Solar Power cost effective calculation?
An average householder uses 160 litres day-1 hot water at a temperature of 55oC, and the specific heat of water is 4.1868 kJ kg-1oC-1 and the inlet temperature of the water to the house is 10°C. Estimate the total energy requirement for hot water supply. If a 2 m2 Solar Collector is installed to save electricity for hot water supply, the efficiency of the solar panel is 55%. Assuming the mean availability of solar energy throughout the year is 115 Wm-2, the cost of electricity is 5.87p kWh-1, the total cost of the installation is £2000, and it has a life span of 20 years, is the scheme cost effective at a 0% discount rate?
I got the total energy required to heat the water as 11.47GJ/Annum and that its not cost effective as the solar panles will provide 34.7% of the heating requirement which is equilivent to £1300 over 20 years, thus as it cost £2000 to install, its not worth it.
Is this correct? I feel i have done it wrong
My calculations show the panels producing 7.25 GJ/year, and 11.00 GJ as the original electrical requirement. That means the panels would produce about 66% of the heating requirement (oddly, this is the complement of 34%).
1 kWh = 3.6 MJ, so the annual energies are
solar 2013 kWh/y
electric 3056 kWh/y
The value of the Solar Heating is therefore 11800p / year. I’m American, but if p are like cents, and pounds like dollars, then that’s £118 / year, or £2360 over 20 years, a bare win over the system price.
It sounds like these calculations are for a place that is right on the cusp of where solar makes sense. In Hawaii, electricity would be 3-4x that price, the system price 2/3 of that (simple panels – freezing not an issue), the insolation 2x that, and the water inlet temperature higher, making the energy requirement 2/3 of that.
Flexible Solar Panel – PowerFilm R14 (14 Watt)
solar panles
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