Solar panel for sale in maplins for £69.99 any good?

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Solar panel for sale in maplins for £69.99 any good?

Post: # 48097Post Andy Hamilton »

Walked past Maplins yesterday and glanced in, out of the corner of my eye I saw a solar panel on closer inspection it was this one it's 5w is that enough to power anything, or £70 down the drain?
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Post: # 48106Post Martin »

far be it from me to yell "rip-off'".............. :wink:
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Post: # 48110Post Andy Hamilton »

BLimey that is a bit of a price difference, still though is it of much use? 5w does not sound like much power. I imagine if you want to use it on a caravan or something it could be of use, but I would use it to charge up a laptop. COuld a cell that small be an alternative to the mains?
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thomas533

Post: # 48112Post thomas533 »

On my sailboat I use a 10w to keep my battery charged. I only need my battery to power my radio a few hours a week and 10watts of navigation lights a few times a year. On occation I plug in my inverter and am able to use a mains device like a power tool or a big work light. For this type of purpose a small cell like that works great. You can also use it to charge a cell phone or your digital camera.

You can see my PV panel below...
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Post: # 48119Post pskipper »

So what sort of solar panel would you need to power a laptop?

thomas533

Post: # 48124Post thomas533 »

My laptop power supply says the output power to the laptop is 1.9 amps at 24.5volts. Watts = Volts x Amps, so I'd need about 47 watts. Solar panels always put their peak effeciency as their wattage so my solar panel will need to have about at output 20% higher. Also since I only get 3-5 hours of good sunlight per day I'd need a battery that can store and supply 47 watts for my 5 hours a day of computer usage and only discharge the battery 60%-80% so as not to cause damage to the battery. On the worst day, I need to gather 250 watts in three hours. Taking into account the 20% effeciency loss I'm going to aim for 320 watt panel with a 100 amp/hour battery.

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Post: # 48125Post Martin »

unfortunately, powering a laptop is not that straightforward!........Most laptops demand something like 19 volts to work, which is usually supplied by a mains transformer unit - a few work direct off 12v, but not many! If you squint hard at the consumption figures stamped on them, they can draw twice the wattage from the mains than comes out of the other end to power the laptop!
(probably somewhere around 100 watts!) - that's what it'll need to draw from the battery! You then have the problem of turning the 12v battery voltage into ac 240v - for which you'll need an inverter (allow 15% for losses)...... :cooldude:
80% taken regularly out of the battery will knacker it out in double-quick time - a conventional lead-acid battery would probably last about a week if repeatedly discharged to that level! - Even top of the range gel batteries at double the price will only take around 300 cycles to 80% .
Also, the thought of 320 watts hurtling into a battery of only 100 amps is fairly frightening too - the rule of thumb is that max charge current shouldn't exceed 10% of the bank's capacity - 320 watts divided by 12 is around 30 amps - you'll need a minimum battery bank of 300 amp/hrs, or you'll fry them! :dave:
you're probably now even more confused! :wink:
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Post: # 48141Post Andy Hamilton »

So the simple anwser is don't charge your laptop off a small solar panel?
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Post: # 48142Post Martin »

in a word - no! :?
A 5w panel would probably give enough power on a summer's day for around half and hour - you really need something a lot larger! Do be careful - there are some folding panels sold as "laptop chargers" for a hefty price - check the actual wattage of the panels they comprise - they are often a very expensive way of buying a couple of smallish panels! :wink:
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Post: # 48145Post Muddypause »

Martin, I'm a bit puzzled by what you seem to be suggesting. Perhaps I've misunderstood - are you saying that the best way to run a laptop from rechargeable batteries is to put the 12v batteries through an inverter, which will change 12v DC into 240v AC, then have the laptop transform it back down to 19v DC. Given all the losses at every stage, this would seem a terribly inefficient approach.

How about two solar cells, charging two 12 volt batteries (or one solar cell charging them successively, if time is not an issue), which then, connected in series, run the laptop (through a voltage regulator if necessay to stabalise it down to 19v - though the laptop may already have an adequate one onboard). In fact with a bit of ingenuity, charging pairs of 6v batteries, which are then used in trios, aiming at providing 18v, would prolly do the job and may be a little more efficient.

I take your other points about charging rates, etc. a 5w charger would probably be incapable of doing the job unless you only used the laptop once a month.
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Post: # 48150Post Martin »

Going the inverter/stepdown transformer route is certainly wasteful of energy, but is very often used because it saves having dedicated circuitry to supply the laptop with 19v - it's also fairly cheap, a £20 inverter will do the job.
The other way you could go about it is to obtain a special "designed for 12v usage" computer power supply unit - there are a few laptop manufacturers who supply them, and I have seen some "universal" models, but they are fairly pricey! :dave:
One thing I have come across is a chap who has bought a selection of 12v and 240v chargers and a cheapie inverter, and while he's driving around, charges all sorts of things! :geek:
http://solarwind.org.uk - a small company in Sussex sourcing, supplying, and fitting alternative energy products.
Amateurs encouraged - very keen prices and friendly helpful service!

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