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The loss of electricity in transmission and distribution is only 6%, so why is it that electric heating is so inefficient?

I would imagine that the generators at power plants are far more efficient than any engine you can put it in my house for heating, and I also assume there is very little energy loss from going to electrical energy to thermal energy (if not, then where does the energy go?).

Where am I going wrong in my thought process?

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closed as off-topic by Leon Heller, PeterJ, Daniel Grillo, Scott Seidman, Adam Davis Jul 22 at 16:40

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This question would possibly fit better on diy.stackexchange.com because it is not about electronic design. –  David Jul 22 at 11:50
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This question sort of conflates expense and efficiency together which can vary widely between locations. Looking over the answers so far while none are technically incorrect and contain interesting info they don't apply universally, for example where I live most power is hydroelectric and an eletric heat pump / reverse cycle air condition is normally cheapest, but even that varies by location and cheap / free access to wood etc. –  PeterJ Jul 22 at 14:36
    
Short: The price is set by a team consisting of the invisible hand and involved regulatory and government agencies. || Electricity costs what the overall market will bear. This includes cost of capital for plant and transmission lines and fuel where needed, depreciation (= amortised cost of replacement), plus profit - subsidies. "Profit" as a % of costs in a competitive market is adjusted so that volume sold x profit % is maximised. You hope. All the other generators do this as well and some scrape by and some go broke and the long term average profit is usually about 0%. –  Russell McMahon Jul 22 at 15:17
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This is an engineering theory question, not an implementation one, so it doesn't belong on DIY. It might possibly be a better fit for physics, but it seems fine here on EE. –  Chris Stratton Jul 22 at 15:49

6 Answers 6

The efficiency of converting electricity to heat is 100% (although sometimes some of the heat ends up in places you don't want it).

However, the conversion of fuel to heat, the conversion of heat to mechanical energy and the conversion of mechanical energy to electricity are far from 100% efficient. Look up Carnot cycle for some insight into the fundamental physical limitations.

This is why it is always more efficient to convert fuel directly into heat in your home.

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You can do even better by using a heat pump, which is conceptually the same as a reverse AC system (in fact some AC systems support this). –  helloworld922 Jul 22 at 13:48
    
So essentially, the electrical energy being produced at a power plant is significantly lower than the heat being produced directly in my house? –  TruthOf42 Jul 22 at 16:26
    
And since I do love to pick nits, your first sentence is not necessarily true. If you're using an old-style space heater with a glowing element, some of that light can escape via a room's windows. I know, I know - I have too much time on my hands. –  WhatRoughBeast Jul 22 at 21:07
    
@WhatRoughBeast: Very good! However, that doesn't make my statement untrue. Even those light photons eventually get absorbed by something and get turned into randomized thermal energy -- just not where you want it, like I said :-) –  Dave Tweed Jul 23 at 1:16

For the same reason it would be uneconomical to burn fine furniture in your fireplace rather than raw logs. Electricity is a more useful and expensive form of energy than heat, and you lose the majority of the energy in the fuel turning it into electricity in a thermal plant (even with a large well-designed plant, about half to two thirds is lost!). When you burn natural gas directly, most of the heating energy goes into your house (in our case, with a high-efficiency furnace, the lost heat is so low that a small plastic tube is used as the "chimney", so you know most of the heat goes into the heat exchanger).

You are correct, however, that centralized large installations have efficiencies. Your own standby electric generator would not be as efficient as the thermal power station. Crowded downtown areas sometimes have central heating plants. For example, in Toronto there is a plant that supplies about 0.6GW of steam to 140 buildings downtown.

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If you use your electricity to run a heat pump you can get more heat out, than electrical power in. –  George Herold Jul 22 at 12:32
    
@GeorgeHerold That's a good point, of course the mechanical complexity and maintenance of a heat pump reduces the savings, and probably a ground source heat exchanger is required for really cold areas. Are there gas absorption heat pumps? –  Spehro Pefhany Jul 22 at 14:17
    
Modern heat pumps require very little maintenance, so the only practical concern is initial investment. Heat pumps can go up to 500% efficiency, so they are worthwhile even in colder climates. For air heat pumps, the efficiency tapers off to 100% at around -20°C. Ground heat pumps aren't affected by outside air temperature, but they take longer to break even due to the higher initial investment. –  ntoskrnl Jul 22 at 14:36
    
@ntoskrnl Lifetime of AC or heat pump systems is around 15 years with regular maintenance, so cost must be amortized over the lifetime, same as a furnace. Maintenance (filters, cleaning the coils, replacing worn fan motors etc.) is necessary or they'll not last as long. –  Spehro Pefhany Jul 22 at 14:53

Your thought processes are fine as far as they go. What you are overlooking is the inefficiency of converting fuel to electricity. Dave Tweed mentioned it, but look at https://www.nema.org/Products/Documents/TDEnergyEff.pdf for an overview. Yes, a central generating plant will do better than a home generator, but better is not nearly good enough.

Burning oil for heat will give efficiencies as high as 98%, although this takes some doing. 80 - 90% is more typical. A conventional coal-fired electrical generating station will run in the neighborhood of 40%. Add on another 6 - 8% transmission loss, and a good general number for relative efficiencies is 2:1 in favor of non-electric heating. There are economies of scale associated with central plants (transportation of fuel is cheaper, for instance, since there is no need for a local distribution network to get the fuel to individual homes), but these are not nearly enough to overcome the basic problem of generator inefficiency.

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If you're looking at cost efficiency as well as energy efficiency, an additional factor is that a significant fraction of your electric bill is for the maintenance and operation of the grid instead of power generation. Depending on where you live those costs may be broken out separately on your bill: on mine they collectively make up about 4 of the 12 cents I pay per kWH of (coal generated) power.

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I believe there are two questions conflated here. One is thermodynamical (Carnot) efficiency and the other is cost in real money. I believe that the heat pump (mentioned in a few answers already) can be more Carnot efficient (even with the coal-generated electricity) than the direct combustion.

There is a nice book that discusses these issues, "Without the Hot Air" by David MacKay. http://www.withouthotair.com/

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Short: The price is set by a team consisting of the invisible hand and involved regulatory and government agencies.

Longer: Electricity costs what the overall market will bear.
This includes
cost of capital for plant and transmission lines,
cost of maintenance,
fuel where needed,
depreciation (= amortised cost of replacement),
plus profit
less subsidies.

"Profit" as a % of costs in a competitive market is adjusted so that volume sold x profit % is maximised.
You hope.

All the other generators do this as well and the system oscillates and the regulators regulate and some scrape by and some go broke and the long term average profit is usually about 0%.

When this stable state is reached the cost is whatever it takes to achieve it.

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Fancy that. A +1 and a -1 and a net +8 score overall already. I wonder what the -1 person is thinking? or thinks they know? or what would seem to be "useful" to them. The above IS why electricity costs what it does. FWIW. –  Russell McMahon Jul 22 at 16:03
    
Russell, I think your answer is a bit vague ("... it depends..."). Yes, the relative cost of electric vs combustive heating depends a lot on the circumstances. For example, if I live on a remote island where it's very windy, I can probably do better with electrical heating (with a wind turbine generator and a heat pump, which can be more efficient in thermodynamical sense than direct combustion), than with fossil fuels delivered to me by boat. Of course, there's a whole host of other issues around start-up and maintenance costs. –  PA6OTA Jul 22 at 16:29
    
The question is about efficiency, not economics. –  JYelton Jul 22 at 16:37

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