Thermal Energy Storage

[NC_hydro]

Sand would make a much better thermal storage medium than the glycol mix in your buried storage container.

 

[Acuario]

With 40kW of panels what are you doing with all the energy generated? Storing in batteries? As many solar batteries are fully charged well before the solar energy is unavailable the excess is effectively wasted.
A system to use the 'unused' energy to run an air to water heat-pump would be my solution (and it's what I do). That along with underfloor heating (and cooling) with the concrete + tiles above the heating pipes keeps us cool in the summer and warm in the winter.

Here are two graphs of solar output, the one with a lovely curve is what you should aim for, the other is a typical installation with wasted production as when the batteries are full they stop charging.

 

[Ptom]

You can DO anything and make it work to some extent, but if cost effectiveness and hassle factor come into play, I'd run from a buried storage tank. I can't imagine it being remotely cost effective, versus a larger PV array at today's low prices. I still use thermal panels from 30+ plus years ago (know of any excavated ones that old, just asking) BUT if they crap out, I would replace their BTU output with an electric boiler (https://electromn.com/, been using them for years, simple and effective) and if needed increase my PV system. It all depends on your utility net meter program of course, and your climate. In the high desert winters of Idaho, I keep my 18' by 40' crane shed (moderately insulated) at 50+ degrees all winter for almost exactly what the grid tied 1.9 PV array produces annually. I run out of KWH credits about the same time I can shut it down as the weather warms. I have natural gas plumbed right to the building, but will pass on that.

 

[Frick]

Passive (no moving parts) solar homes have a long history of doing quite well in many climates. 20 years ago I designed and built my passive solar home and to my pleasant surprise it needs no supplemental heat as long it's sunny outside almost regardless of outside temperatures. No maintenance, no pumps to fail or fluids to replace or leak.

I've been around probably a dozen active solar space heating systems over the years and sadly it was to decommission them for a variety of reasons I'll not dive into it due to time constraints.

What I think I learned is that there's a fundamental problem that no active solar space heating system can escape and still be even remotely cost effective AND reliable. That problem is that the peak load is opposite the the peak resource. Short cloudy days and long cold nights appear to be the doom of most systems. Building a big enough thermal storage system that is even close to cost effective has escaped many very smart people. Oh and it's got to be repairable by someone other than the original builder as well.

I'm not saying you can't do it, just cautioning that many have tried and failed.

Later I'll try put together some of the basic formulas that you need to start trying to figure out what you might be up against.


I'm still not sure what you mean here. How many kW of PV do you have?

This reminds me of a trip to Alaska I did. MEt some crazy and crazy smart people Out there. One designed passive homes using a monolithic stone in the center. He carefully calculated the stone mass, heat loss, seasonal variation. Sun angles through windows…. Honestly it was beyond my skill level back then. But, he did create homes that required almost no heating or cooling in alaska. Yes they had a wood stove for adding heat in the coldest days, but It wasn’t used much. He built many this way. fascinating stuff.

 

[OzSolar]

This reminds me of a trip to Alaska I did. MEt some crazy and crazy smart people Out there. One designed passive homes using a monolithic stone in the center. He carefully calculated the stone mass, heat loss, seasonal variation. Sun angles through windows…. Honestly it was beyond my skill level back then. But, he did create homes that required almost no heating or cooling in alaska. Yes they had a wood stove for adding heat in the coldest days, but It wasn’t used much. He built many this way. fascinating stuff.

That would be wild to see that in action, particularly in Alaska. Thanks for sharing.

 

[JJJJ]

There was an apprentice mechanic who had the opportunity to work with a senior car mechanic for a few days.

At the end of the time period the mechanic expressed his respect for the abilities of the senior mechanic. He asked the senior mechanic what allowed him to have such success.

The senior mechanic replied “good decisions “

Hearing this the apprentice asked how this came about.

The senior mechanic replied “experience “

Now the apprentice was really interested and asked how this experience was obtained at which the senior mechanic replied “bad decisions”.

As I review my build project there have been, despite the best research and study “bad decisions “. This has been part of the journey for many who embark in a new direction.

In my mind The key is to strive towards safe practices which protect life and limb without running the bank account dry.

 

[Acuario]

Now the apprentice was really interested and asked how this experience was obtained at which the senior mechanic replied “bad decisions”.

..there is no such thing as a disaster. Just ways to learn how not to do things.