Not sure why they would use concrete, since water is much less expensive and has a greater capacity for storing heat.
Specific heat of:
water 4.182kJ/kg degC
concrete 0.88kJ/kg degC
IE, water can store nearly 5 times as much thermal energy than concrete per kg. And since concrete density is not anywhere near 5g/cm^3, the specific heat of water per unit volume also exceeds that of concrete by a significant factor. (maybe 2X, without looking up concrete density)
IMO, if you use concrete for storing heat, you must be crazy!
That’s what I have also heard, along with difficulties operating and maintaining (e.g. cleaning) a single mirror compared to multiple smaller mirrors. Also, if one breaks a single mirror, the cost to replace would be more than replacing a smaller mirror.
True, and the energy transfer back to make heat would be very poor unless the same lump of concrete was riddled with multiple pipes/transfer surfaces.
No disagreement with that. Indeed most solar concentrators work on multiple mirror designs. I was referring to @mark_m’s post about Archimedes defence of Syracuse and the test by the Mythbusters. My thought was that to make an effective single mirror back in the times of Archimedes to actually defend a city would have been almost impossible to construct. My musing was that perhaps a multi mirror design was used, if one was at all??
There are single mirror concentrators but each one only produces a relatively small amount of power compared to modern needs. Therefore a farm of even these are required to produce significant power outputs. These from memory are called Parabolic Troughs, they can either produce heat (which I think is the most common way) though I think some actually directly produce electrical energy.
California company SolarReserve has had a molten salt generator for quite some time in Nevada. It is called Crescent Dunes.
Indirect storage has also been commercial with plants like Solana that heat oil first which is used to produce steam from heating water but also is used to heat molten salt which is then used to continue producing steam after the sun sets or is obscured:
There is also Silicon for thermal energy storage, such as by 1414 Degrees, whose system is undergoing testing at Nectar Farms in western Victoria. I haven’t heard any reports about how they are progressing though.
Spot on. I think it was also being used to give an idea of the scale required if using rock mass for a larger capacity storage of captured thermal energy.
In modern building design the notion of using thermal mass within a building to store warmth or cool is no longer bleeding edge. Another extension is the use of ground or geothermal heat pumps.
Such systems can readily incorporate the benefits of solar capture through thermal and or PV.
Grid connection or Utility company rip offs optional.
P.S.
For Australia, unless you are somewhere quite cold in winter, importing the European examples may have limited value.
I’m with @gordon on using water or better still ice as a storage medium for cooling on the humid and more tropical east coast. It is obviously reversible in winter. The technology using heat exchangers and or heat pumps is mature. The missing bit may be packaging it in such a way that it becomes competitively accessible. Firstly on new builds and secondly as a retrofit. Reverse cycle air conditioners plus a well orientated rooftop PV is accessible and may be cost effective. In particular if the house system comes on before you get home in the evening for day workers, to ease the evening load in a thermally smart house.
Residentially water requires a holding tank that is well insulated. Our 270l holding tank for our hydronic system will keep our heat leaky house living and dining area cosy for an hour plus once the heat is turned off. I put the Engineers hat on once and guessed if we had a tank ten times that volume, with our often sunny winters, a couple of flat plate solar HW panels might meet most of our winter evening and morning heating needs. Target +10C while meeting a portion of our HW which has an instantaneous gas heater. I’ll say nothing of the cost of a suitable tank or the need for a gold plated building application and permit. And you only get to store heat or cool at the one time. It’s complex.
For now we can export excess PV at 20c/kWh and our bottled gas bill is only $300-350pa. It does not stack up financially for a small gain environmentally to go the mass water storage root just for winter. The level of investment needed would be more flexible if put into off grid battery power, or a BEV if carbon footprint is a priority.
Some house designs incorporate a water wall that is naturally heated by the sun during the day in Winter as it tracks a bit lower during this period so reaches the water wall. It releases warmth during the day and night.
During Summer the wall is not exposed to the sun (or only for a short period) and the thermal mass of water adsorbs the heat in the house during the day to keep temps more moderate over the day and the night.
This of course is a bit off Solar Power generation but I guess it still is using the Sun or lack of Sun as a means of heating and cooling which do use a lot of power to otherwise do. I often think about whether to install a Solar powered AC system.
LiBr Adsorption ones (lithium bromide) also interest me.
It does offer an alternate way of looking at how to use solar energy. It demonstrates that it is possible to skip the electrical generation step in some instances, by looking at the problem in a different way.
Who knows how much interest there is in the potential or development of solar solutions, for heating or cooling.?
About 10 years ago I enquired about the cost of installing one. I’ve almost recovered from the shock
They are hideously expensive, and the slight benefits over a modern reverse cycle system (air sourced) certainly didn’t go anywhere near making up for the huge extra expense.
In another post on the site I mentioned OS research into compounds that store heat energy for very long periods (they say about 18 years but perhaps more if it is very stable). The collectors are basically parabolic troughs that heat a liquid to change it’s chemical nature to another compound which can then be stored or even transported (endothermic reaction). When heat is required the new compound is passed through a catalyst to revert it to the original compound but releases heat in the process (exothermic reaction)…
In regard to cooling what about using underground pipes to move air through pipes into the house? As it moves through the pipes it becomes cooler due to the ground temp. It would need lots of ducting and some depth into the ground but possibly feasible? I think we discussed it sometime ago.
Certainly doable, and I did look into it extensively years ago, and also visited someone who had made such a system at Coonabarabran, although only for one room. It does work, but the cost and difficulty of digging sufficiently long trenches here, make it impractical for me.
To do a whole house, you need a very long system of paralleled piping in trenches a couple of metres deep, and the pipes need drainage to prevent condensation build up (legionnaires risk). This will certainly occur in humid summer weather, when the dew point is above the deep ground temperature, ~17C here. I’ve seen DPs up to 24C in summer.
Such a system can also supply warmish air for winter too.
There are other considerations. Concrete can be heated to a much higher temperature than water without a pressure vessel. A higher temperature difference more than compensates for the difference in specific heat allowing more energy to be stored and also makes heat transfer quicker.
Whether the broad idea of storing heat (say from the sun) around the house to use later is a really good one or not I cannot say.
Yes it can be heated to a higher temperature, but how are you going to get it there safely? That introduces containment issues too.
Houses with large thermal masses inside (just heated by direct sunlight) can be quite comfy in winter, but after a week of 40C plus weather, I suspect I would find it pretty hard to sleep at night, at least according to the details I have read about a house in this area.
It’s complex, designing such a system needs to consider quite a few more issues than than those mentioned so far but the specific heat issue does not in itself make using concrete crazy.
Is this “PeakSmart” technology smart enough to deal with the complications of a household that has panels or panels and a battery - so that the energy flows are more complicated than simply consumption from the grid? Would it still be appropriate for the power company to turn your air-co down if you are net not consuming from the grid? As long as participation in this remains voluntary, I suppose it doesn’t matter how it interacts with household generation.
