I've got a pretty serious case of sleep apnea, which, when added to my anxiety, makes for a pressing case for relief. As you may know I've been doing a lot of traveling, based out of the Durango, Colorado area, where I have family and so need a power solution when I'm on the road in my pickup based traveling outfit.
The best source on the internet for information on this topic relates to Recreational Vehicle installations, and these are worth reading. The biggest addition I'd make to this base of knowledge is recommending the 'Minn Kota Trolling Motor Power Center' , a battery box that includes two 12v cigarette lighter power plugs, a simple (very) voltage meter, and two separate circuit breakers for additional safety - in addition to the spill protection provided by any basic box.
Please note that I am by no means an electrical engineer, so the following is by no means guaranteed. It is, with this particular combo below, field tested so I'm pretty confident I've got it about right - and also with enough writing chops to communicate same relatively effectively. That said, here's the particular installation I came up with:
Trolling Motor Power Center (Amazon) $60
Group 27 Deep Cycle Battery (Walmart) - $70
50 Watt Solar Panel Options (Amazon) - $100-$150
InstaPark
Solar Panel Charge Controller (might be included with panel) - $20
Plus cabling connections to a vehicle electric system, if you desire. $??
TOTAL COST, $250!
Of course all of the above can be varied depending on your specific needs. As such, I'd recommend educating yourself a bit on both battery options and low voltage electrics before you make your personal, final decision.
BATTERIES
Deep cycle lead acid batteries have more issues than comparable automobile batteries as deep discharges do add wear to a battery - a significant factor if you plan on daily use for much of the year. Deep cycle batteries are designed to minimize this wear, but it is still significant. AGM batteries are a step up, in some regards, but not so much for heavy use. AGM batteries don't require monitoring water levels, maintain charges better for occasional use, and are more durable, like for off road vehicle usage.
I'm not aware of cost competitive large lithium-ion batteries, but that will likely change at some point. One possible alternative, which I'm just beginning to look at is the creation of banks of 'D' cell Nickel Metal Hydride batteries.
Using other batteries in your total setup is worth considering. Powering a lap top or similar device (Camera, etc) with additional after market batteries (much cheaper than what the original manufacturer sells, and, in my experience, of good-excellent quality).is a good option. Similarly, NiMH standard battery powered music devices are readily, and cheaply, available. I keep a good supply of NiMH batteries on hand for my various needs and usually lose them before they go bad (1000's of charge cycles). Of course, a car stereo based music/dvd setup (check out the truck stops!) is an easy and affordable choice too.
You can recharge devices via a solar system, but keep in mind there is at least a 50% power loss (IIRC!) if you have to use an AC based charger, which converts the DC to AC, then back to DC...
With lead acid batteries the crucial factor to remember is that they are most durable if only discharged to 80% of capacity, **on average**.
Here's some simplified math on the above battery that also illustrates some basic low voltage electrics. The above battery is rated at 115 amp hours. Amps times volts = watts, so an amp hour at 12 volts is 12 watts for one hour. An easy to remember, but rough, rule of thumb is that each amp equals 10 watts - about the amount of a decent LED light.
So, if you had 100 watts of 12v devices, one can safely expect 10 plus hours of service from a full discharge of your lead acid battery. But remember, the best case scenario is to stay as close as possible, on average, to only a 20% discharge.
As such, don't expect to run a microwave and a hair dryer for very long on the above set-up - however doing so isn't as difficult to do so as you might think - those RV websites have better info on that type of usage.
Calculating how big a solar panel you need is a good way of checking your math, as these are rated in 12volt Watts. So, with the above battery a 50 watt solar panel is fairly generous - generating - under ideal conditions - enough power to cover a daily cycle in 2 hours. Of course, conditions are not always ideal and you may also want power during the day. If bad weather does set in (hopefully you are using your system where that is relatively rare!) this is a good time to go past the 80% charge level - again, still trying to keep that 80% average.
The biggest thing I learned the hard way is that battery capacity, like with your car battery, varies a lot with temperature. As such, storing your battery in heated (and moderately ventilated) space is a good idea.
Do make sure not to confuse watts at 12 volts with the wattage of your standard household current at approximately 120volts. If I've educated myself correctly, the conversion factor is ten fold and a 50 watt panel will only generate 5 watts of 120v current. In addition to that the loss figure for power inverters, converting from DC to AC, is roughly 50% - as I understand it, leaving you with only 3-4 watts net.
This is a big reason to stay with a 12volt setup for your power consumption. Here again is a good time to take a look at the RV websites, and, also, truck stops.
SOLAR PANELS
There are 3 types of solar panels, amorphous, mono-crystalline, and polycrystalline. Amorphous panels can be the cheapest, but they are also the largest in size. Historically they have not been as durable, but supposedly they are improving rapidly. Mono-crystalline are the most readily available quality alternative but polycrystalline are nearly as efficient and are, by one person I've read, the best overall value.
Where you are mounting your panel makes physical dimensions a possible crucial factor-especially on a vehicle. The most creative installation I've seen was directly to the vehicle hood - something likely NOT an option if your vehicle is newer. I had my first panel under the tie down ropes of my canoe - however in some icy weather it blew off - so don't try that! Bolting to the top of a Yakima or Thule style car top 'rocket box' would work well, especially if you seal the mounting locations with silicon caulk. Any car top sports equipment rack would also work - if your panel is BIG enough! There are some rack solutions on the market, but I didn't find anything that would work well. Hopefully this will improve in time. Meanwhile, I'm working on a design using a collapsible camera tripod that would also make the panel manually adjustable to solar angles!
SOLAR CHARGE CONTROLLERS
Let's take another look at the electrics math with the solar charge controller - which prevent the overcharging of batteries (and are less and less needed with smaller panels). Charge controllers are rated in amps, and our formula is then watts divided by volts = amps. The above 50 watt panel would then require approximately a 6 amp controller. (best to be on the safe side here, if you can - consider also that 12 volt devices, and batteries, often run in the 13-14 volt range!
CABLE CONNECTION TO VEHICLE CHARGING SYSTEM
Not included in the above price total is a connection to your vehicle charging system, which is recommended - if your installation is vehicle based. This may be the best area hire a professional - this being a rather simple job for a qualified automotive battery guy. Same may also be able to sell you the best cable. Because of the concept of electrical resistance, OHMs, (which I won't even attempt to explain as I don't understand the specifics) thicker wire is better. I just used 3 strands of some scrap wire that I had around, and wired directly to my battery terminals using cable ties to secure the wire to the chassis. I disconnect my cable when the battery is used, but for a nominal charge you can get either and 'isolator' or a 'solenoid'. I've been told, by a credible source, that solenoids are better.
THE SOLAR LEARNING CURVE!
This may all seem a bit complicated but solar, in some fashion, is here to stay and going through this learning curve will prepare you for that future. Hopefully you will also join the ranks of us waiting for better battery technology, but that is assured.
