#148072  by Paul-Carter
 Sun Jan 13, 2019 10:07 am
I have recently purchased an RB145 1988 and am working through a bit of a refurb ( see "Hinomania")
I come to the electrics.
I want as much independence as possible. The existing battery was a very tired 120AH lead acid which I have replaced with an AGM of the same capacity for the reason that adding more will be quite a big exercise, the only place I can think of is to suspend it underneath somewhere. So I have decided to come at the problem from two other directions first.
1, add two more 100w solar panel to the existing one which I assume to be 80 -100 will add more if necessary
2, reduce existing load as much as possible with LED lights everywhere.
This all rotates around that big question how much?
There must be some sweet spot where demand, storage capacity and input balance.
your opinions greatly appreciated
I am even giving thought to a small fold down 200-300w wind unit to help on cloudy days and at night
 #148073  by Derb
 Sun Jan 13, 2019 10:54 am
With regard to wind generators - all vanners I have spoken to with these would not go down that road again (including one bloke who sold them! Most of the units for sale have "undervoltage/overvoltage" cutouts to accommodate regulators and given our flukey winds they spend more time off than generating.
 #148074  by petercw
 Sun Jan 13, 2019 12:02 pm
I'm not an expert but everything I have read says more of everything ..that's more battery as you can get and more solar panel power as you can put up but perhaps it would be best to remove the old panel and put new panel in its place as Solar panels have got cheaper and work better than the older ones.. in my opinion.
I have 200amphrs and 160w solar and I run a tv at night and a12v fridge, but have back up with my alternator when driving.. Good for summer but if winter is your thing then more solar and more battery would be needed.
 #148127  by Neddy
 Mon Jan 14, 2019 1:50 pm
Paul-Carter wrote:
Sun Jan 13, 2019 10:07 am
How much?
There must be some sweet spot where demand, storage capacity and input balance.
There certainly is a battery capacity "sweet spot" for any given installation. A battery that is too small will have a shorter life and, while cheaper, will need more frequent replacement. A battery that is too big will die of old age long before it wears out. The most most cost-effective battery capacity can be calculated for any given nightly draw-down. A battery smaller or larger that this will cost more to run. For example…..
Say an installation has an average nightly battery draw-down of 25 AmpHours.
A 55Ah battery would be too small and have a lifespan of just 3.6 years at a cost of $57/year.
A 600Ah battery would be too big and die of old age at 10 years having cost $190/year.
A 120Ah battery is the most cost-effective option, lasting 8.9 years at a cost of $44/year.

A bigger installation might have an average nightly battery draw-down of, say, 40 AmpHours.
A 55Ah battery would be much too small and have a lifetime of just 2.1 years at a cost of $99/year.
A 600Ah battery would be too big and die of old age at 10 years having cost $190/year.
A 200Ah battery is the most cost-effective solution, lasting 9 years at a cost of $70/year.

You should do your own, individual calculations. Here is a battery life-cycle graph. The figures will vary from brand to brand but these are fairly typical of a reasonable quality deep-cycle AGM battery.
There is no equivalent “sweet spot” to be found for solar panels.
More is better, that’s all. Most of us end up simply mounting as much as we can on the limited amount of roof-top real estate we have available.

 #148146  by Kumarakid
 Tue Jan 15, 2019 12:34 am
Hey Paul. Well just to add my 2 cents worth I am also a newish owner of a 1985 RB145 and purchased it with an 80watt panel & 150ah battery which ran 3 led lights, a car stereo and water pump, fridge was a 3way.
I replaced the fridge with a 12volt one, added a 12volt tv and a couple of double usb charging points, lpg/c02 sensor. I added a second complete solar setup to the existing one with a 260watt panel and mppt 30amp controller. I replaced the single 12volt 150ah battery with 2 x 6volt 286ah batteries which fitted snuggly in the same spot being a cage slung up under the right hand side of the bus. Both solar setups are charging the same common batteries. Obviously being summer this is working very well but I think may fall short in winter so still have the option and room to swap out the 80watt panel for another 260watt. I am not sure then if my battery set up will be a little light. All the very best Rog.
 #148151  by Skiwi
 Tue Jan 15, 2019 7:38 am
All I know is I've seen plenty of posts on here about getting more solar and batteries and none about needing to decrease their capacity ;)

I'm sure their is a "sweet spot" but unless money is tight I'd recommend you are generous with your math, its amazing how many must have electrical appliances you will find if you have a little spare energy capacity ;)

Also how you use the bus will influence your set-up, are you going full-time or holidaying?
We use our for holidaying and sometimes for work, we have been very happy with how our energy performs, but we haven't spent a month in the snow under cloudy skies etc..

Check my signature for our solar set-up. What it doesn't mention is that we also have a 24-12v step-down transformer that kicks in to top up our house batteries when required if the bus is running, and a 240v shore charger that can also help for the very rare times we are in a powered site.

We have a few high draw items but to date we have never gone below about 80% capacity.

 #148155  by Neddy
 Tue Jan 15, 2019 9:37 am
Paul and Rog, more than anything else, you both need to fit a Battery Monitor. Without one, you can only guess as to your solar and battery needs. For what it's worth, my take is that you are both focussing too much on battery capacity and need to place greater emphasis on power production.

 #148165  by Sarmajor
 Tue Jan 15, 2019 12:34 pm
Just my $0.02 worth.
I installed a small solar system for a Garage / Batch and all was good with it meeting all of their needs.
After about 6 months the customer (a friend) called in to see us and mentioned that he though that there was something wrong as his battery’s were not charging up as much as they used to.

We spoke for a while and said that we would call in next time we were up his way.

A coupe of days later he came back in looking a bit sheepish. He had gone home and had a good look at things and worked out that two things had happened.
1, The trees had grown a bit.
2, More importantly it was now mid winter in the winter less north and the sun was a lot lower in the sky making those trees seem even taller to the solar system.

SO generation is very important, because if you cant fill the batteries effectively especially when parked up for a while then you either have to start the vehicle or run a aux generator.

Solar power stations in remote Pacific Islands are designed to operate for several days of reduced generation due to weather events before the standby generator has to kick in and charge the batteries and run the connected load as well.

The posting that pointed out the sweet spot for batteries makes very valid points and bigger is not always better especially if you lack the ability to fully charge those big batteries.

Given the cost per watt for solar the putting biggest panels that you can fit on the roof make sense.
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