1. © Oxford University Press 2011 IP1.9.5 Solar panels and payback time: Overview Solar panels and payback time: Overview

2. © Oxford University Press 2011 IP1.9.5 Solar panels and payback time: Overview Look at this solar panel. How is the water heated?

3. © Oxford University Press 2011 IP1.9.5 Solar panels and payback time: Overview Energy transfer: Infrared radiation from the sun is absorbed by water, increasing its temperature.

4. © Oxford University Press 2011 IP1.9.5 Solar panels and payback time: Overview Payback time = This is the equation for calculating payback time. To decide whether a method of insulation is worth doing you need to calculate the payback time. cost savings per year

5. © Oxford University Press 2011 IP1.9.5 Solar panels and payback time: Overview a)50 mm loft insulation b)270 mm loft insulation Payback time = = Look at the two payback equations above for insulating a loft. Calculate the answers and decide which method is most cost effective. cost savings per year £100 £20 per year Payback time = = cost savings per year £250 £100 per year

6. © Oxford University Press 2011 IP1.9.5 Solar panels and payback time: Overview Can you think of the three areas of a house which are commonly insulated? 1windows – double glazing 2walls – cavity wall insulation 3roof – loft insulation