PV to run a laptop - recommendations

MrG · Post by **MrG** » 06 Jul 2011, 08:59

That fits in well with what I've been thinking this morning, which is double up the battery (since this is much cheaper) but not the panel. Since the doubling up is for emergency use and you said the battery will at a push i.e. an infrequent deep discharge, give me a week of power.

A spare battery with a week of power is plenty of as you say 'thinking time' to get the other one hooked up to the genny, or the vehicle or god forbid get a train back to civilastion and actually go to work!

Plus the second solar panel mate I mentioned in the bove post doesn't sell panels he rents them (I think) for events and stuff. So that's sorted isn't it. Rent a 220W (or thereabouts) panel for a couple of months, buy two 200 A/H deep cycle batterys, two car chargers (one spare) and I reckon 3 spare laptop batterys because that gives me a day of thinking time without even having to worry about a 12V system.

I'll use it as a couple of months to learn about using 12V renewables as well as getting my head together.

Just see how it goes for a while and who knows maybe I'll end up staying for the winter too.

Post by **adam2** » 06 Jul 2011, 10:21

Sounds good, but 200 A/H deep cycle batteries are not that common, and are challenging for one person to move.
You might do better with 4 batteries each of 100 A/H as these are widely sold and easily handled.
Each battery should work the laptop for 2 days (if deeply discharged which is unwise on a regular basis)
4 batteries therefore give 8 days, which at 4 days a week is 2 weeks without any charging.

220 watts of PV should keep the batteries charged, and even if it does not keep up with use, it will greatly delay running out.
If the solar input is only half of that expected, the batteries should last a month before any external charging is needed.

MrG · Post by **MrG** » 06 Jul 2011, 10:30

Yeah but 80% then is 80 A/H so I can only run 'off the battery' for half a day.. which means I'm basically running off the panel with the battery as a buffer.

With a 200A/H I've got a days use straight from the battery without damaging it.

But that's how I should be doing it then right? Having both the laptop and the panel (via charge controller) connected to the battery at the same time.

Or take 20 A/H out of a battery (half a day) swithch to the other battery and put the first one on charge... then the next day swithc again.. etc?

So how long can you leave the deep cycle battery charged up for without having to discharge or reuse it?

220 watts of PV should keep the batteries charged, and even if it does not keep up with use, it will greatly delay running out.
If the solar input is only half of that expected, the batteries should last a month before any external charging is needed.

That sounds perfect thanks adam

DominicJ · Post by **DominicJ** » 06 Jul 2011, 10:38

I think he means two 100ah batteries instead of 1 200ah battery.
These things are seriously heavy.

Either way, an 80% discharge is 160ah

But in reality, thats not really what would happen.
Everything should be connected.
Panel into battery, battery into laptop.

Laptop drains battery, but at the same time, panel charges battery.
You'd only suffer any discharge if it was cloudy, or you used the laptop at night.

Post by **adam2** » 06 Jul 2011, 10:56

I would connect the batteries in two pairs.

Charge one pair from the mains or generator at the start of the project and leave these to one side as spares or reserves.

Connect the other pair to the PV module, via a fuse and a charge controller. Power the laptop from this pair of batteries via a fuse and the car power lead.
Hopefully this will supply all your needs, whilst keeping one fully charged pair of batteries in reserve for at least a weeks use if something goes wrong.

Every few weeks change the two pairs of batteries over so as to keep both in good condition.
It is very important to make this changeover ONLY when the batteries in use are known to be fully charged. DONT change over the batteries if the ones in use are not full. The idea is to ensure that the spare pair of batteries are allways full or nearly so.

If after a week or two, the batteries in use are slowly running down because the solar input was less than hoped for, then consider charging them from the generator or a vehicle. When fully charged, put aside as the spare pair and use the others.

Some complex automatic system could no doubt be devised, but I prefer the simplicity of manualy changing batteries and allways having a fully charged pair in reserve.

Obviously in an emergency, fully discharge all batteries rather than risk your job.
Once you start use of the reserve pair, then it is time to think about mending the generator, buying a cheap generator, charging from a vehicle etc.

The reserve pair of batteries might never be needed but should be regarded as insurance if your job depends on power for laptop.

A fully charged battery should remain in good condition for a couple of months, after which time it will no longer be full, but should retain a large percentage of the full charge.
A fully discharged battery may be damaged if not charged in a day or two.

MrG · Post by **MrG** » 06 Jul 2011, 11:46

Brilliant. thanks Adam.

I'll phone solar panel guy tonight and ask him about renting a panel. I'll ask him if he knows a good place to get leisure batteries as well.

sam_uk · Post by **sam_uk** » 06 Jul 2011, 20:47

I am considering one of these to compliment a very small solar system
http://www.alu-windrad.de/windmillengl.htm

Longevity may be an issue, but you never know with German Engineers, it may be a gem.

It is certainly the cheapest 12v wind gen I have seen

GlynG · Post by **GlynG** » 06 Jul 2011, 21:29

You could always consider one of those $100 laptops they make for the Africans? They only use 5-8 watts and can be powered by solar or winding them up.

If you do keep your existing laptop consider swapping the hard drive for a solid state drive as these can use less energy (shop around for a specifically low energy one).

JohnB · Post by **JohnB** » 07 Jul 2011, 17:21

My solar powered Acer is currently drawing between 1.4 and 2.0 amps. When I'm off grid I remove the battery, as it seems pointless charging a battery from a battery. In a while I'll need to charge my phone to stay online, but that doesn't draw much.

I've got a 60w PV module flat on my van roof, and a 100ah leisure battery, that also runs my mostly LED lighting, and stereo. I've got a cheap square wave inverter that I use for my printer, as it needs 35 volts. I've got a Steca PR1010 charge controller, so I can double the PV if I want to (that's all that will fit on the roof!).

This isn't enough to provide all my power, as the battery gets it's biggest charge from the alternator when I'm travelling, and won't keep it going 8 hours every day. The van last moved on Monday, and the PV will keep a fully charged battery going for a good number of days. I hope it will keep me going until at least Sunday, as I've got no plans to move before then!

DominicJ · Post by **DominicJ** » 08 Jul 2011, 08:15

I thought you were in a house now?

JohnB · Post by **JohnB** » 08 Jul 2011, 10:50

DominicJ wrote:I thought you were in a house now?

I own a house (:( ), but that doesn't mean I live in it

.

MrG · Post by **MrG** » 18 Jul 2011, 18:06

Adam.. when I asked my mate for a 220W solar panel (actually I asked for 250W) he said the bigger ones were cheap now (£1 a watt like I said) but that they were all at too high a voltage for 12V charging.. that they were all suitable for grid connection but not really off grid application like I want.

I think he said they were 24V? Which still wouldn't be mains voltage. What's he on about?

Sorry if not making much sense.. slightly pissed.. posting from a pub in Glasgow

hardworkinghippy · Post by **hardworkinghippy** » 18 Jul 2011, 20:14

Mr G, which pub ?

If the panels are a really good deal then you can buy a dropper to convert 24v to 12v. They're not expensive, so buy two in case one breaks down.

Alternatively you can probably buy an adaptor to covert 24v DC to the voltage of your laptop. (Usually 19v)

Is it possible for him to sell me some panels at that price ?

Post by **adam2** » 19 Jul 2011, 12:20

MrG wrote:Adam.. when I asked my mate for a 220W solar panel (actually I asked for 250W) he said the bigger ones were cheap now (£1 a watt like I said) but that they were all at too high a voltage for 12V charging.. that they were all suitable for grid connection but not really off grid application like I want.

I think he said they were 24V? Which still wouldn't be mains voltage. What's he on about?

Sorry if not making much sense.. slightly pissed.. posting from a pub in Glasgow

Larger PV modules are often higher voltage, often about 35 volts, these are primarily intended for use in series for grid tied applications, but can also be used for charging 24 volt batteries.

The simplest answer is to obtain modules with a 17/18 volt output, intended for charging 12 volt batteries.
If this is not feasible, then use the higher voltage module and a 24 volt charge controller to charge a 24 volt battery.
Power the laptop from this 24 volt battery by means of a suitable power supply, as sold for vehicle use in a 24 volt vehicle.
This would be slightly more efficient than the 12 volt system proposed, but has the drawback that a 24 volt power lead for your laptop is probably more expensive and less available than a 12 volt one.
Charging from a 12 volt vehicle will be more complex.

Converters to step down from 24 volts to 12 volts are available but add another layer of cost, complexity, and another point of failure.

hardworkinghippy · Post by **hardworkinghippy** » 19 Jul 2011, 13:29

I've been using this laptop I'm posting here with from a cheapo dropper from a 24v system which has been running OK for the past three years. (Touch wood.)

If you get a dropper which can handle the amperage it should be OK but as I said, buy two - just in case.

A 24v system also means that you can use slightly thinner wiring and you don't beak your fingernails when you're wiring it up and you can actually get the wires into all the connectors without swearing too much.