The two obvious renewable energies were wind and solar. After a bit of investigation there appeared to be very few wind charging options for small 12v systems. Those that I did find, didn’t seem as though they would stand up to the harsh salt water environment experienced on the AI. It became fairly obvious early on that solar was the solution for a yak.These may be of interest if wind power takes your fancy. http://store.sundancesolar.com/15-watt- ... rbine-kit/
As most of the earlier expeditions were hit and run style, where we didn’t camp in the same place for more than a day or two, I looked for a solar solution that was capable of charging batteries and devices on the yak. Subsequent expeditions see us spending multiple days in the one location, so for the most part I now use the same setup on land with far better results than on the water. I do occasionally use it when I want to drive the hobie live well all day to keep precious slimies alive.
My solution is designed to charge VHF Radios, Gopros and Smart phones for six people over a seven day period. For a personal solution simply reduce the amount of 12V charge battery used. The remaining charge and discharge theory described below applies. I would not recommend anything less than a 14W panel regardless of how small your 12V charge battery is. The maximum possible output @ 12V from a 14W panel is 900mA. It is also the current used in the initial charge stage of an SLA battery. If you find my explanations confusing or too light on, a friend recently pointed out there is a similar article buy a member of the kayak fishing NZ forum, in which he has pretty much come to the same solution as myself. He uses a water and pipe analogy to describe how currents and volts flow. The article is in the Do It Yourself section and has been marked sticky. As a supplement to what I have written here, his article is well worth a read.
Before I begin, it is prudent I provide a warning to those wishing to do something similar.
Danger: DC CURRENT, SOLAR PANELS AND BATTERIES CAN PRODUCE CURRENTS CAPABLE OF DESTROYING YOUR EXPENSIVE ELECTRONICS AND CAUSING PERSONAL INJURY AND WORSE. USE ANY OF THE INFORMATION PROVIDED IN THIS ARTICLE AT YOUR OWN RISK.
I did a fair bit of DC theory in an Electrical Engineering degree I did at uni, back before the light hit the earth. However, I left engineering for IT pretty much straight after qualifying and I can only claim to have a working knowledge of what’s going on here. Many of you are far more qualified in electrical\electronic theory\practice and as stated in previous posts, I am happy to be corrected where ever you see blatant porkies. The only thing worse than no information is mis-information.
1. You need to Fuse ALL of your circuits. I achieve this by connecting an inline 3A fuse holder between the battery +ve terminal and the external connection point on the battery box. I carry a good few spare fuses. Get the multimeter connection wrong and you will blow a fuse every time. Better than frying a radio or camera.
2. If you know little about DC theory I would recommend gaining a rudimentary understanding from one of the many good tutorial sites on the web. This is just one: http://www.eng.cam.ac.uk/DesignOffice/m ... /DC_5.html
3. I also highly recommend you gain an understanding of the battery technology you are going to use and in particular its charge\discharge behavior and requirements. Get this wrong and the results will at best reduce the life of your batteries and destroy your equipment and in extreme cases cause your batteries to heat up and possibly explode. This is a really good resource for information on all of the battery technologies you are likely to be using. http://batteryuniversity.com/
These are the basic ingredients you need to get going
- 12V Solar Panel
Solar charge regulator
Battery(s) (SLA or LIFePO)
Connector plugs and sockets
12V USB Port
Step Up Transformer (Optional)
When I began looking four years back there were very few players in the flexible, water-proof solar panel market place. Investigation shows there are many more options available now but I still believe the Powerfilm range of rollable panels are the most rugged, light weight, efficient solution for my situation. I shipped mine in from the US but they are readily available in Aus now.
Most panels are made up of smaller discrete panels that are connected together within the fabric the panels are bonded too. These connections are prone to breakage and the loss of power when one panel is damaged or disconnected, is one over the number of discrete panels in your charger. One in six and you have lost one sixth of your power output. If the 12V panel is made of three parallel connected sets of 2 x 6V cells in series, one third of your panel's output may be lost or the panel may no longer operate at the required 15 odd volts to charge 12V batteries and effectively be useless. It all depends on the manufacturing process and the materials used to produce the panel. The likelihood of damage to fragile equipment is magnified when you add it to a yak in a saltwater environment.
“PowerFilm is manufactured using internally developed, proprietary manufacturing processes. The core process is a true roll-to-roll process. The general process steps are Vacuum Deposition (Back Metal, Amorphous Silicon, Transparent Top Contact), Printing and Laser Scribing, Bus Bar/Lead Attachment, Encapsulation, and Die Cutting. PowerFilm is patterned on a 13 inch wide web on a roll up to 2400 feet long.”
Solar panel manufacturers often express the efficiency of their product as a percentage. Solar cell efficiency refers to the amount of ambient light that can be converted into usable electricity by a discrete cell. However, connecting discrete cells to form a solar panel results in a decrease in efficiency due to connections and in the case of rigid panels, covering the panels with glass (or a PET plastic material on cheap folding panels), to protect them from the elements. Powerfilm panels are etched into the panel fabric and in effect are continuous for the entire panel. Essentially, due to the manufacturing process, they could be treated as a single cell without joins, regardless of what size panel you buy. Efficiency ratings are at best arbitrary and can be influenced by many factors.
Though Powerfilm only claim 5% cell efficiency, there are many video examples showing where they outperform other more efficient, higher wattage panels of a different make in all sun conditions. http://www.powerfilmsolar.com/education/videos/
Check out this page where they compare other panels and damage their own with golf balls and even a 40 caliber glock test to show how little power is lost when parts of the panel are damaged or shaded.
The panel used in the NZ article seems much higher output but it doesn’t appear to be available in 30 watts anymore. The smallest @ 40W is comparable in price to the Powerfilm 14W I use but is capable of producing a higher output and claims 22% efficiency. Unfortunately it comes in a 0.5m square that you can’t roll or fold. Not a problem if you intend using whilst on the yak.
http://www.powerfilmsolar.com/products/ ... tID=271516
Shop around if you purchase this panel. It should be $250-$300. Prices vary widely with some asking over $500.
These are the specs of my panel:
- Operating Voltage: 15.4
Current: 0.9 amps
Width (mm): 368.3
Length (mm): 1066.8 unrolled
Width (in): 14.5
Length (in): 42 unrolled
Weight (kg): 0.445 kg
Weight (lb): 0.981 lbs
In electrical terms P=VI (Watts = Volts x Amps). Corollary I=P\V.
A 14W panel is capable of supplying (14w\15.4v) 0.9 Amps at maximum output. This is the most I can expect from my panel in ideal conditions.
No matter which panel you use, it is important the panel is angled towards the sun and I generally move mine twice throughout the day, to capture the best angle for morning, midday and afternoon sun.
The table below gives a rough idea of light intensity under various conditions. Intensity is rated as a percentage of full sun intensity (also called AM1.5)
Energy Available at Various Light Conditions Relative to Full Sun A blocking diode is recommended between any solar cell and battery. This will prevent the battery from draining back out through the panel when cloudy conditions see the panel’s output voltage drop below the required charge level. Powerfilm panels come standard with a blocking diode.
A charge controller is used to prevent overcharging. As a general recommendation, a charge controller should be used if the current output of the solar panel, in Amps, is more than 1% of the battery capacity, in Amp-hours. For example, a charge controller is recommended if the R14 panel (delivering 0.9 Amps) were connected to a battery that is less than 90 Amp-hours. I am a charging 18Ah battery so the maximum solar panel current of 0.9A is 5% of the battery's capacity.
Lead acid batteries should be charged in three stages:
1. constant-current charge
2. topping charge
3. float charge.
The constant-current charge applies the bulk of the charge and takes up roughly half of the required charge time; the topping charge continues at a lower charge current and provides saturation, and the float charge compensates for the loss caused by self-discharge.
During the constant-current charge, the battery charges to 70 percent in 5–8 hours; the remaining 30 percent is filled with the slower topping charge that lasts another 7–10 hours. The topping charge is essential for the well-being of the battery. Fail to do so and the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation. The float charge in the third stage maintains the battery at full charge.
A charge controller lowers a high voltage and boosts a low one to the desired level. It also modifies voltage and current levels when the various stages of charging are detected.
There are two basic type of charger, PWM and MPPT.
MPPT – ( Maximum_power_point_tracking ) tracks the output of the panel more efficiently but is twice the price of a PWM charger
PWM – (Pulse Width Modulation) is cheaper and tracks the solar panel well enough for my application http://www.powerfilmsolar.com/products/ ... yIDs=k6574
I chose the Sunguard 4.5amp (PWM) because it is fully waterproof and is fitted with the plugs required to connect it directly to the solar panel. They are resold by Powerfilm distributors. It is capable of charging both SLA and Fusion LifePo4 batteries in my setup. I have discovered that the current flow stops if I leave the charge controller in full sun in the middle of the day. To prevent this I cover charge controller and batteries with a $2 reflective car sunshield pegged down to stop it blowing away.
Warning! – Do NOT attempt to charge the li-ion packs based on 18650 cells with this controller. Li-ion requires a different charging profile and to do this from a solar panel you will need a MPPT regulator matched to the battery pack’s voltage.
These charge Li-ion or lipo batteries and are robust and popular @ $115. http://genasun.com/all-products/solar-c ... ontroller/
If you decide to charge Li-ion or lipo batteries from a solar panel, in addition to the charge controller, I highly recommend a lipo charge bag to keep your batteries in whilst charging. On eBay they are between $5 and $10. Here's a link to a hobby store site that shouldn't disappear. http://www.hobbyking.com/hobbyking/stor ... _sack.html.
The bag is designed to contain any fire that may occur whilst charging your batteries. I have visions of my batteries overheating and starting the largest grass fire Fraser Island has ever seen, whilst I am 5km away on the yak, fishing. Not to mention losing all my food, camping gear, etc in the fire and having to sail home, followed by a trip to court and a possibly the big house for a while, no doubt. In fact I will be purchasing a few of these when my Li-ion packs arrive for charging at home. Overkill perhaps, but at $5, a worthwhile precaution when you consider the possible alternatives, especially if you live in a timber house.
Battery(s) (SLA or LIFePO)
I use SLA batteries in my setup but also charge my LifePo4 battery for my sounder directly from the panel. The fusion brand of LifePo4 battery I am using, claims twice the output of an equivalent rated SLA battery, more charge cycles and can be charged using a standard SLA charger, AC or DC (It is also half the weight and 4 times the price). My usage to date confirms the greater capacity. I use two 9Ah batteries to charge everything for 6 people. To just look after yourself, a single 9Ah would suffice. No doubt I could get away with a single 9Ah for all six people but having the additional capacity means the battery voltage isn’t dropped too low after an evening charge session and essentially only requires a topping charge for 5-6 hours to take it back to full capacity. It also means we can get by if there is a heavily clouded day and little solar charging occurs.
Parallel and Series Circuits
The most efficient way to charge more than one battery is to connect the two batteries in parallel. Batteries connected in series double the voltage but retain the same output capacity as one single battery. Two 12V 9Ah batteries connected in series provide a single cell of 24V @ 9Ah. Not what we want. Batteries connected in parallel, double the output capacity but retain the same voltage. Two 12V 9Ah batteries connected in parallel provide a single cell of 12V @ 18Ah. This is what we are after for both charging and discharging circuits. You connect two batteries in parallel by joining the positive terminals on each battery together and the negative terminals of each battery together. Connect the positive output of the solar panel to the positive terminal on one battery and the negative output of the solar panel to the negative terminal of the second battery. Ensure the two batteries are at a similar voltage level when connecting in parallel. Batteries of a wide variation in potential will see one batter charging the other once the two are connected. Best to charge and drain them to the same levels.
I have a cheapy voltmeter from Aldi for $20. You can pay hundreds of dollars for super accurate ones but this is all you need to make surel your cables and connections are right (resistance), the panel is charging (current) and your batteries are at full charge (voltage). By placing it at various points in the circuit you can see exactly what is going on.