The issue with seasonal storage is that efficiency is much less important than capital cost. The cost of inefficiency is proportional to the number of charge/discharge cycles, the capital cost is not.
So, it makes sense to look at systems like ones using hydrogen, since hydrogen can be stored underground as a compressed gas at a storage capacity cost of $1/kWh. Minimizing that capacity cost is crucial. Sure, the round trip efficiency will be poor (maybe 40%?) but as argued above that doesn't matter much.
Primary batteries based on molten salts ("reserve batteries") have been standard in military applications since just after WW2. They are ideal for munitions (fuzes, missiles) that need long storage life but don't need recharging.
You can't exactly harness heat; what can be harnessed is a temperature differential , to convert into some form of mechanical motion or electrical potential. You'd need some apparatus that connects the hot mass and some cold sink with thermocouples. Whether that's possible or feasible on the scale of the London Tube, I don't know. https://en.wikipedia.org/wiki/Thermoelectric_effect Instead of that, probably a more fe…
Heat is energy, so I find it surprising that it can't be harnessed. Is it really not possible to take some of the energy out of a system and use it for something?
If it got hot enough you could use a geothermal-type generator for reasonable efficiency, but that is (of course) still exploiting a temprature differential (a place where water remains liquid, and a hot place where it becomes high pressure steam to drive a turbine). However sadly that is unlikely to happen before the tunnels become unlivable :)
Stupid question: can we harness this 100 year old heat to power something today?
You can't exactly harness heat; what can be harnessed is a temperature differential , to convert into some form of mechanical motion or electrical potential. You'd need some apparatus that connects the hot mass and some cold sink with thermocouples. Whether that's possible or feasible on the scale of the London Tube, I don't know. https://en.wikipedia.org/wiki/Thermoelectric_effect Instead of that, probably a more fe…
An additional dumb question. If all the expense was undertaken to build all the piping to functionally turn the tube into a heat source for buildings, how long would it take to sap the stored heat from the soil to the point where the temperature differential doesn't work anymore? At some point would they have to switch from having it be a heat source in winter to making it a heat dump in summer?
Seasonal storage and thermal batteries are pretty easy and cheap to construct. The materials tend to be cheap commodities. All you need is space to construct them and a way to produce the heat you use to charge them. For example, I know of an experimental setup in the Netherlands called CESAR ( https://materialdistrict.com/article/battery-natural-stone/ ) that uses basalt rock. The basalt is heated up using solar ene…
It seems really difficult to make the economics for seasonal electricity storage work. The article mention a materials cost of 23$ per kWh for their battery. Let's say this battery lasts 23 years. Transferring 1 kWh from summer to winter would than cost 1$ per kWh. That is before the cost of constructing the battery, R&D, sales, insurance, etc. Cost for 1 kWh is now below $0.10. That would mean generating electricity in summer and transferring it to the winter would come at a 10-fold increase in cost of winter electricity. For any currently available method, it seems that it would be far cheaper to simply have overcapacity in electricity generation from renewables and discard the excess electricity generated in the summer.
You're assuming that the battery needs to store the total energy requirements of a house for the entire year. Much of the time the energy needs can be met by conventional energy generation (wind turbines, solar, hydro, etc) and the battery is only called upon when there's a shortfall. So you'd only need a fraction of the annual consumption to make it useful. The whole idea is to make renewables more effective by stor…
If you use solar power in a climate like Germany you will get that kind of math. Let's say you use 8000 kwh per year, and you have the solar capacity to create 8000 kwh per year. Assume you already have a normal home battery of ~14kwh so day/night is not an issue, the solar production during daytime charges the battery and all night time power comes from the battery. Now your big problem is that 70% of the 8000 kwh s…
I use 6000/8000kWh between September and May though, because that is when I'm using a Heatpump to generate electricity.
You heat you house with oil? I thought Germany was environmentally conscious
Germany is still mining coal but they are environment conscious so they sell it to Poland to burn and buy electricity from them.
That seems like complete bullshit, since Germany doesn't mine anything apart from lignite, which can't feasibly be transported. Do you perhaps have a source on coal export to Poland? Also, Germany exports more electricity than it imports.
This doesn't seem cost efficient at all, my (medium sized) house in Germany consumes about 3000kWh of electricity during winter. This does not include heating, which consumes another 15.000kWh (of heat energy from oil, so around 5000kWh electrical energy with a heat pump). If I were to use this battery I would need to get 3000(8000)kWh of energy storage at 23$ per kWh which would amount to 69000(184000)$. There are b…
You heat you house with oil? I thought Germany was environmentally conscious
Unfortunately, Germany has been ruled by a conservative party for the last 16 years and they did everything in their power to sabotage renewable energy so that lignite mining could stay longer.
However, heating in Germany is a difficult problem to solve with renewable energy: You need lots of power in winter, when there is (close to) no power from solar. One solution would be excessive wind power and heat pumps that can be controlled remotely by the power grid operators.
For more on the general problem of storing thermal (rather than electrical) energy on a seasonal basis see https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag... I was especially surprised to learn that serious attempts at storing heat in soil and rock have been made https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag... https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community which in the winter…
Storing heat in rock is very natural. It's how geothermal works, after all. The basic idea is that the thermal time constant of a uniform sphere (or other shape of fixed aspect) is proportional to the square of its radius. So, for a sufficiently large sphere, the time constant can become very long, >> 1 year. Rock is a good choice because it's very cheap. The other thing one can do is store cold . This is useful not…
> The basic idea is that the thermal time constant of a uniform sphere (or other shape of fixed aspect) is proportional to the square of its radius.
Shouldn't the thermal mass go like volume (radius cubed) while the power conducted away go like surface area (radius squared) so the time to cool should go like mass/power ~ volume/area, so linearly in radius?