[lazide]

They didn’t say home geothermal, they said home heatpumps. In that setup, the earth is not an energy source, just a very massive source of thermal inertia. They are not the same thing.

‘home geothermal’ isn’t really a thing unless you’re already living on a hotspring, which is quite unusual. (delta-v is not sufficient)

At the point someone is drilling km+ boreholes and installing MW+ turbines, it’s safe to call it commercial.

[robocat]

> home geothermal

  More than 900 shallow wells have been drilled at Rotorua for space and water heating for private homes, hospitals, schools, motels, hotels, and other commercial and industrial uses. At peak use, around 430 wells were operating. Currently fewer than 300 production and injection wells are operating, for approximately 140 consents takes. About 90 of the wells are less than 200m deep and typically recover geothermal fluid at temperatures of 120 to 200°C.

[lazide]

That is ‘sitting on a hot spring’ if you can go less than 200m down and get 200 c water - that is superheated steam.

[foobarian]

How is it not an energy source? The point of a heat pump is to move more heat energy around than was consumed running the device.

[lazide]

How does that make it an energy source? It makes it a pump. That still consumes energy to run. And none of the home heat pump setups I’ve seen are tapping into enough thermal inertia (or high grade heat) to do more than keep a house warm. They also, of course, PUT HEAT BACK there in the summer to help cool the house. They’re just moving heat around, and not with any particularly high quality either. If they used the atmosphere for thermal inertia (also common), would you say they were using the atmosphere as an energy source?

Geothermal turns turbines with steam that then produces massive quantities of electricity. That makes it an energy source. The water way down under the ground in these cases is superheated by the surrounding rock, and provides plenty of high quality heat. There are no heat pumps involved.

It’s like the difference between having a pool in your backyard, and damming a huge river and installing turbines.

[foobarian]

The point of a heat pump is to bring more Watts of heat into the home than the electricity consumed. Otherwise you could just use a resistive heater and heat the home with electricity directly. So ask yourself, if more energy came into your home than you put in from the electric socket, where exactly did the extra energy come from?

[lazide]

That is not what ‘power source’ means. You probably want to read up on some thermodynamics and definitions.

I’m guessing you think that if you connect the heat pumps output to it’s input, you’ll have infinite energy?

[foobarian]

> So ask yourself, if more energy came into your home than you put in from the electric socket, where exactly did the extra energy come from?

I notice you didn't answer this question.

[lazide]

I did. The question is for you. I've answered it in several different ways in this thread. There is a sibling comment I replied to which breaks it down even more clearly.

You used the energy from the wall socket to pump the heat from outside into the inside, less efficiently than you could use that heat to generate more electricity or do other work later.

Aka you pumped the energy inside and concentrated it a bit. You didn't generate more energy than you had before. You did make existing energy more useful for you, comfort wise.

Actually operating one, you'll see that the energy cost of a heat pump becomes proportionally higher as the temperature difference gets bigger, so you spend more energy moving the heat when the source is low temperature and the output is high temperature.

Many people have gotten quite frustrated when they end up chilling the ground in their ground source heat pump too much, and they end up with very inefficient systems.

You could do the exact same thing (with better or similar efficiency) by using some other source of thermal mass. Air sourced heat pumps do it with the atmosphere. It's possible to use lakes and other bodies of water.

No net usable power is being extracted from the earth in this scenario. The earth is being cooled in order to heat your house. And heated, in order to cool your house.

Geothermal power systems do produce actual usable power, and they do so by running a heat engine (the opposite of a heat pump) off an extremely large temperature difference from a very large source of underground heat. You can't run a heat engine on the output of a heat pump and produce net power, anymore than you can hook a generator to an electric motor and produce net power.

[quickthrowman]

> Geothermal turns turbines with steam that then produces massive quantities of electricity. That makes it an energy source. The water way down under the ground in these cases is superheated by the surrounding rock, and provides plenty of high quality heat. There are no heat pumps involved.

Geothermal systems don’t strictly need to produce energy with steam, I just completed a project to convert some boilers and chillers with heat recovery chillers and a geothermal loop for heating and cooling at a research lab for an S&P 500 constituent. I’m doing another project to replace some existing geothermal heat pumps for another customer this fall, no power generation, just heating and cooling.

[lazide]

That is using the earth as a source of thermal inertia, not producing power off earths heat - unless you're going down pretty deep. Again, not power generation.

The different between these two ideas, is that a heat pump is not producing heat (as it's primary goal). It's concentrating and moving heat from point A to point B. The amount of heat moved may exceed the amount of raw energy used to perform this process (and should, in most situations), HOWEVER, it can not exceed the amount of energy you would get back by trying to reverse the process to extract energy. It is still a net energy consuming process.

This is important, because if it wasn't - you could power the heat pumps off their own output, and you'd literally have infinite energy/perpetual motion machine. Which would be awesome. It is also impossible, near as we can tell.

What actually happens is everything grinds to a halt, because the useful (Actual) energy output from the heat pump is lower than the energy required to run it.

Chances are, that system isn't even really geothermal (as in using latent heat of the planet) - any large enough mass would do the same thing. People just like to say the word because it sounds 'green'. If the ground was hot enough (for instance) to provide actual heat itself, a heatpump would be a waste for heating the building - and extremely inefficient for cooling it. It would be better to just pipe water straight out of the ground to heat, and use air based HVAC to cool.

Geothermal power generation does produce power - by tapping into a source of heat so hot that the difference between normal atmospheric temperatures and that heat source allows us to generate useful power. A heat pump gets in the way and causes losses in these situations.

Unless you're sitting (quite literally) on a hotspring, this requires going VERY deep into the ground. Which is what this article is about.

[foobarian]

> That is using the earth as a source of thermal inertia, not producing power off earths heat - unless you're going down pretty deep. Again, not power generation.

I get the vibe that your definition of "producing power" is electrical power generation. However the original argument is that there is energy being extracted that is not in the form of electricity.

[grosswait]

Geothermal power generation is energy conversion, while a heat pump is energy movement.