I have permanently humid walls (due to a construction error, not uncommon around here) that I need to dry out occasionally.

I live off the grid, with all power coming from solar panels. That works great, but run-off-the-mill dehumidificators would drain the system too much.

Do powerful dehumidification options exist that don't require a lot of electricity?

All I can see in shops is those small packages with some sort of salt that you can put in your closet. I need something more serious than that.

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    Thousands of pounds of silica gel? – bib Mar 8 '15 at 22:30

For an off-grid dehumidification system, you have two or three choices that I can think of. One is to install additional power panels to support the additional load of a "standard-type" electric refrigeration-based dehumidifier, and purchase the most efficient version of that type that you can.

The most likely alternative, which I'm not aware of being commonly available "pre-built" though it's possible that it's out there and I'm not aware of it, is to use solar heat to dry a desiccant, and then switch that desiccant into the airspace to be dried (either by switching airflow over fixed desiccant containers, or by physically moving it.) You would generally want to have at least 2 sets of desiccant, so that one set can be dried while another is absorbing water. This is fairly amenable to DIY implementation. It may need to be quite large to keep up with any significant drying load.

An outlier, which is more likely to be seen in a "commercial" or fairly large-scale offgrid setup would be to use an absorption refrigeration loop driven by solar heat to generate the "cold" for dehumidification (and possibly also for other refrigeration purposes) - the complexity of which typically makes it impractical and/or hazardous for a one-family sized situation. By the time you've gone through all that's required, option 1 looks inexpensive, normally, even though this has the potential to be more efficient in conversion of sun to cold; it's a complex and not very common setup, which can leak, has typically noxious chemistry (ammonia) and needs maintenance.

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  • Thank you, this is great. For #1 I worry about batteries, which I'd likely have to extend too if I put any more panels on the roof, and #3 would probably be too complex for me to implement. But #2 is a very interesting idea, I'll look into that! – Pekka Mar 8 '15 at 20:40
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    For #1, one option is to only run it when the sun shines, or when the sun shines and the batteries are "full enough." But do add more panels, at least. – Ecnerwal Mar 8 '15 at 20:59
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    If you need dehumidification when it's also hot, just air-condition - or get a mini-split type system that can cool or dehumidify (or heat, but that seems less needed, especially if the sun is shining.) – Ecnerwal Mar 8 '15 at 21:18

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