Polar expedition power: Batteries or Solar?
A bit of a techi-post today for you all! As anyone who has travelled for long periods in any environment will know, electrical power is a major challenge. In stark contrast to the polar expeditions and global travels of many decades ago, the demands for electricity have never been higher.
In 1910 you would navigate by chart, compass and sextant. In 2010 you navigate by chart, compass and GPS receiver. The fundamentals have remained the same but the means of finding your global location has become quicker and more accurate than ever before. My £60 Garmin eTrex H can tell me my grid coordinates in 30 seconds and accurate to 10 feet. This convenience does however come at a cost. Despite low power consumption, it does require good batteries to work. So does my satellite phone from Iridium. So does my iPod. So does my camera. So does my HD film camera.
These items are of course ranked in varying levels of importance and are given appropriate priority. Safety and navigation come first, GPS and sat phone, all the way down to an iPod, which is a 'nice-to-have' but unlikely to save my life. But where does this electricity come from after being away from a power socket for weeks?
There are two options, the first being batteries. In cold places, batteries behave badly and drain faster than they would in the warmth of your home. The best options for non-rechargeable and reliable power are currently AA lithium cells like those from Energizer. They are high capacity (3000mAh) and offer great power to weight ratio as they are lighter than normal AA batteries (15g vs 23g). They are however single-use and must be discarded or carried once emptied. Using a clever battery pack system to make a 12V unit, they can be used as a stable source from which to charge other units such as the Li-Ion batteries in sat phones and iPods. The inescapable problem with this is the complication and weight of all the individual chargers and cables. Cables and plugs are notoriously fragile in cold temperatures, most being designed for home use, and any serious polar traveller needs a good knowledge in rewiring in order to survive.
One obvious alternative to this is to make your system 'AA-universal' and ensure that everything can run off a simple and reliable Lithium AA supply. You can use an AA GPS, AA mp3 player, AA camera but there is no AA sat phone as yet.
The great drawback of these small batteries is that you still have to haul their significant cumulative weight even after they're empty and useless. They do however provide peace of mind due to their high performance, pre-charged and ready-to-go state.
The second and most common modern tactic is to use a lightweight rollable or foldable solar panel. These can generate anything from 1W to 25W+ depending on the size and efficiency of the solar cells. The main drawbacks of solar charging are due to the light conditions which allow them to operate. They can clearly only operate in daylight, perfect for 24hr sunlight in the Antarctic summer but a major problem in the long dark periods during the arctic spring. An arctic expedition needs to decide whether the amount of time available to charge using solar panels is worth carrying the weight. The other drawback is the fact that the (usual) 15V output of a panel is not a constant current - it fluctuates when the sun disappeared behind a cloud for example. As a consequence, only a small number of low-drain items can be charged DIRECT from the panel. These include particular iPods (not all) and Iridium satellite phones when luck is on your side. The best solution for this is to charge up a Lithium rechargeable 12V pack, a heavy and expensive investment, and then charge everything else from this stable source just like a 12V car battery, using a cigarette lighter charger. The number of batteries, chargers and cables involved can be quite daunting, especially if you are taking spares for vital equipment.
In the end, power in the polar regions is a huge compromise between weight and reliability. Even after a large number of expeditions, I am still optimising my charging procedure and learn something new each time. An example is that iPods all seem to need different charging currents and chargers - just because one works doesn't mean a new generation model will!
Let me know your experiences about expedition power and charging. I'll also try to answer any questions you might have. The best bit of advice I can give is to learn about your electronic system in quite some detail and get very handy with pliers and wiring whilst still in the warm!