3 ms·

My guess would be that this is a poor choice for backup energy for similar reasons that nuclear is a bad choice: drilling deep is rather expensive, so geotherma

My guess would be that this is a poor choice for backup energy for similar reasons that nuclear is a bad choice: drilling deep is rather expensive, so geothermal costs are mostly capex. That means you want to run the power plant at max output as much as possible to maximize profits. To use it as a backup plant for renewables however you would need to leave it mostly idle. Depending on how much renewable energy you have available you need full backup only for a few days to a few weeks per year.

londons_explore 4y ago
I'm thinking the reverse... since the thermal conductivity of rock is low, you can either have the well operating at a very low level continuously, or you can have bursts of much higher output for a few hours/days with the same drilled boreholes. Obviously you will still have to pay the capex for the turbines and generators for whatever peak level you decide, but I'd guess they're a smallish chunk of the total budget. If you think energy prices will be more volatile in the future (more extreme climate means more peak-usage days, and more renewables means more days/hours with a shortfall in generation), then it makes sense to overbuild turbines so you can rake in the $$$'s in that 1-2 days per year when energy prices spike up 1000x.
- adrianN 4y ago
  That is a very good point, thanks for bringing it up. I have changed my opinion.
- lazide 4y ago
  Geothermal has serious issues if water flow is not kept constant - dissolved minerals in the borehole water are just waiting for an excuse to crystallize/precipitate, and it’s already an issue at most active running plants, even when run continuously. Silica crystallization on heat exchangers, for instance, is a constant maintenance cost. Stopping the flow (and letting it cool in the pipes ) for any length of time or with any frequency could mean not being able to ever start it again.
  - loufe 4y ago
    You could continue cycling the water, filtering out contaminants, without extracting heat from it.
    - janef0421 4y ago
      That would likely require frequent filter replacements, which would could be quite costly.
      - lazide 4y ago
        You can’t really filter this stuff out - it’s things like dissolved magnesium, iron, silica, boron, arsenic, etc. at least not without making it uneconomic I believe. The link below references concentrations of 250g/L or more (though often most of that seems to be salt). It isn’t generally particulate until it’s too late. It’s the nature of water contacting hot rock. From the environmental impact perspective [https://www.sciencedirect.com/topics/engineering/geothermal-water https://www.sciencedirect.com/topics/engineering/geothermal-...]
deleted 4y ago
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londons_explore 4y ago

I'm thinking the reverse... since the thermal conductivity of rock is low, you can either have the well operating at a very low level continuously, or you can have bursts of much higher output for a few hours/days with the same drilled boreholes. Obviously you will still have to pay the capex for the turbines and generators for whatever peak level you decide, but I'd guess they're a smallish chunk of the total budget. If you think energy prices will be more volatile in the future (more extreme climate means more peak-usage days, and more renewables means more days/hours with a shortfall in generation), then it makes sense to overbuild turbines so you can rake in the $$$'s in that 1-2 days per year when energy prices spike up 1000x.

adrianN 4y ago
That is a very good point, thanks for bringing it up. I have changed my opinion.
lazide 4y ago
Geothermal has serious issues if water flow is not kept constant - dissolved minerals in the borehole water are just waiting for an excuse to crystallize/precipitate, and it’s already an issue at most active running plants, even when run continuously. Silica crystallization on heat exchangers, for instance, is a constant maintenance cost. Stopping the flow (and letting it cool in the pipes ) for any length of time or with any frequency could mean not being able to ever start it again.
- loufe 4y ago
  You could continue cycling the water, filtering out contaminants, without extracting heat from it.
  - janef0421 4y ago
    That would likely require frequent filter replacements, which would could be quite costly.
    - lazide 4y ago
      You can’t really filter this stuff out - it’s things like dissolved magnesium, iron, silica, boron, arsenic, etc. at least not without making it uneconomic I believe. The link below references concentrations of 250g/L or more (though often most of that seems to be salt). It isn’t generally particulate until it’s too late. It’s the nature of water contacting hot rock. From the environmental impact perspective [https://www.sciencedirect.com/topics/engineering/geothermal-water https://www.sciencedirect.com/topics/engineering/geothermal-...]

deleted 4y ago

[deleted]