7 ms·

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 elect

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

dasudasu 4y ago
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.
bufferoverflow 4y ago
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.
- beambot 4y ago
  Is hydrogen -> methane -> turbine more efficient for electricity generation than just hydrogen -> fuel cell?
  - bufferoverflow 4y ago
    Probably not, fuel cells are quite efficient. The problem is, do you want to deal with storing hydrogen? It's very annoying.
ZetaZero 4y ago
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. https://www.bbc.com/news/science-environment-61996520 https://www.bbc.com/news/science-environment-61996520
WaxProlix 4y ago
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 1 https://www.resilience.org/stories/2018-05-18/ditch-the-batteries-off-grid-compressed-air-energy-storage/ https://www.resilience.org/stories/2018-05-18/ditch-the-batt...
- hashtag-til 4y ago
  Regarding water pump solution, it is used in the UK as mitigation for the "TV Pickup phenomenon" See https://en.wikipedia.org/wiki/TV_pickup https://en.wikipedia.org/wiki/TV_pickup
jewel 4y ago
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.
ZeroGravitas 4y ago
Buying more solar panels and insulation is probably cheaper. Seasonal storage struggles to compare with overbuild and lithium batteries. Might be worth playing around with vertical installation if that's an option, this lets you shift the power curve towards winter.
- bryanlarsen 4y ago
  This is even more attractive if you have some way of not wasting your summer over production.
Tagbert 4y ago
The new developments in Aluminum-sulphur batteries look promising for this kind of grid buffering usage. https://arstechnica.com/science/2022/08/new-aluminum-sulfur-battery-tech-offers-full-charging-in-under-a-minute/ https://arstechnica.com/science/2022/08/new-aluminum-sulfur-...
kitkat_new 4y ago
You are missing that you get more electricity from wind in the winter: https://www.wind-energy-the-facts.org/understanding-variable-output-characteristics-of-wind-power-variability-and-predictability.html https://www.wind-energy-the-facts.org/understanding-variable...
brightball 4y ago
There was an article in Wired around 2006/2007 where a guy built exactly that. Basically built a solar powered hydrogen collector in his back yard. Found it: https://www.wired.com/2007/03/backyard-fuel-cell/ https://www.wired.com/2007/03/backyard-fuel-cell/
ok_computer 4y ago
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.
mduerksen 4y ago
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. [1] https://www.homepowersolutions.de/en/product/ https://www.homepowersolutions.de/en/product/
- pstuart 4y ago
  That looks like exactly what OP was looking for. One would assume that over time and at scale the price would come down significantly. Hydrogen embrittlement seems to be an unavoidable problem so not sure how that plays out.
  - elsonrodriguez 4y ago
    Looks like the system uses standard tanks. There's probably a scheduled tank replacement schedule.
- tpmx 4y ago
  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.
  - Ekaros 4y ago
    At that price, wouldn't a diesel generator burning cooking oil be cheaper?
    - tpmx 4y ago
      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.
  - 4y ago
tekno45 4y ago
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.
Thlom 4y ago
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?
- hebrox 4y ago
  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. Power to the people ;)
- rapsey 4y ago
  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.
- ephbit 4y ago
  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.
rch 4y ago
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). - https://www.allpowerlabs.com/products/gasifier-kits https://www.allpowerlabs.com/products/gasifier-kits
- DubiousPusher 4y ago
  > 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. I mean sure but like in the worst case, window shades are a thing. Edit: Or maybe this isn't about passive heating and you're saying long term storage might not be necessary in winter?
  - rch 4y ago
    The largest windows didn't have shades, but some did. We'd also use free standing shades to help keep specific areas cool. Some of the features of RMI's Carbondale office would probably be worth considering as part of a more thoughtful design. Also, you're correct that there was never a need to store energy for months on end, at least at our latitude.
    - DubiousPusher 4y ago
      I expect altitude plays a role as well. I grew up in Montana. 5,000ft plus sunrays are gnarly.
- ZeroGravitas 4y ago
  This prompted me to think about oversizing pv and solar gains, then using a heat pump to extract the excess heat in the summer. Seems like it would work: https://www.researchgate.net/figure/Concept-for-enabling-increased-passive-solar-gains_fig1_321336459 https://www.researchgate.net/figure/Concept-for-enabling-inc...
marcosdumay 4y ago
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.
Fiahil 4y ago
> and then during the summer, would convert excess energy to a long-term storage Like this ? https://en.m.wikipedia.org/wiki/Gravity_battery https://en.m.wikipedia.org/wiki/Gravity_battery
laurencerowe 4y ago
That sounds like an awful lot more infrastructure than simply over-provisioning cheap solar panels.
KaiserPro 4y ago
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.
- dahfizz 4y ago
  The UK has a much more moderate climate than most of the US. Compare London avg temps[1] with Boston[2] or Dallas[3]. The UK temperature averages are pretty close to LA, which is well known for being so moderate. [1] https://www.timeanddate.com/weather/uk/london/climate https://www.timeanddate.com/weather/uk/london/climate [2] https://www.timeanddate.com/weather/usa/boston/climate https://www.timeanddate.com/weather/usa/boston/climate. [3] https://www.timeanddate.com/weather/usa/dallas/climate https://www.timeanddate.com/weather/usa/dallas/climate
  - KaiserPro 4y ago
    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.

dasudasu 4y ago

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.

bufferoverflow 4y ago

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.

beambot 4y ago
Is hydrogen -> methane -> turbine more efficient for electricity generation than just hydrogen -> fuel cell?
- bufferoverflow 4y ago
  Probably not, fuel cells are quite efficient. The problem is, do you want to deal with storing hydrogen? It's very annoying.

ZetaZero 4y ago

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. https://www.bbc.com/news/science-environment-61996520 https://www.bbc.com/news/science-environment-61996520

WaxProlix 4y ago

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 1 https://www.resilience.org/stories/2018-05-18/ditch-the-batteries-off-grid-compressed-air-energy-storage/ https://www.resilience.org/stories/2018-05-18/ditch-the-batt...

hashtag-til 4y ago
Regarding water pump solution, it is used in the UK as mitigation for the "TV Pickup phenomenon" See https://en.wikipedia.org/wiki/TV_pickup https://en.wikipedia.org/wiki/TV_pickup

jewel 4y ago

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.

ZeroGravitas 4y ago

Buying more solar panels and insulation is probably cheaper. Seasonal storage struggles to compare with overbuild and lithium batteries. Might be worth playing around with vertical installation if that's an option, this lets you shift the power curve towards winter.

bryanlarsen 4y ago
This is even more attractive if you have some way of not wasting your summer over production.

Tagbert 4y ago

The new developments in Aluminum-sulphur batteries look promising for this kind of grid buffering usage. https://arstechnica.com/science/2022/08/new-aluminum-sulfur-battery-tech-offers-full-charging-in-under-a-minute/ https://arstechnica.com/science/2022/08/new-aluminum-sulfur-...

kitkat_new 4y ago

You are missing that you get more electricity from wind in the winter: https://www.wind-energy-the-facts.org/understanding-variable-output-characteristics-of-wind-power-variability-and-predictability.html https://www.wind-energy-the-facts.org/understanding-variable...

brightball 4y ago

There was an article in Wired around 2006/2007 where a guy built exactly that. Basically built a solar powered hydrogen collector in his back yard. Found it: https://www.wired.com/2007/03/backyard-fuel-cell/ https://www.wired.com/2007/03/backyard-fuel-cell/

ok_computer 4y ago

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.

mduerksen 4y ago

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. [1] https://www.homepowersolutions.de/en/product/ https://www.homepowersolutions.de/en/product/

pstuart 4y ago
That looks like exactly what OP was looking for. One would assume that over time and at scale the price would come down significantly. Hydrogen embrittlement seems to be an unavoidable problem so not sure how that plays out.
- elsonrodriguez 4y ago
  Looks like the system uses standard tanks. There's probably a scheduled tank replacement schedule.
tpmx 4y ago
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.
- Ekaros 4y ago
  At that price, wouldn't a diesel generator burning cooking oil be cheaper?
  - tpmx 4y ago
    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.
- 4y ago

tekno45 4y ago

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.

Thlom 4y ago

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?

hebrox 4y ago
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. Power to the people ;)
rapsey 4y ago
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.
ephbit 4y ago
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.

rch 4y ago

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). - https://www.allpowerlabs.com/products/gasifier-kits https://www.allpowerlabs.com/products/gasifier-kits

DubiousPusher 4y ago
> 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. I mean sure but like in the worst case, window shades are a thing. Edit: Or maybe this isn't about passive heating and you're saying long term storage might not be necessary in winter?
- rch 4y ago
  The largest windows didn't have shades, but some did. We'd also use free standing shades to help keep specific areas cool. Some of the features of RMI's Carbondale office would probably be worth considering as part of a more thoughtful design. Also, you're correct that there was never a need to store energy for months on end, at least at our latitude.
  - DubiousPusher 4y ago
    I expect altitude plays a role as well. I grew up in Montana. 5,000ft plus sunrays are gnarly.
ZeroGravitas 4y ago
This prompted me to think about oversizing pv and solar gains, then using a heat pump to extract the excess heat in the summer. Seems like it would work: https://www.researchgate.net/figure/Concept-for-enabling-increased-passive-solar-gains_fig1_321336459 https://www.researchgate.net/figure/Concept-for-enabling-inc...

marcosdumay 4y ago

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.

Fiahil 4y ago

> and then during the summer, would convert excess energy to a long-term storage Like this ? https://en.m.wikipedia.org/wiki/Gravity_battery https://en.m.wikipedia.org/wiki/Gravity_battery

laurencerowe 4y ago

That sounds like an awful lot more infrastructure than simply over-provisioning cheap solar panels.

KaiserPro 4y ago

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.

dahfizz 4y ago
The UK has a much more moderate climate than most of the US. Compare London avg temps[1] with Boston[2] or Dallas[3]. The UK temperature averages are pretty close to LA, which is well known for being so moderate. [1] https://www.timeanddate.com/weather/uk/london/climate https://www.timeanddate.com/weather/uk/london/climate [2] https://www.timeanddate.com/weather/usa/boston/climate https://www.timeanddate.com/weather/usa/boston/climate. [3] https://www.timeanddate.com/weather/usa/dallas/climate https://www.timeanddate.com/weather/usa/dallas/climate
- KaiserPro 4y ago
  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.