Sustainable Energy—Without the Hot Air

By David MacKay (2008)

If the free market is allowed to build houses, we end up with houses that are poorly insulated. Modern houses are only more energy-efficient thanks to legislation.

Climate modelling is difficult and is dogged by uncertainties. But uncertainty about exactly how the climate will respond to extra greenhouse gases is no justification for inaction. If you were riding a fast-moving motorcycle in fog near a cliff-edge, and you didn’t have a good map of the cliff, would the lack of a map justify not slowing the bike down?

This book is available for free here.

See also David MacKay’s carbon calculator.

My Notes

Emissions by Country

Current emission rates:

Cumulative emissions:


British per capita energy consumption on the left, potential renewable production on the right:

This requires:

☝️ Without taking into account the costs.

What about reducing consumption?

Action kWh/d saved
Stop flying 35
Efficient heating; thermostat at 15-17 ºC 20
Drive less, more slowly; car-pool, cycle, etc 20
Buy fewer things 20
No meat for six days/week 10
Review meter readings and adapt consumption 4
Don’t buy new 4
Use fluorescent or LED lights 4

Energy used (kWh) per person per 100km.

… electric vehicles can deliver transport at an energy cost of roughly 15 kWh per 100 km. That’s five times better than our baseline fossil-car, and significantly better than any hybrid cars.

Compare this with the typical consumption figure of 195kWh/d (the red stack in the figure above).

More savings here.

What other potential solutions are there?

Death rates of electricity generation technologies:

First, the energy requirements for carbon capture from thin air are so enormous, it seems almost absurd to talk about it… But second, I do think we should talk about it, contemplate how best to do it, and fund research into how to do it better, because capturing carbon from thin air may turn out to be our last line of defense…

… to fix a European’s output of 11 tons of CO2 per year we need 7,500 square metres of forest per person. This required area of 7,500 square metres per person is twice the area of Britain per person. And then you’d have to find somewhere to permanently store 7.5 tons of wood per person per year!

Every Little Bit Does NOT Help

All the energy saved in switching off your charger for one day is used up in one second of car-driving. The energy saved in switching off the charger for one year is equal to the energy in a single hot bath.

Don’t be distracted by the myth that “every little helps.” If everyone does a little, we’ll achieve only a little. We must do a lot. What’s required are big changes in demand and in supply.


What price would CO2 need to have in order to drive society to make significant changes in CO2 pollution?

At present it’s much cheaper to buy a new microwave, DVD player, or vacuum cleaner than to get a malfunctioning one fixed. That’s crazy. This craziness is partly caused by our tax system, which taxes the labour of the microwave-repair man, and surrounds his business with time-consuming paperwork.