5 ms·

I was expecting some sort of cool focused-light cooker like a solar oven, but it's basically just an electric cooker powered by solar cells.

actionfromafar 11mo ago
This should scale up for heating a house at night, too.
- kirab 11mo ago
  It even scales up to a whole town: https://polarnightenergy.com/news/worlds-largest-sand-battery-now-in-operation/ https://polarnightenergy.com/news/worlds-largest-sand-batter...
  - trollbridge 11mo ago
    For reasons I don’t understand, American cities seem allergic to installing new municipal steam or hot water utilities, even though things like cogeneration were an obvious use case for it, and now things like solar heat storage.
    - blitzar 11mo ago
      It sounds like communism / socialism / marxism to people that are unable to define what those things are.
    - thyristan 11mo ago
      Steam and hot water pipes are extremely expensive to install, far worse than electricity, fibre, water or sewage. You need to be more leak-proof than cold water pipes, because loss of pressure with steam and hot water is much more of a problem than with cold water and cannot easily be solved by just adding more cheap water. Pipe materials have to be more resistant to corrosion because higher temperatures and pressures make them corrode so much faster than with cold water. Closed hot water/steam circuits also mean that there won't be a protective limescale coating on the inside. You need insulation that you can bury and which will last for at least 40 years, which is even more expensive than the pipes. And the insulation will double the pipe diameter. And the insulated pipes have a larger keepout area that needs to be kept free of rocks, other pipes and mechanical strain because the insulation is soft and sensitive to those things. Since usually the pipes aren't operated in summer, and since generally thermal variance is far higher than with cold water, thermal expansion needs to be taken into account, so you need expansion corners, sliding sections, different valve constructions that are tight in all temperatures, etc. And even with perfect insulation, you will loose approximately 30 to 40% of heat in your piping. So all of this is only viable if you don't care about the cost of the heat, your consumers can (be forced to or persuaded to) accept at least 30% higher prices per kWh compared to their local boiler, not to mention the capital cost. There are only some areas in Europe even, where those kinds of installations take place: Densely packed inner cities with largely rented-out flats in appartment buildings. There, the landlords/owners avoid the cost and risk of a local boiler and don't care about the running cost of heat, because they don't pay for it. In smaller towns, like in the example, mostly public buildings like schools use those kinds of district heating systems, because the municipality doesn't care as much about cost of the heat, and more about cost of maintenance of a hundred local boilers vs. one centralized system. And in the end, it's taxpayers' money, so they don't actually care that much, headlines and opening ceremonies are more important than that. Individual home owners usually do have their local systems, which can be run cheaper than what district heating will charge you. And since city density is lower and home ownership is more widespread in the US, district heating is even less competitive there.
      - adgjlsfhk1 11mo ago
        lots of industrial processes produce waste heat that can't easily be turned into energy, so the comparison isn't to a boiler, but to not having the heat.
        thyristan 11mo ago
        It is true that the heat can be used if it is there anyways. But usually not in a big city-wide network. Instead a more localized, larger consumer is far better, because running the hot water network is far too expensive. For example, large producers of heat like data centers, dairy processing or chemical plants around here deliver their heat to public swimming pools, schools or greenhouses that are intentionally built nearby. Even the grandparent's article says so if you read carefully: "A large portion of the town’s own buildings, including the municipal school, town hall, and library, are connected to the district heating network.". They didn't even attach all of the public buildings. Not to mention about the rest of the town.
        trollbridge 11mo ago
        That's exactly what I was thinking of. Cogeneration plant goes up right next to datacentre, and then various municipal services are built near that - including other factories, high density commercial and high density residential that can take advantage of cogeneration and use district heat. In particular commercial and industrial uses actually do need heat in the summer. In some areas, natural-gas fired cogeneration only is really necessary in the winter during dark months/cold weather - which is an ideal situation to be producing district heat.
      - jabl 11mo ago
        > And even with perfect insulation, you will loose approximately 30 to 40% of heat in your piping. At least here in Finland the norm is losses in the range of 5-20%, with the upper end of the scale for smaller scale networks with smaller diameter piping and low flow rate. In the larger cities losses are closer to the low end of that scale. In the summer when the consumption is very low (essentially only hot tap water production) losses can rise up to 50%.
    - quickthrowman 11mo ago
      There are district heating and cooling in cities where it makes sense, both Minneapolis and St Paul, plus the University of Minnesota all have district heating and district cooling systems. The Minneapolis and U of M systems are operated by Cordia Energy and the St Paul system is operated by Evergreen Energy. This is the coldest large metro area in the lower 48 states, so it’s economical to do district heating and cooling here.
      - zdragnar 11mo ago
        These heating districts don't cover a very large area. It's impressive in its own right, but if you're using them as an example, it just shows that it only works at very specific scales.
        quickthrowman 11mo ago
        Agreed, you need a fairly dense concentration of buildings with heating and cooling requirements in the tens of millions of BTUs per hour for it to make economic sense.
        trollbridge 11mo ago
        Right, but quite a few of such places do indeed exist (and new ones are being built).
    - PunchyHamster 11mo ago
      hot water also have pretty high losses, because you need to keep it cycling constantly to keep the heat up (you don't want a case where opening a tap in the morning means letting up the hot water from the 30m length of pipe from the street to your house). So paradoxically, if your heat is not "free" (cogenerated with electricity) it might be far more efficient to have a boiler in each house (and definitely a heat pump), than to push the heat that far away.
      - trollbridge 11mo ago
        In a modern system, you'd pull the heat from the hot water using a heat exchanger or a heat pump. (I'm also assuming a closed-cycle.)
- gsf_emergency_6 11mo ago
  Yep! focussed light anything is a hassle really-- mirrors have to be maintained and positioned. For anything larger than a family, mirrors have to be unrealistically large.. There was a concentrated light power station in north of Vegas, but it bankrupted the company that built it. They didn't think about storage at the time https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Project https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Pr... >As of 2023, it is operated by its new owner, Vinci SA, and in a new contract with NV Energy, it now supplies solar energy _at night only_, drawing on [molten salt] thermal energy stored each day.
  - gsf_emergency_6 11mo ago
    Sorry my wording was misleading. SolarReserves lived and died on the thermal storage hill. The point about mirrors being a hassle is still relevant, though: >When the plant finally opened in 2015, solar panels had left the Concentrated Solar Power technology in the dust [desert sand?] in terms of efficiency and cost. https://jpt.spe.org/becoming-obsolete-how-high-tech-solar-plant-found-its-way-bankruptcy https://jpt.spe.org/becoming-obsolete-how-high-tech-solar-pl...
- dagss 11mo ago
  In buildings with water heating this is already commonly done, accumulating heat in water tanks. Size of water tanks is dimensioned after how much heat you have to store. Electric heating with water heating is sometimes used in Northern Europe at least, often with a heat pump. Ultimate would be solar panels on the roof, heat pump to multiply the electricity 3x-5x and water tank storage to last 24 hours.... Never recoup the investment though..
  - actionfromafar 11mo ago
    Especially if panels continue to drop in price, a heat pump will just add needless complexity.
    - thyristan 11mo ago
      Depends on the location, but around here solar for heating is completely useless. In Germany (which is farther south than the nordics and gets far more sunlight), solar panels are already insufficient for heating half of the year. On a typical single-family home, you will get at most 10kW peak power solar on the roof, which you can reach in the summer months when there are no clouds. In winter, those 10kWp will generate at most 5kWh of energy per day. Which is a factor of 4 to 5 below the 20 to 30kWh per average day for heating (with generous insulation). The farther north you go, the worse this gets. Half of the nordics get essentially no sun at all in winter, and are quite a bit colder than Germany. So you need something other than the sun to heat your home in winter. A heat pump can double, maybe triple the solar energy you might get on sunny winter days, but that doesn't usually cut it. So you need grid electricity, wood or fossil fuels. And when electricity prices are as low as in the nordics (around or below 20ct/kWh), heat pumps are totally viable. Adding solar can be sensible for cooling in the summer months, and maybe a bit of hot water, and heating in late spring, early autumn. But for winter? Totally useless. And while you could do long-term storage, that will cost you several arms and legs, tons of space and a huge maintenance hassle. And if anything should go wrong with your storage, you have no heat all winter and better have an emergency plan...
      - PaulDavisThe1st 11mo ago
dv_dt 11mo ago
Because of their simplicity solar-cell based systems have become lower-cost and easier to install and maintain for water heating as panel + electric water heater, vs a piped direct solar thermal heating system. Higher "efficiency" for the direct thermal system, but overall system costs are lower for panel + heat. I still love seeing the interplay with different combinations of physical systems and clever things humans figure out. Including with solar panels + other system items.
- taneq 11mo ago
  Is this a good point to mention that simple solar heating circuits work better if you use diodes in series (for a fairly constant voltage drop across the solar cells) than if you just use a resistive element? :)
  - dv_dt 11mo ago
    You hint at something that is interesting to think about - that question might be: is there a different charge controller, heating element controller pairing that is possible with much less complexity and cost than using an inverter to ac and back to driving a resistive element. would it be worth a system cost of dedicating some panels to just that kind of control
  - kragen 11mo ago
    Diode heating does a better job of "MPPT tracking" than a resistive wire, but diodes are orders of magnitude more expensive, and they only work at low temperature (typically up to 175°, though SiC diodes can go a little higher). Resistive wires can easily work up to 500° or 1000°, which is potentially much better for sensible-heat thermal energy storage like this sand system. It might be better to run your resistive wire with a 3¢ microcontroller running an MPPT algorithm and controlling a 60¢ power MOSFET, something like a PSMN4R0 (https://www.digikey.com/en/products/detail/nexperia-usa-inc/PSMN4R0-30YLDX/4368826 https://www.digikey.com/en/products/detail/nexperia-usa-inc/...), which is rated to control almost 3000 watts (30 volts at 95 amps).
k7sune 11mo ago
I thought it would be heat pump related
MomsAVoxell 11mo ago
I have a solar oven on my wishlist for Christmas this year, I have a perfectly great spot for it, and generally think that if I can use it to bake bread, even if it takes a bit longer, its gonna get some serious usage ..

actionfromafar 11mo ago

This should scale up for heating a house at night, too.

kirab 11mo ago
It even scales up to a whole town: https://polarnightenergy.com/news/worlds-largest-sand-battery-now-in-operation/ https://polarnightenergy.com/news/worlds-largest-sand-batter...
- trollbridge 11mo ago
  For reasons I don’t understand, American cities seem allergic to installing new municipal steam or hot water utilities, even though things like cogeneration were an obvious use case for it, and now things like solar heat storage.
  - blitzar 11mo ago
    It sounds like communism / socialism / marxism to people that are unable to define what those things are.
  - thyristan 11mo ago
    Steam and hot water pipes are extremely expensive to install, far worse than electricity, fibre, water or sewage. You need to be more leak-proof than cold water pipes, because loss of pressure with steam and hot water is much more of a problem than with cold water and cannot easily be solved by just adding more cheap water. Pipe materials have to be more resistant to corrosion because higher temperatures and pressures make them corrode so much faster than with cold water. Closed hot water/steam circuits also mean that there won't be a protective limescale coating on the inside. You need insulation that you can bury and which will last for at least 40 years, which is even more expensive than the pipes. And the insulation will double the pipe diameter. And the insulated pipes have a larger keepout area that needs to be kept free of rocks, other pipes and mechanical strain because the insulation is soft and sensitive to those things. Since usually the pipes aren't operated in summer, and since generally thermal variance is far higher than with cold water, thermal expansion needs to be taken into account, so you need expansion corners, sliding sections, different valve constructions that are tight in all temperatures, etc. And even with perfect insulation, you will loose approximately 30 to 40% of heat in your piping. So all of this is only viable if you don't care about the cost of the heat, your consumers can (be forced to or persuaded to) accept at least 30% higher prices per kWh compared to their local boiler, not to mention the capital cost. There are only some areas in Europe even, where those kinds of installations take place: Densely packed inner cities with largely rented-out flats in appartment buildings. There, the landlords/owners avoid the cost and risk of a local boiler and don't care about the running cost of heat, because they don't pay for it. In smaller towns, like in the example, mostly public buildings like schools use those kinds of district heating systems, because the municipality doesn't care as much about cost of the heat, and more about cost of maintenance of a hundred local boilers vs. one centralized system. And in the end, it's taxpayers' money, so they don't actually care that much, headlines and opening ceremonies are more important than that. Individual home owners usually do have their local systems, which can be run cheaper than what district heating will charge you. And since city density is lower and home ownership is more widespread in the US, district heating is even less competitive there.
    - adgjlsfhk1 11mo ago
      lots of industrial processes produce waste heat that can't easily be turned into energy, so the comparison isn't to a boiler, but to not having the heat.
      - thyristan 11mo ago
        It is true that the heat can be used if it is there anyways. But usually not in a big city-wide network. Instead a more localized, larger consumer is far better, because running the hot water network is far too expensive. For example, large producers of heat like data centers, dairy processing or chemical plants around here deliver their heat to public swimming pools, schools or greenhouses that are intentionally built nearby. Even the grandparent's article says so if you read carefully: "A large portion of the town’s own buildings, including the municipal school, town hall, and library, are connected to the district heating network.". They didn't even attach all of the public buildings. Not to mention about the rest of the town.
        trollbridge 11mo ago
        That's exactly what I was thinking of. Cogeneration plant goes up right next to datacentre, and then various municipal services are built near that - including other factories, high density commercial and high density residential that can take advantage of cogeneration and use district heat. In particular commercial and industrial uses actually do need heat in the summer. In some areas, natural-gas fired cogeneration only is really necessary in the winter during dark months/cold weather - which is an ideal situation to be producing district heat.
    - jabl 11mo ago
      > And even with perfect insulation, you will loose approximately 30 to 40% of heat in your piping. At least here in Finland the norm is losses in the range of 5-20%, with the upper end of the scale for smaller scale networks with smaller diameter piping and low flow rate. In the larger cities losses are closer to the low end of that scale. In the summer when the consumption is very low (essentially only hot tap water production) losses can rise up to 50%.
  - quickthrowman 11mo ago
    There are district heating and cooling in cities where it makes sense, both Minneapolis and St Paul, plus the University of Minnesota all have district heating and district cooling systems. The Minneapolis and U of M systems are operated by Cordia Energy and the St Paul system is operated by Evergreen Energy. This is the coldest large metro area in the lower 48 states, so it’s economical to do district heating and cooling here.
    - zdragnar 11mo ago
      These heating districts don't cover a very large area. It's impressive in its own right, but if you're using them as an example, it just shows that it only works at very specific scales.
      - quickthrowman 11mo ago
        Agreed, you need a fairly dense concentration of buildings with heating and cooling requirements in the tens of millions of BTUs per hour for it to make economic sense.
        trollbridge 11mo ago
        Right, but quite a few of such places do indeed exist (and new ones are being built).
  - PunchyHamster 11mo ago
    hot water also have pretty high losses, because you need to keep it cycling constantly to keep the heat up (you don't want a case where opening a tap in the morning means letting up the hot water from the 30m length of pipe from the street to your house). So paradoxically, if your heat is not "free" (cogenerated with electricity) it might be far more efficient to have a boiler in each house (and definitely a heat pump), than to push the heat that far away.
    - trollbridge 11mo ago
      In a modern system, you'd pull the heat from the hot water using a heat exchanger or a heat pump. (I'm also assuming a closed-cycle.)
gsf_emergency_6 11mo ago
Yep! focussed light anything is a hassle really-- mirrors have to be maintained and positioned. For anything larger than a family, mirrors have to be unrealistically large.. There was a concentrated light power station in north of Vegas, but it bankrupted the company that built it. They didn't think about storage at the time https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Project https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Pr... >As of 2023, it is operated by its new owner, Vinci SA, and in a new contract with NV Energy, it now supplies solar energy _at night only_, drawing on [molten salt] thermal energy stored each day.
- gsf_emergency_6 11mo ago
  Sorry my wording was misleading. SolarReserves lived and died on the thermal storage hill. The point about mirrors being a hassle is still relevant, though: >When the plant finally opened in 2015, solar panels had left the Concentrated Solar Power technology in the dust [desert sand?] in terms of efficiency and cost. https://jpt.spe.org/becoming-obsolete-how-high-tech-solar-plant-found-its-way-bankruptcy https://jpt.spe.org/becoming-obsolete-how-high-tech-solar-pl...
dagss 11mo ago
In buildings with water heating this is already commonly done, accumulating heat in water tanks. Size of water tanks is dimensioned after how much heat you have to store. Electric heating with water heating is sometimes used in Northern Europe at least, often with a heat pump. Ultimate would be solar panels on the roof, heat pump to multiply the electricity 3x-5x and water tank storage to last 24 hours.... Never recoup the investment though..
- actionfromafar 11mo ago
  Especially if panels continue to drop in price, a heat pump will just add needless complexity.
  - thyristan 11mo ago
    Depends on the location, but around here solar for heating is completely useless. In Germany (which is farther south than the nordics and gets far more sunlight), solar panels are already insufficient for heating half of the year. On a typical single-family home, you will get at most 10kW peak power solar on the roof, which you can reach in the summer months when there are no clouds. In winter, those 10kWp will generate at most 5kWh of energy per day. Which is a factor of 4 to 5 below the 20 to 30kWh per average day for heating (with generous insulation). The farther north you go, the worse this gets. Half of the nordics get essentially no sun at all in winter, and are quite a bit colder than Germany. So you need something other than the sun to heat your home in winter. A heat pump can double, maybe triple the solar energy you might get on sunny winter days, but that doesn't usually cut it. So you need grid electricity, wood or fossil fuels. And when electricity prices are as low as in the nordics (around or below 20ct/kWh), heat pumps are totally viable. Adding solar can be sensible for cooling in the summer months, and maybe a bit of hot water, and heating in late spring, early autumn. But for winter? Totally useless. And while you could do long-term storage, that will cost you several arms and legs, tons of space and a huge maintenance hassle. And if anything should go wrong with your storage, you have no heat all winter and better have an emergency plan...
    - PaulDavisThe1st 11mo ago

dv_dt 11mo ago

Because of their simplicity solar-cell based systems have become lower-cost and easier to install and maintain for water heating as panel + electric water heater, vs a piped direct solar thermal heating system. Higher "efficiency" for the direct thermal system, but overall system costs are lower for panel + heat. I still love seeing the interplay with different combinations of physical systems and clever things humans figure out. Including with solar panels + other system items.

taneq 11mo ago
Is this a good point to mention that simple solar heating circuits work better if you use diodes in series (for a fairly constant voltage drop across the solar cells) than if you just use a resistive element? :)
- dv_dt 11mo ago
  You hint at something that is interesting to think about - that question might be: is there a different charge controller, heating element controller pairing that is possible with much less complexity and cost than using an inverter to ac and back to driving a resistive element. would it be worth a system cost of dedicating some panels to just that kind of control
- kragen 11mo ago
  Diode heating does a better job of "MPPT tracking" than a resistive wire, but diodes are orders of magnitude more expensive, and they only work at low temperature (typically up to 175°, though SiC diodes can go a little higher). Resistive wires can easily work up to 500° or 1000°, which is potentially much better for sensible-heat thermal energy storage like this sand system. It might be better to run your resistive wire with a 3¢ microcontroller running an MPPT algorithm and controlling a 60¢ power MOSFET, something like a PSMN4R0 (https://www.digikey.com/en/products/detail/nexperia-usa-inc/PSMN4R0-30YLDX/4368826 https://www.digikey.com/en/products/detail/nexperia-usa-inc/...), which is rated to control almost 3000 watts (30 volts at 95 amps).

k7sune 11mo ago

I thought it would be heat pump related

MomsAVoxell 11mo ago

I have a solar oven on my wishlist for Christmas this year, I have a perfectly great spot for it, and generally think that if I can use it to bake bread, even if it takes a bit longer, its gonna get some serious usage ..