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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

by 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.
    - macspoofing 7y ago
      >there are plenty of people who live off grid and do not always need gas or biofuel backup. I'm sure there are plenty of such people, but those people don't really factor when you take into account the society as a whole. The vast majority of people and businesses cannot live off grid.

by asteli 7y ago

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.
  - macspoofing 7y ago
    >there are plenty of people who live off grid and do not always need gas or biofuel backup. I'm sure there are plenty of such people, but those people don't really factor when you take into account the society as a whole. The vast majority of people and businesses cannot live off grid.