electrical calculations and stuff...

[Big Al]

Ok good people.

I'm wanting to go over to solar PV for a few things and I need help sorting out the right equipment. I do a lot of reading on the net but the mild dyslexia gives me grieff at times.

We are all on laptops now and the batteries only last about 2 hours, even less if they play music... (son = slipknot = headaches... ) so I'm looking to power these laptops by solar instead of the chargers / power packs. How do I work out the size of the panel I would need if one of the chargers is 19 v and amps is 4.74. Also would this be a good time to buy an inverter. Looking on the maplins site the blurb for this inverter http://www.maplin.co.uk/Module.aspx?Mod ... 8#features
says that you can run two items off it at the same time such as laptops.

Next question is this. Once I get the correct wattage solar panel do I conect the wires direct to the battery then also conect the inverter from the same battery and then into the inverter I plug the laptop chargers......

Sorry for the questions but I really need help on this one. Ask me about evacuated tubes, thermal stores, internal insulation and wood burning stoves and I'm ok but electrics.....Being eco green isn't all plain sailing..

Take care,

Big Al

[Clara]

If you are just looking to use them to charge things you can get little solar gadgets for your laptop, ipod, mobile that would work out far far better value, even if you had to buy more than one to keep everyone connected and listening to slipknot

http://www.nigelsecostore.com/acatalog/Freeloader.html

That was the first thing I managed to google up, not a recommendation as I have no experience but just so you get the idea.

Really if you're not planning on using solar in a big way then I would go with something like this, invertors (good ones that work well) and batteries cost LOTS......trust me I just spent 15K on the whole caboodle and I still have to go without some things that you would consider essential (and I have a shedload more sunlight than you guys).

[Clara]

Don't think that gadget was exactly what I meant but there is something out there that will do the job cheaper than a standard installation......surely.......

[Odsox]

OK, I'll give it my best shot.

First off, for the laptop you specified you need a power supply that can deliver 19 x 4.74 = 90 watts, so if your other laptops are similar you need 90 x number of laptops = final wattage.
The problem with laptops are the awkward voltage they need. All the cheap PV arrays are 12 volts and although I'm sure you could charge your laptop's battery at 24v, I wouldn't recommend you try it just on my say so.
That Freeloader gadget that a lot of people are raving about only gives 120 mA at I assume is 5 volts (it doesn't say) which is a meagre 0.6 watts, so not really an option.
You could use the inverter that you mentioned but that seems a bit inefficient ... 12 volt PV > battery > 220 volt inverter > 19 volt charger

Looking at Maplins they seem to have the answer for your situation, see .. http://www.maplin.co.uk/Module.aspx?Mod ... r&doy=12m8

It looks like all you need then is a PV that gives you 1.5 amps or 18 watts to feed the gizmo (throw away the mains adaptor or keep it for when the sun doesn't shine)

Looks a bit of an expensive route though as an 18 watt PV panel is £150 although you can probably find cheaper ones, plus the output quoted is almost certainly at maximum summer sunlight, to be sure of it working halfway decent you really need to double the output to 40 watts.

[contadino]

Like others have said, there are built-for-purpose solar laptop chargers which may do the job.

However, if you can see yourself wanting to running other appliances (reading lights, etc..) by solar in the future, you're probably better off getting the parts and wiring it up yourself. It sounds like you're up to speed on how it all plugs together. By going this route, you'll be able to add other panels, batteries, etc.. in the future.

At this point, it may be worth investing in one of those electricity consumption units so you can see exactly how much each computer draws. It'll enable you to size your batteries & panel much better. Laptops don't draw a constant current - it goes up when the battery is charging, or the DVD or hard drives are in heavy use, and even when the processor's doing lots of work. The fan makes quite a difference too.

[Big Al]

Been away a bit so sorry for the late past. Thanks to all for the replies, I'll be onto it asap.