Configuring for max power. Panels, controller, element..

Configuring for max power. Panels, controller, element..

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, however, the GeyserTECH+ Micro is only suitable for geysers up to 150L, whereas the GeyserTECH+ iX can be used on geysers up to 300L.

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. For a given solar array and controller combination, a smaller element may restrict the output of the system to less than that theoretically available. The GeyserTECH+ Micro can handle a maximum element size of 3KW whereas the GeyserTECH+ iX can handle up to 4KW. 

THE SOLAR CONTROLLER 

The GeyserTECH+ 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+ iX should always be selected.

  • The GeyserTECH+ iX can utilise 90 - 325Vmp and deliver up to14A
  • The GeyserTECH+ Micro can utilise 90 - 200Vmp and deliver up to7.5A

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 limitations being voltage (minimum and maximum at maximum power (Vmp)), amperage (the Micro will limit output to 7.5A) and power (the maximum capability of the Micro is 1500W).

The GeyserTECH+ Micro:

The Micro is capable of utilising up to 1500Wp. For the Micro, we suggest using either: 

  • 3 x standard panels in the 450-550Wp range - these would give you a total voltage around 150Vmp able to supply around 11A (bear in mind that the Micro will limit output to 7.5A) or
  • 2 high voltage (HV) panels of around 460Wp - these would give a total of around 160Vmp and able to supply around 5.5A

NB: When choosing panels for the Micro, prefer panels with a higher voltage output as opposed to amperage, whilst staying below the 200Vmp maximum. This will ensure better usage of available PV power (if using standard panels, use panels with a minimum of 40Vmp (Voltage @ maximum power)

The GeyserTECH+ iX:

The iX is capable of supplying significantly more power than the Micro. However, the panels and element must be appropriately sized to achieve the maximum available.

The iX can handle up to 325Vmp and deliver up to 14A. An effective combination is to use 3 to 4 panels in the 450 to 550Wp range (again, use panels with a minimum of 40Vmp (Voltage @ maximum power).

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" because of the element.
  4. Everything below the yellow line is used by the element.
  5. The average geyser uses around 5kWh 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 calculator at https://www.telemetric.co.za/micro.html? to input your own values.

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