121–130 of 181 posts
In general, I'm impressed that there's so much research and investment in this field (storing excess renewable energy). I think most people don't realize how much and that the problem of the sun not shining and wind not blowing all the time will be solved much more quickly than most people think is possible.
You can DIY this on the cheap by connecting solar panels directly a $10 hot water heating element and burying it in sand. You will need to pair the right spec element with your panels No charge controller, inverter or battery needed.
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Any system that involves an electrical solar panel connected to a low-temperature electrical heater is likely to be better served with a solar hot water panel, by about a 10:1 ratio.
Are you including the maintenance costs of the water panel in your estimate? I used to buy this argument, but then: A) PV panels got ridiculously cheap B) everyone I know with solar hot water has emptied their systems because the maintenance hassles were not worth dealing with Using high grade intermittent current to produce resistive heat isn’t high on my list of efficient things to do, but unfortunately neither is…
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More like 4.5:1 solar is 20% or so efficient and solar thermal is only like 90% when including losses. Anyway, the real question here costs both in equipment and labor. Solar hot water panels involve plumbing and need radiators etc they quickly pay for themselves when heating a large home but don’t scale down very well. Running the numbers I was surprised how cost competitive the sand bucket is for something like a c…
The monetary case of PV does not account for the damage that is done to the environment over the entire lifecycle. Solar hot water panels are ecologically superior. Not only are they more efficient in W/sqm. Their production is not as energy intensive (plumbing included), the recycling process is less complex, poisonous materials can mostly be avoided. If heat is the desired product, they probably beat PV by an order…
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But this would stop you getting the sand hotter than 100c - which is one of the main advantages of using sand over water for heat storage.
You can make it work under pressure and/or add salt.
solar panel with sand is mechanically and electrically much simpler
sand's heat capacity = 830 J/kg degree C
sand battery size is "13m tall and 15m wide". Assuming most voluminous possible shape that's 13m * 15m * 15m = 2925 cubic meters of sand (100% fill, no account for insulation, etc.)
Dry sand density is about 1600kg/m3
Total weight of sand would be 2925m3 * 1600kg/m3 = 4.7Mkg (4.7kt)
4.7Mkg of sand has a heat capacity of 830J/kg * 4.7Mkg = 3.9 * 10^9 joules / degree C (it takes this much energy to heat up entire battery by one degree C)
So from this, we get that 100MWh of energy would heat up the battery by (3.6 * 10^11 J) / (3.9 * 10^9 J/C) or about 100C.
If we include a different shape (a cylinder), and account for a thick insulation needed, this becomes closer to 200C of temp diff.
I guess it checks out... It is going to be more difficult to estimate heat loss.
But sand is quite expensive so my question is, why sand and not water? Water has 5 times higher specific heat per weight, about 3 times per volume. Water is way cheaper than sand and much easier to find, transport and extract energy from. The only real problem with water is you can only heat it up to 100C.
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Some Youtube folks tried a much simpler approach: Take a large metal bucket or barrel. Put a heating element and a simple oven thermostat on the bottom. Fill with sand. Connect to a solar panel or other enrgy source. The air between the sand particles seem to actually provide a bit of convection and insulation. The thermostat turns the circuit off before getting too hot for the heating element. The heat accumulated d…
Any system that involves an electrical solar panel connected to a low-temperature electrical heater is likely to be better served with a solar hot water panel, by about a 10:1 ratio.
At least in residential and commercial installations, you get a much higher ROI by putting in solar electric, using the electricity to power your home/facility, and dumping the excess into the grid to earn money/credit.
Resistive heat storage is also a thing these days; hundred-plus gallon tanks that will take power from the panels if it's more cost effective than returning it to the grid or the grid doesn't have the capacity to take it. That water then feeds a second water heater which brings it up to the final temperature, if necessary.
The efficiency relative to area doesn't really matter, as rooftop space is rarely at a premium.
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Might be a location thing; there are vast numbers of solar hot water systems here in W.Australia and typical maintainence is maybe just replace the tank outright and flush the lines every 20 years or so. How 'clean' of salts, etc. is the water being put through your panels? Hard water clogs up faster.
As you allude to, our water in WA is notably soft, maybe that helps? I mean it's full of iron but that mostly just seems to cause staining not clogging. That said, a heat pump running at 4:1 COP coupled to 20% efficient solar panels gets you right back to the same efficiency as solar thermal, with a lot more flexibility.
No single point of failure, sun heats the water directly and provides power, with a breakout box that accepts power in from the grid (if required), exports excess for points, hopefully that gets better over time, and accepts a local generator input if the PV panels are offline for some reason when there's a local grid power outage.
This is pretty good for now, there's loose neighbourhood discussion about perhaps getting a local area battery in a sea container that can buffer ~200 standard homes to further secure the town's energy stability.
Flexibility, in rural settings, is about having options not a single point of failure | dependency.
Eg: Way up the hill it's good to have PV panels on the bore pumps and better to have these independant of the house circuits with cables in place to route power "in case" .. along with option to use a generator if needed.
Obviously works better the better insulated a house is. Has the advantage of turning everything in your home into a thermal battery with the only real cost being furnace controller, potentially even just software. At one point I meant to do the math to figure out the rough storage/efficiency for an average home but never got around to it.