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Buy a generator. Solar panels are fine with limitations. For prolonged travel I would not be without a small generator.

Your need at least a 120W panel to run a fridge / freezer and charge the
batteries and that assumes sunny days.

I suggest you measure the current being drawn by each fridge when its running.

The panel specs indicate you'll get around 2A per ie 4A total.

Thus when both fridges are running your still drawing at least 1A from the batteries, allowing for 50% duty cycle your only going to put 1.5A into the batteries per hour, assuming 10 hours of sunshine thats 15A. Over night your going to use 14*5A or 70A.

As you can see one 90W ain't going to cut it, two 120W panels would probably just cope, assuming no cloudy days.

Cheers
LeighW

Nick,

You may find Electricity for Camping a useful read.

Your 80W of solar panels won't get you far. With the 2 fridges, especially with one running as a freezer, you'll probably need to generate at least 60 amphours per day to break even. With 6 hours strong sunlight, that means you need to generate an average of 10 amps, plus say 20% for inefficiencies and contingencies. To be totally reliant on solar will require about 170W of panels, and a good MPPT controller (and sun every day!) That's a fair investment.

You have over 200 Ah of storage, which sounds good.

An option is to invest in a dc-dc charger. You will not charge your batteries properly from the vehicle without one. Depends on your usage patterns, but if you drive for a couple of hours each day, a 30A charger will meet your daily requirements without any solar input. Your present 80W solar panels will meet about half of your needs. The combination of 80W solar plus a dc-dc charger may be all you need, depending on your usage patterns. If you camp for a week without running the vehicle, you will need at least another 80W of solar (or run the engine for an hour a day.) If you are traveling for a couple of hours per day a 30A dc-dc charger such as this one will handle your needs without solar support.

Something to bear in mind if you do go for a dc-dc charger - a 30A one would be good in your case, but will pull 35-40 amps from the alternator. It would be worth checking that the alternator can handle that extra load in addition to its other jobs.

Our rig has 200 Ah of storage, 180W of solar and on a big trip this year we had a 30A dc-dc charger for the first time. The charger did most of the work as we did some traveling most days. I'll probably downsize the solar to 140W for future trips.

HTH

John

Just a quick note on panels (but note; electrons and their behaviours usually stump me too) - from posts I've seen here and elsewhere, plus reading my book on Solar from an acknowledged guru, my understanding is that while a panel's stated performance specs might be true, they are lab test only, for rating purposes - not achievable in the field - count on 70% of the nominal output, at best.

Nick - you seem to be disappointed in the performance of your panels. Apart from there being insufficient panel size (as pointed out above) you probably have the regulators mounted on the panels. If you have then the cable from the regulators will probably also be woefully small in size.

To get the best output from your panels you need a good regulator/charger. You also should mount as close to your batteries as possible.

I'll start by saying opinions will vary, bassed on expectations.
AND there is a lot of twaddle going arround that favours the complicated over the simple basics.

Firtsly
your fridge will run at a relativly low duty cycle, assuinimg you are using it smart.

Your freezer may run almost continuoulsy and that is, if it is already down to temp, if you are actually freezing stuff, expect it to run CONtinuously for at least 24 hours.......expect 4 to 6 times the consumption from the same unit run as a freezer as it would run as a fridge under the same conditions.

Don't believe any of the average consumption or duty cycle information published..it will always be optomistic.

At least you have a solid battery bank.....BUT.....expect to spend 120AH of that just to keep the freezer going for a full 24 hours.
24hours x 2.5 amps = 60 AH.......that is if the 2.5 amps is realistic....and that is about as deep as you want to cycle for good life.

And you will need at least 80AH of solar pannel input per day to keep up with the fridge reliably and account for losses.

you can speculate on the duty cycle of the fridge all you like, but at best it will be a guess, and it will change so don't be optomistic.

Remember this is power budjeting not actual.

So iff you are carefull and lucky ya might get 2 days out of ya 240AH of batteries without hammering them....but don't be optomistic.

now to the solar pannels.
Nowhere in Australia will you ever get 100% rated output from your pannels for very long, in the far south the output may be as low as 20% in winter.

If ya pannels are not at right angles to the sun, you have a loss there too.

Yes you can only rely on 6 good hours of sunshine a day..um sometimes less

then, can be cloud, rain and shade...for how many days.

so it pays not to be optomistic on pannel size too..very much so.

some people are reporting that they do pretty well on a single 120 or 180 watt pannel......yeh but..how reliably and for how long.

If you want the whole thing to be reliable in varying amounts of sunshine, you need to be generous on pannels.

remember you need enough to both run the gear and charge the batteries at a decent rate, in unfavorable conditions.


I recon in my view that 240AH of battery and 360 watts ( 2 x 180 watt) of pannel and it will be barely adequate for your demand.

If you have spent that much on other gear you would have rocks in your head not to be running a MPPT regulator on your solar......if you arent expect losses.

I'm not as strogly in favour of DC to DC chargers as some.....but there are some devices that have a MPPT solar reg, dc from car input and mains charger input all managed for you in one box.

Y'd have to consider one of those for this application..but y'd need the biggest one you could reasonably lay ya hands on.
30 amps would be barely adequate

If you want reliabilty, and you don't want t be disapointed, be pesimistic in your expectations.

cheers