The books is good(ish) for it's time, but some of its analysis and forecasts are fundamentally flawed since it falls for the primary energy fallacy by comparing the chemical potential energy (in J) directly to electrical energy (also in J). The two are fundamentally different things and called be compared 1:1. E.g. To heat up your home with natural gas you need ~1J of chemical energy to get 1J of heat into the home, but with a electric heat pump you only need 1/6 J to get 1J of heat.
It is also a product of its time in terms of wind/solar vs nuclear. His forecasts of the impact of solar and wind is based on prices and performance from 2008. Prices have come down an order of magnitude since then, and performance and lifespan have increased drastically.
Heat pumps, and their efficiency (getting more than X Joules of heating for X Joules of electricity) are discussed in chapter 21 Smarter Heating, see for example the diagram and discussion on page 150: <a href="https://www.withouthotair.com/c21/page_150.shtml" rel="nofollow">https://www.withouthotair.com/c21/page_150.shtml
I imagine the economics (and perhaps technical improvements) of some things may have changed more than the book could forecast. But heat pumps were definitely understood by the author.
I’m not saying he was unaware of heat pumps, I’m saying he’s comparing apples to oranges simply because they use the same units.
Look at “3 - Cars” on page 29. He says the typical car uses 40 kWh/day. 40 kWh of what? Chemical energy in the gasoline.
The go to page 33 where he looks at how much energy onshore wind could produce per days in the UK. His number is 20 kWh/d. 20 kWh of what? electricity
He then compares those two numbers directly and uses that comparison as the basis of his arguments: “Britain’s onshore wind energy resource may be “huge,” but it’s evi-
dently not as huge as our huge consumption.”
This is simply incorrect. A combustion engine converts less than half of the chemical energy in the gasoline into mechanical work that can move the car. The electric model converts >90% of it. So we don’t have to replace 40 kWh/day, we have to replace less than half of that since the electric process is more efficient.
This same issues, the primary energy fallacy, underpins large parts of the book.
The average Brit drives under 20 miles per day. A Tesla will do 4 miles per kWh, meaning it requires 5 kWh per day. That's 1/8 of 40 kWh. I'm not sure where the discrepancy is.
The book says 50km/30 miles per day in a petrol car is 40kWh. For a Tesla that would be 7.5kWh of electricity. It also assumes 12 km/litre - which in UK terms is 33 mpg. A Tesla has regenerative braking, so it would be better to compare the fuel efficiency to an aerodynamic hybrid. A Toyota Prius gets 61 mpg (UK) - which would mean 21.6 kWh per day.
So really the comparison is 7.5kWh of electricity compared to 21.6kWh of petrol. The Prius gets 34% of the miles compared to the Tesla for a given energy input. In the olden days when renewables didn't do much, the chemical energy input for 7.5kW of electricity was probably 15 kWh. So the electric car is a little bit more efficient (taking advantage of the efficiency of large power plants).
These days, thanks to renewables the fossil fuel input into the electricity is lower.
Yeah, I assumed 50% to account for various losses and other less efficient generators. I don't know what the actual number is - probably in the 40-50% range.
Interestingly thanks to renewables the "carbon intensity" of a kWh of electricity is already better than a kWh of fossil fuels in some countries. A kWh of petrol releases about 250g of CO2, and quite a few countries (predominantly developed ones) have lower carbon intensities per kWh of electricity. Considering round trip efficiencies the carbon released by an electric car in those countries is easily 1/3 to 1/4 of the carbon released by a petrol car.
In the USA it's not as good, but electric cars are still releasing about half the carbon.
The big question in my mind for efficiency figures is whether it's with respect to the Lower Heating Value (LHV) or Higher Heating Value (HHV) of the fuel. The latter includes the latent energy from condensing the water of combustion.
_aavaa_ · · focus · HN ↗
It is also a product of its time in terms of wind/solar vs nuclear. His forecasts of the impact of solar and wind is based on prices and performance from 2008. Prices have come down an order of magnitude since then, and performance and lifespan have increased drastically.
azornathogron · · focus · HN ↗
I imagine the economics (and perhaps technical improvements) of some things may have changed more than the book could forecast. But heat pumps were definitely understood by the author.
_aavaa_ · · focus · HN ↗
Look at “3 - Cars” on page 29. He says the typical car uses 40 kWh/day. 40 kWh of what? Chemical energy in the gasoline.
The go to page 33 where he looks at how much energy onshore wind could produce per days in the UK. His number is 20 kWh/d. 20 kWh of what? electricity
He then compares those two numbers directly and uses that comparison as the basis of his arguments: “Britain’s onshore wind energy resource may be “huge,” but it’s evi- dently not as huge as our huge consumption.”
This is simply incorrect. A combustion engine converts less than half of the chemical energy in the gasoline into mechanical work that can move the car. The electric model converts >90% of it. So we don’t have to replace 40 kWh/day, we have to replace less than half of that since the electric process is more efficient.
This same issues, the primary energy fallacy, underpins large parts of the book.
pfdietz · · focus · HN ↗
Much less. Your typical gasoline IC vehicle converts maybe 1/4 of the chemical energy into work.
bryanlarsen · · focus · HN ↗
leoedin · · focus · HN ↗
So really the comparison is 7.5kWh of electricity compared to 21.6kWh of petrol. The Prius gets 34% of the miles compared to the Tesla for a given energy input. In the olden days when renewables didn't do much, the chemical energy input for 7.5kW of electricity was probably 15 kWh. So the electric car is a little bit more efficient (taking advantage of the efficiency of large power plants).
These days, thanks to renewables the fossil fuel input into the electricity is lower.
pfdietz · · focus · HN ↗
Also, natural gas to electricity in CC plants is ~60% efficient.
leoedin · · focus · HN ↗
Interestingly thanks to renewables the "carbon intensity" of a kWh of electricity is already better than a kWh of fossil fuels in some countries. A kWh of petrol releases about 250g of CO2, and quite a few countries (predominantly developed ones) have lower carbon intensities per kWh of electricity. Considering round trip efficiencies the carbon released by an electric car in those countries is easily 1/3 to 1/4 of the carbon released by a petrol car.
In the USA it's not as good, but electric cars are still releasing about half the carbon.
pfdietz · · focus · HN ↗