Thermal Energy Storage

[OzSolar]

@OzSolar, looks-like you know it well

Anyone knows this: Drake Landing

Boy howdy do I know DK well, too well in fact. I'd like go at least a month before I'm at the "peak of mount stupid" again.

Actually I had heard of Drake Landing many years ago and found it both fascinating and completely unbelievable. Do you have any firsthand knowledge of it?

On a few occasions I tried to get some actual data on it and never could. They had a public online portal for real time monitoring but suspiciously it was always offline when I went to view it further feeding my disbelief in it.

 

[Warpspeed]

That area must be a complete geological freak, without any ground water flowing either in or out of the thermal storage.

 

[OzSolar]

That area must be a complete geological freak, without any ground water flowing either in or out of the thermal storage.

Either that or it's a fine example of greenwashing.

Many years ago I was partially involved in installing the controls and monitoring of a similar project at a college in my backyard. Seasonal energy storage using geothermal wells. It failed miserably but not I'm sure if it was because it was so badly designed or was fundamentally flawed. *I didn't design it, in fact I was pretty vocal about it having a pretty low chance of success but it was all funny money so no one listened.

Case in point: I have a closed loop geothermal HVAC on my own house and I monitor the return temp.

During the hottest parts of summer we will have 15 days out of 20 where we hit 100 or higher. I should mention we keep our home shamefully comfortable during this time so we are asking a lot from the wells.

On day one of that 20 days the return temp from my wells starts of the morning at ~68f and by 8 or 9 pm it's climbed to ~75f. By day 5 it's starting off the morning at ~72F and ending at ~78f. Fast forward to day 20 and temps are still trending up, 75 and 83. Looks like we're starting to saturate the wells with heat, right? Then the heat breaks and we return to highs of 90f. You guessed it, by the 2nd day of that we are starting the morning back at 68f again.

 

[JoergK.]

Ground water aquifers are deep here. I have looked at many records for wells drilled and many report static water levels deeper then 60-80' and deeper.

Here you can look: Wells Drilled

 

[Warpspeed]

I suppose it depends where you are.
Here in the Melbourne suburban sand belt, its very soft sandy soil down to about two metres, then very sold clay bed, as hard as concrete just below that. Its always wet down there, horrible smelly water too, from suburban leaking drains and domestic irrigation soak down.
I am also only about fifty feet above sea level here anyway, and the beach is only a few hundred yards away.

Sure, my particular circumstances are rather unusual too, but it might be really difficult to find a suitable location for storing hot water underground.

Solar ponds can and do work well for long term heat storage, because they are extremely shallow, and have an impermeable plastic liner.
But you would still have to insure the ground beneath is perfectly dry for a considerable depth for best long term results.
Full heat buildup takes months and years, not days and weeks. The thermal gradients downward absolutely must be extremely low.

 

[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.