Re: Building a Hybrid System (Solar, Wind, Generator, Batteries, etc.)

[Greener]

you cannot run a geothermal system off the grid. well – let me re-phrase that – you can if you have a lot of money. Here is why….

Geothermal requires the use of compressors (similar to an air conditioner unit). Those compressors require 220/240 volt power, which can only be provided with two stacked inverters…not cheap. Further, the amp draw (not peak surge) is at least 30 amps. This equates to 6600 Watts of instantaneous power, every hour they run through a compression cycle. That is just the compressor. Excluded from that equation are the pumps and monitoring systems. Forgetting all the rest of the stuff (like your home), just to run the compressors you will need the following….a battery bank to store 7 kW of energy. Conservatively assume you will allow your batteries to discharge to 50%, which means you need storage of 14,000 Watts per hour to run a geothermal unit. At 24 volts, this equates to an amp-hour rating of 583. We haven’t talked about the rest of your home yet (fridge, tv, lights, radio, computer, etc.). If you want three days of autonomy, and the compressor cycles for three hours a day, the energy needed JUST FOR THE GEOTHERMAL COMPRESSOR UNIT works out to 583 amps x 3 hours/day x 3 days = 5247 amp-hours….a system to hold that much juice will run you well over 100K..that is just the batteries…you need two inverters which run at least $3,500 each, a battery bank of at least 24 to 36 batteries, at least two charge controllers, and we haven’t even got to the solar panels or anything else….

Geothermal is great – just not for off-gridders without a lot of money.

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