Nowadays, there is a lot of public debate about energy storage. Just for clarity: there are two applications of storage: daily storage and seasonal storage.
Daily storage is not such a big problem. A solar water heater, for example, is perfectly capable of storing the sun's heat (in water) for up to almost a week, so that you can take a warm shower in the morning and for the following few days (efficiency around 95%) plus have supplementary heating in the spring/autumn. A standard current (AGM or lithium) battery can also store energy perfectly well so that you can watch TV off-grid in the evening and even the next day (efficiency around 80-90%). The only issue with batteries is that a battery only lasts a few years and is extremely polluting; partly for this reason, it is better to have a huge solar collector system off-grid than a lot of solar panels and a polluting battery. Hydrogen is already unsuitable for daytime storage with an efficiency of only 40%, and that is expensive in terms of storage and complex in terms of safety, so that is ruled out (see the blog "hydrogen" for more information). Actually, daytime storage is more like peak storage. Sustainable energy generation is simply not constant (sun and wind), so you see a lot of large-scale, multi-million dollar projects to store energy for the short term as a sort of buffer. So that when people come home in the evening, the energy from the sun can still be used during the day, for example. You can also see some examples of this in this blog.
The major issue, however, is seasonal storage. We need seasonal storage because we have enough sun in the summer and too little in the winter to heat our homes. Currently, there is actually no storage available that can handle seasonal storage for off-grid use; at least, I do cover it in my one-day course Self-Sufficient Off-grid, but it is minimal. Remarkably, the persistent misconception among just about everyone is that the seasonal storage of the future would be electric, and it is definitely NOT going to be electric. No, electric storage is not the storage of the future, not even if it were to have a so-called "unlimited number of charge cycles" later on, because you would then need to have a shed completely crammed full of such (unaffordable) batteries, since heating a house for an entire winter simply costs a bizarre amount of energy. Not everyone has a million and a large shed. There is a 100% chance that we will work with non-electric storage, and you will see many examples of that in this blog.
If you live in a standard on-grid home, forget about seasonal storage anyway, because there will likely be plenty of coal-fired power plants to shut down *and* solar panels and wind turbines to install over the next 20 to 30 years, before it becomes even remotely sensible to inefficiently store local summer energy yourself. For the time being, you are better off using green power, and perhaps, perhaps, opt for non-electric solutions in decades to come—if you happen to be very wealthy, moreover. With even Europe having less than 17% green energy, it really makes absolutely no sense for a private individual with their own on-grid home for a very long time to come. You help society more by using on-grid green power than by going off-grid with polluting batteries.
In my courses, I notice that there is more confusion. For example, solar panels plus a heat pump plus solar collectors is extremely convenient for the next few years, because you are currently still allowed to use the electricity grid as a large battery free of charge. Being energy-neutral seems ideal, but from an environmental point of view, it is not. The fact that the coal-fired power plants are still running for you in the winter and at night/morning if you are energy-neutral is usually forgotten. Once net metering is permanently abolished, a solar water heater is the very best thing to have at home (and therefore not: just as many solar panels as possible and a heat pump).
There are many more confusions in these chaotic times, because everyone is looking for solutions. A prime example of confusion is this DC-electric thermal battery, because this thing is actually just a disguised, inefficient water heater. Very stupid. You put 230V into it, and you get hot water out, but without the efficiency of a heat pump. An expensive joke to use this to provide your hot water. We are still a long way off, and at the same time, it is very nice that they are trying.
It is sometimes said that we have a surplus of sustainable energy, which then makes it seem as if we have a lot of sustainable energy. It is truly scandalous that there is so much journalistic attention for this, because that few days a year of surplus obscures the other 348 days a year when we are barely doing anything green. Only 7.3 percent of all energy was generated sustainably in 2018, and 60% of that is biomass—in other words, the Canadian forests that we cut down here to burn in power plants under the title "biomass". In reality, therefore, less than 3% comes from wind turbines and solar panels. It is increasing annually, but don't count that deforestation.
So why is there sometimes talk of an electricity surplus? Because in Germany, for a few days a year (6 in 2015), you actually get paid for electricity because more energy is generated than can be consumed – in practice, solar panel fields are never switched off. Oh dear, a few million less in profit; well, the world really won't end because of that. The world *will* end if we don't go green. On these few sunny holiday and weekend days a year, big industry just happens not to be running. These are negligible surpluses: so negligible that the solar panel fields aren't even switched off, because: that is, of course, also simply possible. Only if this were the order of the day would it be technically practical to spend money on. So we really don't have surpluses; there are still plenty of coal-fired power plants to switch off before we have a surplus.
The first solution is to look at the scale. There are various alternatives, such as: placing a surplus of wind turbines and solar panel parks such that we, as a society, still have surplus electricity even in the middle of winter. This self-sufficient alternative is the most ecological (assuming that we humans are allowed to use all the space) but the least economical, because you get paid poorly for green electricity in the summer since there is an abundance then. Because this idea is the least economical, we are unfortunately not yet moving in this direction societally. We could do it, though: just fill it up with solar panels and wind turbines so that we still have enough with the winter sun; we would then have so much energy left over in the summer that we can do enough other things with it.
My favorite solution on a societal level is sacrilege: you hardly have an energy storage problem if you live with the sun. Of course, you still need extra energy for winter heating, but if you use energy when it is available, then you can really start shutting down coal and gas power plants. So I propose: large industry on during the day and off at night, lots of activity in the summer and less in the winter. Instead of unfair net metering: make electricity 5 times more expensive during the day, and make electricity 5 times cheaper at night. I predict that this will solve more than half of all our energy problems in a few months. I do that myself too: I only have the refrigerator on during the day, charge my laptop, smartphone, etc., and in the evening and at night I don't burden the battery any more than with a few LED lights illuminating my house. In the summer, I do electric drilling and sawing (because I have an abundance of electricity then anyway), and in the winter, I read books. During the day, I run a load of laundry; in the evening, my electrical network is almost completely switched off. This is where politicians can take the lead. You will see that within a few months, we will be consuming less electricity. Only the climate veteran dares to bring up this "behavioral change" right now; however, behavioral change here and there—whether or not stimulated by financial pressure—can save the planet. The fear that we will have slightly less luxury currently outweighs the realism that our children will face a very terrible future when they are the same age as us. However, behavioral change does not mean less luxury: it only means luxury at a different time.
A somewhat low-tech solution is storing energy on a large scale using gravity. On such a large scale, these types of systems are perfect as a replacement for gas to match supply and demand on the electricity grid because they can be switched on and off quickly. I still have old brainstorming plans lying around to use a refrigerator in the shed as a battery using a hoist, but reality is catching up with me: Energievault and Gravitricity use gravity with enormous weights (up to 12,000 tons) to store energy. Currently, old mines worldwide (such as in Finland) are being converted into "gravity mines" where enormous amounts of green electricity can be stored. Flywheel systems from QuinteQ Energy, amberkinetics.com, and s4energy.nl are also examples of this: 5,000 kilos of flywheels that can add 5MW of energy within just a few milliseconds so that our power grid continues to provide enough power at exactly 50 Hertz, even if multiple people turn on heat pumps simultaneously or if the sun briefly disappears. Gravity is therefore very suitable for quickly switching on power, and thus for replacing expensive gas power plants (which currently ensure a stable electricity grid).
The most beautiful transport energy storage is absolutely not hydrogen or electric batteries, and certainly compressed air. You can run cars (MDI) on that, with a comparable range to an electric car, but with much shorter charging times and 0% battery pollution. Very simple charging with an ordinary compressor. If you ask me why we aren't investing heavily in this as a society, I have no answer for you, other than the fear of a smaller range (well, better no future for our children than refueling twice as often, right?).
Incidentally, compressed air is a great solution for energy storage in general. The strange thing is that we do almost nothing with it, even though we have known all the technology for a very long time. We have been successfully storing air at very high pressure for over 100 years. There is nothing special about that. If you combine this technique with thermal storage, you can use compressed air as storage quite successfully without adding extra external energy (for cooling and heating air). This is called CAES: Compressed Air Energy Storage, and examples include hydrostor.ca (in caves, etc.) and a ridiculously large Chinese project called Nengchu-1 (underground storage), and that is just the beginning of what the Chinese are going to build. In a decade, the Chinese will be truly completely self-sufficient in green energy thanks to these kinds of things; we in Europe cannot say that in 10 years (I think we will still be arguing about money then).
In my blog "hydrogen," I explain how hydrogen can indeed serve as bridging seasonal storage, but is not entirely ideal. Electricity isn't either, because the conversion of radiant heat into electricity (solar panels) and back (heat pump) results in too much energy loss on all sides, and regular batteries discharge too much daily for seasonal storage. So how can it be done? It can be done in many materials, as long as it isn't electric. The systems below are not always a 100% solution, by the way; sometimes an electric heat pump is used in the winter to boost the stored heat to 45 degrees.
I am deliberately not discussing nuclear energy here. Not that I necessarily have anything against it, but it costs sooooo much that, for that very reason, it is many times more effective to put that money directly into wind turbines and solar panel parks. Per MW of electricity, nuclear energy is so expensive (calculated from start to decommissioning) that ultimately green electricity is several times cheaper; this is evident from *all* existing nuclear reactors. It also takes far too long for those plants to be built; ecologically speaking, you need to start saving *now* and not wait 15 to 20 years, by which time it will be too late to change course. On duurzaamnieuws.nl, you can read a wonderful article here showing that this nuclear energy lobby is really missing the mark. There is a lot of money to be made in it, so probably for that reason alone we will get new nuclear power plants anyway. Once again: preferring to make money over a livable planet.
Why don't we store heat from the sun in water, just like with a solar collector but on a somewhat larger scale? It is also possible at the household level with Summerheat (which has stopped), and GEP water management with a well (plus unfortunately inefficient PVC panels instead of extremely efficient heat pipes). At the neighborhood level, Ecovat was working on it, and now Hocosto is doing the same with, among others, a large project in Vlieland, the solar thermal project in Ramplaankwartier Haarlem (unfortunately with PVT panels instead of heat pipes), and at the residential block level, as students from Eindhoven are proving with CASA 1.0. The coffee I am drinking now (October 2021) comes from my solar water heating system, which currently has 500 liters at 95 degrees, so I can imagine that storing this surplus energy in water works just fine. The larger the scale, the better. In the winter, you can then use the heat, or efficiently raise the last few degrees with a heat pump to 40 to 45 degrees for underfloor/wall heating and showering.
Water has an absurdly high energy storage capacity; however, water only goes up to 100 degrees. That is why other materials are much more interesting. At the neighborhood level, you can store heat in basalt, which can get much hotter than boiling water (450 degrees). In the ecovillage of Boekel, the CESAR system by Kees van Nimwegen is used – although here, heat is first generated electrically using solar panels. At the neighborhood level, Siemens Gamesa ETES is such a system in Basalt with warm air. And in Finland, another such system reaching up to 600 degrees with ordinary sand from Vatajankoski / Polar Night Energy. According to EnergyNest, concrete is also an alternative. If you want to go for a private and very affordable do-it-yourself system, you can heat the sand in your own garden with a large solar collector system and a buried pipe system; this is the most ideal system I know that you can actually build yourself right now!
Finally, you can also store heat in chemical compounds. The most promising one is: salt. Explained in simple terms: salt plus water yields heat, and salt can be dehumidified using heat. This is the basis for storing a great deal of heat in salt. This is most likely where the future of our heating lies, even though it is currently extremely expensive and in an experimental phase. I only know of the Eindhoven-based company Cellcius that they are working on an affordable system (for private individuals). Some other parties: no longer for sale: sodium ion saltwater battery for sale 12V/56Ah for 850 euros, AquaBattery (salt water), Eindhoven University (salt water), Dr.Ten (salt water), Merits (heat and salt, strangely enough without solar water heaters), Suwotec (biobased battery with salt, sand, and leaves), Aquion Energy (salt water).
A somewhat stranger and technologically more complex outlier (recovering heat from electricity) is heat storage in tin; This seems like an industrial niche, but it is a clever idea.
It is very realistic to say that we will always continue to need some electrical daytime storage at the private level. I am typing this using pure solar energy during the day on an off-grid system, but there is also a battery connected to it for the lighting this evening. A great deal is happening in the battery category, particularly a new generation titled solid state, and also batteries based on salt (see previous paragraph) and bromide and hydrogen+bromide (see bottom left). The storage capacity and the price will determine the extent to which these batteries will be used en masse for off-grid applications; currently, it is all still terribly expensive or simply not yet for sale.
About 90% of the articles and discussions I read (including journalists from newspapers and online websites) confuse daily storage with bridging seasonal storage. Specifically for bridging seasonal storage (to heat in the winter using the energy of the summer sun), a huge amount of storage capacity is needed, and, sorry, for that—once again:—all electrical storage is therefore truly very unsuitable. I know that 95% of the people reading this do not believe me. There is a persistent idea circulating in this society that we can do seasonal storage with better electric batteries, and that is simply not the case and it is never going to happen. Batteries discharge too quickly to still be able to use the energy half a year later, it takes up too much space, and the heat demand for an entire winter is far, far, far too much. And, batteries become unusable after a few years. Oh, you don't believe me? Judge for yourself: what good is a super expensive 0.7kW salt battery if you need 900kW for heating for the entire winter? ;) That would currently (2023) cost 740 thousand euros, plus an extra shed of at least 870 m³ filled entirely with batteries, covered with solar panels on the roof that capture nowhere near enough energy to even charge those salt batteries. Do you get it now? Do we have enough room to expand every house with a shed and make everyone pay an extra 740 thousand euros? Surely not. For the sake of completeness: with AGM batteries (which you cannot sustainably charge with electricity unless you have a field of solar panels, plus those would have long since run out of power in the winter) you would be 175 thousand euros worse off (and that again every 5 years!), and with Tesla Powerwalls you would be about 600 thousand euros worse off (and that again every 10 years). As I hope you agree with me, these amounts are impossible to cough up per house, nor is the surface area, so after a few months you end up with empty batteries anyway because they don't stay charged long enough. And as mentioned, you also need an extra small field to charge those electric batteries. Electric storage really is not storage that bridges the season.
I hope you enjoy reading this list of additional links that are not included in the text above:
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