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# Energy Calculation for Solar Water Heating

Please see attached file for full problem description.

It is often said that one of the best things you can do to safe energy in a house is to install a solar water heater. "You pay back the investment in four to five years" is a common remark.

Another common assumption is that a geyser contributes about 40% to the energy consumption of a residential house in South Africa (assuming a house without a central heating system).

Calculate the payback time on a solar water heater based on the following assumptions. Cost of a new 200 liter system is R13,800. Monthly average electricity cost of R600. Geyser contributes 40% to the electricity bill. Neglect the effect of inflation.

After installing a solar water heater on your roof most the people in your street is very excited and start asking you questions. One man remarks that he has a holiday house in Stilbaai. The house is occupied for about 50 days a year. His annual electricity bill is R1200 of which R50 is a fixed connection fee. What would his payback time be assuming the geyser contributes 40 % to the electricity bill and a similar installation cost as above. Is it worth installing the solar water heater on a financial basis?

#### Solution Preview

In the 1st case:

payback time = 13800 rand /( 0.4*600 rand/month) = (13800/240) months = 57.5 months = 4.8 years
In ...

#### Solution Summary

This solution determines the payback time using energy calculation to make a decision to buy the solar water heater to cut costs. Brief explanations are included.

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