First, I'll start by saying that the photo above is misleading, but is typical of photos you will see around the internet on sites promoting solar power.

The truth is... you cannot usually charge a laptop directly from a solar panel.

Why?
1. The output voltage of the panel probably won't match your computer
2. The panel likely doesn't come with a connector for your computer
3. Laptop batteries are not easily charged from a passive source like solar
4. You certainly cannot 'run' a 30 Watt device from a 10 Watt power source

So, how can a solar powered laptop be created?
Actually, it isn't too difficult, but it does require a little planning.
So here it is. Step-by-step...

1. Choose a solar panel

We'll assume that your laptop is like most others, and consumes about 30 Watts while it is running. Some laptops with big dual processors etc can consume up to 100 Watts if they are burning DVDs or other intensive operations. But for our purposes, and assuming that you are a practical person who knows how to dial back their power settings, we will go with the standard number of 30 Watts continuous.

Now, you need to determine your usage time.
How many hours a day do you absolutely have to have on the computer? The bare minimum now, with no coffee breaks.

Let's say you need 1 hour per day.
And let's say you are only using it during your summer research period of May through August.

Without getting into gory details, here are your solar panel options...

5 Watt Panel = 30 minutes laptop use per day
7 Watt Panel = 30+ minutes use per day
10 Watt Panel = 1+ hour laptop use per day
14 Watt Panel = 1.5+ hours laptop use per day
20 Watt Panel = 2+ hours laptop use per day
21 Watt Panel = 2+ hours laptop use per day
28 Watt Panel = 3+ hours laptop use per day
30 Watt Panel = 3+ hours laptop use per day
60 Watt Panel = 6+ hours laptop use per day

* Remember that these are estimates only, based on typical solar intensity during these months, some allowance has been made for the fact that these panels are portable. Stretches of bad weather is beyond anyone's control.

Now, what do you do with the panel you've chosen?

2. Store the solar power

Common question: "Can I run my laptop computer direct from solar?"
No. Well, usually the answer is 'no'.
The reason is simple. A 10-Watt solar panel cannot magically provide the 30-Watts your laptop needs. Even a 60 Watt solar panel can't guarantee it. One lonely cloud drifts over, and you have a 30% drop in power and the solar equivalent of a brownout. Also, maybe you don't have the $800+ on hand to buy one of these 55-Watt panels!

Common question: "I see solar products that claim to be able to run laptops from solar power... what's the deal?"
They aren't telling you the whole truth.
Laptops have their own built-in lithium battery. All you need is a 12V DC power adaptor that supports an output voltage your laptop wants, and you can "CHARGE" your laptop from solar - just plug the 12V DC adaptor into the solar panel.
Note that we say "CHARGE" and not "RUN", because as soon as you turn your laptop "on", it will see that it does not have enough external power, and it will switch to its internal battery to "RUN". Laptops are equipped with an either/or power system. They run from an external power supply, or their battery, but not both. When the laptop is plugged into the wall, it runs off that power and uses still more to charge its internal battery. If the grid power fails, it switches in the blink of an eye over to its internal battery for power. So, if you want to "RUN" your laptop from solar, read on...

Sunlight & hence solar power is unpredictable. So most good, reliable, solar power systems provide a means of storing the power produced by the panel so that it can be used when & how it is needed. You can run a 1-Watt GPS direct from a solar panel on a cloudy day, because even on a cloudy day, a 5-Watt solar panel should be able to provide 20% of its peak output (ie 20% of 5Watts = 1Watt). But what do you do when the device you need to run is larger than the peak output of your solar panel? How can a 10-Watt solar panel power a 30-Watt computer?
Simple, put the panel out all day connected to a battery so that all the power collected will be stored in the battery. Equipment can then be connected to the battery as needed - batteries are typically able to release more power than was used to charge them, and only their capacity will dictate how long you can run from them.

The sun goes behind a cloud, and the battery picks up the slack. Beautiful!
We like to size solar batteries for mobile applications equal to one-day's power needs. This provides a balance between the power generated, the power used, and the power stored. It ensures that you will have power to get through at least one day of bad weather, without having to lug a larger battery than you have to. Batteries are heavy. So, for our 1-hour laptop, we would recommend using a battery with close to 30 Watt-Hours of power reserve (ie: a 7.5 Amp-Hour 12V SLA battery would do nicely).

Battery pack chemistry...
You have a couple of options here: Sealed Lead-Acid (SLA) or lithium.
If you need to use an AC inverter for anything, then an SLA battery is the only way to go, but in DC systems lithium is your lightweight option.

BUT, be aware of lithium battery drawbacks... many have a significant system design issues when used with solar... Just like laptop batteries, most external Li-Ion packs are selfish. They would rather charge themselves than put through power to your computer & other equipment. So when power is scarce, like it often is with solar, where the power source is less than the equipment's needs, an external Li-Ion pack will not let power through. This means that most lithoum batteries will not let you charge them from solar & power a laptop at the same time.
If you want lithium, stick to the models we feature here at Modern Outpost. They have been proven with solar laptop power systems.

SLA : DC direct, or AC inverter support
An SLA battery is dumb, and in solar, dumb is beautiful. Heavy, but beautiful. An SLA battery will act as a buffer, taking the power from the panel, passing it through to your laptop, and offering some of its own reserve if the laptop needs more. A 7.5 Amp-Hour SLA battery will weigh about 5 lbs, but they are cheap & replacements are usually easy to find worldwide.

Lithium-Ion : DC direct, & limited AC inverter support
A Li-Ion pack will charge itself from solar, and it will power/charge your laptop by itself, but only a select few models are able to act as a pass-through buffer like an SLA battery will. Lithium batteries have strict charging & discharging limitations & specialized circuitry, which makes them challenging for use with Solar.
NOTE: Some external laptop batteries (Li-Ion) like the Tekkeon myPower All 3450 & 3300 require a minimum amount of power in order to charge, something that is wasteful & not at all convenient in the solar world. Avoid this type of battery in solar applications.

The Solo 7.5 & Solo 15 lithium packs from Brunton are designed & proven to work with Solar. They also come with a small AC inverter for small household AC appliances (under 60 Watts like most laptops).

Voltaic systems has developed a lithium battery pack for their solar generator laptop case. This battery comes with a huge array of connectors for almost every brand of laptop. We go one step further by providing the connector you need to charge the Voltaic Generator pack from any portable solar panel. See the Voltaic Battery page here.
** ATTENTION MAC USERS! **
This Voltaic Generator battery is the one you want. A MAC MagSafe connector is available as an option for this battery pack, which works with MacBook, MacBook Pro, MacBook Air.

Check out our new YouTube video on a solar MacBook power system...

3. Give the stored power to the laptop

Let's avoid AC power if possible...
An AC inverter is a small device that converts battery power to household outlet "AC" power.
AC power is something you will want to avoid in a portable power application if at all possible. It is documented in other areas of our website how an AC inverter is quite inefficient, and requires system support that makes portability a bit difficult.
So, in this application note, we will be throwing out your laptop's AC wall adaptor, and replacing it with a 12V DC car adaptor for your laptop that can plug into your solar panel just as easily as it plugs into your car dashboard. Your laptop won't know the difference, and your back will appreciate the lighter load.

12V DC adaptors plug into your solar panel, and provide various tips to connect to your laptop. Make sure you set your adaptor's voltage to what your laptop needs (check the output specs on your laptop's AC power supply box). You will also need to make sure that the specific adaptor tip is set to the correct polarity for your computer. Most are "Center-Pin-Positive", but some aren't. There should be a little icon/diagram on the back of your computer or laptop power supply that shows the correct polarity.

If you have a unique laptop, or would rather run from an AC inverter, then we recommend a small 150 Watt model that uses very little space in your pack.

++++++++

As always, the systems described below contain conservative estimates for solar performance in portable applications. Better performance from the same system can be obtained if the solar panel is deployed for the entire day in an orientation perpendicular to the sun during the course of the day (ie manual tracking).
We have balanced the solar power production with battery storage capacity. This permits operating your laptop for equivalent periods at night while the solar panel is inactive.

We also advise that you use effective power save settings on your laptop in order to reduce its power consumption as much as possible.

Solution... 6+ hours run time per day

Laptop via DC Adaptor
When a laptop car adaptor is used to get from the battery pack to the laptop. It's more efficient to do it this way.
Solar: 60 Watt PowerFilm
Battery: Brunton Solo 15 -or- Outpost Power 26
Converter: 100 Watt laptop DC power adaptor
Mac users will have to purchase a compatible DC car adaptor

Laptop via AC inverter
When you don't have a car adaptor, or have other AC devices you need to run, or would simply like to use the laptop's proper charging system. This is a less power efficient solution, and introduces additional complexity, but it is a solid portable AC solution.
Solar: 60 Watt PowerFilm
Battery/inverter combo: Brunton Solo 15
-or-
Battery: Outpost Power 26
AC Inverter: 150 Watt smart AC power inverter

Solution... Up to 4 hours run time per day

Laptop via DC Adaptor
When a laptop car adaptor is used to get from the battery pack to the laptop. It's more efficient to do it this way.
Solar: 30 Watt PowerFilm
Battery: Brunton Solo 7.5 -or- Outpost Power 12
Converter: 100 Watt laptop DC power adaptor
Mac users will have to purchase a compatible DC car adaptor

Laptop via AC inverter
When you don't have a car adaptor, or have other AC devices you need to run, or would simply like to use the laptop's proper charging system. This is a less power efficient solution, and introduces additional complexity, but it is a solid portable AC solution.
Solar: 30 Watt PowerFilm
Battery/inverter combo: Brunton Solo 7.5
-or-
Battery: Outpost Power 12
AC Inverter: 150 Watt smart AC power inverter

Solution... Up to 2 hours run time per day

Generator Solar Laptop Case
by Voltaic
Laptop case with integrated solar & universal lithium battery pack. This has been designed well, and is the only turnkey system we know of with any decent level of performance.
* MacIntosh MagSafe connector is available!
See below for other systems comprised of off-the-shelf components.

Solutions... 1 hour run time per day

Laptop via DC Adaptor
When a laptop car adaptor is used to get from the battery pack to the laptop. It's more efficient to do it this way.
Solar: 10 Watt PowerFilm -or- Powerfilm Rollable
Battery: Brunton Solo 7.5 -or- Outpost Power 7
Converter: 100 Watt laptop DC power adaptor
Mac users will have to purchase a compatible DC car adaptor

Laptop via AC inverter
When you don't have a car adaptor, or have other AC devices you need to run, or would simply like to use the laptop's proper charging system. This is a less power efficient solution, and introduces additional complexity, but it is a solid portable AC solution.
Solar: 10 Watt PowerFilm -or- Powerfilm Rollable
Battery: Outpost Power 7 Battery
AC Inverter: 150 Watt smart AC power inverter

Solid State Laptops
These are the new compact laptops that don't use hard drives, and consume far less power than normal laptops. This is a lightweight power system, that will power the laptop directly - it will not charge the laptop battery (note that this system is only for solid state laptops with 7.2V internal batteries).
Solar: 5 Watt PowerFilm solar panel
Battery: Voltaic Lithium Battery Pack

PDA & BlackBerry system
We recommend using a Solio, or a SolarMio for these small devices

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