1.3 Need for an auxiliary heater
From what has been previously mentioned, it is obvious that in winter, city water
temperature is lower and there is less available solar radiation. In summer, however,
city water temperature is higher and more solar radiation is available. Therefore,
during the winter, it will be necessary to use a supplementary energy source. The
back-up heating system of your solar water heater is an electric resistance.
The electric heater, as a supplementary source of energy, is also used in cases of
insufficient or no sunshine (at any period of the year) or very high demand for hot
water.
1.4 Heat losses during the night
Quite often, hot water is left in the solar water heater during the night. The hot
water storage tank has strong thermal insulation, which prevents heat losses
during the night. However, since ambient temperature during the night is low, the
temperature of hot water in the storage tank decreases slightly. If hot water at a
temperature of between 50
o
C - 60
o
C is left inside the solar system during the night,
its temperature may drop by 4
o
C - 10
o
C by the next morning, depending on the
area and the weather conditions (ambient air temperatures of 0
o
C - 10
o
C).
Detailed data exist in the test report, based on relevant standards (EN 12976-2,
ISO 9459-2), available by SUN&HEAT.
1.5 Use of hot water in a household
Hot water in a household is usually used in the bathroom, in the kitchen (20% -
25% of the total hot water needs) and for washing clothes (30% - 35% of the total
hot water needs).
You can make the most of your solar system by using its hot water for washing
clothes in the washing machine, as well as washing dishes in the dishwasher.
From measurements made in households with a solar water heater in Southern
Europe, it is estimated that the average consumption of hot water is 35 liters to 50
liters per person per day. This amount refers to hot water which is drawn by the
consumer directly from the storage tank of the solar system.
