While there are many ways to go about the task of charging batteries & electronic devices via solar power, we will focus on several solutions that have been tested & proven, and which cover the most common needs. We also recommend using PowerFilm Rollable solar panels that are the most appropriate on the market for portable marine applications and for strapping to the decks of kayaks & canoes.
Step 1: Estimate your power needs
The first step in creating a solar power system for kayak expeditions or canoe trips is to estimate your total power needs, and choose a solar panel to match. Watt-Hours is a measure of a battery's capacity. For example, most digital cameras require 5-10 Watt-Hours, mp3 players require 5, laptops require up to 65.
Next, decide how often you will need to charge your various devices. For example, if you want to charge your digital SLR camera while canoeing or kayaking, and you know that under typical use, you get 3 days from the camera battery before it needs charging, then your needs are 15 WHrs over 3 days = 5 WHrs/day
To complete this example, we'll add the need to charge two AA batteries each day for a GPS unit, and an iPod every other day. Total daily power needs: 12 WHrs
For portable applications, we like to be conservative when estimating the power production from solar panels. It is nearly impossible to get ideal exposure for a solar panel when it is simply strapped to the deck of your kayak, draped over your tent, or spread from rail to rail on your canoe. So, solar production may be only about half of what a properly engineered roof-mounted system might be. Based on this assumption, we can calculate that a 5Watt panel would meet our needs, minimize costs, and minimize size & weight to carry. Remember that this is our power budget, and therefore we must live within this amount. The other advantage of minimizing the solar as much as possible is being able to fit it to the deck of your canoe or kayak. PowerFilm Solar produces a range of flexible solar panels designed for use on boats. They are designed to take the splashes associated with marine applications, and come equipped with the best connectors we have seen on a portable solar panel. The R-7 7Watt rollable panel is the smallest in this marine-grade line, so that is the panel we would choose for our example system.
Step 2: Choose a power storage battery & conectors
Next is to choose a battery pack to store your solar power. It should be small & light so as to not load your canoe or kayak any more than necessary. It needs to provide the connectors you need to charge all your devices. It should also store enough power to get you through times when the sun isn't as bright as we would hope. We like to make an estimate that is at least equal to your daily needs. In our example, this would mean a storage capacity of at least 12 Watt-Hours.
Want to work direct from the solar panel, and not carry a power storage battery pack? We'll have to see if the devices you want to charge will be able to do this. Read on...
In our example from above, we will need the following connectors... USB: for our smart phone AC outlet: for our camera & AA battery charger. Wait! AC power is not an option in these small power systems. AC power inverters will not operate direct from solar panels, and the small lithium-based power storage battery packs are not able to power even a small inverter. What to do?
Fortunately, many after-market lithium camera battery chargers come equipped with 12VDC car adaptors in addition to AC adaptors. There are also AA chargers that can operate from USB or 12VDC car sockets. So, since we can get 12VDC output direct from the solar panel, and USB via a car adaptor, at this point it appears that we could choose to charge all our devices direct from solar and not include the power storage battery pack. But, should we go solar direct?
We almost always advise using solar-direct only when the trip is short, the weather forecast is positive (& reliable), and the solar panel is really only needed to top-up your batteries when needed. Having the power storage pack provides an important source of back-up power for times when the sun is not cooperating. It also allows your battery chargers to operate at their best rates instead of limping along at whatever the solar panel is able to get from the sun. You will also be able to capture more of the sun's energy over the course of the day.
For our example, we would recommend the Voltaic Pack. It's capacity is slightly larger than our one-day needs, and it is very small & light. It also includes all the USB & 12V connector capability we would need. Although the Voltaic Pack will not support a Targus camera charger for 7.4V battery packs, this function can be obtained by connecting the camera charger direct to the panel. If the power storage pack is needed to drive the Targus charger for 7.4v battery packs, then the best option would be to choose the Voltaic "Generator" battery unit.
What About AA Batteries?
For most canoe & kayak expeditions, one of the most common needs we hear about is AA battery charging for things like GPS receivers & radios. We advise customers to consider two scenarios... 1. Direct solar charging of AA batteries 2. Using an intermediate power storage battery
In the first option... The solar panel is connected directly to a DC-input AA battery charger. We recommend the following equipment pair... PowerFilm R15-300 or PowerFilm R-7 Targus Mini 12V DC AA Charger
The charger will operate any time the daylight gets bright enough, and will charge at the maximum rate of the solar panel in the light conditions. For example, this 5 Watt solar panel will charge 2 batteries per day from late spring through early fall. Most people will create a "battery rotation" whereby pairs of batteries are in the charger, charged & ready, in the device, & waiting to be charged. Every day, the batteries are changed & moved up the rotation. This way, charged batteries are never mixed with partially charged batteries in your device. If you want faster performance, and more batteries per day, upgrade to the 10W or 14W PowerFilm panel. These will charge as many as 8 AA batteries in a summer day.
The second option... This power system allows you to store solar power during the day, and draw power when you need it, even at night. Besides having access to power anytime, an important advantage of using an intermediate battey is being able to operate the battery chargers at their peak rate, and not just at the present rate of the solar panel. We recommend the following equipment... PowerFilm R15-300 or PowerFilm R-7 ZAP! R07-PL2 Battery Pack Targus USB AA Battery Charger
Or, for more power, combine the 10W or 14W panels with the Voltaic Battery Pack and the Targus USB AA Battery Charger.
NOTE: It is imperative that all batteries have ample airspace and be vented somewhat while they are being charged. If using a dry bag, be sure to leave an airspace, and preferably do not completely seal the bag. That's It... You are Ready to Start Paddling with Power!
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