


It's interesting to calculate (or measure) the amount
of energy in sunlight  and to work out how much energy
one might get.
Let's think about photovoltaic panels. These
are the ones which you see at the side of the road near
speed cameras and other trafficcontrolling devices.
The price of these has come down quite a lot
in the last 20 years but the efficiency is more or less
the same  10% and you're doing well.
Right let's take a square metre of ground.
These are the approximate figures I use for solar panel
calculations; they refer to midday:
1000 Watts  Death Valley, or African desert on a hot day
600 watts  hottest day you'll ever get in the UK
500 watts  hot summer day
200 watts  hot summer day with light cloud cover
100 watts  sunny, clear day in December
50 watts  overcast day in December
Divide the figures by 10 and you'll get a slight over
estimate of the power from your metresquare photovoltaic panel.
It's a sobering thought that most solar panels are net consumers
of energy. A panel which generates as much energy (over its lifetime)
as it took to make it in the first place is doing well.
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