Installation manual

5.7.7. Summary: Matching your turbine to an MPPT controller and your battery

The various voltage criteria are as follows:

 Maximum power point voltage (MPPV) at the controller must be greater than battery

charging voltage

 MPPV at the actual turbine will be controller MPPV plus cable losses

 Turbine design MPPV will determine turbine open circuit voltage (Voc = 3 x MPPV)

 Controller maximum voltage must be higher than turbine Voc

(Where there are large % losses in the pipe and the cable, you may see even larger

differences between MPPV and Voc. It may be harder to find a controller or inverter that will

work in such cases without a voltage clamp.)

5.7.8. Illustrative example

Here is a practical example using a TRG40 on a 24V battery. The controller maximum

voltage is 150V and so the above criteria are all met.

This set-up could also be used to charge a 12V battery (within the current limit of the

controller) but it would not charge a 48V battery. Also, the cable voltage is only 40V which

may lead to a costly cable or high cable losses, if the distance is more than a hundred

metres.

What are our options for a higher MPPV? We can either use a controller with higher

maximum voltage (a 250V controller with 80V MPPV) or we can use a crowbar to clamp the

voltage. The next chart shows the PLT100C with crowbar circuit in the turbine: