Let's be clear I'm talking about PV panels not a HW system. 15%...

Let's be clear I'm talking about PV panels not a HW system.

15% is often quoted but is backed up by the math

here's the math

the earth receives 1000w/sqm peak

commercially available 250w PV panel measures 1m x 1.6m = 1.6sqm

so by extrapolation 1.6sqm receives 1600w peak from the sun

our 1.6sqm panel produces just 250w peak

Efficiency = 250/1600*100 = 15.625%

These are the commercially available roof-ready panels on the market today without going into exotics or lab produced one-offs.

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