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Solar Panel power rating.


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A bit of guidance from the more electrically proficient please:


Am I right in thinking that my 85 Watt panel will only give a maximum of 72 Watts, and the resulting battery output no better than 60Watts?


My reasoning:

The panel Voltage is marked as 17, so the current at 85 Watts would be 5 Amps.

The regulator has a 14.4 volt output, so at 5 amps this is 72 Watts to the Battery.


Further does this mean that its charging the battery at a rate of 5 AH, but as the battery only yields circa 12 volts output [ when off charge] that my once 85 Watts is further depleted to about 60 Watts usable battery output?


Clearly there are some inefficiencies as well to make it even less.


Its probably academic I know but I would like to get my mind round it.

Thanks John


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Here's my take on how my system works, are they all the same?

Regulator does not limit panel to 14.4v output, but cuts output from panel when battery voltage reaches 14.4v.

Forgeting about losses for the moment, your panel is outputing say 5ah for say 5 hours, then it has produced 25ah which is inputed to your battery, in theory this is availible to be used at whatever voltage.

Of cause non of this happens in reality, as you say there will be losses in the system, but worse than this, your panel ever producing 85watt is very unlikely.


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Some regulators are very clever and when properly matched to the panel will match the panels output impedance so as to maximise output power to the battery. But by far the biggest aspect is how strong the sun is, how much garbage there is in the atmosphere between the sun and your panel, how the panel is aimed (or not) at the sun.

On a good day our 80 watt BP panel laying flat on the roof might just go in escess of 3.8 amps indicated on the moving coil ammeter I have connected in series. For a MH that is otherwise quite economical in 12 volt consumption that for a few hours in the summer can keep us going.

In the winter (like this Easter with all the hookups taken) it will be running on Methanol! (Fuel cell)

Hope that helps.




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In the process of swapping our old Hymer, which has two roof top solar panels, for a Pilote Galaxy which has none. Thinking about a portable ie non fixed solar panel. Any experience of these? Are they effective? Also the "new" van has only two 3 pin sockets (one of those where the TV sits, so not very useful for owt else) so extra sockets would be useful. I'm thinking instead of having extra sockets fitted I could just use a "gang" socket. Does this make sense?

thanks Irene

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