Sunday, 27 March 2011

PV panels vs. double glazing - which has the best energy payback?

Some people think solar PV panels are a waste of resources because they take such a lot of energy to make that they won't generate enough to pay that back in their lifetime. However, this is not true, even in the UK. It turns out that the energy payback time for PV panels in the UK is very similar to that for double glazing, and allowing for the longer lifetime of PV panels (at least 25 years) the energy payback ratio, based on whole life generation/savings, is better for the PV.

A typical estimate[1] for PV panels is 3-4 years energy payback time based on 1700 kWh/m2/year insolation. However the UK is not as sunny as this; the insolation in London is about 1150 kWh/m2/year and allowing for this takes the payback time to 4-6 years. For double glazing, I estimate 4-5 years based on 830 kWh embodied energy for a 1.2 m2 PVC window [2], giving a U-value of 2.0, replacing a single glazed window with U-value 4.8, in a room heated to 17C.

You may disapprove of PV panels because they are more expensive per kWh than other renewable technologies, or because their return is too seasonal to be useful. However, if you accept that double glazing is a good thing you can't criticise PV panels for energy payback. 

PV panels on our house (wall not yet painted)

Double glazing in our house


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