Solar panel help

Thanks Matt. We are pretty power hungry so will be interested to see what people will say we would get. Using two of these units would be reasonable, but if you had to have more than that it would be a bit silly. I'm guessing we use in exccess of 100 amp's a day. 2 x fridges (in the tropic's cooling lots of beer :-), a fan over night (sometimes during the day) + lights etc.
Cheers Lyndon

Hi Lyndon

As a starting figure most panel in good light facing directly into sun will give a little over 1amp per 20watts
Depending on orientation of panels to sun will determine how many hrs a day you will get that output.

AmpsXhours gives amphrs.
100ahrs per day??I believe you would need minimum of 400watts to be reasonably self sufficient.
Remember it takes more to recharge than what you take out @ night

Thanks for that. I didn't realise you run your stuff from the panel + it puts in charge. I thought you would run your stuff from the batteries and the panel would keep them full?

Lyndon

" I didn't realise you run your stuff from the panel + it puts in charge. I thought you would run your stuff from the batteries and the panel would keep them full? "

It's a moot point - if your panels are putting out 8 amps and your loads are drawing 8 amps then all the panel current will be going nto the load, none into the battery.

If you're drawing 7 amps, 1 amp goes into the battery. If you're drawing 9 amps, the battery is supplying 1 amp.

To keep calculations simple, people usually work out how many amphours a day are supplied by the panel and how many amphours a day are used by the loads.

Hi Mike
Yes the point is moot, but do you actually run stuff from the panel directly?
If so why?
Thanks Lyndon

NEVER connect an appliance to a solar panel without a battery being in circuit.

A "12 volt" solar panel will put somewhere between 20 and zero volts into the appliance, depending on the amount of sunlight and the current drawn by the load.

lyndon,
You say: " I didn't realise you run your stuff from the panel + it puts in charge. I thought you would run your stuff from the batteries and the panel would keep them full? "

what I said is:
" it runs the appliances during the day and also maintains your battery fully charged "
The solar panels are wired via a solar regulator, the solar panels supply the power, the regulator then supplies that modified power to the accessories via a copper cable.

The four pictures below show it pictorially

Maîneÿ . . .

Mainey,

I am (at the request of others) trying to stay away from 12v discussions, but I don't get your point. You often trot out this line about how appliances can draw directly from the solar regulator; but so what?

Don't get me wrong, I have the same regulator as you (20 amp one) and I do run my fridge from the regulator, but only because I am interested in measuring how the fridge is using and the Steca lets me measure that, but there is no other practical advantage is there?

In simple terms, on any given day the solar panel will output X amount of power. Similarly, on any given day your appliances will consume Y. Subtract power consumed (Y) from power produced (X) and the left over (or deficit) will go into or come from the battery. Does it matter if the power consumed is being drawn from the battery of directly (via the regulator) from the panel? Surely the equation remains the same?

I must be missing something here or is there a significant loss associated with putting energy into the battery that I am not accounting for in this equation? Not forgetting that if the solar panel can not provide enough power to run and appliance at any given time, then the deficit still gets drawn from the battery and the battery won't maintain full charge anyhow.

Cheers,

Matt.

If you assume the battery has 80% charge efficiency, then to get 8 amphours to the load, you would need to put 10 amphours into the battery.

If you were supplying the load while sun was shining, you would only need to supply 8 amphours because it wasn't going via the battery.

That's the interesting thing about communicating using words - you write something with a very clear understandng of what you mean - then someone else points out that it could be easily interpreted in a totally different way !!!

A BIG thanks for that