Solar Powered Laptop... Realities

Need a solar powered laptop? This article covers everything you need to know to take your laptop off-grid.
Editor: Graham Morfitt, BSc (Physics)

POP QUIZ
Take a close look at this photo…

See the problems?
1. The panel’s output voltage may not match the needs of the notebook computer
2. The panel likely does not have the correct connector for your notebook.
3. The notebook would switch to its battery and ignore the panel (ie no charging) if the panel was not providing what the computer needed to operate (ie 50+ Watts)
Laptop would have to be ‘OFF’ to charge from this panel.
Want to protect yourself from disappointment and get the equipment you need?
Read on…
Resources
Portable Solar Panels Buying Guide

Running a laptop from solar power for field work, or just for the ability to get unplugged from the grid, is one of our most common application requests. The answer may seem simple, and there are many products claiming to solve this problem, but they almost always neglect to provide all the information you need to avoid disappointment when you plug your computer into their equipment.

The Core Challenge…
Laptops have their own built-in lithium battery and sophisticated power management system, and are what might be referred to as an “either / or” power system. They run from an external power supply, or their battery, but not both. If you are connected to a variable source of power like solar, as soon as you turn your laptop “on”, it may see that it does not have enough external power, and it will switch to its internal battery to “RUN” & will ignore the external source completely. When the laptop is plugged into the wall, it runs off that power and uses some of it to charge its internal battery. If the grid power fails, it switches over to its internal battery for power in the blink of an eye.

So, the purpose of this note is to shed a little sunlight on this issue, let you know what products can and cannot do, and suggest several solutions to solve your solar powered laptop needs.

If you have any questions after reading through this application note, please do not hesitate to contact us.

Don’t want to read the entire explanation?
Go straight to our solution packages at the bottom of this page.

Solar Powered Laptop : Plug N Play (sort of)

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. A laptop will not take the 10 Watts from the solar panel, and add what else it needs from its own battery pack.
One lonely cloud drifts over, and you might have a 50% 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!

A solar panel needs to have a storage battery to deliver power to your laptop because…

1. The output voltage of the solar kit needs to match your computer
2. A solar battery will provide 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, let’s put together a solar powered laptop system.
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 60 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 some of the most popular solar panel options when it comes to putting together a laptop system…

For Canadian latitudes, coastal adventures, or where it might get wet…
7 Watt Marine-Grade Panel = 30-60 minutes use per day

For Canadian latitudes, & lightweight packability is key…
10 Watt Folding Panel = 30-60 minutes laptop use per day

For summer use, mountain treks, or tropical locations…
20W Folding Panel = 60-120 minutes laptop use per day

… there are smaller panels, and there are larger ones.
See our entire collection by clicking here

* Remember that these are estimates only, based on typical solar intensity during these months. An allowance has been made for the fact that these panels are portable.

Now, what to do with the power generated by the panel you’ve chosen…

2. Store the solar power

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 solar storage battery so that all the power collected will be stored & available for use regardless of what the sun is doing moment to moment. Equipment can then be connected to the solar storage battery as needed… day or night. Batteries are 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 with a little room to spare. 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 at least 30 Watt-Hours of usable capacity.

So… what batteries are available…

Lithium-Ion : The lightweight option
A Lithium battery pack designed for solar use is the best way to go when you are packing it all on your back. A lithium solar storage battery far lighter than the old SLA (sealed-lead-acid) variety, and typically offers on-board voltage conversion to provide your laptop with the correct voltage (see the V72 below). Some batteries that don’t offer DC output voltages for laptops will rely on an inverter to create household AC power for your laptop’s normal 3-prong plug. Inverters waste a lot of power in creating AC that your laptop is going to convert back to DC anyway, so best to avoid them if possible.

Here are a few popular models. Note that all of these are ‘solar ready’, and offer pass-through charging, so you can keep them plugged into a solar panel while they are plugged into your laptop…

Goal Zero Sherpa 50 : 50 Watt-Hours
Voltaic V72 : 72 Watt-Hours
Enerplex Generatr 100 : 100 Watt-Hours
… to see our complete line, click here

** for comparison, your laptop’s internal battery is 50-60 Watt-Hours.

MacBook users…
The best option for you remains the V72 & its available MagSafe & MagSafe 2 connection options. However, the other models can support via AC inverter.

SLA : Heavy, but reliable & available worldwide
An SLA battery is dumb, and in solar, dumb is beautiful. But they are heavy. 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 12 Amp-Hour (70 Watt-Hour) SLA battery will weigh about 10 lbs, but they are cheap & replacements are usually easy to find worldwide.

BUT, an SLA battery requires that you pack along either a DC(car) power adaptor for your laptop, or an AC inverter so that you can use your laptops wall adaptor like you do at home. The problem with either of these is that it introduces one more thing to carry, not to mention that AC power inverters will waste upwards of 25% of your storage battery power in creating household AC power just so your laptop can convert it back to the DC power it wants.

Here are a few examples of popular SLA battery options. Note that solar-ready kits are available for each battery size…

Goal Zero Yeti 150 : up to 60 minutes of laptop use
Goal Zero Yeti 400 : up to 3 hours of laptop use
Goal Zero Yeti 1250 : up to 9 hours of laptop use
… see all our SLA battery options, click here

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.
But, most importantly, when you are in the power desert, you shouldn’t spill any electrons!
So let’s look at your best options for DC support first…

Lithium Storage Batteries : The built-in & ready to go
Some lithium solar storage batteries, like the Voltaic V72, & Generatr 100, have built-in DC voltage converters. This means they can support laptops directly, without any additional equipment (just make sure to get your particular connector).

The Voltaic V72. battery offers MagSafe 2 & MagSafe 1 connectors as options.

SLA Battery Pack : Adaptor or Inverter required
Sometimes, you simply must have AC power. Maybe you have a special set of research equipment, or a device that needs a DC voltage not available via one of the lithium batteries, in these cases, it makes sense to use a battery pack that can support AC power inverters or DC-DC voltage converters.

The other advantage of SLA batteries is that they are available worldwide. So if you run into trouble in the middle of Africa, you have a better chance of finding a car battery to use than to get service on a fancy lithium battery pack.

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.

Here are some examples of popular Inverters & Converters…

AC Inverters…
120W +USB Pure Sinewave for the cleanest power
350W Pure Sine for the cleanest power
… see all our inverters here

DC Converters…
12V DC adaptors plug into your SLA battery just like they plug into your car’s dashboard, 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.

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.

Solar Powered Laptop Solutions…

Solution… 6+ hours run time per day
Solar: Powerfilm 60
Battery: Enerplex Generatr 1200 -or- Goal Zero Yeti 1250

Solution… Up to 4 hours run time per day
Solar: PowerFilm 30 -or- Voltaic Arc 20W
Battery: Enerplex Generatr 100 or Goal Zero Yeti 400

Solution… Up to 2 hours run time per day
Fuse 10 Solar Laptop Pack -or- Array Solar Backpack
by Voltaic
Solar backpack 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!

Solutions… 1 hour run time per day
Solar: PowerFilm 10 -or- Powerfilm R7 Rollable
Battery: Voltaic V72 -or- Yeti 150

Other Devices…

Netbooks, & other Solid State Laptops
Netbooks don’t use hard drives, and consume far less power than normal laptops.
Combining a Powerfilm 10 with the Voltaic V72 is an excellent choice for netbooks & the MacBook Air..
You might also consider an all-in-one solution like the Fuse 10 Solar Laptop Pack.

PDA’s, iPads, iPods, iPhones, & BlackBerry systems
We recommend using a Voltaic Fuse 4W or Voltaic Fuse 6W charger for these small devices. iPads & tablets need the bigger USB 2.1A power, and the Fuse 9W can handle those.
We have more information on these small solutions in another article.