Running a laptop or and ipad from solar panels

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Running a laptop or and ipad from solar panels
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Penny Outskirts

Joined: 18 Sep 2005
Posts: 23385
Location: Planet, not on the....

Posted: Fri Aug 30, 13 11:16 am Post subject:

mark wrote:

2) If using laptop try to use in car laptop pwer supply that runs off 12V rather than mains inverter withnormal power supply - you will save double inffeciency of changing 12 V up to 240 V in the inverter and then back down to around 19V the laptop uses - you just do one conversion instead .

I think all the people I know who use the laptop on a solar charged leisure battery use it off 12v.

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Fri Aug 30, 13 12:33 pm Post subject:

Mark your post is so wrong / negative its hard to know where to start.

Remarks like solar can only trickle charge or keep it charged when not in use are completely wrong.

Would you consider 80 amps of charge a trickle? Would you consider 7 kWh per day just enough to stop self discharge?

May June & July are not the best months by a long margin.

Ours work well from March till well into late sept or early Oct. Ok Dec & Jan are dire. Peak months tend to be either side of the main summer months as the sun is strong yet the air temp is colder.

"they just are not up to keeping the battery topped up without a massive (and expensive) array"

really? 50p per watt for the panels will hardly break the bank.

Your comments are only valid when the install was done without due consideration to the actual needs or the budget not suitable for the requirements.

mark

Joined: 14 Jul 2005
Posts: 2191
Location: Leeds

Posted: Fri Aug 30, 13 2:15 pm Post subject:

I'm talking about wild camping here - for me in a tent that is not practical to have the sort of array you are talking about! - and it is hard to keep a ground mounted panel in the sun all day - as shade from tents and cars get in the way if you don't move it!

But even in a camper van where they can be mounted on the roof there are issues - often theroetical figures assume - the van is parked away from trees and building so the panel is not shaded! - in my experience that is just not always possible!

I'm not being negative- I'm planning 3 months living camping in europe next year where these facilities will matter to me! So I have been researching this widely and really wanted to use solar and have talking to others about the actual NOT theoretical performance they achieve. However having looked at the options I have come to the conclusion I can't rely on solar charging for all my needs alone - so my priority in my budget is to increase my storage so i can last between charges.. (most camping leisure batteries don't like being taken below around 40% on a regular basis and without extra storage that is a real possibility if you get an overcast or rainy week and use a laptop .

I am presuming by your remarks about the install you are talking about a more permanent array optimally placed not one that has to sit wherever you can find to park your van/pitch your tent - and where placement may also have to meet other needs like security when you are out all day when it can't be fixed like in a home!

I think solar is very useful in fixed situations - but I've always been a little disapointed by what can be achieved in real life situation when camping in temperate latitudes. It does hlep but not enough

My laptop with 17" screen uses about 80 watt -

If you know a truly portable light weigh small packing solution that can meet my needs I'd love to hear about it !!

mark

Joined: 14 Jul 2005
Posts: 2191
Location: Leeds

Posted: Fri Aug 30, 13 2:23 pm Post subject:

just to add to the above i am also concerned that the use of solar panels just for camping trips tips the the ecological and economic balance the wrong way.

there is a break even point economically and in terms of carbon footprint / eco impact that you need to reach before a solar panel is better than spending a night in a campsite to get a hookup replenish you leisure batteries.

For the same price as a panel i can substantially increase my battery storage which keeps me more independent !
For installations used all day/ all year the eco and financial break even point is reached much sooner!

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Fri Aug 30, 13 4:21 pm Post subject:

I know of many mobile installs that out perform (over a year) my fixed install.

At least they have the option to move if the weather is bad or there is a high horizon (like I suffer from due to the trees).

The primary issue is that people spend what they feel should be enough & not actually what is needed.

Wild camping = no tech for me.

I do agree that using stuff just for short holiday periods is just adding to the issue.

Bigger storage is ok but at some point you have to fill them up again. The more you have the more you need to refill & a bigger charge source is needed. Its all about balance.

You could easily pole mount a small array to be sited above the tent shade line. Depending on tent type you might even be able to fix it to the tent pole tops.

Edit to add, just spotted that you are going to be using a car. Fit the array to the roof rack & mount the bats in the boot. Simple to just plug the tent into the boot as needed. You could also then add in a split charger system to get the best of both worlds.

paul1963

Joined: 15 Nov 2010
Posts: 2161
Location: No longer active on the forum

Posted: Sat Aug 31, 13 6:43 am Post subject:

Chez wrote:

That was my conclusion when I looked in to it a few years ago, although I am now about to look at it all again in view of the camper van. As an aside, when we had arvo's vaio, it was the most power-hungry machine we have ever had.

Funnily enough Chez, that's what I use and I need a personal Drax power station to run it, only about a one hour battery life

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Sat Aug 31, 13 7:28 am Post subject:

paul1963 wrote:

Funnily enough Chez, that's what I use and I need a personal Drax power station to run it, only about a one hour battery life

Making changes in the power management can make lots of difference in how long it will run on a full charge.

Tarrel

Joined: 17 Nov 2012
Posts: 18
Location: Ross-shire, Scotland

Posted: Mon Sep 23, 13 6:56 pm Post subject:

FWIW, I put the power meter on my iPad charger yesterday while I charged the iPad from almost flat. The mains charger took 11W, and used a total of 0.04kWh to charge to full. (It's an iPad 3, which has double the battery capacity of the earlier iPads).

Ignoring inverter losses, you could therefore do this 30 times off a 100Ah battery. Or, another way of looking at it, a 40W solar panel in full sun for one hour would be enough to replace the battery charge used to fully charge the iPad.

Obviously one would be better off using a 12V charger rather than a mains one plus inverter.

HTH.

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Mon Sep 23, 13 8:39 pm Post subject:

Tarrel wrote:

Ignoring inverter losses, you could therefore do this 30 times off a 100Ah battery.

Well you could but you will soon kill the battery. Better to do less than 15 cycles & keep to 50% discharge max.

50% is the rule of thumb for cost effectiveness for recharging costs & battery replacement costs.

Using more will increase battery replacement costs but reduce recharge costs. Decreasing is will reduce battery replacement costs but increase recharging costs.

The above is valid for when the recharge has a cost so less valid when recharging with solar.

mark

Joined: 14 Jul 2005
Posts: 2191
Location: Leeds

Posted: Mon Sep 23, 13 8:55 pm Post subject:

the useable range of a leisure battery is about 40-50% of quoted theoretical capacity. They are not designed to be run to flat (you will wreck them if you do that) -and they will cease to power an inverter before they are fully empty in any case - they would certainly cease to power a laptop before this stage..

Inverters can never be assumed to be fully efficient - you are probably best estimating around 20% for a 12V inverter - worse if you then step it up again to power a laptop..and introduce a second ineficiency

I successfully recharge my tablet (7") phone and flying instruments on paragliding holidays for about a fortnight off my battery without recourse to solar power so its not a problem with tablets..

laptops are another matter though .. and can discharge a battery really quickly!

mark

Joined: 14 Jul 2005
Posts: 2191
Location: Leeds

Posted: Mon Sep 23, 13 9:25 pm Post subject:

On solar panels the quoted out put is what you can expect on sunny summer day in teh UK at noon if the panel is facing the sun.

In our long summers day the average day produces the equivalent of 4 such hours if we leave the panel out all day and it is facing the sun

In the shorter winter days with a lower sun we only get one hours worth if we leave the panel out all day!

So I reckon mid summer a panel can knock your battery up 13.31 Ah per day if you have it said up out of any shade and facing south or a quarter of that in the winter. ie it will take you over a week to recharge a 100Ah battery .
In reality that's hard to achieve unless its a roof mounted static installation - and it will never be achieved if you can't leave it out all day

That is why if you simply want more power and especially if you camp for a week or so in spring our autumn I recommend you are often better simply taking an extra battery fully charged - if you want to extend you battery life in the cheapest manner !

Of course if you like using solar go for it - but be aware solar panels that are packed away and not used for much of the year have a worse environmental impact than charging from the grid. It is only if you use them for longer ie on your roof at home that the environmental equations shifts in favour of solar.

Having said all that I think they a fun and really wish they were a more practical option!

Tarrel

Joined: 17 Nov 2012
Posts: 18
Location: Ross-shire, Scotland

Posted: Mon Sep 23, 13 10:44 pm Post subject:

RichardW wrote:

Tarrel wrote:

Ignoring inverter losses, you could therefore do this 30 times off a 100Ah battery.

Fair comment. I mentioned it more to give relative scale to the demand from the iPad compared to the capacity of even a fairly modest storage.

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Tue Sep 24, 13 7:17 am Post subject:

mark wrote:

On solar panels the quoted out put is what you can expect on sunny summer day in the UK at noon if the panel is facing the sun.

No its the rated output under fixed test conditions.

In our long summers day the average day produces the equivalent of 4 such hours if we leave the panel out all day and it is facing the sun

We are finding that in summer on a good day we get 6.6 times it peak rated output. So our 1.2kWp array produces 8kWh. In December & Jan we are lucky if we produce that much in a month due to the low sun & our high horizon. With no shading issues an hours worth per day would be about right.

In the shorter winter days with a lower sun we only get one hours worth if we leave the panel out all day!

So I reckon mid summer a panel can knock your battery up 13.31 Ah per day if you have it said up out of any shade and facing south or a quarter of that in the winter. ie it will take you over a week to recharge a 100Ah battery .
In reality that's hard to achieve unless its a roof mounted static installation - and it will never be achieved if you can't leave it out all day

That is why if you simply want more power and especially if you camp for a week or so in spring our autumn I recommend you are often better simply taking an extra battery fully charged - if you want to extend you battery life in the cheapest manner !

Of course if you like using solar go for it - but be aware solar panels that are packed away and not used for much of the year have a worse environmental impact than charging from the grid. It is only if you use them for longer ie on your roof at home that the environmental equations shifts in favour of solar.

Having said all that I think they a fun and really wish they were a more practical option!

Also do not forget that FLA's (Flooded Lead Acid) batteries can self discharge at a rate of upto 10% per month when not being used.

mark

Joined: 14 Jul 2005
Posts: 2191
Location: Leeds

Posted: Tue Sep 24, 13 7:47 am Post subject:

Please everyone take my comments as relating to 1-2 weeks camping trips! Or trips where there will be substantial driving (to recharge batteries) more than once a fortnight

Different factors such as self discharge come into account for longer trips.

But if you want more power for a typical short holiday the cheapest way to do it is still to buy another battery! It is also the best option if you get a weeks crap weather..

The problem is we all use our laptops and lighting most when it is dark and overcast outside - and most of all on that week when it rains all week so we up indoors - or in the spring holidays when it is dark evenings its not usually the sunny weeks when we put extra demand on our batteries and need the extra boost - as most of us wil go our walking and enjoying the outdoors then ..

now if we could have rain powered generators we'd be fine!!

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Tue Sep 24, 13 9:17 am Post subject:

mark wrote:

I agree.

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