Configuring a Solar Geyser System for Maximum Efficiency

Configuring a Solar Geyser System for Maximum Efficiency

Arriving at the optimal configuration for your solar PV geyser system depends on the four interdependent components:

  1. Geyser
  2. Element
  3. Solar controller 
  4. Solar panels

THE GEYSER 

Larger geysers are better suited to solar due to the fact that geysers heat up at a slower rate from solar power than from grid power. A smaller percentage of the hot water would thus be used with every use and the residual temperature in the geyser would stay warmer.

W.R.T. the controllers:

THE ELEMENT 

A more powerful element is able to use more of the available solar power than a smaller one. For solar efficiency, ideally use the maximum size of element that the controller is able to handle.

THE SOLAR CONTROLLER 

The GeyserTECH Pi2R iX controller is capable of delivering around double the power of the Micro. However, the output is dependent on sufficient supply of solar power and should be configured with this proviso in mind. In any event, for geysers in excess of 150L the GeyserTECH Pi2R iX should always be selected.

Note: the solar array and controller components must be sized correctly to achieve the maximum output.

THE SOLAR ARRAY

Lastly, the solar panel configuration should be chosen to maximise the capability of the controller. 

The GeyserTECH Pi2R Micro:  

The quick answer is use 3 panels of 550Wp or more. 

  • however, you can use any combination of panels that would give you a total Vmp (voltage at maximum power) of between 120V and 200V (the higher the voltage, the more effective the heating). Bear in mind that the Micro will limit itself to an output to 7.5A, even if you supply more.
  • Alternatively, if space or cost is a factor, you can use 2 high voltage (HV) panels of around 460Wp. Bear in mind that the average High Voltage panel is only able to supply around 5A, which would be a limiting factor.

The GeyserTECH Pi2R iX:

The optimum configuration is to use 4 panels of 550Wp or more.

  • The iX is capable of utilising and supplying significantly more power than the Micro. However, the panels and element must be appropriately sized to achieve the maximum available power.
  • For the iX, use a combination supplying a Vmp between 120Vmp and 325Vmp and Imp (max amperage) up to 14A. A very effective combination is to  use 4 panels of 550Wp or more. However, 3 panels would also work and, if required, you can even use up to 6 panels.

To illustrate the effect of different configurations, we have supplied a few examples below:

NOTES:

  1. The maths behind power throughput can be expressed as: Power = Volts²/Resistance
  2. The Micro will limit output amperage to 7.5A
  3. Everything above the yellow line in the graph is "lost" due to the power rating of the element (using a more powerful element - if the controller can handle it - would use more of the available solar.
  4. Everything below the yellow line is used by the element.
  5. The average geyser uses around 5kWh per day (a large family, however, can use up to 10kWh per day).

Illustrative calculations:

In this example, we have used a typical installation with a 3KW element and 3 standard (generic) 500Wp solar panels. Note that PV power available is 1500Wp but that max power is limited to 1125W due to the size of the element. Total kWh produced in this example is 5.27kWh using 4 hrs of sunshine as an illustration.

In this example, a 2KW element is used and the remaining variables kept the same. Whilst the available PV power remains at 1500Wp, max power is now limited to 750W and kWh production reduced to 3.94kWh.

In this example, we have used 4 x 500Wp solar panels instead of 3 and kept the rest of the parameters used in the first example the same. Note that available PV power is now 2000Wp and that the full 2000W of power is able to be used (only applicable to the GeyserTECH+ iX)

 
This example illustrates the use of 2 high voltage panels. A characteristic of high voltage panels is that the amperage output is naturally lower. They are therefore well suited to the Micro as the output of the panels will not be limited. Note, however, that the total output is comparatively lower.

You can find the PV Power Calculator here to input your own values.

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