5 ms·

When I first saw this, the concept of "rejected energy" from the pink boxes seemed to need some explanation. From the outside view, nothing is "wasted"--there's

by evdev 9y ago

When I first saw this, the concept of "rejected energy" from the pink boxes seemed to need some explanation. From the outside view, nothing is "wasted"--there's just the cost and benefit. You compare alternate sources and alternate uses this way. Losses don't really mean anything unless they are comparative, and the only thing that matters is the ultimate value of the work, not what you would get if you ran a science experiment to figure out the joules. Even the losses in electrical transmission don't really mean anything unless compared to an alternative, which will have its own losses, and which can't really be compared kWh but instead relative cost. Someone can correct me if I'm off-base.

sandworm101 9y ago
Where energy generation is tied to some evil (ie c02 emmissions) then any energy not harvested, or lost in transit to users, is waste regardless of the financials. Even where no alternative exists, the waste lable is appropriate as a description of an area ripe for innovation and improvement.
olau 9y ago
Yes, all else being equal, cost is the only thing that matters. But often all else is not entirely equal, and then an analysis like this may be helpful. For instance, if you look at the transportation sector, you don't actually need to supplant all the energy there, only the actually useful part. And batteries + an electric motor is in fact much more efficient than gasoline + an internal combustion engine.
cjensen 9y ago
Losses mean something because they demonstrate the efficiency of a particular conversion, and demonstrate the overall size of the inefficiency compared to other problems in the system. Two quick examples: (1) LED light vs incandecent where incandescent's rejected energy is waste heat (2) Natural gas used to heat a house versus natural gas used to generate electricity to run an electric home heater. The direct use rejects far less heat. This is information that can lead to policy. If you see a lot of waste in a particular path that could be substituted with a different path, policy could be used to encourage the more efficient path. For example, due to abundant hydroelectric energy, the Northwest US used to use a lot of electric heating. Once hydro no longer met demand, the government had a commercial campaign to educate consumers about how they could save money by switching to gas.
- ZeroGravitas 9y ago
  The home heating thing is interesting, since burning gas for that is roughly 100% efficient. Burning gas for electricity maxes out in the best possible case at 60%, and then there's some tranmission loss (though I suppose gas leaks from pipes need to be counted as well then). But, electric heat pumps don't generate heat but, as the name suggests, "pump" it from one place to another, so they can be more than 100% efficient, generating something like 2-3x the input energy for air source, or up to 5 for ground source pumps. Which puts electrity ahead again (especially as some of that electricty can come from low carbon sources rather than gas).
  - Declanomous 9y ago
    Heat pumps only work in mild climates though. From what I understand, you can't heat your home with a heat pump in a place like Wisconsin, where the temperature is below 0F for a fairly substantial part of the winter. I hadn't even heard of a heat-pump until recently, which makes sense, since they seem to mostly be concentrated in warm, dry areas. Edit: According to Wikipedia, I'm specifically thinking of Air-source heat-pumps, which have a terrible coefficient of performance below 17 degrees Fahrenheit. Geothermal is better, though I believe you still have problems with saturation in cold climates.
    - s0rce 9y ago
      If you don't have natural gas or want to burn wood, basically your only choice is electric resistive heating (COP = 1) or an air source heat pump (COP > 1, above 10-15F) (other options like ground/water source heat pumps are possible but expensive/need specific conditions), the heat pump option will be more efficient, even in a cold place. When it gets cold enough that the heat pump isn't performing you simply turn on the auxiliary resistive heaters instead, there will at least be some days in the shoulder season where the heatpump is beneficial from an efficiency standpoint. If it makes economic sense is another matter. I think if you are going to get central AC or a minisplit its not that much more expensive to get a heatpump. If you have natural gas it makes sense, economically, to use that to heat most places in the USA.
    - 9y ago

by evdev 9y ago

sandworm101 9y ago

Where energy generation is tied to some evil (ie c02 emmissions) then any energy not harvested, or lost in transit to users, is waste regardless of the financials. Even where no alternative exists, the waste lable is appropriate as a description of an area ripe for innovation and improvement.

olau 9y ago

Yes, all else being equal, cost is the only thing that matters. But often all else is not entirely equal, and then an analysis like this may be helpful. For instance, if you look at the transportation sector, you don't actually need to supplant all the energy there, only the actually useful part. And batteries + an electric motor is in fact much more efficient than gasoline + an internal combustion engine.

cjensen 9y ago

Losses mean something because they demonstrate the efficiency of a particular conversion, and demonstrate the overall size of the inefficiency compared to other problems in the system. Two quick examples: (1) LED light vs incandecent where incandescent's rejected energy is waste heat (2) Natural gas used to heat a house versus natural gas used to generate electricity to run an electric home heater. The direct use rejects far less heat. This is information that can lead to policy. If you see a lot of waste in a particular path that could be substituted with a different path, policy could be used to encourage the more efficient path. For example, due to abundant hydroelectric energy, the Northwest US used to use a lot of electric heating. Once hydro no longer met demand, the government had a commercial campaign to educate consumers about how they could save money by switching to gas.

ZeroGravitas 9y ago
The home heating thing is interesting, since burning gas for that is roughly 100% efficient. Burning gas for electricity maxes out in the best possible case at 60%, and then there's some tranmission loss (though I suppose gas leaks from pipes need to be counted as well then). But, electric heat pumps don't generate heat but, as the name suggests, "pump" it from one place to another, so they can be more than 100% efficient, generating something like 2-3x the input energy for air source, or up to 5 for ground source pumps. Which puts electrity ahead again (especially as some of that electricty can come from low carbon sources rather than gas).
- Declanomous 9y ago
  Heat pumps only work in mild climates though. From what I understand, you can't heat your home with a heat pump in a place like Wisconsin, where the temperature is below 0F for a fairly substantial part of the winter. I hadn't even heard of a heat-pump until recently, which makes sense, since they seem to mostly be concentrated in warm, dry areas. Edit: According to Wikipedia, I'm specifically thinking of Air-source heat-pumps, which have a terrible coefficient of performance below 17 degrees Fahrenheit. Geothermal is better, though I believe you still have problems with saturation in cold climates.
  - s0rce 9y ago
    If you don't have natural gas or want to burn wood, basically your only choice is electric resistive heating (COP = 1) or an air source heat pump (COP > 1, above 10-15F) (other options like ground/water source heat pumps are possible but expensive/need specific conditions), the heat pump option will be more efficient, even in a cold place. When it gets cold enough that the heat pump isn't performing you simply turn on the auxiliary resistive heaters instead, there will at least be some days in the shoulder season where the heatpump is beneficial from an efficiency standpoint. If it makes economic sense is another matter. I think if you are going to get central AC or a minisplit its not that much more expensive to get a heatpump. If you have natural gas it makes sense, economically, to use that to heat most places in the USA.
  - 9y ago