Thermal Energy Storage

[JoergK.]

Here my thoughts on developing and building a sizable thermal generating & storage system

Some facts that direct my thoughts:

1. I can produce heat and or electricity from sunshine, but not natural gas that fires my heating system right now
2. My area (southern Alberta) has great sunshine hours year round and PV works fine, but like most, have no sunshine at night and less in the winter when we need the heat & power. On the electrical side, this is covered with a grid tied system, but one needs a sizable buffer, storage system for making thermal energy work year-round.
3. I hope all agree that evacuated tube solar collectors are the best on the market right now to capture heat and, with 50:50 glycol mix work year round.
4. I have 40 kWh of PV panels and can add the same size as evacuated tube solar collector, giving the potential of 650 - 2000 kWh/day (data from manufacturer)
5. Problem is the collector size & storage calculation to not over produce, but set this so it works year round with minimal NG needed to buffer.

Could one burie a 20' or 40' ocean container, insulated it good, line it with a double or triple bulk liner (used for ocean shipment of grain, fertilizer etc. & cheap), insert stainless tubes in the bottom to inject the heat and stainless steel tubes near the top to retrieve the energy and fill the whole volume with a liquid salt & glycol mix? The whole heat sink could be covered with new railroad ties or a concrete slap and covered with 4-5' of dirt to be out off the way.

To carry this on, my heating systems run on a minimum of 70°F in the return and max. 100°F on the hot side. So, 100°F is a minimum, 200-220°F is achievable in the storage tank. A heat pump could be added to retrieve energy below 70°F, down to probably 10-20°F.

Questions:

1. does this make sense in general terms?
2. is it doable?
3. how to calculate this all so I don't have anything overheat or freeze?
4. is it viable over 25 years?
5. Most could be done with own equipment & labor just the supplies need to be bought.

BTW: I had the big dream of 2x4 geothermal wells 100m (330') deep, but the costs of $120,000-$160,000 knocked me out of the dream.

Await your comments!

 

[LeoThomson]

Have a look over at electrodacus, he is heating an insulated slab of concrete floor using solar pv for winter, he has super insulated his entire home and runs 100% of solar, including winter heating, which I understand can be quite brutal. The system he designed is open source and while he is short of parts right now, he does sell them when he can.

 

[Supervstech]

Here my thoughts on developing and building a sizable thermal generating & storage system

Some facts that direct my thoughts:

1. I can produce heat and or electricity from sunshine, but not natural gas that fires my heating system right now
2. My area (southern Alberta) has great sunshine hours year round and PV works fine, but like most, have no sunshine at night and less in the winter when we need the heat & power. On the electrical side, this is covered with a grid tied system, but one needs a sizable buffer, storage system for making thermal energy work year-round.
3. I hope all agree that evacuated tube solar collectors are the best on the market right now to capture heat and, with 50:50 glycol mix work year round.
4. I have 40 kWh of PV panels and can add the same size as evacuated tube solar collector, giving the potential of 650 - 2000 kWh/day (data from manufacturer)
5. Problem is the collector size & storage calculation to not over produce, but set this so it works year round with minimal NG needed to buffer.

Could one burie a 20' or 40' ocean container, insulated it good, line it with a double or triple bulk liner (used for ocean shipment of grain, fertilizer etc. & cheap), insert stainless tubes in the bottom to inject the heat and stainless steel tubes near the top to retrieve the energy and fill the whole volume with a liquid salt & glycol mix? The whole heat sink could be covered with new railroad ties or a concrete slap and covered with 4-5' of dirt to be out off the way.

To carry this on, my heating systems run on a minimum of 70°F in the return and max. 100°F on the hot side. So, 100°F is a minimum, 200-220°F is achievable in the storage tank. A heat pump could be added to retrieve energy below 70°F, down to probably 10-20°F.

Questions:

1. does this make sense in general terms?
2. is it doable?
3. how to calculate this all so I don't have anything overheat or freeze?
4. is it viable over 25 years?
5. Most could be done with own equipment & labor just the supplies need to be bought.

BTW: I had the big dream of 2x4 geothermal wells 100m (330') deep, but the costs of $120,000-$160,000 knocked me out of the dream.

Await your comments!

Panels aren’t grouped by kWh, they are grouped by kW. kWh is an accumulated quantity. So, do you have an array that is 40kW, or an array that can produce 40kWh per day?

 

[JoergK.]

Panels aren’t grouped by kWh, they are grouped by kW. kWh is an accumulated quantity. So, do you have an array that is 40kW, or an array that can produce 40kWh per day?

Sure supervstech you are right and I will not argue. I have 40 kWh theoretical production not per day, but per hour that's why it is 40 kWh

 

[Supervstech]

Sure supervstech you are right and I will not argue. I have 40 kWh theoretical production not per day, but per hour that's why it is 40 kWh

Gotcha, so you have a theoretical 40kW of panels, and during an hour of peak perfect sun, you should have 40kWh. I’m not sure why so many want to make it difficult and ignore convention and make us weed through the pst to discover what is actually there and needing answered… then argue about it. While posting they won’t argue about it…

We’re here to help, and teach…

 

[Vigo]

I am doubtful that trying to seal a shipping container will end up being more viable than to simply bury actual liquid tanks. For one thing, they cannot realy be buried without internal or external bracing or they can cave in. A liquid filled liner would help the walls but not the ceiling. It would have to be buried pretty shallowly with some extra bracing on top.

Unless you have some serious excavation equipment it is probably cheaper to insulate above ground storage than it is to pay to dig a hole that size in the ground if the ground conditions are difficult (rocky, frozen, etc). Or partially bury. Dig halfway down and build up earthen berm around it.

 

[OzSolar]

Await your comments!

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 have 40 kWh theoretical production not per day, but per hour that's why it is 40 kWh

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

 

[JoergK.]

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?

OzSolar - you are probably right for your location, but right now the sun comes up around 7.27 and sets at 16.57. On Dec. 21. it is 8.24 to 16.28, so it gets a little nippy at -22°F if it does happen. Anyway, it would be great if you have some calculation in the future.

For the PV system, 40kWh is the potential to produce 40,000 watt in one hour at max. sunshine and proper direction of the panels to the sun. This is equivalent to 136,486 BTU or 136 ft3 natural gas. It could run a 53.6 HP electric motor for one hrs about.

 

[Northernchateau]

I have and tested a mini version of what you are talking about I call my solar load dump heater.
On the floor in my basement which is spray foamed floor to ceiling I have a water filled a 55 gal plastic drum on it's side that I fitted with a 1400 watt 120v RV water heater element. If we get enough sunny days in a row that my battery bank is topped up instead of wasting the energy I press a keypad switch I got and select how long I want the heater to stay on. For safety I do have a programable limit switch to shut it off over 200 deg F just in case. The heater heats the water, the drum heats the air and my basement is warm and so is my floor. It's simple but effective.

 

[SolarRich]

Our house uses the concrete slab in the basement as thermal storage. We built this over 25 years ago. The house is basically a well insulated box that is situated to collect sunlight during the winter. The active part of the system is a variable speed blower that pulls warm air from the vaulted ceilings in the house into duct work in the 12" thick slab. The air then returns via floor vents in each room.
This system gives us about 50% of the heat needed in winter. The remainder of the heat is from a resistance 12kw unit in the air handler. A custom made house thermostat runs it using temperature differentials to control the speed of the blower.

I'm playing with the idea of increasing the house thermostat by a couple of degrees during the day and then lowering at night. This will store PV generated power in the slab during sunny days instead of pushing it back to the grid.

This type of system can only be used in a house that is designed for it from the start. Not possible to retrofit as I looked at this option to convert a conventional house to solar heat as opposed to building a new house. The main issue with conventional houses is that the in-ground-basement or slab-on-grade is part of the earth.

But it proves that concrete can hold alot of BTUs

 

[OzSolar]

OzSolar - you are probably right for your location, but right now the sun comes up around 7.27 and sets at 16.57. On Dec. 21. it is 8.24 to 16.28, so it gets a little nippy at -22°F if it does happen. Anyway, it would be great if you have some calculation in the future.

For the PV system, 40kWh is the potential to produce 40,000 watt in one hour at max. sunshine and proper direction of the panels to the sun. This is equivalent to 136,486 BTU or 136 ft3 natural gas. It could run a 53.6 HP electric motor for one hrs about.

It sounds like you are assuming that 40 kW of PV will produce 40 kWh per hour from sunrise to sunset.

Below is the monthly energy for a 40kW array in my location and I suspect yours will be lower than mine, particularly in the winter when you are looking for it most. Drop your location in NREL's PV watts and report back with what the kWh/m2/day results are. That may help you better understand some of the challenges I am trying to caution you of.

 

[OzSolar]

But it proves that concrete can hold alot of BTUs

Nice!

We live in a passive solar house I designed and built 20 years ago. Walk out basement and the first floor is concrete. 2nd floor is standard wood decking. We need no supplemental heat and the house never overheats.

Edit: "we need no supplemental heat as long as it's sunny" Only when temps drop below ~30f and it's cloudy do we need supplement heat. I just checked and it looks like the ground source heat pump used an average of than 10 kWH per day last December and January.

Case in point: It was sunny and 70f three days ago but the temps finally dropped to 20's the last few nights. We went to bed with a 72f degree house and woke up to a 68f degree house each of the last two mornings. No other supplemental heat was used, just coasting off of the flywheel of heat stored in ~100 tons of concrete built into our floors and walls.

 

[LeoThomson]

I have 40 kWh theoretical production not per day, but per hour that's why it is 40 kWh

That is the wrong unit to use, it also confuses people (as is evident here), which means you will get questions for clarification or people will just ignore your number, as 40kW in solar, while not unheard of, is quite a large system for home use.

I have seen other paces where the wrong units are used, in commercial application to intentional deceive people. Don't get me wrong, I have no problems people making mistakes and part of the learning process is that we use common units.

 

[JoergK.]

Sorry, the 40kWh have nothing to do with my initial question or theoretical discussion and I add them again below with the PV production removed so nobody hangs himself on that hook again.

Some facts that direct my thoughts:

1. I can produce heat and or electricity from sunshine, but not natural gas that fires my heating system right now
2. My area (southern Alberta) has great sunshine hours year round and PV works fine, but like most, have no sunshine at night and less in the winter when we need the heat & power. On the electrical side, this is covered with a grid tied system, but one needs a sizable buffer, storage system for making thermal energy work year-round.
3. I hope all agree that evacuated tube solar collectors are the best on the market right now to capture heat and, with 50:50 glycol mix work year round.
4. Problem is the collector size & storage calculation to not over produce, but set this so it works year round with minimal NG needed to buffer.

Could one burie a 20' or 40' ocean container, insulated it good, line it with a double or triple bulk liner (used for ocean shipment of grain, fertilizer etc. & cheap), insert stainless tubes in the bottom to inject the heat and stainless steel tubes near the top to retrieve the energy and fill the whole volume with a liquid salt & glycol mix? The whole heat sink could be covered with new railroad ties or a concrete slap and covered with 4-5' of dirt to be out off the way.

To carry this on, my heating systems run on a minimum of 70°F in the return and max. 100°F on the hot side. So, 100°F is a minimum, 200-220°F is achievable in the storage tank. A heat pump could be added to retrieve energy below 70°F, down to probably 10-20°F.

Questions:

1. does this make sense in general terms?
2. is it doable?
3. how to calculate this all so I don't have anything overheat or freeze?
4. is it viable over 25 years?
5. Most could be done with own equipment & labor just the supplies need to be bought.

 

[Warpspeed]

Have to agree with OzSolar.

Its all been done before, many have tried, spent a lot of money (many from government grants) building active thermal storage systems, and all have had problems and been a big disappointment. When the government money stops flowing, the owner usually ends up ripping the system out, because its just too much trouble and expense to maintain.

Many years ago I was a technical officer with the Victorian Solar Energy council (Melbourne Australia) and I have painful memories of several failed solar thermal projects. The one most similar to the proposed system was a solar thermal heating system at "The Patch" primary school in the Dandenongs (Melbourne). This had a 50,000 gallon above ground water storage tank two stories high, a massive array of solar/thermal panels along the roof, and the tank had off peak (reduced electrical tariff) heaters in the tank to heat the tank at night if the previous day was cloudy.

Hot water was circulated through fan coil units in every classroom, and it never worked properly.
In summer it boiled, in winter there was never enough heat stored, it ran cold by mid morning.
The electric heating elements would then kick in, 120 amps per phase, around 100Kw on full day tarff, and the electricity bills were horrific.
The education department were having a fit, and later ripped it out.
They have heat pumps these days which work great at any time of year and only cost a tiny fraction to run compared to the solar system.

I could also tell you about a rock pile heat storage project. A massive basement sized hole was first excavated under a newly constructed house, and the hole filled with very coarse gravel. Air was circulated around the system, through solar thermal heat collectors (not vacuum tubes) but insulated hot boxes built into the roof, then through the rock heat storage, and through the house at night for heating.

It worked great during a summer heat wave, and hardly at all during the colder winter months. Moss and mold accumulated in the rock pile over time, and the air quality soon deteriorated to the point that it became unusable. Another expensive failure.

By far the best proven method for storing heat is the solar pond. These have been successfully built in many countries. They do require maintenance though, but can store heat at up to boiling temperatures, and the pond can be of unlimited size.

A large hole is dug, like a dam or oversized swimming pool about three feet deep. Its lined with ordinary heavy duty black plastic, so it cannot leak. Its filled with a salt/water mixture in layers. The lowest layer has the densest heaviest brine which stays at the bottom. Subsequent layers are added, being less salty, and the top layer is just fresh water. So there is a density gradient, that does not easily mix.

Sunlight travels straight through the clear water and only the lowest most salty layer over the black plastic gets heated. It takes a couple of years to gradually heat up, but eventually there will be an extremely hot lower layer, and it will stay hot for months. The secret to this is that the salt gradient is high enough to completely suppress convection. So heat is trapped in the lower layers, and the ground beneath.
A coiled pipe at the lowest level then acts as a heat exchanger, and heat up to boiling temperatures can be obtained right through the winter months.
I suggest you do some further research on solar ponds. If you have plenty of land available, its a proven workable system. The Israelis have lots of these generating heat and electrical power. The advantage over solar panels is that it continues working at night and during cloudy weather, and you don't need a battery.

People in very cold climates will be very aware of permafrost. The ground freezes completely solid in winter, but in summer only the upper couple of feet feet usually thaw. If you go down several feet, the ground is frozen solid all year round. A solar pond is the exact opposite. The ground heats up and stays hot right through the coldest winter. But it takes a long time for that heat to slowly accumulate.
So if you do build a solar pond, it may take a long time to really get going, but it will get better and better over several years.

The main thing is to keep the salt layers intact. rainwater adds, and evaporation removes the top layer. Also the water can become cloudy through microscopic life. The ph of the water is important too to solve that problem. Its rather like maintaining a swimming pool. But overall solar ponds have been around for decades, so there is plenty of knowledge and experience out there if you do the research.

 

[OzSolar]

I'm just going to leave this and be on my way.

It's called the Dunning Kruger Curve.

 

[JoergK.]

@OzSolar, looks-like you know it well

@Warpspeed, you are probably right and we let it rest.

Anyone knows this: Drake Landing

 

[solarsimon]

Sorry, the 40kWh have nothing to do with my initial question or theoretical discussion and I add them again below with the PV production removed so nobody hangs himself on that hook again.

Sorry, there's only one person hanging themselves on that hook. And thanks for the abstract lesson on how people get confused with units of power & energy.

One of the challenges is using materials that don't break down with long term use at elevated temperatures.

 

[SolarRich]

the Dunning Kruger Curve.

I'm trying to use my cognitive abilities to figure out if "I know everything and I'm always right" or "I'm completely incompetent and don't even know it".

 

[Warpspeed]

There is also the "been there, done that, and it didn't work" syndrome.

One really good thing about working for the Government on projects.
Its a great way to learn how not to do things.