5 ms·

It reads a bit overhyped, considering they claim to power a house with a generator the size of an envelope; that's a hard no since there is a limit on how much

by zaarn 7y ago

It reads a bit overhyped, considering they claim to power a house with a generator the size of an envelope; that's a hard no since there is a limit on how much energy hits every square meter and it's not THAT much.

asteli 7y ago
To elaborate, solar energy hitting the Earth’s surface is about a kilowatt/m^2 if conditions are perfect. If you were able to convert solar power at the maximum theoretical PV efficiency (the Shockley-Queisser limit, 33.7%), you’d need about 3 square meters to just to make toast.
- sbierwagen 7y ago
  For those confused by that oddly low theoretical limit: it applies to single junction cells. Panels that achieve higher efficiencies do it by stacking multiple cells.
- wyattpeak 7y ago
  Your broad point is right, but the SQ limit only applies to conventional PV cells, it's not a theoretical limit on PV efficiency and in fact has been exceeded by other cell architectures.
- numlock86 7y ago
  Is this supposed to sound bad or good? Well, 3m² to make toast intuitively sounds bad I guess. Well, consider this: It's enough to run 2 small office PCs with all peripherals. Considering that it sounds much more positive. Really just anything producing heat would sound bad because of power dissipation. A toaster is probably one of the most extreme ... (Imagine putting 1kW into a slice of bread without power dissipation!)
  - asteli 7y ago
    Someone else wrote the comment I meant to, essentially doing the math to show that one would need an awkwardly large solar panel to power something like a quadrotor drone.
- xsace 7y ago
  The idea behind individual solar energy is not consuming it real time but associating it with a storage solution to allow bigger throughput. You're not going to make toasts all day
  - macspoofing 7y ago
    >You're not going to make toasts all day I bet you're doing something throughout the day. Maybe not making toast, but cooking, ironing, heating, cooling, watching TV etc. I'm not sure you can rely on any excess energy being available for storage if you're not connected to the grid. >The idea behind individual solar energy is not consuming it real time but associating it with a storage solution to allow bigger throughput. If that's the idea then you are exposing a major issue with solar. Namely: in order to rely solely on solar (+battery), you need a solar deployment that covers your energy needs now + energy to charge battery for when the sun isn't shining (taking into account the associated loss of storing and retrieving power from battery). This means that you need to oversubscribe/over capitalize solar to charge up the battery (which then lowers your total efficiency) in order to bridge daily and seasonal variability in solar output. This means that you need generation capacity that probably exceeds the surface area available to what a typical house or apartment can provide and explodes your costs. This has major implications for large scale solar+battery deployments because at that scale, there is no grid to fall back on (which is why solar ALWAYS needs reliable backup generation - which is typically gas or biofuels). This is why solar+battery is never going to be cost-effective because you're always going to be forced to over-build infrastructure that will sit idly doing nothing most of the time. This doesn't even touch on the fact that there is no actual battery technology that keep enough load to power a modern city overnight, much less to bridge seasonal variability at that scale (where the battery would be expected to keep enough energy for weeks at a time).
    - travisporter 7y ago
      “Forcing over building of” solar is still cheaper than building a new coal or gas plant in some areas. I am positive there are plenty of people who live off grid and do not always need gas or biofuel backup.
wumms 7y ago
Yes, the max. energy from sunlight on earth hitting an envelope should be around 20-30 Watts (at 100% efficiency). Also, the reported 29.1% efficiency have been reached at a temperature of 1,207 °C.
- IanCal 7y ago
  This isn't about sunlight, but about putting this with a furnace or something else generating heat.
  - wumms 7y ago
    Yes, the original article is about thermophotovoltaics. Regarding the article posted here (and since a drone with a furnace is not feasible) I went with solar.
    - IanCal 7y ago
      The corresponding author to be fair did say unmanned aerial vehicles.
      - wumms 7y ago
        True, though it is combined (in the article) with a maximum power consumption: "those that require as little as 100 watts, [such as] a lightweight unmanned aerial vehicle" The original paper says "unmanned vehicles" (no aerial) and has a reference [0] to "unmanned undersea vehicles". [0] https://www.pnas.org/content/early/2019/07/15/1903001116#ref-33 https://www.pnas.org/content/early/2019/07/15/1903001116#ref...
        rebuilder 7y ago
        The article says "a wide range of applications, from those that require as little as 100 watts, [such as] a lightweight unmanned aerial vehicle, to 100 megawatts"
IanCal 7y ago
That is talking about heat and power cogeneration, not solar power if that's what you're thinking. The paper they site [0] says the density can 300-400kW/m^2 and so at 300kW, 50% efficiency and a small C5 envelope you're looking at over 5kW. [0] https://scholar.google.com/scholar_lookup?author=M.+Bianchi&author=C.+Ferrari&author=F.+Melino&author=A.+Peretto&title=Feasibility+study+of+a+thermos-photo-voltaic+system+for+CHP+application+in+residential+buildings&publication_year=2012&journal=Appl.+Energy&volume=97&pages=704-713 https://scholar.google.com/scholar_lookup?author=M.+Bianchi&...
- usrusr 7y ago
  Solid-state cogen that is simple to include in heating furnaces would be very interesting for old stock high density residential in cold regions. Mire modern heating options than gas furnaces (various variations of heat pumps, usually coupled with solar) don't scale down to individual flats and anything more central (ideally district heating) is effectively impossible to retrofit in a free market economy. But the very high efficiency electricity conversion component of cogen is just too good to skip, so a smallest-scale cogen option would be a welcome addition to the energy mix.
- baking 7y ago
  The device is mentioned in this talk (https://youtu.be/lDxJsa8miNQ?t=3105 https://youtu.be/lDxJsa8miNQ?t=3105) and provides 1kW of electricity and about 1kW worth of "waste" heat used for hot water. The key idea is that the amount of light would be the equivalent of 280 suns so you don't need a large panel.

by zaarn 7y ago

asteli 7y ago

To elaborate, solar energy hitting the Earth’s surface is about a kilowatt/m^2 if conditions are perfect. If you were able to convert solar power at the maximum theoretical PV efficiency (the Shockley-Queisser limit, 33.7%), you’d need about 3 square meters to just to make toast.

sbierwagen 7y ago
For those confused by that oddly low theoretical limit: it applies to single junction cells. Panels that achieve higher efficiencies do it by stacking multiple cells.
wyattpeak 7y ago
Your broad point is right, but the SQ limit only applies to conventional PV cells, it's not a theoretical limit on PV efficiency and in fact has been exceeded by other cell architectures.
numlock86 7y ago
Is this supposed to sound bad or good? Well, 3m² to make toast intuitively sounds bad I guess. Well, consider this: It's enough to run 2 small office PCs with all peripherals. Considering that it sounds much more positive. Really just anything producing heat would sound bad because of power dissipation. A toaster is probably one of the most extreme ... (Imagine putting 1kW into a slice of bread without power dissipation!)
- asteli 7y ago
  Someone else wrote the comment I meant to, essentially doing the math to show that one would need an awkwardly large solar panel to power something like a quadrotor drone.
xsace 7y ago
The idea behind individual solar energy is not consuming it real time but associating it with a storage solution to allow bigger throughput. You're not going to make toasts all day
- macspoofing 7y ago
  >You're not going to make toasts all day I bet you're doing something throughout the day. Maybe not making toast, but cooking, ironing, heating, cooling, watching TV etc. I'm not sure you can rely on any excess energy being available for storage if you're not connected to the grid. >The idea behind individual solar energy is not consuming it real time but associating it with a storage solution to allow bigger throughput. If that's the idea then you are exposing a major issue with solar. Namely: in order to rely solely on solar (+battery), you need a solar deployment that covers your energy needs now + energy to charge battery for when the sun isn't shining (taking into account the associated loss of storing and retrieving power from battery). This means that you need to oversubscribe/over capitalize solar to charge up the battery (which then lowers your total efficiency) in order to bridge daily and seasonal variability in solar output. This means that you need generation capacity that probably exceeds the surface area available to what a typical house or apartment can provide and explodes your costs. This has major implications for large scale solar+battery deployments because at that scale, there is no grid to fall back on (which is why solar ALWAYS needs reliable backup generation - which is typically gas or biofuels). This is why solar+battery is never going to be cost-effective because you're always going to be forced to over-build infrastructure that will sit idly doing nothing most of the time. This doesn't even touch on the fact that there is no actual battery technology that keep enough load to power a modern city overnight, much less to bridge seasonal variability at that scale (where the battery would be expected to keep enough energy for weeks at a time).
  - travisporter 7y ago
    “Forcing over building of” solar is still cheaper than building a new coal or gas plant in some areas. I am positive there are plenty of people who live off grid and do not always need gas or biofuel backup.

wumms 7y ago

Yes, the max. energy from sunlight on earth hitting an envelope should be around 20-30 Watts (at 100% efficiency). Also, the reported 29.1% efficiency have been reached at a temperature of 1,207 °C.

IanCal 7y ago
This isn't about sunlight, but about putting this with a furnace or something else generating heat.
- wumms 7y ago
  Yes, the original article is about thermophotovoltaics. Regarding the article posted here (and since a drone with a furnace is not feasible) I went with solar.
  - IanCal 7y ago
    The corresponding author to be fair did say unmanned aerial vehicles.
    - wumms 7y ago
      True, though it is combined (in the article) with a maximum power consumption: "those that require as little as 100 watts, [such as] a lightweight unmanned aerial vehicle" The original paper says "unmanned vehicles" (no aerial) and has a reference [0] to "unmanned undersea vehicles". [0] https://www.pnas.org/content/early/2019/07/15/1903001116#ref-33 https://www.pnas.org/content/early/2019/07/15/1903001116#ref...
      - rebuilder 7y ago
        The article says "a wide range of applications, from those that require as little as 100 watts, [such as] a lightweight unmanned aerial vehicle, to 100 megawatts"

IanCal 7y ago

That is talking about heat and power cogeneration, not solar power if that's what you're thinking. The paper they site [0] says the density can 300-400kW/m^2 and so at 300kW, 50% efficiency and a small C5 envelope you're looking at over 5kW. [0] https://scholar.google.com/scholar_lookup?author=M.+Bianchi&author=C.+Ferrari&author=F.+Melino&author=A.+Peretto&title=Feasibility+study+of+a+thermos-photo-voltaic+system+for+CHP+application+in+residential+buildings&publication_year=2012&journal=Appl.+Energy&volume=97&pages=704-713 https://scholar.google.com/scholar_lookup?author=M.+Bianchi&...

usrusr 7y ago
Solid-state cogen that is simple to include in heating furnaces would be very interesting for old stock high density residential in cold regions. Mire modern heating options than gas furnaces (various variations of heat pumps, usually coupled with solar) don't scale down to individual flats and anything more central (ideally district heating) is effectively impossible to retrofit in a free market economy. But the very high efficiency electricity conversion component of cogen is just too good to skip, so a smallest-scale cogen option would be a welcome addition to the energy mix.
baking 7y ago
The device is mentioned in this talk (https://youtu.be/lDxJsa8miNQ?t=3105 https://youtu.be/lDxJsa8miNQ?t=3105) and provides 1kW of electricity and about 1kW worth of "waste" heat used for hot water. The key idea is that the amount of light would be the equivalent of 280 suns so you don't need a large panel.