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Storing heat in sand?

The problem with rock bed heat storage is that over time dust, bacteria, fungus and other crap builds up on your rocks, and the circulated air can then become a real health hazard.
This problem also exists with ducted heating and airconditioning, its commonly called "sick building syndrome".
Its usually more economic to demolish and rebuild an older building than to completely strip and replace the entire heating and ventilation ducting system.

I only know personally of one Government funded experimental solar/rock bed heat storage project in a domestic home. A large pit was dug and filled with loose rock below the concrete slab on which the home was built. Hot air from solar collectors was used to heat the rock storage during the day, and at night circulated air air was warmed by the stored heat.

It did not work very well in spring or autumn, and not at all during winter. After about five years (I think it was) people started to come down with various illnesses that were finally traced to bacteria in the air.
 
Mart Hale said:
I agree I am not heating the sand as you suggest. The problem with your suggestion is that dry sand is an insulator It may heat the first few inches like on a beach but unless you had good insulation the heat would be loss. Both of our methods use the sun... I do agree yoru method is different. Perhaps to test your method one could fill a Sun Oven solar cooker with sand and see what the results would be.
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Sand on a beach or uninsulated will lose its heat to the earth fast. I read someone mention "its cool just a few inch's below", well yeah.. Most of the US has soil temperatures about 50 so heat will travel to cold. I don't think there is a larger heat sink, so you cant compare it to sand in a highly insulated vessel. .

Warpspeed said:
The problem with rock bed heat storage is that over time dust, bacteria, fungus and other crap builds up on your rocks, and the circulated air can then become a real health hazard.
This problem also exists with ducted heating and air conditioning, its commonly called "sick building syndrome".
Its usually more economic to demolish and rebuild an older building than to completely strip and replace the entire heating and ventilation ducting system.

I only know personally of one Government funded experimental solar/rock bed heat storage project in a domestic home. A large pit was dug and filled with loose rock below the concrete slab on which the home was built. Hot air from solar collectors was used to heat the rock storage during the day, and at night circulated air air was warmed by the stored heat.

It did not work very well in spring or autumn, and not at all during winter. After about five years (I think it was) people started to come down with various illnesses that were finally traced to bacteria in the air.
Click to expand...

Wow. To bad this situation wasn't well documented to prevent it from happening again. Do you have any more details?
 
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spazatak said:
Wow. To bad this situation wasn't well documented to prevent it from happening again. Do you have any more details?
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Back in the mid 1980's I worked for a State Government department that funded and became involved in many different kinds of alternative energy projects. My job as Technical Officer was doing maintenance and data collection, as well as assisting at the original planning stage.
It was one of the most interesting jobs I ever had, and I learned a lot about grand plans that turned out to be less than wonderful. Or put another way, how to spend large amounts of Government money on projects that do not actually work.

Politicians love this stuff. They like the publicity and being seen on TV and in the newspapers as being green, and making the world a better place.
Making long speeches, and cutting ribbons, is great public relations for them.

Anyhow, this particular rock bed heat storage project was old, even back in the mid 1980's, long before my time. So I heard a bit about it, and once visited the site. By then it had all been shut down. The home was still there and occupied, but the rock bed was sealed off, and the solar collectors removed from the roof.

I suppose in retrospect, some mechanism could be built into it to flush and disinfect the rock bed heat storage, maybe annually. But the truth is, any type of practical solar heating through mid winter is just not possible. When its frosty cold and the sky is solid grey for several days in a row, it obviously cannot keep your whole house toasty warm. At least not if running off 100% solar. The whole concept is completely impractical.

If it had worked better (or at all) no doubt some system to overcome the health issues could have been tried in another project.
But the sad truth is, it was a very expensive failure, swept under the carpet and forgotten about.
 
Warpspeed said:
The problem with rock bed heat storage is that over time dust, bacteria, fungus and other crap builds up on your rocks, and the circulated air can then become a real health hazard.
This problem also exists with ducted heating and airconditioning, its commonly called "sick building syndrome".
Its usually more economic to demolish and rebuild an older building than to completely strip and replace the entire heating and ventilation ducting system.

I only know personally of one Government funded experimental solar/rock bed heat storage project in a domestic home. A large pit was dug and filled with loose rock below the concrete slab on which the home was built. Hot air from solar collectors was used to heat the rock storage during the day, and at night circulated air air was warmed by the stored heat.

It did not work very well in spring or autumn, and not at all during winter. After about five years (I think it was) people started to come down with various illnesses that were finally traced to bacteria in the air.
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That is certainly an issue at low temperatures. However, in a well insulated tank at high temperatures of say 500F or more no mold or bacteria could survive and if being used for domestic heating any residual solid would easily be filtered out of the tempered final air thru conventional furnace filters prior to discharging into the rooms. Other options would be to just recirculate air thru the tank in a closed loop that has an air x liquid heat exchanger. Or maybe directly to a high temperature Sterling motor to produce useful energy.
 
Sure, plenty of alternatives are possible, but may be neither practical or economic.
These days, the way forward for non combustion heating seems to be a ground sourced, or solar sourced heat pump.
These are proven to work well and are commercially available.
 
Both requiring mechanical (typically electrical) input. To provide heat in the winter, when the sun may not show its face for weeks.

Biomass, anyone?
Is there a crop other than trees you would suggest cultivating, to store the sun's energy in summer for use in winter?

Maybe closed-cycle fossil fuel to algae or biomass, where ever fossil fuel is still used, and ship the captured carbon to places with more harsh winter. (at least that uses the carbon twice before atmospheric release.)
 
Hedges said:
Both requiring mechanical (typically electrical) input. To provide heat in the winter, when the sun may not show its face for weeks.
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Yes, but the coefficient of performance for heat pumps is reaching about x4 or x5 these days.
Electrical input might come from wind or hydro as well as solar.

Combustion is always going to be the cheapest to install !!!
Geothermal heating would be perfect.
Move to Yellowstone, and live in complete peace and contentment.
 
Warpspeed said:
Sure, plenty of alternatives are possible, but may be neither practical or economic.
These days, the way forward for non combustion heating seems to be a ground sourced, or solar sourced heat pump.
These are proven to work well and are commercially available.
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That is very true, but we are talking mostly about how to store energy in a thermal battery for future use. My contribution is to suggest that round rocks can have advantages over sand and that excess PV DC could be directly used to heat the rocks. There are lots of potential ways to store heat, but few are as safe, simple, or cheap as sand and rocks. PS: If you need rocks, I will give you all you can gather from my yard. Free, please!
 
Agree, rocks are great for heat storage, but you still need to harvest the heat to store.

A solar pond both harvests the heat directly and stores it efficiently for months (and years) in very salty water. These have been in use for decades around the world, not just for direct heating, but electricity generation. Israel generate some large fraction of their electrical power from solar ponds.

https://en.wikipedia.org/wiki/Solar_pond

Solar panels are much more efficient for electricity generation from solar, but as we all know, solar panels don't work at night.

A solar pond can boil a fluid and drive a turbine to full output 24 hours per day, and continue working through very long periods of cloud or cold weather.
A solar pond can take several years to build up to full temperature, but then it just keeps on going right through winter.
It is a lot cheaper and potentially a lot more more reliable than equivalent battery storage.

I was involved in some research into solar ponds with one of the universities here, that was a very long time ago. Much has been learned since those days. The biggest problem back then was turbidity in the water due to microscopic flora and fauna in the cold upper layers. The solution was very close control of Ph in the water. Much like maintaining an ordinary swimming pool. Solar ponds can reach 100 Celsius right at the lowest level, and can store enormous amounts of heat energy.
 
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Warpspeed said:
These have been in use for decades around the world, not just for direct heating, but electricity generation. Israel generate some large fraction of their electrical power from solar ponds.
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One Wikipedia page says 80 degrees C, with 20 C ambient.
Another says the Israeli plant generated 5 MW

"The world's largest operating solar pond for electricity generation was the Beit HaArava pond, which was operated until 1988."

Might have been large fraction of electricity for a small town, many decades ago. Probably all nukes today? Nope, none. Mostly fossil fuel.

1688347186910.png

What method used to turn a turbine? Boiling something like propane?

I think Carnot said (80 - 20)/273 = 22% or something like that theoretical cap on efficiency.

I suppose even 5% or 10% wouldn't be terrible, with large volume.
 
The working fluid could be many different things, it depends on the pressures involved where boiling/condensing occurs.
I believe some of the halogen gasses (various types of freon) are very popular. Propane should work too. And so probably might ammonia, but that is too toxic and not environmentally friendly to be considered.

As the article says, these ponds are extremely cheap to build, so overall efficiency is not a big factor. If you need more heat, just dig a bigger pond.
If you have almost unlimited miles of flat desert that is not much use for anything else, and plenty of local salt, the whole thing becomes quite practical.
 
Hedges said:
Is there a crop other than trees you would suggest cultivating, to store the sun's energy in summer for use in winter?
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Miscanthus Giganteus: https://en.wikipedia.org/wiki/Miscanthus_×_giganteus

Miscanthus is unusually efficient at turning solar radiation into biomass, and its water use efficiency is among the highest of any crop.
The typical UK winter harvest of 11–14 tonnes dry mass per hectare (1.1–1.4 kilograms per square metre (0.23–0.29 lb/sq ft)) produce 200–250 GJ/ha (22,000–28,000 kWh/acre) of energy per year
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1 acre = 580 - 736 gal of diesel equivalent energy per year in northern climate.
 
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According to that link, most plant crops including those usually yield < 1 W/m^2, some as low as 0.05 W/m^2
If units are comparable, PV panels today yield 200 W/m^2 (in full sun, may average 5 hours/day in some regions.)

Of course capital equipment to spread seeds is much less than fabricating single-crystal solar panels.

Per unit area, producing H2 from PV and storing as hydrocarbons or carbohydrates would deliver much more.

Maybe some food crops would be most useful. Harvest corn to eat, and use everything else as fuel in the winter.

I was hoping algae, fed concentrated CO2 from existing power plants, would lead to closed cycle power production.
 
Warpspeed said:
Agree, rocks are great for heat storage, but you still need to harvest the heat to store.

A solar pond both harvests the heat directly and stores it efficiently for months (and years) in very salty water. These have been in use for decades around the world, not just for direct heating, but electricity generation. Israel generate some large fraction of their electrical power from solar ponds.

https://en.wikipedia.org/wiki/Solar_pond

Solar panels are much more efficient for electricity generation from solar, but as we all know, solar panels don't work at night.

A solar pond can boil a fluid and drive a turbine to full output 24 hours per day, and continue working through very long periods of cloud or cold weather.
A solar pond can take several years to build up to full temperature, but then it just keeps on going right through winter.
It is a lot cheaper and potentially a lot more more reliable than equivalent battery storage.

I was involved in some research into solar ponds with one of the universities here, that was a very long time ago. Much has been learned since those days. The biggest problem back then was turbidity in the water due to microscopic flora and fauna in the cold upper layers. The solution was very close control of Ph in the water. Much like maintaining an ordinary swimming pool. Solar ponds can reach 100 Celsius right at the lowest level, and can store enormous amounts of heat energy.
Click to expand...
A solar pond would lose a lot of heat to evaporation. For every pound of water that evaporated from the hot pond about 1,000 BTU's or 3,410 Watts of heat would be pulled out of the brine plus that water would have to be replaced.
 
Gold Country Russ said:
A solar pond would lose a lot of heat to evaporation. For every pound of water that evaporated from the hot pond about 1,000 BTU's or 3,410 Watts of heat would be pulled out of the brine plus that water would have to be replaced.
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No it does not.
That is the whole point.

The upper most layer is fresh water near average ambient wet bulb temperature, just like any lake.
Sure there will be some evaporation, but also replenishment by rain.
In a hot dry desert environment, evaporation WILL be high and sufficient fresh water will need to be added at the top layer.

The next layer down is slightly salty, and slightly warmer.
The layer below that is even saltier and warmer still.
The increasing saltiness and higher density the lower you go totally prevents convection, so the heat is trapped.

At the lowest level, the salt brine is so dense, you can almost pick it up with a shovel, and the temperature up near boiling (if you don't pull out any of the heat to use). The ground underneath is also just as hot, and as long as the natural water table is well below your pond, and the ground below dry, the heat is trapped there too.
It takes a very long time for the temperature to build up that high, but once it does, it also stays hot as the heat is almost totally trapped.
 
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Hedges said:
PV panels today yield 200 W/m^2...
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More like 15 W/m^2 averaged across one year if you include 15% capacity factor for northern climates and 50% solar field fill ratio (have to leave some space between panel rows). But that's still 20x more energy yield vs. Miscanthus grass (531 MWh vs 28 MWh per acre). But you lose half when converting to H2 or more if directly into hydrocarbons. I wish humans would stop being fools and just go all in on Nuclear. It makes so many problems with integrating renewables just disappear. I suspect in 50 - 100 years this will be the case and renewables will just not be competitive when space on earth starts getting expensive due to overpopulation.
 
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run air conditioner and collect the condensate to replenish the solar pond :)

would need some PV to cover the heat pump water maker energy needs.
 
Hedges said:
Biomass, anyone?
Is there a crop other than trees you would suggest cultivating, to store the sun's energy in summer for use in winter?
Click to expand...
Trees, where abundant, make good sense - not the whole tree, the parts the lumber mills can't use.
My business (3,000sqft) is heated completely with wood pellets, in a factory built wood pellet furnace (not a stove), the pellets are generated locally from wood wastes from sawmills. I do some work for the pellet plant and in exchange get the pellets I need at cost.
The pellet furnace uses my solar power for controls and fan for heat circulation around the shop.
Brine Ponds, planting/growing plants just for the biomass and other such options never seem to compare to the efficiency of re-directing the waste from one (profitable) industry to create another profitable one. In the case of the pellets, these are made from the by-product of the lumber industry, all the costs associated with planting, harvesting, trucking are already part of the lumber business model, the pellet plant simply collects the waste products, processes these and packages them. No new land is required, and no cost of planting or harvesting is part of the pellet production costs, as these functions are part of (and paid by) the sawmill industry. The sawmills actually benefit from diversion of the wastes, since huge wood waste piles tend to spontaneously combust otherwise, and without the pellet plant the lumber mills have a cost to deal with the wood waste.
Not a model for every location, since huge forestry industries do not do well in arid climates, the point is to look for an under utilized waste product from one local industry and see where it could be applied to another.
 
Yeah, why not sell what you otherwise burn or pay to dispose of?

1688399107665.png

(Compost would be another good use. For now, that's where my yard trimmings go although I've mused about heat. I have what could be a wood lot as well, so might just cut firewood.)
 
We have cut "fire wood" for over 20-years on a 30 acre lot. But never clear cut - we thin and remove damaged or leaning trees. Since we have a band-saw mill, the larger trees provide a few saw logs from the base, while the upper tree portions and saw-mill-slabs all go to heating fuel. All these years on, and you can't tell we cut at all, an opening in the forest quickly fills in with new growth reaching for the sun light.
I consider this my first 'solar energy' system before the PV was installed. LOL.
Compost, bark, crop residues could be a good heating source, if managed and a method of heat collection was buried into the waste.
I worked on construction of an OSB plant back in the early 1980's - the waste wood burner heated the log ponds (where they thaw and clean the logs before the debarker and chippers) those ponds were designed to be coverd, but the mill had us remove the covers to avoid boiling the water off since the wood waste funace generated 'too much heat'. That entire building and huge ponds were heated with just wood waste. There was a farm next to the OSB plant, I often wondered if that farm could have run some heating pipes under ground to extend their growing season, or heat a huge green house (nearly for free) and grow high value veggies all winter rather than shipping these all the way from Mexico. Yeah, no one ever used the waste heat for farming, seemed like a lost opportunity.
 
A Sterling engine driving a Sterling Heat Pump requires no external source of electrical/mechanical energy.
 
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