Warning - LONG solar post
Another GREAT forum for solar power needs is:
Solar Forum - Discussion Board on Solar Panels and Solar Power Products
One thing for sure - you don't get into hobby solar power to save money - you do it for other reasons (take your pick.)
This is kind of (sorry - really long), so I don't know if this belongs in this thread or maybe in the DIY or Electronics subforum....
Admittedly, it can be overwhelming, but a great way to start is with a small project - like powering a scanner for 10 hours. What is the panel and battery size I need?
* The Pro-163 draws 600ma
* You want to power it for 10 hours before having to recharge with no load on it.
* Total current draw .600 amps * 10 hours = 6 amps total. But you DON'T want a 6ah battery!
Lets pick a battery. For simplicity and safety, I recommend an SLA DEEP-CYCLE sealed lead acid AGM (NOT Gell!). You can get these around the corner at RS if you want like the UB series. You can use them indoors, but like all batteries, do NOT charge them in a closed box. If you develop the solar habit, you'll be hunting down Concorde, Deka, Trojan, and Rolls-Surrette deep-cycle types - but the typical small SLA/AGM is fine for starters.
Here we want to develop a good habit of not drawing out more than 50% of the battery capacity. For one thing, it is good for cycle life. And, at a 50% DOD depth-of-discharge, you'll find the battery just a bit above 12 - 12.2 volts, which is convenient since some gear doesn't like going lower in voltage. If you want to take this measurement, do so when the battery is not being charged, nor has a load on it, AND has rested for at least 2 hours. Don't rely on shirt-pocket meters - get something a little more decent.
* This is a long way to say that a 12AH SLA-AGM battery will do - basically you are just doubling the total amount of current calculated above because of the 50% DOD requirement.
* What panel size would be appropriate? The SLA-AGM type battery can usually withstand a maximum charge rate of C/4. (but always check the manufacturer spec!) To avoid frustration and charge as quickly as possible, lets shoot for C/4. (Flooded wet-cells usually a max of C/8 to C/10 - but we're not covering those here.) You can go lower, but understand that it might take days to charge. A typical SOLAR day consists of only 4 hours, typically between 10am to 2pm despite it being light from 8am to 5pm at your location. This is called solar INSOLATION, basically meaning that these are the hours when your panel will actually do some real work. You can consult charts for your area and season. Pros usually design for the worst - wintertime etc, but we'll keep it simple for now. We're not factoring in going multiple days of rain or going solar in the Alaskan winter.
* A nominal 12V solar panel is actually about 18V or so measured open circuit. It has to be higher than the battery terminal voltage to work. Batteries under charge usually reach about 14.2 - 14.6 volts at the end of bulk charging, so the panel has to be at least 3-4 volts higher. So we'll use a standard panel of 18V to calculate our needs. Some panels are rated a little lower, and some go a bit higher. Once the charger is removed, the fully charged battery voltage drops quickly to about 13.3 volts, and then rests somewhere above 12.7 volts. But this is good enough for back-of-napkin engineering. If you DO end up trying to use your equipment AND charging at the same time, be SURE your gear can withstand 14.6 volts - but here we are just charging out in the backyard with no gear attached.
PIE-Chart time. (P=I*E) (watts = current * voltage)
Our 12ah battery can withstand a max charge rate of 12A/4, so we only need a panel of about 3amps.
18 volt panel * 3 amps = 54 watts. A 60-watt panel would do nicely. Check the Panel's IMP current rating - you might want to go a bit smaller like 50-55 amps to stay within the manufacturer's max current spec.
Because we are only using up 50% of the 12ah battery, and need to put 6amps back in, that means that this battery will reach the absorption stage (about 80% charge) in 2 hours. An additional 2 hours or more of lower-voltage absorption/float will be good to get it fully charged. So in the span of 4 hours, you've got a fully charged battery - assuming perfect conditions. A quality charge-controller will take care of automatically switching between bulk and absorption/float stage charging.
Got more time on your hands, more solar insolation hours, or want to keep within budget? Halve the current rating of the panel and get a 30 watt panel (about 1.6 amps)
You've GOT to have a charge controller to go between the panel and the battery. Quality types with temperature compensation like the Morningstar Sunguard 4.5a controller is a good way to do it right on a small scale, and only a tad more expensive than the cheaper on/off types. Spend a little more up front, and you won't have to buy things twice. Follow their instructions on which connections to make first, and don't accidentally short the controller's leads.
As always, be SAFE. Take your time around the connections, do not wear rings and jewelry and drop those across the terminals. Fuse the leads. There is so much more to discover with solar, and this is only a very simple project to whet the appetite while reading what the real pros have to say in the forums.
