solar powered laptop
February 10, 2008 4:42 PM   Subscribe

I would like to power my laptop with the sun.

I'd like to work from home while on the road.....

I have an IBM X41 tablet and plan on keeping it for a few more years.

I just purchased a converted Econoline van that is perfect for kiteboarding, which I want to do lots of this summer.

It's also ideal for working, as long as I have a cellular connection for my wireless card and for my phone. My work depends on online access and phone access.

My van has an inverter and a second battery (marine deep cycle). They are both fed energy from the stock alternator. I'd like to use it as little as possible, as I have other energy needs.

My laptop uses a 16V DC input from its power adapter. It says it uses 3.5 A.

I'd like to camp out at kiteboard spots and work from there, however the bottleneck I experience is getting power to my laptop and possibly phone (though I have a long-range phone battery and can purchase another).

I'd like to find a way to power my laptop (actually its battery) while I'm working without draining my van's battery. The ideal solution would be one with a solar panel on the roof directly charging the laptop's battery. I searched the net and didn't find anything that seems suited for this purpose.

Another idea is to wire a voltage converter to the extra battery to step it up from 12V to 16V and bypass the inefficient inverter.

Does anyone have any experience with any of this?
posted by sonicbloom to Travel & Transportation (19 answers total) 13 users marked this as a favorite
This might not be the answer you are looking for, but check out the Juice Bag. It's a laptop bag with a solar panel built into the flap.
posted by LightMayo at 4:53 PM on February 10, 2008

It would probably help if you could tell us how many hours you plan to work in a row, how long a fully charged battery will run and how long it seems to take you battery to fully charge from a wall outlet.
posted by slavlin at 5:01 PM on February 10, 2008

Unless you only plan to work a short time each night, you are going to need to incorporate the deep cycle battery somehow, because you will otherwise be out of luck if you run down the battery one night and then there isn't much sun the next night. Have you considered taking the battery out of the laptop and running it directly from deep cycle battery? You'll have a far greater storage capacity than in your laptop's battery and you will find it easier to find something to charge the deep cycle battery because there are a lot of solar systems designed to charge 12V batteries. You'll need a step-up voltage converter, but I think you'll need one in any case. If you decide to go this route, check out systems intended for RVs, e.g. like this, though you may need a bigger panel depending on how long you intend to use the laptop daily.
posted by ssg at 5:25 PM on February 10, 2008

Sorry, that should read "there isn't much sun the next day" not night.
posted by ssg at 5:26 PM on February 10, 2008

I've been planning the same thing for a while now. I've looked into a bunch of different approaches that should work, of varying complexity, depending on how much electrical DIY experience you have.

For simplicity sake, and for future-proofing, and caution, I suggest finding an efficient 12V-16V DC-DC converter designed to run your laptop off the car's lighter socket (or just use the one you've got). This is because:
a) 12V is a major standard, and the majority of solar panels and off-the-shelf solutions are designed either to charge 12V lead-acid batteries, or for a 12V system, which means once your laptop looks like a lead-acid battery, it will work with most solar panels as-is, no DIY electronics required.
b) This in turn means you can start with a smaller/cheaper solar panel but are future-proofed for subsequent harder-core solar panel purchases. Or could expand your existing purchase incrementally simply by buying more of the same smaller-cheaper panels and wiring each additional one to the rest in parallel.
c) Solar power voltage is hugely variable (eg clouds passing over sun, angle in sky, etc etc), so let a DC-DC converter deal with that, shielding your laptop from it, rather than subjecting the voltage regulator in your latop to the kind of voltage out-of-range abuse that can eventually ruin it.
d) Universality of 12V/lead-acid is useful - when not powering your laptop, you can now plug the panel into your car and use it to charge the battery, or charge the marine battery. (for best results, an off-the-shelf lead-acid solar charger is a good idea if you splash out on a large enough solar panel to potentially over-charge the car battery)

As for solar panels, check out these. They fold up to the same size as your laptop, and the larger ones, unfolded, can supply as much or more than the max capability of your laptop's power supply. I'm not sure what the difference is (other than price), but there are similar products claiming to be military grade. Perhaps that just means some dudes in Iraq bought some. I don't know.

Note that the advantage of these panels is that they are very lightweight, and fold up to fit in your laptop bag. They are not very efficient. "not very efficient" in solar panels, means only that they take up a larger surface area than a more expensive (and heavier) panel would to produce the same amount of energy. If you are NASA sending a robot to mars, the available surface area is highly limited, so using solar cells of max efficiency is critical, and it is worth the cost of paying through the nose for that extra efficiency. If you are in a park, and can unfold a panel as large as you like, then surface area is not your constraint - funds are, so a lower efficiency panel gives far more power for your dollars. If you want to permanently mount a panel on the roof of your car, then you have a surface area constraint, but it's probably quite a large and unhindering limit - but if cheap panels don't fit, you might need to spend more. But I doubt area-constraint is something you need to worry about,

So I suggest looking for the best watt-per-dollar solar panel you can find, preferably a panel that folds up into a lightweight compact unit, designed for 12V systems.
posted by -harlequin- at 5:27 PM on February 10, 2008

I'd be tempted to cover as much of the top of your van with solar panels as you could afford, and put another battery (or two) into the equation. Solar power will top up the reserve batteries while you are kiteboarding, and will essentially charge sun up to sun down. You can then run an inverter from there straight to your laptop power feed.

To save any losses from conversion of voltages, try and get hold of a direct car charger for the laptop.

Also, if you connect the batteries with a diode pack, when full, your solar batteries will top up your existing batteries (but not drain them), and so allow you greater power flexibility. It is up to you exactly how you charge and distribute power, but storage and peak demand are the hardest things to deal with. Batteries are cheap, solar panels are not. You could even just use one battery for the laptop (a decent sized marine/car one would be ideal) and let that govern your working hours. Once you run out of power, the day is over until the sun has got ahead of the game.

A couple of 12V outlets would let you charge your phone and laptop, too. If all else fails, you can run your engine and charge the working batteries up with the inverter/charger and again work until they are flat.
posted by Brockles at 5:28 PM on February 10, 2008

Some more notes:

My laptop uses a 16V DC input from its power adapter. It says it uses 3.5 A.

That means it maxes out at 56 Watts. In reality, your laptop will normally draw about a third of that. It's maximum real-world power draw will probably approach about 45W draw, this will occur when the CPU is maxed, the HDD and DVD drive is running, while the battery has just started charging from a state of close to full depletion.

Here is a folding panel that supplies 16V DC at up to 3.5 A. You might be tempted to hook it directly to your laptop, and doing so would work, it really is a dead simple solution, but it's not a good solution. It will strain the voltage regulator in your laptop and, over time, likely damage it. The voltage regular is a cheap component to replace, but unless you can replace it yourself, it's NOT cheap to get a technician to take a soldering iron to your laptop's motherboard. The 16V your power supply outputs is regulated - it never varies from 16V, whereas 16V from a solar panel really means 16V plus or minus up to 5V depending on the sunlight. So they're not apples and apples. Use a DC-DC converter. A DC-DC converter for your laptop should accept a fair range of voltage input and voltage variability, yet outputs a nice regulated 16V just like your laptop was designed for.
posted by -harlequin- at 5:43 PM on February 10, 2008

fixed link - 16V 3.5A panel
posted by -harlequin- at 6:03 PM on February 10, 2008

Remember that a solar panel is rated for volts and watts when full sunlight is shining on it. It doesn't put out nearly as much when it's cloudy or the sun has moved and isn't hitting the panel squarely, or (of course) the sun has set. So ditch the idea of hooking the solar panels directly to your laptop.

I like the idea of using solar panels to charge 12 volt deep-cycle batteries, which you use to power your laptop.
posted by exphysicist345 at 6:43 PM on February 10, 2008

Response by poster: I'm still reading all the responses, nice to see all the discussion.

I will be using this about 6 hours a day during daylight hours, and my laptop battery has a 2 hour life. I will be doing this 2-4 days in a row, depending on my workload and the wind.

I would consider connecting this directly to the deep cycle battery, and solar panels + separate battery just for the laptop sounds nice.
posted by sonicbloom at 6:47 PM on February 10, 2008

There really isn't any reason to make yourself a separate panel + battery system for your laptop. Just think what happens when one battery is full and the other isn't full. You don't want to be messing around switching things from one battery to the other. Get however many watts of solar panels you want and however many deep cycle batteries you want and then connect them together with an appropriate charge controller and hook your laptop (via the DC/DC converter) up to that (as well as any other devices you want to use).
posted by ssg at 7:11 PM on February 10, 2008

Oh, and it looks like your laptop doesn't use much power at all. Assuming you have the 4-cell battery and using your two hour figure, you only need about 15W to run it. I'd think that you could probably get by with about 30W worth of solar panels, which would give you enough power to run your laptop even when the sun's intensity is not as high (lightly cloudy days, bad angles, etc.) You would want more solar power and more battery capacity if you absolutely need to use your laptop even if the conditions aren't good.
posted by ssg at 7:17 PM on February 10, 2008

If you're doing this somewhere windy, what about a collapsible wind generator? Then it'd certainly charge your battery when you were off gallivanting on cloudy days, too. I can't find a link for one less than $500 at present, but if you consider what is more likely to be prevalent where you are - wind or sunlight - it may be worth slightly changing tack, or maybe even a hybrid system.

Incidentally, the solar panels on the roof could easily be maximised in efficiency with a little DIY. Make a wooden frame with some sort of foam or carpet on the bottom of it with folding supports and raise it at a slight angle to the sun and park appropriately for maximum exposure. It it were me, I'd make a frame that was bolted to the rook (out of aluminium or steel) and allowed one side or the other to be raised, but I'm not sure how in depth you want to make this. You either want to take the panels off, or have them covered/fold together while driving, though, to prevent damage to the cells.
posted by Brockles at 7:20 PM on February 10, 2008

Two thoughts:
I would get an extra battery with an external charger if you can find one for your model.


Get an external battery for your laptop that you can charge off of whatever solar solution you come up with, even while you use your laptop of the existing battery or the deep cycle.

(No experience with either seller, just looking for examples).
posted by shinynewnick at 7:23 PM on February 10, 2008

This guy seems to be using a Xantrex XM1000 inverter and this panel to run two laptops, lights, and the rest of his trailer. I doubt you need all that, but Xantex has a web calculator to help you figure out how many batteries you're going to need.
posted by Orb2069 at 7:35 PM on February 10, 2008

The IBM X41 has a 1900mAh battery at 14.5 volts. The energy stored is 1.9 x 14.5 = 28 watt-hours.

A typical marine battery is 100-Ah at 12 volts. The energy stored is 100 x 12 = 1200 watt-hours.

So the marine battery has about 40 times the energy of your laptop battery. If your laptop battery lasts 2 hours, the marine battery would last about 80 hours. At 6 hours per day that is almost two weeks.

Even if you cut that time in half for conversion losses you should be fine. Forget about the expensive solar panels. Just get a voltage converter and run everything from your marine battery. If you want more time, a second marine battery is a lot cheaper and more reliable than a solar panel. Don't even bother hooking the batteries up to your car's alternator. Just use a trickle charger at home to keep them topped off. Two marine batteries should keep you going for weeks.
posted by JackFlash at 10:32 PM on February 10, 2008

Response by poster: All interesting comments!

JackFlash, in response to your post above, say that I dedicated a deep-cycle battery to the laptop and kept it charged up with a solar 12V battery charger. Would you recommend stepping up the voltage to 16V, or hooking two in series and stepping down?
posted by sonicbloom at 11:34 PM on February 10, 2008

Electrically, stepping up and stepping down are pretty much a wash for efficiency assuming a well-designed DC-DC converter. But for practicality, there are lots of off the shelf devices made exactly for powering a laptop off a 12 volt input from a car battery. For example here. (I have never used this particular device but it just happened to come up first on a search for IBM X41 car battery charger. I'm sure you can find others.)
posted by JackFlash at 11:53 PM on February 10, 2008

Tom's Hardware Guide did a solar powered PC series. Parts 1, 2 and 3. Not exactly what you asked for, but it could probably help out a bit.
posted by electroboy at 6:52 AM on February 11, 2008

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