Solar Hot Water Systems: PV Therm Units

PV is now connected seamlessly to your existing geyser for hot water from the sun.

PV is used to heat water by converting the DC to a chopped AC current. It uses the existing 2-4kW heating element and thermostat.


  • No plumbing at all
  • No maintenance
  • Similar costs as thermal systems
  • Low installation cost
  • MPPT for high energy conversion
  • No water issues such as scale and water interruptions
  • No freezing and glycol issues
  • PV panels does not have to be close to geyser, saves money
  • Systems produced by leading SA Electronics Company.
  • Designed according to SANS60669 for safety
  • One year warrantee
  • Two types-one with and one without backup
PVTherm installation

PV Therm Process

  • The PV Therm unit interfaces photovoltaic panels to a standard geyser with AC elements of 2-3 kW.

  • This will allow the water in the geyser to be efficiently heated with solar panels.

  • The PV Therm unit is mounted close to the existing DB board in the house, and power is fed from the solar panels to the unit.

  • This DC power is converted to AC and applied to the existing geyser wiring. 

  • No modifications are necessary to the geyser circuit and the existing thermostat will still determine the maximum water temperature.

  • If the desired temperature cannot be reached with solar, a timer in the DB board ensure enough hot water during the preset times.


  • MPPT efficiency >  93%
  • DC disconnect fuse
  • AC backup for element
  • PWM output
PVTherm controller


Maximum DC power 1.4 kW
Maximum DC voltage VOC 230 Volt
Maximum DC current 10 Amp
Recommended system voltage 180 Volt
MPPT range 140 – 190V
System start up voltage 90 Volt
Maximum DC current 10 Amp
Output voltage 100 – 230 Vac
Output frequency 50 – 500 Hz
Unit self consumption < 5 W
Recommended PV for 150L geyser 780 Watt
Recommended PV for 200L geyser 1040 Watt
Recommended string open circuit voltage 200 Volt
Dimensions (H x W x D) 300 x 220 x 120
Weight 2.6kG

The modules are mounted on the roof close to the geyser if possible on a north facing roof. The panels are wired in series and have two dc wires going to the unit.

The PV Therm unit is mounted close to the electrical DB board.

PVTherm diagram

The DC cables are connected to the contact on the left, observing polarity!  (The DC fuse must be in the open position during installation)

A  4-core, 4mm surfix cable is used between the DB board and PV Therm unit. The existing wires are removed from the geyser circuit breaker in the DB board and taken to the AC contacts of the unit.

The OUT terminals then get connected to the wires going to the geyser.


Usage and Recommendations

Under normal operation there is no AC connected to the unit. The unit will make use of the solar to heat the water. The existing thermostat will limit the maximum temperature reached in the geyser as before.

The unit has a MPPT controller to achieve maximum power with the available power generated by the PV panels. To get maximum heat storage it is recommended that the thermostat is set to 65 degrees.

If it was a sunny day the temperature of the water will be adequate for use – 45 to 65 degrees.

The AC input can be used for backup in the case of rainy days. When AC is applied to the unit it will disconnect the PV output, delay 15 seconds for safety, and then switch the AC supply through to the element.

A timer can be inserted in the DB board for backup at certain times if necessary, although many prefer to control the AC circuit breaker manually as required.

If a timer is installed, we recommend that it switches on for half an hour before hot water is going to be used.