Just Decorating
Generate your own
sun power
Use the hot summer sun to heat your water
C
an you afford to keep paying 40 to 60%
of your electricity bill for a job the sun can
do for most of the year? If so, then install
photovoltaic (PV) panels that uses the hot summer
sun as a sustainable way to heat your water and
lower the costs of your electricity bill too.
A PV system can pay for itself if you keep it simple.
Batteries can almost double the price, so unless you
really want to go off the grid start with a basic PV
system. This will cover most of your consumption
costs during daylight hours, without stroring for
night-time.
Firstly, mount a 300 litre tank full of water
horizontally onto your roof. Then, install two 2.5m2
flat polycrystalline silicon PV panels below the water
tank.
Installing only one PV panel (rated at 255 watts)
and a 230 watt inverter (to convert DC power to
AC) on your roof will generate about 230 watts of
electricity during peak times (this is the maximum it
can produce in full sun conditions).
Power generated from this system covers most of
what is required to run your home efficiently.
Energy from the sun will indirectly heat your water.
The tank has an electrical element to top-up the
temperature during cloudy weather or when extra
hot water is needed.
For a family of four or more, this high-pressure
hot water system can reduce your electricity spend
by more than R400 a month. If this performance
continues, the R28 000 price tag — after a R9 000
Eskom rebate advanced by the installer — will be
covered within the expected four to five years
payback period.
48
Issue 7 2015
CHOOSING A SOLAR WATER HEATER
• A flat-panel or an evacuated-tube system: Flat panels
are more durable, but evacuated tubes create more hot
water with limited sun exposure. For a north-facing roof
in full sun, flat panels provide most of your hot water
needs. If your roof gets limited sun, evacuated tubes
are necessary.
• A direct or indirect system: An indirect system, uses the
sun to heat tubes of glycol, which then heats the water.
• Ensure that you select the right size tank — a minimum
of 50 litres per person and an extra 50 litres for general
household use. Tanks with water flowing between them
in series is ideal for high efficiency.
• A close-coupled or split system: Because a close-coupled
system uses the thermosiphon effect of rising heat to
circulate the water, it is less expensive to buy and is
the most commonly used. If you prefer to have the
tank inside the ceiling or in the house, a split system is
highly efficient, but it requires a circulation pump.
• An electrical back-up element in the tank is standard
in high-pressure systems, but must be managed by a
timer to control when the back-up element kicks in.
• If your roof pitch is not ideal (flat, not steep) consider
installing brackets to ensure the optimal angle for your
latitude. This can increase heat gain by up to 20%.
• Once you have decided on what you want, get some
quotes for the system and installation. Don’t grab the
lowest quote without considering quality.
Just Property Magazine