UK: The power of raw sunshine at midday on a cloudless day is 1000W/m2 minus tilt (distance to equator) 40% minus reduction because it is not midday the entire useful time 68% minus cloud cover 66% = 100W/m2. This power can be used in foru ways:
1. Solar thermal direct heating of buildings or water.
10m2 of panels/p, 50%-efficient 50%× 10m2 ×110W/m2 = 13kWh/d/p
2. Solar photovoltaic: generating electricity. 20%× 110W/m2 = 22W/m2 (30% efficiency is likely the theoretical maximum!). At 10m2/p –> 5 kWh/d/p. If we covered 5% of the UK with 10%-efficient panels, we’d have 10%×100W/m2 ×200m2 /p = 50 kWh/day/person.
3. Solar biomass: using trees, bacteria, algae, corn, soy beans, or oilseed to make energy fuels, chemicals, or building materials.
There are four main routes to get energy from solar-powered biological systems:
– grow specially-chosen plants and burn them producing electricity or heat: “coal substitution.”
– grow specially-chosen plants, or algea/bacteria to turn into ethanol or biodiesel: “petroleum substitution.”
– burn by-products from other agricultural activities: “coal substitution”. Burning methane gas
from landfill from wasted food; people in Britain throw away about 300 g of food/d/p
– grow plants and feed them directly to humansn or other animals.
PV covering south-facing roofs of homes may cover quite a big chunk of personal average electricity consumption, but are not enough to make a huge dent in our total energy consumption. The true potential power from biomass and biofuels cannot be any bigger than 24 kWh/d/p. Biofuels made
from plants can deliver so little power, I think they are scarcely worth talking about.
Water heating and cooking
Taking a bath uses about 5 kWh, a shower 1.4 kWh. Hot water adds up to 12 kWh/d/p