If I had a battery of infinite size and a charge source of infinite capacity then no doubt my system would be able to operate for an infinite time, until then...?

3200 W panels and 15kWh battery keep us going pretty well even in southern Australia in the middle of winter, but still needs help from the big alternators when we travel. No mains inlet and no generator and no gas, so an all-electric rig still requires some solar input every two or three days and that doesn't always happen

Hi Mike,

800W panels: Good. Victron electronics: Good. 210Ah AGM: Weak Link.

My understanding is that only 50% of an AGM battery is safely usable otherwise deterioration of battery will occur within a short time.

Correct me if I am wrong.

So, you may need another AGM battery to meet your required needs.

LiFePO4 batteries, on the other hand, are usable down to 10% or less and are, therefore, regarded as being of nearly double the usable capacity of AGM.

Mike Harding wrote:

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Hello Dick0

No, you're not wrong but it's not a solution either and, I agree, I am light on battery because I'm going through a lengthy process of assessing exactly what is the best solar setup for me and the way I live.

However all more battery does is to allow you to go longer without sun. I could double my battery capacity and that would increase my no sun time to maybe three days *providing* the batteries were fully charged to  begin with. More battery equals your assessment of how many dull days in a row you're going to experience, sooner or later you'll be wrong and you *will* run out of power.

As the sun is our only power source it doesn't matter a toss what your system is... if it doesn't get sun it ain't going to work. Unless you have a generator.

Yobarr spends most of his time in the hot and sunny areas of Australia and given his system is extensive (I once calculated it cost about $45,000) I'd be amazed if it didn't work as well as he claims. Indeed I doubt Tony's system was much cheaper but I don't think he spends as much time in the sunny areas hence his occasional need for a gen.

The point I try to make with my occasional posts whinging about lack of sun is that PV solar is a great system for our way of life but it's not perfect and I do this because many people, without electrical knowledge, read these forums and get the impression all they need is a battery, a solar panel from Ebay and they're set up for a couple of weeks in the bush with a fridge/freezer, lights, TV, computer, phones etc - they are usually disappointed.

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 Well Mike, I hope you sort out your power deficiencies to a point where you do not need to run the gennie so often.

I am sure you will solve the problem as many of us have.

 

My own caravan has 2 x 220 Ah agm batteries, charged by 2 x 120 Watt solar panels. Mppt solar controler is a must. I run 2 x 40 Ltr Engle fridges, 12 volt tv and sattilight dish, diesel heater, led lighting both inside the caravan and out side. Water pump and my amature radios and charging both our mobile phones. I also have a smart bridge in my battery system and it tells me of the avaliable capacity i have left. I do have a smart 30 Amp battery charger that is pluged into the mains power outlet under the bed and also a small Gentec 2 Kw 240 volt charger if needed and so far and even after two weeks of free camping was not needed. We have been free camping for up to 2 weeks and no problems with lack of power. Most days my batteries have around 90 ~95% capacity left and by lunch time the house batteries are back up to 100 %. At home we just plug the caravan into the power and the battery charger takes over if needed.

If anythink, and as others have said, you need to increase your battery capacity from 100 Ahs to 200 or even 300 Ahs. You can only use around 50% of your battery and this is were your system is failing.

-- Edited by valiant81 on Tuesday 13th of December 2022 10:15:16 AM

As they say, knowledge is power. Knowing all the underlying theory, mechanics, and environmental behaviour (clouds, trees, mountains etc) helps hugely before going off grid. A bare minimum of 3 days of autonomy, really 7 is what I'd be going for. It just gives a comfortable buffer. Basically the size of the battery is purely a personal choice. But less than 3 days of reserve gets annoying. As the battery gets bigger so to must the charger. Or else the system is poorly balanced. The golden rule of running a generator is to pump as much into the battery in the shortest time frame, essentially the battery is just a small reserve or buffer in the whole system Every 3 days I run the genny for 3 hours, or every 6 days for 6 hours. In vic there literally is no other way to get by. This practice is about as efficient as it gets. Unfortunately solar in Victoria is a complete utter joke. It's common to get 2 weeks of cloud cover in summer with just a few sunny days in between. The trees and mountains destroy any hope with power consumption over ~50ah per 24hours. In non summer months if the panel is not aligned in the ballpark position you loose straight up 30% of the panel wattage. For me (120 to 220ah per day) I would need at l least 90% efficient solar panels, since most of the time there is only diffused sunlight which most silicone mono panels are only good for about ~10% output. So this means even in 10 trillion years time solar will still never be practical for me. The best mankind can do in the real world is about 50 to 55% efficient panels. Far far short of what I need, never mind induction, airconds, etc, I'm just running the essentials required for a practical day to day life.