Series or Parallel @ What Wattage

Hi Allan,

Qn1 - Hard to give a definitive answer because personal usage patterns vary so much. Obviously you need sufficient charging capacity to replace the charge you are using, plus a little for inefficiencies plus a contingency to cover cloudy days..... The fridge will be your biggest consumer (how big is it?) How cold do you run it, very, not very...? Do you have kids who go to the fridge frequently? Are we talking about a fridge running in a Darwin summer or in a Canberra winter?

Another unknown that has a big impact on solar sizing is how long you want to be totally reliant on solar - 1 day, 3 days, indefinitely? Do you travel most days, so can use the vehicle to help charge the batteries? You might benefit from a dc-dc charger rather than lots of panels.

Our own system uses 150W of panels, two x 100Ah batteries, and a 30A dc-dc charger. We are pretty frugal with electricity, and this handles are needs well, though we rarely remain stationary for more than a few days.

Suggest you might find our blog Electricity for Camping a useful read.

Qn2. For a standard 12v setup, there are two options - a) series connect two panels of the same size/capacity and use a controller capable of taking the resultant higher voltage and converting it into the voltage required by your batteries. or b) parallel the two panels and use a standard 12V controller.

The latter (b) is much more commonly used, the controller is generally cheaper and suitable controllers are more readily available. So the straight answer is - for a simple quiet life, connect panels in PARALLEL and use an MPPT controller with sufficient current capacity to handle at least 20% more than the total provided by your two (or more) panels. A further advantage of parallel is that you can add more panels of any size (all in parallel) if you need to.

HTH

John

Without over complicating the matter.
In general solar pannels for 12 volt systems are connected in parallel.....there are complicated exceptions.

12 volt panels, 12 volt regulator and 12 volt batteries...simples squirk.

you have said the word "fridge".....if you want any hope of keeping up with a fridge even a small one on an ongoing basis you need a minimum of 2 x 160 watt solar pannels.

Double that is far from unreasonable.

If you say the word "freezer" or its a big fridge double the panels minimum.

some MPPT regulators will take 24 volts in and charge 12 volts out...why.....because they can and there are lots of 24 volt pannels out due to home solar.
There may be some advantage with voltage drop in cables.


The above is given not knowing details.

cheers

WRT series or parallel connection of the solar panels.

For recreational applications, parallel is much better because if they are in series and one panel is even partially shaded, then the output of the regulator will drop to virtually zero. However if one panel is shaded in a parallel set up then the output will half.

On top of that you must put diodes in series with each panel. ( your panels probably already have parallel diodes in the termination box). These diodes should be schottkey diodes with their voltage and current rating higher than the panel. If you don't do this then much of the current from the generating panel will be lost in the shaded panel. ( available at Jaycar or ebay)

The downside of parallel connections is that the cables must be thicker to handle the extra current while minimising the voltage drop. Use 10 awg speaker cable, it's much more flexible and cheaper than smaller auto cable.

A good wiring set up if you have portable panels is to use Anderson connectors, but get the red or blue ones, not grey. Then have 2 wired in parallel near the regulator which should be near the batteries.

Then have 2 cables of say 10m long with the Anderson connectors at each end.

Also make up a Y cable with 3 Andersons, about 1.5m long per segment.

Now you can have 2 x 10m cables going in different directions, 1 x long 20m cable with a double adapter at the end and 2 panel,s or if you just need a top up then you only need to connect 1 panel, either 1.5, 10 or 20m away.

Here is another tip. If you are using portable panels, get the semi flexible ones from ebay - Yes ebay. There are some Australian sellers and the price has dropped significantly over the last 12 months.

I just changed from my 2 80W framed panels at 12kg each to 2 semi flexible ones at 2.5kg each. They work just as well and may even be more shade tolerant. I stuck them to the roof with velcro so I can easily move them if I am parked in the shade.

With the power requirements, easy, you need at least 160W and more is better. 200W min if you crank up the stereo a bit or if you often go to shaded, cloudy areas. 250W may be a minimum in the high country in summer at most camping spots if you don't want to be moving the panels every hour or so.

Hi Allan

I just did a test using both regs last week.
40ltr Engel empty with bag at -6 sitting in car drawing 2.7amps in the shed at 40 outside.
Plasmatronic reg in parallel got 4.4 amps from 2x42 watt Uni Solar rated 2.54w max each. With a Morningstar Sunsaver MPPT in SERIES, it put out 5.2 constant load, peaked at 6.4 when the sun came out from behind clouds.
This was all running through 1 100amp dual purpose battery, first 2 days it got down to 12.4v in morning, 3rd morning it got down to 12.2v 50% of battery. At -8 on the fridge it could not keep up the charge dropping down to 12.2v overnight.
These panels do not loose any power in the hot weather, where other panels loose 5% for every 5 degrees above 25c. On the days I tested normal panels could have lost 30% of power each.

Hi Allan,

I have the same setup as you running the same gear, more or less, and I have 1X200 watt panel, newly fitted, and the original 80watt panel hooked up in parallel.

Do not hook up 12 volt panels in series as you then have 24 volts.

These are 12 volt panels running a 12 volt system through a PWM regulator.
I use a PWM Fangpusun Regulator because I like this particular regulator, no other reason.This Reg.

The mixed size panels are not the most ideal mix but it works.

At the current price of panels I would suggest 2 X 200 watt panels and that way you will always be charging even on cloudy days.

For my usage, which sounds very similar to yours, my batteries are mostly at 100% State Of Charge (SOC) nearly all the time, according to my regulator display.

Cheers, Bruce.

Thank you everyone for your reply, has given me food for thought.

Allan