solar/battery capacity.

Smooth Hound · solar/battery capacity.

i have a 300 amp hour 12v forklift battery, i want to use it for, basic stuff to keep the electric down, lap top, radio, couple of lights,tv that sort of thing.
does anyone know what sort of solar panel would be good for it, i would like to be able to be able to move it around without it breaking

Martin

you lucky thing - that sounds like a lovely battery!

OK, renewable design parameters here we come............. a 300 amp/hr battery should be charged at a maximum rate of 10% of it's capacity, probably 5% as an optimum, so you're talking 15-30 amps charge.
If you have a 12v panel giving 100w, that'll give you circa 8 amps full tilt - your battery could cope quite happily with anything up to around 400 watts of pv panel (at around £4 per watt, that's about £1600-worth!)

A good rule of thumb in designing battery systems is "10%" for nearly everything - maximum charging rate, 10% of the battery capacity, amount to take each day - 10%, etc........SO, if you planned to take circa 30 amp/hrs per day you'd be around the right level to give the battery a really long life
(the more you take out regularly, the faster the battery knackers out- the usual sums show "10%" is a good safe level).
You then need to put what you use back in - in the height of summer, a pv panel will give roughly 6 times it's rating per day (that 100w panel would give around 50 amp/hrs per day), in winter, around a sixth of that - 8amp/hrs
-Which is why many people go for pv/wind turbine combinations - if properly sited, the turbine can make up for the pv panels shortcomings in midwinter..........
-probably all as clear as mud!

Smooth Hound

so a 100 watt one would be 400 quid, would that be sufficient for me to start with, then as i can, add another one, oh and is it wise to buy a second hand one

IainC

TBH, unless you are getting a *healthy* discount (or getting it free) then IMO you'd be better with a newer one. Solar panels have only been getting better and better as the years go by.

Maplins often have some good deals on solar panels, ranging from the 12-13W ones and upwards.

Sounds like a crackin' battery to have got hold of though.

Martin

I'm prejudiced (they're friends of mine), I recommend the Navitron pv panels, they are good value, and really well made - you can probably pick up something off Fleabay a smidgeon cheaper, but these are the dog's danglies!

I've attached a picture showing the nice solid ally frame, with my own idea for mounting - simple - L-section angled ally bolted to the panel, then use a piece of the same L-section on a wooden block - then bolt or padlock the l-section together - nice and solid, and relatively cheap!
I once bought an el cheapo panel that was essentially 2 bits of glass edged with placcy, and ended up having to build a frame somewhat akin to a window frame before I could mount it safely....

[/img]

Martin

I'm prejudiced (they're friends of mine), I recommend the Navitron pv panels, they are good value, and really well made - you can probably pick up something off Fleabay a smidgeon cheaper, but these are the dog's danglies!

I've attached a picture showing the nice solid ally frame, with my own idea for mounting - simple - L-section angled ally bolted to the panel, then use a piece of the same L-section on a wooden block - then bolt or padlock the l-section together - nice and solid, and relatively cheap!
I once bought an el cheapo panel that was essentially 2 bits of glass edged with placcy, and ended up having to build a frame somewhat akin to a window frame before I could mount it safely....

[/img]

IainC

Smooth Hound

navitron is a good site and ive been looking at it,

what are the dimensions of a 100w panel?

Martin

ps, the panel shown in the photograph is a 20 watter, which has been raced, rallied and festivalled, and is still going strong.........it's been rail mounted on my shed, left propped up against the back of the shed for months, and has at times been unceremoniously mounted on my caravan roof using heavy-duty velcro!

Smooth Hound

looks good, i need to know the measurements of that one then, and how much for a new 20 watt one, would that be 80 pounds

IainC

Smooth Hound

martin

Martin

110w panel is 1470 x 680 in foreign (haven't a clue what that is in English!)
around £418 plus carriage -

Smooth Hound

so about 4 and a half ft by 2 and a bit

thats not so big, i could put 2 of them on the van roof

Martin

and the 20w is either 610 x 291mm or 525 x 350mm, and around £76 plus carriage. To be honest, I could flog them to you through my own company, and take a tiny profit, but it's barking bats to have Navitron send them to me in Sussex from Rutland, then punt them back up to the frozen wastes of the north - deal direct, it's greener!

Smooth Hound

ta, think thats the way ill have to do it, just keep adding as i can afford it, i have about a1000 amphours of forklift batteries , so alot of potential eventually, maybe on day ill be able to phone up the leccy board and say, come and switch off that power

, what sort of kw age could i use with a 1000 amp hours, providing i had the stuff to keep it charged of course

Martin

it's all bally sums...........

Here's the theory - you do the sums!
If you take the "10%" rule pretty seriously you won't go far wrong - with 1000 amps of battery, you can draw 100 amp/hrs without stressing it at all,
which would enable you for instance to run a tv, computer, radio, and energy saving bulbs for a day without any problems (bearing in mind you need to replenish each day what you've taken out).
Biggest mistake is buying a thumping great 2kw inverter, and trying to run fridges, deep freezers and washing machines off the bank........unless you've got a seriously big bank, a hefty turbine, and a few kw of pv panels, I'd go for a "only use electricity where nothing else can do the job" philosophy - that way you can survive well off a relatively small and affordable system.
(I've done the sums for people who want to run a fridge freezer off pv panels - just to do that can mean you need to spend another £5,000 on the system just to make up the ginormous gobbets of power they consume)

To expand on the "10%" draw thing -
A brand new el cheapo leisure battery is probably rated at something like "200 cycles to 50% DOD" - in simple terms, that means you can discharge half it's capacity 200 times before it'll keel over stone dead, and roughly pro rata (DOD is depth of discharge)
SO, if you were a plonker, and bought a brand new caravan battery, and used it every day, and used 50% of it's charge, in about 7 months time, you'd be buying a new battery..............if you used 10%, it would probably last 5 times as long (around 3 years).
Your forklift battery is designed to really take a bashing (probably something like 5 or 600 cycles to 80% DOD, so if you took the nominal 10%, you could be looking at 15 years or more of useful life........

-hope that helps a bit!

Smooth Hound

sounds good,