NEEPS

Martin · Neepster Joined: 16 Sep 2007 Posts: 663

I received the following query from a board member following the posts about the "micro renewables fair", and thought it best to answer it "in public"
The question was "We need to get a light in a mobile field shelter. Are there any solar versions worth bothering with or should I just go down the car battery route? "

Like everything, nothing is EVER that simple....... here's a long, rambling, and hopefully complete answer......
Firstly, always "start backwards" - decide for a start how much light you need, for how long, how often, and during which seasons........THEN look for the pragmatic solution.......
If, for instance you need minimal lighting for a few minutes a day throughout the year, you MAY just scrape by with one of the proprietary "solar shed lights", but be aware that the light output is not great, the batteries don't last long, and worst of all, they get least charge in winter, usually when you need most light.... They're "ok" as an "entry light" to enable you to find a feed bin or similar, but little else - they are pretty cheap, especially if wait for the sales (£20-30)
Next there's the "pukka solar panel" route - sometimes you can pick up a "12v car charger panel" with built-in diode (stops it emptying the battery overnight), they're usually 1 or 2 watts, and can be used to keep a small battery (car or mobility scooter battery) charged, but again, in winter, when you most need the light, you'll get the least charge........
Then there's the "do it properly route" - here's the sums for a simple, and properly specified system - 20w pv panel, circa £70, simple controller £15
Gel "scooter battery" £50 - £60 -from which on a winter's day, you should be able to run a small (8w) fluorescent "inspection lamp" ,for 2-3 hours (every day), and the battery should never go flat (in midsummer, you could run the light for up to 12v hours per day, as the panel will put in some 6 times more power during the summer than midwinter)........

A quick note on "car batteries" - the stock advice for this sort of use is "don't" - they really aren't designed for this sort of use, and if you deeply discharge them they WILL knacker out really fast (sometimes in one or two "flattenings") - BUT, being pragmatic, if you can get hold of a good car battery for a fiver, keep it near fully charged, take very little out of it before recharge (no more than 10% of it's capacity), and it may do the job for a while. If you're on a budget, an "ex mobility" scooter gel battery in good nick is a good find, they'll take deeper discharge safely (but still never take more than 50% of it's capacity)- EVER........

What would I do? (being a pragmatist), invest in a cheap voltmeter (under a fiver at a pound shop), then start scouring boot sales, markets etc for good used mobility gel batteries, leisure batteries, car batteries...... if it's showing over 12v, buy it, 11v buy it if it's cheap, under that, probably best used as a doorstop...... At the same sales, look for an "automatic" 12v car
charger (usually a fiver or so) - aim for 2 batteries, and one charger - take them home, and charge each of them until they're showing a decent voltage (a GOOD battery should take charging up to 14.5 or more volts)- you've now got your battery system for around £20 all-in
Then do some sums - say you've got a car battery that's taken a full charge, and it's rated at 40 amp/hrs - aim to use 10% of it's capacity before swapping it for the other one - 4 amp/hrs - which at 12 volts is 48watt/hours - if you're using an 8w light, that's 6 hours.......

During the last fortnight, Lidl have been flogging "Electronic shop floor lamps" (!2v fluorescent) with a long lead "cigar lighter" adapter for the princely sum of £2.99 - couple of those (one as a spare), you have light in your remote shelter - just swap the batteries at the right time, and immediately recharge, and they should last.....
Hope that helps!
_________________
http://solarwind.org.uk

IainC · Posted: Fri Aug 07, 2009 8:36 pm Post subject:

Might also be worth keeping an eye on the likes of Maplins (or anyone else that can be suggested?) as sometimes solar panels/briefcases can be had for almost half price. I bought a 12W, 12V panel for about £40 IIRC. Use it to charge the battery in the discovery (which I'm finally getting shot of now... start queuing here... or not

). Works pretty well, and if I was looking to put lights into a barn/garage without running mains cables there, then with the right battery, I'd give it a good go using the same panel.

Martin · Neepster Joined: 16 Sep 2007 Posts: 663

It's all a "sums thing" - ignoring losses, your 12w panel on a winter's day will on average supply an "hour's worth" of charge - 1 amp/hr (12 watt/hrs) - which'll run the "example" 8w light for about 90 minutes, sod's law, it'll do circa 6 times that in midsummer - enough for 9 hours or so.......

_________________
http://solarwind.org.uk

IainC · Posted: Fri Aug 07, 2009 10:38 pm Post subject:

Yeah... comes down to how you use the battery.

If it's fully charged as you enter the lower "sunny days" then you should manage a while with it.

Obviously by the middle of winter-ish then you are probably close to stuff storage wise.

pete_inthehills · Posted: Sat Aug 08, 2009 2:48 pm Post subject:

I've got a solar panel charging a battery that runs a light in our field shelter. I put it up last autumn and it survived the snows and -18C of feb.

It not entirely elegant as the battery is in a plastic box on the side of the shelter to make it water proof. The panel is on a wooden board nailed to the top, but it does a good job.

It was a cheap kit from ebay. You had to buy the battery yourself, but everything else was in the kit.

pete
inthehills
_________________
Pete
www.beggshillbothy.co.uk

IainC · Posted: Sun Aug 09, 2009 8:35 pm Post subject:

We have a solar shed light, £20 from the place we got the shed from, similar ones available at Maplins, etc for similar prices.

Seems to have worked okay for us so far, and as it uses LED lights, its bright enough, and seems to last long enough. Works on a proximity sensor as well which is angled towards the house, so goes off more often than we need it to.

It's dead handy for coming home late though, lets you see the door and lock for getting into the house, even though it's set on the shed.

JamesB · Posted: Wed Sep 09, 2009 6:59 am Post subject: an alternative

also worth considering do you need a fixed light?

the niMH or NIcad batteries used in portable tools work really well with a torch (flourescent are best, i keep looking for LED ones but not seen them). if you get a decent make such as dewalt with an intelligent charger then its works really well. you can get torches with small flourscent tubes which you can place on a surface.

James
_________________
JamesB
Mintlaw area