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The red stack in figure 18.1 adds up to 195 kWh per day per person. The green stack adds up to about 180kWh/d/p. A close race! But please remember: in calculating our production stack we threw all economic, social, and environmental constraints to the wind. Also, some of our green contributors are probably incompatible with each other: our photovoltaic panels and hot-water panels would clash with each other on roofs; and our solar photovoltaic farms using 5% of the country might compete with the energy crops with which we covered 75% of the country. If we were to lose just one of our bigger green contributors - for example, if we decided that deep offshore wind is not an option, or that panelling 5% of the country with photovoltaics at a cost of £200000 per person is not on - then the production stack would no longer match the consumption stack.

Furthermore, even if our red consumption stack were lower than our green production stack, it would not necessarily mean our energy sums are adding up. You can't power a TV with cat food, nor can you feed a cat from a wind turbine. Energy exists in different forms - chemical, electrical, kinetic, and heat, for example. For a sustainable energy plan to add up, we need both the forms and amounts of energy consumption and production to match up. Converting energy from one form to another - from chemical to electrical, as at a fossil-fuel power station, or from electrical to chemical, as in a factory making hydrogen from water - usually involves substantial losses of useful energy. We will come back to this important detail in Chapter 27, which will describe some energy plans that do add up.

Here we'll reflect on our estimates of consumption and production, compare them with official averages and with other people's estimates, and discuss how much power renewables could plausibly deliver in a country like Britain.

The questions we'll address in this chapter are:

1. Is the size of the red stack roughly correct? What is the average consumption of Britain? We'll look at the official energy-consumption numbers for Britain and a few other countries.

2. Have I been unfair to renewables, underestimating their potential? We'll compare the estimates in the green stack with estimates published by organizations such as the Sustainable Development Commission, the Institution of Electrical Engineers, and the Centre for Alternative Technology.

3. What happens to the green stack when we take into account social and economic constraints?

"Defence": 4

Transporting stuff: 12 kWh/d

Stuff: 48+kWh/d

Food, farming, fertilizer: 15 kWh/d

Gadgets: 5

Light: 4 kWh/d

Heating, cooling:

37 kWh/d

Jet flights: 30 kWh/d

Geothermal: 1 kWh/d

Tide:

11 kWh/d

Deep offshore wind:

32 kWh/d

Shallow offshore wind: 16 kWh/d

Biomass: food, biofuel, wood, waste incin'n, landfill gas: 24 kWh/d

Solar heating: 13 kWh/d

Solar heating: 13 kWh/d

Figure 18.1. The state of play after we added up all the traditional renewables.

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