MPPT controller for solar panels??

[Hughmer]

I'm considering adding another solar panel and came across an alternative energy site promoting MPPT controllers which will handle higher voltages.

 

I can see the logic of generating higher voltages at the panel end to reduce losses over longer cable runs. This would suit me as I like the idea of a "free range" panel so that I could e.g. lean it against a post away from the van to optimise the rays.

 

The site claims that "New" type solar panels can generate up to 150 volt (wow!!), so if you step that down to 12 volt with a mppt controller, the argument goes you only need thin (ish) cable from panel to controller whilst still getting a good wodge of current into the batteries.

 

This prompts the question. If you have 2 or three panels attached to your camper (roof or free range) - could you wire them in series and use a mppt controller to manage the system more efficiently?

 

[kedavi]

I suspect you also need to consider the current available from the solar panels too. For a given area of solar panel the total output power (in watts) is likely to be nominally the same regardless of the output voltage. Lets say a particular area of panel gives 100 watts. At 12 volts the current will be about 8.3 amps and at 150 volts the current will be 0.67 amps. You are correct that in transmission the higher voltage will suffer less voltage drop and could be run in a smaller diameter cable over longer distances, but whatever you save here will probably be lost in the conversion down to 12 volts in the controller as the conversion is inherently inefficient. If you stay with 12 volt panels but series them up in multiples then you will have the higher voltage and the higher current. For example if you had three 100 watt 12 volt solar panels in series they would give you 36 volts at 8.3 amps, ie a total power of 300 watts. Even if the controller could handle 300 watts, if it normally operates at 150 volts then the current would be expected to be only 2 amps. You would have to be sure that the controller could handle the alternative ratio of voltage and current on its input side.

 

150 volts is dangerous, especially if it is coming off the panels as DC. Trailing cables should be robust enough to withstand mechanical damage, such as the tough 'Arctic' cable used for mains hook up.

[Paul-]

Most panels produce power at 18 to 21 volts (aprox)

 

MPPT controllers are also very expensive at the moment, but would be a better way to go, rather than having a motorized system to move the panels.

 

It seems strange mentioning the 150 volts to prevent power loss when they are selling mttp controllers, the reason for buying an mttp is because they adjust the voltage & amps to suit the conditions of battery & light levels.

 

Another option would be to add another panel & morningstar regulator :-)

 

Paul