a) Family Smith has already installed PV in their house. Now, they also want to cover their needs for warm water with solar energy. For this, they consider having a solar thermal water heating system. Considering that the need for warm water is 100L/day, the water has to be heated from 10 to 60ºC and the specific heat capacity of liquid water is 4.18 J/gK.

What is the total energy, in Wh/day, that the system will need to supply to cover the warm water demand?

b) Considering an efficiency of 70% and an irradiance of 1000W/m2 for 3 equivalent sun hours, how much collector area, in m2, will be needed to cover the demand?

c) If only half of the hot water needed has to be stored, at least how big, in L, should the storage tank be?

d) The cost per m2 of collector is estimated as 120 Euros, and the extra costs for water tank and piping are 6 Euros per L of storage. How much will the whole system cost?

e) However, Mr Smith has read an article in the newspaper in which it was claimed that at the moment it is more expensive to install a solar thermal system for water heating than directly using the PV electricity to heat up water. Therefore, he wants to make some calculations to check such assessement. If the price for Wp of a PV panel is 1 Euro and the external costs are 400 Euros, and considering an efficiency of electricity to heat conversion of 85%, how much (in Euros) will it cost to cover the same amount of energy with PV technology?

f) Assume that the lifetime of both systems is 20 years and the maintenance costs are also equal for both cases. Which will be the better choice for water heating?

1)Solar thermal system
2)Photovoltaic system
3)Both systems are equally good