Been thinking (daydreaming) a lot about a fully off-grid house and how in the summer, you get more solar than you need and in the winter you use much more electricity than you produce. What I'd love to see is some sort of system that used batteries for short term storage, and then during the summer, would convert excess energy to a long-term storage format like methane or LNG.
I have not run any numbers on this, but the idea behind it is to stockpile your energy in the summer to be able to make it through the winter without having to resort to some outside source of energy like wood or gas delivery.
I initially thought about hydrogen, but given it's storage density, and the problems that SLS has had with leaks, taking the additional step to convert into methane would greatly simplify storage and use, and likely improve reliability since you'd be able to use COTS products for natural gas instead of custom hydrogen storage
There is a working system commercially available in Germany, but it is pretty expensive [1]:
Long-term energy storage with hydrogen, with 1-5x 300 kWh. Which allows for full electric independence (not including heating though).
Price: 85,000-125,000 €, minus government subsidies.
Let's say you want to use the system for heating with a heat pump.
Your energy consumption for heating might be ~ 3000 kWh/month during the winter months (Nov-Mar) for a moderately insulated house.
Assuming your PV produces only 10 % of the demand during these 5 months (so you have to rely on stored energy for the remaining 90 %) and your heat pump delivers a Coefficient of Performance of 3.5 then you'd need to store ~ 3900 kWh.
As to my back of envelope calculation, one standard 50 l bottle of hydrogen contains ~ 30 kWh worth of energy when filled at 200 bar.
So you'd need ~ 130 such standard bottles to store enough hydrogen.
That's quite a lot. But of course with a well insulated home, you'd maybe only need a third, so that'd be 3-4 bundles (with 12 bottles each).
Its definitely worth it to use all available space.
Still, it definitely cannot generate enough to bring you through the german winter.
Some example numbers I have read: A 10kWp solar system that generates up to 1,400 kWh in a summer month will only provide about 200 kWh in December.
You can get more power in summer by using a vertical bifacial panel positioned E-W.
And if you position it N-S you'll get slightly less power than a standard setup, but it'll be less concentrated in the summer, and also spread through the day more.
So 57-83 €/kWh, or on average about 175x more expensive than the current already insane electricity prices in central Europe. This is the concept that will save us according to the (qoften German, for some reason) anti-nuclear fundamentalists who have gotten into this pickle in the first place.
Diesel in a diesel generator is already roughly on par with the current insane electricity price, dunno about cooking oil, but it's probably roughly similar.
You could have made the same argument against solar panels 15 years ago.
This is a pioneering product for early adopters - expect prices to go down significantly with economics of scale. And further research in this area is far from exausted.
I mean, I don't disagree. The problem is that lots of anti-nucluear-fundies are comparing existing nuclear power to hypothetical hydrogen storage - "it's just a matter of research".
My point is: Deploy nuclear power now, continue RND on large scale hydrogen storage that maybe will pan out in 20 years.
Yes, I was not proposing such system as a large scale solution for the coming winter. It would be prudent to keep our nuclear reactors running for now.
As always, There is No Silver Bullet™.
Nuclear is not the perfect solution. It cannot be powered on and off on short notice, which would be useful for complementation of solar and wind that have high power output, but also sudden slumps. Ironically, the ideal companion for renewables would be gas...
Lithium batteries could compensate short outages, but don't have enough (feasable) capacity for long seasonal shortages.
Enter Power to Gas. Hydrogen can be a good tool in that area.
A commerically available hydrogen storage system (that is in high demand even despite its price point) will definitely accelerate innovation very effectively. I think this tool will be available quite soon for mere mortals.
I'd add that it's also prudent to build new nuclear reactors now. The tech exists and there is a very clear lack of mostly plannable power supply in many countries/regions.
The tech for building reliable, safe, affordable, large-scale hydrogen "batteries" isn't here yet.
New nuclear reactors are also not here yet. They might become ready in 8+ years if started now.
So the solution is simple. Nuclear has its place. Power2Gas too. Build and invest in both. And in the meantime, use what we have without ideolgical eye patches.
Please respond to my argument instead of implying bad faith.
I can sharpen my argument even further:
Existing nuclear reactors - keep them going. They are here today.
Solar - leverage its decentralized, bottom up expansion by the people that can use their own roofs, reduce beaurocratic hurdles. Its expansion does not have to wait 8 years. The products are here today.
Power 2 Gas - celebrate existing products on the market. They are here today.
All these things are here today and part of a solution which contains many parts. I welcome each and every betterment, because we will need it.
You on the other hand are dismissing key tools and instead focus on one thing that is not here today and will maybe be ready in 8+ years.
Nuclear power plants take years to build. Even if a plant were approved today, it wouldn't be finished before large scale hydrogen storage either fails or takes hold, at which point it would be an expensive and unnecessary boondoggle.
Reminder: You're comparing the construction of existing tech (nuclear power plants) vs tech that doesn't even exist: large scale, safe and affordable hydrogen storage.
Based on my experience living in a large home in Colorado designed for passive solar heating, the trees would block the windows in summer so we'd stay comfortable without AC, but the sun was really intense in what should have been the cooler months. I'd definitely do some thorough modeling before building one of my own.
Along with solar thermal and photovoltaics, I'd use a redox flow battery for long term storage, and a GEK for emergency generation (too loud for casual use).
It might not be a solution on its own, but you can get a little ways with compressed air energy storage (CAES). There's a bit of discussion on how it can scale up and down to various sizes of installation around the internet[1] but I don't know how much actual storage you get in terms of kilowatt hours.
But used as a part of a more robust system, I think there's promise here. The other type of low-chemical physical potential energy storage that gets some attention nowadays is pumping water to a higher location, only to let it out via a hydro generator later. Not sure how that scales into winter though. (actually air tanks might lose a certain amount of pressure to cold as well; perhaps buried tanks would work better, so that the ambient temp is cooler?)
It's fun to apply this pattern to other types of gravity-based energy. Maybe take excess in the summer and use it to ratchet your water tower up higher, or roll a large boulder up a hill? Or force two magnets really close together :p
Ammonia as a hydrogen store air+methane+temp and high high pressure. Pump liquid uphill as another option for potential energy minus evaporation losses and friction. Geothermal as year round steady state thermal process, I don’t know how those scale capacity.
My question about completely off grid housing and renewable sources and energy stores is that an isolated small scale unit will assuredly operate industrial processes at a lower efficiency than a centralized industrial facility, barring transmission loss. Economy of scale is real for thermodynamic costs and monetary cost. So any gas compression or thermal cycle or liquid pumps is self serving with higher personal capital cost and cost of run and maintenance reliability. And if enough of your neighbors do it it’s “renewable” but nowhere near sustainable.
How to turn sunlight into methane? Electrochemistry and membranes or catalysts? That seems like not a worthwhile question facing us if there is earnest need for energy transition for sustainability.
If you’re wealthy enough to have an off grid ranch or cabin and don’t want the baggage of society to replenish your winter energy needs then purchase in W texas and build a boutique diesel rig and refinery. Or purchase a bunch of land with fast growing pines and run a logging operation.
If you want to live off grid but can manage paying money for society goods and services run diesel generators with long term fuel oil contracts and rig up a decarbonization unit on the exhaust stack.
Localized next gen storage isn’t a pressing matter in my opinion. Especially that benefiting anti-social people with means to live off grid but comfortably. If you have millions of emissions points it’s harder to control than a centralized regulated plant.
Ideas are easy. Implementations are either hard or expensive.
Converting solar to hydrogen, then to methane, then to electricity requires a pretty big setup. If you want to be efficient, you have to do all that at a large scale with a proper power plant turbine. It will not work well at a scale of one house.
For a house-sized storage, you may want flow batteries. Handling gases is expensive and full of unexpected problems, while molten solids is relatively easy.
Hydrogen storage makes sense for a country, not for anything smaller. LNG storage may make sense for a city grid, if our tech advances. Anyway, you really don't want those on your backyard.
Anyway, even though they are simpler, flow batteries may create enough problems so that you don't want them on your backyard either. I will repeat the sibling that recommended just getting more panels.
There have been recent advances in sand batteries to store heat. Use the excess energy to heat the sand. Then pull heat from it in the winter to heat the house. Unsure if this would scale down to personal usage.
It would probably make more sense to store the heat of summer into the ground directly, using something like a ground source heat pump. An additional benefit is that the same system cools the house in the summer cheaply.
My friend has an off-grid cabin and his solar panels were easy to size for all other energy needs during winter by having them installed angled towards the winter sun position.
He does have a small generator just in case there is a particularly bad winter storm, but even in that circumstance it just has to run long enough to charge his batteries, so fuel consumption is minimal.
Vanadium redox flow batteries have a decent energy storage density and can scale very well but ultimately it does add to the cost of the energy being produced as opposed to some tech that doesn’t need it.
What is the value of having the house off-grid? Wouldn't it be better for you and the rest of society if your house was on-grid and you could pump excess energy to the grid and buy it back during winter if necessary instead of trying to store energy long-term in your house?
I understand it is an interesting problem and all that, just thinking the energy used to solve this esoteric problem might be better used for more large scale solutions?
I'd guess we'll see mid to large scale electrolyzer plants pop up in many locations throughout a country as soon as the build out of PV on roofs of private houses (also everywhere else) leads to daily overload on the electric grid.
These electrolyzers will then take up the excess electricity and convert it to hydrogen as seasonal storage and thus stabilize the grid.
Additionally, you'd combine these sites with either fuel-cell or hydrogen powered gas turbine plants, to then generate enough electricity when PV generation cannot meet demand.
I’ve been dreaming about this for 15+ years and for me an important ideological aspect is decentralization.
The amount of Bad Things tm that happened related to energy is immense.
Exporting power to the grid requires a grid capable of that. In many places this is highly limited. Where I am the vast majority of applicants wishing to do this are rejected.
assuming that you insulate well, then your electricity needs should be pretty small.
In the UK we have a 5kw array, and a 13kwhr battery. this year we have been 93% self sufficient.
we have triple glazing and 90mm of external wall insolation (but its not passivehaus) to cover our heating as well, we'd need to do a proper insulation survey. I am reasonably confident that if we insulate the floor and loft properly(and figure out air exchanger) we could cover our heating and hotwater as well, (assuming solar water heater)
In the US, depending on where you are, you have aircon/heating as the main energy draw, but with the option to have a boatload more solar. However insulation/glazing standards are patchy, so with good insulation a 20kw array, plus 30kwhr battery would cover you for most things and a car as well.
but thats the point right? aircon in dallas is the biggest energy sink in summer.
combined with the shorter days (compared to the UK) that means that insulation, solar gain control & thermal mass management is critical to reducing power usage.
Boston has double trouble, as in hot(ish) summers, high humidity, and cold-arsed winters.
If you're willing to have wood, you can also turn this into biochar. With excess energy you would get essentially good soil base and syngas, which can be used for heating.
This would be my off grid project if i could get the land.
I have not run any numbers on this, but the idea behind it is to stockpile your energy in the summer to be able to make it through the winter without having to resort to some outside source of energy like wood or gas delivery.
I initially thought about hydrogen, but given it's storage density, and the problems that SLS has had with leaks, taking the additional step to convert into methane would greatly simplify storage and use, and likely improve reliability since you'd be able to use COTS products for natural gas instead of custom hydrogen storage