PV Direct. Batteryless.. Thermal battery

[rebar]

I found some interesting videos about pv direct and sand batteries the other day. Similar to hot water storage, but with greater capacity and no leaks. One company in Finland was resistance heating sand with a closed forced air loop that would bring temperatures up to about 600 degrees. They could store this heat energy for days or weeks.

I'm wondering if this process could be adapted for a residential home for heating. I've already read about some folks in cold climates installing heat tape in the sand under their house to keep it warm with low off peak rates. Why couldn't you install PV panels to heat a similar system with no controller inverter or batteries involved?

Thanks

[bcroe]

Interesting, but with resistance heat, you give up any COP
multiplyer of a heat pump. Will not solve my problem of
storing summer energy for near sunless winter heating.
Bruce Roe

[rebar]

Interesting, but with resistance heat, you give up any COP
multiplyer of a heat pump. Will not solve my problem of
storing summer energy for near sunless winter heating.
Bruce Roe

Run heat pumps off pv with the condensers buried in the sand battery, but resistance is 100% efficient and no moving parts so throw three times the amount of PV at it given the space. ..

I'm in Iowa. Where can I find out historically how many hours of good daylight I would receive during the winter? Or are you telling me there's no way winter PV could resistance heat a insulated two or three cubic meter sand battery in Iowa? Which is fine, you'll have saved me some time lol.

[J.P.M.]

Nothing new under the sun and that includes this stuff which is no more than the old idea of thermal storage with another iteration using sand instead of water, rocks or other thermal mass in a confined and insulated space.
This is approx. equivalent to the well developed pebble bed (or sometimes called packed bed or rock bed) thermal storage idea but with a small(er) rock radii.
The idea's been around for thousands of years. The engineering is well developed.
1.) Get lots of cheap mass with a high mass density and a decent specific heat.
2.) Contain it using a lot of insulation and find some way to transfer heat (energy) across the insulation boundary.
3.) Size according to needs. Stress high mass over high temps. consistent with energy end use.
4.) Keep the design storage temps. down to minimize thermal losses and to keep the design realistic and safe.
5.) Design for as high thermal time constant (high UA/(m*cp)) as possible consistent with economic reality.
6.) Avoid using the heat to generate electricity on a small/residential scale as that will be financially counterproductive and entropically unsound.

Those people from Finland seem almost as ignorant of the subject as the Americans interviewing them.

[bcroe]

Run heat pumps off pv with the condensers buried in the sand battery, but resistance is 100% efficient and no moving parts so throw three times the amount of PV at it given the space. ..

I'm in Iowa. Where can I find out historically how many hours of good daylight I would receive during the winter? Or are you telling me there's no way winter PV could resistance heat a insulated two or three cubic meter sand battery in Iowa? Which is fine, you'll have saved me some time lol.

Am in N ILL here, lots of clouds, worse in winter. A couple years
ago we had 29 days in a row you could not see the sun. Net
Metering uses the PoCo as my infinite capacity, 100% efficient,
zero cost and maintenance, storage battery.

Panels only deliver best energy with an MPPT controller of some
sort, otherwise their potential output is largely wasted. The temp
range you mentioned is not directly within range of the usual home
heat pumps. I need 26,000 KWH of generation, 13,000 KWH of
storage to cover electric and HVAC annually for this typical house.
400 panels (3X) you suggest would be a project.

Best listen to J. P. M.

Bruce Roe

[rebar]

Ever hear a song you can't get it out of your mind? Thanks for getting the sand batteries song off my mind guys.

My rental property, where I'm going to retire in a few years, the bills really skyrocketed last winter with the propane costs. Propane's basically two bucks now.. I'm aware that air source heat pumps could be competitive with propane at 13 cents a kWh. But now that propane has basically doubled in cost, and that my power company offers $400 rebates and a lower 7.7 cents per kWh winter rate for the pumps if I switch to a electric water heater on the high rate (2 meters), is that the best path?

Or if I get a GT PV , I don't get the winter rate, and the backfeed only pays 2.7 cents per kWh.

I'm not moving in anytime soon so I'm not too worried, but would you install PV with the rates that I have?

[J.P.M.]

Ever hear a song you can't get it out of your mind? Thanks for getting the sand batteries song off my mind guys.

My rental property, where I'm going to retire in a few years, the bills really skyrocketed last winter with the propane costs. Propane's basically two bucks now.. I'm aware that air source heat pumps could be competitive with propane at 13 cents a kWh. But now that propane has basically doubled in cost, and that my power company offers $400 rebates and a lower 7.7 cents per kWh winter rate for the pumps if I switch to a electric water heater on the high rate (2 meters), is that the best path?

Or if I get a GT PV , I don't get the winter rate, and the backfeed only pays 2.7 cents per kWh.

I'm not moving in anytime soon so I'm not too worried, but would you install PV with the rates that I have?

Reads to me like you need an education.

If I was in your situation I might or might not install PV but whatever my decision, it wouldn't be until I got more education (more than the usual utube garbage) and after that spend some time thinking about just what it is I want to accomplish, set realistic and achievable goals based on what my self education taught me, and set a plan to make those goals a reality.

But whatever I did, after my self education, I know that if keeping my energy bills low is to be a priority, my first task will be to examine my lifestyle with an eye toward reducing my need for energy. The second thing I'd would do is to take energy conservation measures that reduce how much energy I use to maintain that reduced energy lifestyle.
An example of the first task is to take shorter showers. An example of the second is task to replace your shower head with one that has a lower flow rate.
More examples of the first task is to change your thermostat setting(s) so as to be closer to the outside air temp. and then either add or remove layers of clothing to your comfort level.
Another example of the second task is to insulate your domestic water heater, the hot water distribution lines and any HVAC ducting, especially those running though unconditioned spaces.

The idea behind all this is that until you've exhausted most every means of conserving energy starting with an attitude that focusses on lifestyle changes (which cost nothing), most any and all of those conservation measures are almost always more cost effective than buying more energy or generating more of it from PV or most solar thermal energy generation methods including sensible passive solar building methods and measures.

Keep the horse before the cart and set your priorities in order so as to first focus on measures that return the most bang for your energy buck. If you use your newly acquired energy knowledge to do some easy back of the envelope analysis, you'll quickly find that saving (and so not using )energy is way more cost effective than getting more of the stuff - at least by any legal means - and that measures that reduce your use to the max consistent with your lifestyle, comfort level and economic sense will also make any subsequent alternate energy additions to your energy mix smaller (and hence less expensive).

After those conservation measures, whatever eventual mix of conventional energy/alternate energy you choose will be more cost effective than if you never used lifestyle changes and conservation measures to pre-reduce your energy needs as much as possible.

Take what you want of the above. Scrap the rest.

[bcroe]

My net metering pays nothing, but they trade me back winter KWh 1:1
for my summer surplus KWh. Your results may vary. Heat pump water
heaters are available.

Energy of a gallon of propane about equals 27KWh, with a 95% gas
heater it is more like 26KWh. An air source heat pump multiplies the
electric advantage, several times in warmer weather, might drop to unity
for those times well below zero. A geo thermal does better then. It
works here, I only pay an electric monthly connect fee.

The gas industry has deliberately created a shortage (and peak prices),
esp in mid winter, by exporting it as fast as possible. That was the reason
I went complete PV solar a decade ago, it looks better every year.
Bruce Roe

[PNPmacnab]

If starting from scratch, there are things to do. I've seen homes with a large concrete block in the center of the house which can absorb heat or release it. Not a new concept as this used to be done with massive fireplaces in pioneer days. What concerns me with these large mass storage systems is if there ever is a problem with piping or wires it is cheaper to just start over than repair them.

[J.P.M.]

If starting from scratch, there are things to do. I've seen homes with a large concrete block in the center of the house which can absorb heat or release it. Not a new concept as this used to be done with massive fireplaces in pioneer days. What concerns me with these large mass storage systems is if there ever is a problem with piping or wires it is cheaper to just start over than repair them.

One of the pillars of passive solar design is effective use of thermal mass. again, a well developed technology that has deep and aged roots going back literally thousands of years.

It ain't complicated, doesn't need to be made so and in fact works best when well thought out and as uncomplicated as possible.

With an architect, I designed a passive solar home which I called my solar opus in the desert that got through plan check and building permits before I walked away from it for reasons unrelated to the project. I did get certified as a HERS auditor as part of the plan to help the permitting process along rather than try to convince some other (and probably inexperienced) auditor about the soundness of some of my ideas incorporated into the design. I still had a P.E. license at the time and that helped.

The building was to be in a desert climate almost identical to Phoenix and due to the design including among other features the use of a lot of thermal mass and a lot of insulation on the outside of the large distributed mass, the design building thermal time constant was about 240 hours. The building design called for complete HVAC capability as required by the CA building code, but with seasonally appropriate ventilation using whole house fans, the HVAC would not get much use either in summer or winter.