you would have the large efficiency loss of converting heat into electricity.
Doubt that you would end up with very much of a gain after all that.

crutschow said:

The "excess" is in the form of heat so you would have the large efficiency loss of converting heat into electricity.
Doubt that you would end up with very much of a gain after all that.

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Hi C2,
I think the same, although I wondered if anyone had any experience of any tests.

I know electric can be generated from high quality heat, like volcanoes etc, so I suppose it comes down to the quality of the heat surce. Perhaps a hot field in Spain doesn't have eneough heat?
C

camerart said:

Perhaps a hot field in Spain doesn't have eneough heat?

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It's not the quality or amount of heat you need to efficiently convert heat to electricity, it's that you need a large temperature difference from the hot to the cold.
Volcanos and fuel-fired boilers have that, a hot field in Spain does not.

crutschow said:

It's not the quality or amount of heat you need to efficiently convert heat to electricity, it's that you need a large temperature difference from the hot to the cold.
Volcanos and fuel-fired boilers have that, a hot field in Spain does not.

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Hi C2,
I agree, I use the terms high or low quality as hot as in volcanoes and low as in fields. Perhaps I should use different terms?

I did a search and found one company making heat pumps that used ground source heat and produced 120°C and another that took water less than 100° and produced electricity, so it is possible, but as you say the efficiency may not be good enough yet.

There is a lot of low quality heat in the sea that needs lowering (global warming and all that), so this is why I'm interested.

As I'm not going to be making these, I'm not going to spend much time researching, but to me it is interesting, and it was 'just a thought'
C.

camerart said:

There is a lot of low quality heat in the sea that needs lowering (global warming and all that), so this is why I'm interested.

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Taking energy from heat is similar to taking energy from eg. Hydroelectric power - you do not "use up" or reduce the amount of the medium, you just extract energy as you allow different levels in different places to equalise.

No difference means no extractable energy.
The only way to extract heat energy from the sea would eg. use the difference between that and the ice caps at the poles, melting them in the process!

That's the essence of "Entropy" - the only way any energy can be used, in the longest term sense, is by the "difference" that is lessened in the process.

rjenkinsgb said:

The only way to extract heat energy from the sea would eg. use the difference between that and the ice caps at the poles, melting them in the process!

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Hi R,
Are you sure?
The heat energy can be taken out of a glass of water by putting it in the feezer, in an average kitchen. The extracted heat, is cooled by a radiator, and wasted.

The heat energy can be taken out of the sea, in a similar way, but instead of wasting the extracted heat, put it to some use, and electricity generation could be one of them.

C.

You are using a "heat pump" to move the heat energy around, like a water pump for moving water.
The heat is not "cooled", it's just moved from the evaporator side to the condenser side - at a cost of using yet more energy to operate the pump.

It's basic Thermodynamics:

The first and second law prohibit two kinds of perpetual motion machines, respectively: the perpetual motion machine of the first kind which produces work with no energy input, and the perpetual motion machine of the second kind which spontaneously converts thermal energy into mechanical work.

In electrical terms, think of it like something that has eg. a charge of a thousand volts on it - but you cannot connect it to something a _different_ voltage to get a current flow and therefore power (watts); if the flow (amps) is zero, any number of volts * zero = zero watts.

rjenkinsgb said:

You are using a "heat pump" to move the heat energy around, like a water pump for moving water.
The heat is not "cooled", it's just moved from the evaporator side to the condenser side - at a cost of using yet more energy to operate the pump.

It's basic Thermodynamics:

Laws of thermodynamics - Wikipedia

en.wikipedia.org

The first and second law prohibit two kinds of perpetual motion machines, respectively: the perpetual motion machine of the first kind which produces work with no energy input, and the perpetual motion machine of the second kind which spontaneously converts thermal energy into mechanical work.

In electrical terms, think of it like something that has eg. a charge of a thousand volts on it - but you cannot connect it to something a _different_ voltage to get a current flow and therefore power (watts); if the flow (amps) is zero, any number of volts * zero = zero watts.

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Hi r,
Note: It wasn't me that mentioned perpetual motion, I think you misunderstand me.

Ok, I'll leave it to the experts and time, but thanks for all comments.
C.

using thermally insulated metal rods, or using "heat pipes" (such as used in PC cooling systems), you could probably sink a rod down in the ground deep enough to get to the soil that stays at a constant temperature year round, and have surface heat collector, and put a peltier junction or peltier pile between them and get a small amount of current out of it... it's probably not going to be much, but there may be some limited uses you could put it to...

When the air source heat pump works, it does not use any fuel, will not produce open fire and will not emit toxic and harmful waste gas. Therefore, the use of air source heat pump will not pollute the environment, nor will it have potential safety hazards such as fire, explosion and poisoning. The power consumption of air source heat pump heating is very low, which is only one quarter of that of ordinary electric boilers. It is a very power-saving heating equipment.

Markyyyy said:

When the air source heat pump works, it does not use any fuel

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Fuel of some sort is needed to provide energy for moving the air. Welcome to ETO, Mark.

alec_t said:

Fuel of some sort is needed to provide energy for moving the air. Welcome to ETO, Mark.

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Yes, but it only consumes a small part of the energy

You sound like the people that state that electric vehicles produce no pollution. No they don't but generating the electricity to power them does. It reduces emissions but doesn't prevent them, just moves where they're generated.

Mike.

Pommie said:

It reduces emissions but doesn't prevent them, just moves where they're generated.

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And that's true even if wind turbines or solar panels are used to generate the electricity, because not all the mines and factories involved in manufacturing the turbines or panels will necessarily be entirely powered by renewable sources of energy. Likewise transporting and installing the turbines/panels.

Markyyyy said:

...one quarter of that of ordinary electric boilers."

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It is true that one can typically heat a house using a heat pump for about 1/4 the cost of a simple resistive heater. To clarify, a 1000 watt space heater (resistive) uses 1000 watts of electrical power to generate 1000 watts of heat energy, i.e. 1000 joules each second. A heat pump can use 250 watts of power to heat the house at the same rate of 1000 watts of heat. No energy has been created, just moved from one side of the heat pump to the other. The other 750 watts of power were taken from outside and moved inside. There is also the caveat that if it's too cold outside, the heat pump won't have enough heat to move from outside to inside. Therefore, most heat pumps come with a secondary heat source, a resistive heating element or a gas or oil backup.

All of this this is meaningless when trying to generate electric using a heat pump. A heat pump moves heat from one side to the other. I'm not sure how one is supposed to use the temperature difference to generate electric using a traditional freon based heat pump.

As noted above, a Peltier thermocouple can be used to generate electric but even in this mode of use they are terribly inefficient. The same principle holds, that the temperature difference must be large in order to generate a reasonable amount of power.