1890. For all the fanfare, the difference between the new and the old is
really quite disappointing!
Notice that the building power consumptions, per unit floor area, are
in just the same units (W/m2) as the renewable powers per unit area that
we discussed on pages 43, 47, and 177. Comparing these consumption and
production numbers helps us realize how difficult it is to power modern
buildings entirely from on-site renewables. The power per unit area of
biofuels (figure 6.11, p43) is 0.5 W/m2; of wind farms, 2 W/m2; of solar
photovoltaics, 20 W/m2 (figure 6.18, p47); only solar hot-water panels
come in at the right sort of power per unit area, 53 W/m2 (figure 6.3, p39).
You might think that the coefficient of performance of a condensing boiler,
90%, sounds pretty hard to beat. But it can be significantly improved upon,
by heat pumps. Whereas the condensing boiler takes chemical energy
and turns 90% of it into useful heat, the heat pump takes some electrical
energy and uses it to move heat from one place to another (for example,
from outside a building to inside). Usually the amount of useful heat
delivered is much bigger than the amount of electricity used. A coefficient
of performance of 3 or 4 is normal.