Vision Solar Systems - 100 L Gravity Fed Type
Copyright © 2013 - 2016 Enervision. All Rights Reserved.
Issue 2.0 Mar 2013
12
Always remember that the solar performance will depend on the amount of sun on the collector.
Cloudy weather will decrease performance and reduce the amount of energy harvested from the
sun. In addition, shade from trees and other objects during the day will mean that less solar
energy is harvested. There is a backup element that can be fitted to the system to cope with bad
weather and lower solar irradiation and also for abnormally high hot water demand. The backup
element is thermostatically controlled and is normally used in conjunction with a timer so that
the use of electrical energy can be controlled and used only when there is no solar harvesting
likely to take place.
In order to heat the water in the tank with the electrical element some time is needed to attain the
required temperature. Shown below is the graph of the time taken to heat water from 20ºC to
70ºC.
If the tank is at a higher temperature the time for 20ºC to the starting tank temperature can be
subtracted from the full reheating time. Note that you will need to take into account the timer
exclusion zones if these are active in the electrical element reheat cycle or alternatively put the
timer into the bypass mode.
20.0
30.0
40.0
50.0
60.0
70.0
80.0
0
0.5
0
1.0
0
1.5
0
2.0
0
2.5
0
3.0
0
3.5
0
4.0
0
4.5
0
5.0
0
5.5
0
6.0
0
Wate
r Te
m
p
e
ratu
re
in
t
h
e
Tan
k
Time in Hours
Reheat Time with Electric Element
1.5 kW Element
Average Energy Saving per Day (kWh)
Area
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Johannesburg 4.7 4.6 4.5
4.5
4.5
4.5 4.7 5.2
5.1 4.7 4.7
4.7
Cape Town
5.7 5.6 5.1
4.4
3.6
3.3 3.5 3.8
4.5 5.1 5.5
5.6
Durban
4.1 4.2 4.2
4.2
4.1
4.0 4.1 4.3
4.2 3.8 3.9
4.1
Port Elizabeth 4.8 4.6 4.3
4.0
3.7
3.5 3.7 3.9
4.3 4.3 4.6
4.8
East London
4.6 4.5 4.2
4.1
4.0
3.8 3.9 4.2
4.4 4.3 4.5
4.7
Bloemfontein 5.2 5.0 4.7
4.6
4.4
4.3 4.5 5.0
5.1 5.0 5.1
5.3
