Figuring out a suitable system for electric can be confusing as hell. While there are lots of electricians and handymen out there who have skills or knowledge in different areas of installing or explaining electrical components, its difficult to get someone to competently explain how electricity works and how to build a system to meet your off grid needs. I will not try to comprehensively explain this either..but I will relate some of the important things that were frustrating initially for me to figure out.
When designing a system you have to assess your electrical needs. How many watts will you be using? A small fridge is about 150 watts per hour(average), lights? 50 watts. A laptop..100 watts. A tv(lcd or led)….30 watts. Its not difficult to compile a list and add up your total. the key to remember here is that these appliances run on 110 volts alternating current(ac) your solar and batteries will likely be 12 volts direct current(dc)…SO, you will need an inverter to step up the 12 volt power to 110 ac volts. This is the important part….you might have 1000 watts of solar but you need to divide that by about 10 to see what you will have in 110 volt wattage. so a 30 watt tv will really be using abuot 300 watts of 12 volt power. Plus you are losing about 10 percent for the inefficiency of your inverter and cable attenuation. so its really divided by about a power of 11. So all of a sudden, it doesnt seem so feasible to slap a few solar panels on the roof and get away with running an ac unit, a microwave or those sorts of power hungry appliances. It’s not going to happen. However, there are ways around those roadblocks. Firstly, propane takes care of your heating and cooking without using any electric. Propane is liquid gold. You might even find a refrigerator that runs mostly on propane. Cooling the motorhome can be tricky without using a ton of voltage. If your motorhome has AC on the dash then you can run your vehicle to cool your cabin or use your electric to run a fan. I have a 10 inch turbo style fan and it uses about 40 watts. It can get sweltering inside but being in the direct line of the fan and covering all the windows to block the sun makes it tolerable. I also use a small USB fan that only uses about 5 watts to help keep a breeze inside. Your inverter will tell you the voltage of your battery bank and its imprtant to be vigilant of this number and also how your usage affects the movement of the number. a 12 volt battery chargers at 13 volts of higher. when the battery is charging your voltage level will be pulled up artificially high. So if your battery is not under load and is being charged by solar or your alternator then your inverter voltage reading will be raised higher than the actual charge of your battery bank. Conversely if you put your batteries under load, the voltage reading will be pulled lower than the batteries actual are. In other words, it can be confusing as fuck. I have found that when my batteries are fully charges and not under any load, the inverter will ready about 12.4. Fully charged batteries will drop through the first few levels of voltage quickly and then get much more time out of the middle levels. In other words, if our battery bank is fully charged and i turn on my PS3 and TV, the inverter will go from reading 13.0 to 12.4 very quickly. It might show 12.3 for about 40 minutes, 12.2 for 60 minutes, 12.1 for 90 minutes and so on. I turn my system off as soon as the inverter shows 11.7. this is your battery bank at 50% while not under a load. You can set your solar charger to automatically shut down at some point around 11.5 if some circumstance prevents you from being able to manually shut it off. Being attentive of your system will mean a much longer lifespan of your batteries.
I have about 600 watts of solar panels on the roof and I can also charge my battery bank from the alternator of my motorhome. You dont get too much juice by running the motorhome, just a trickle charge really but if your goal is just to watch an extra hour of TV than you can accomplish that. My battery bank is comprised of 4 105 ah lead acid batteries. They weigh about 100 pounds each and cost about $100 each. when using deep cycle lead acid batteries such as these you can only discharge them down to 50%. Anything more than that will lose a cycle and shorten the lifespan of the battery. If you are good to your batteries you can expect them to last about 2 to 4 years. Another option is lithium ion. While lithium is more than 3xs as expensive as lead acid you can discharge them all the way to nothing without hurting the lifespan of the batteries. The lithium lifespan is also triple that of a lead acid battery and there is no discharge of dangerous gasses. Lithium batteries also weigh a fraction of lead acid batteries which is important if you dont want your battery bank to make your motorhome look like its sitting down. When buying your appliances keep in mind their energy usage. Most 30 inch led or lcd TVs only use about 25-35 watts. A small roku streaming stick only uses about 4 watts so between those two and a wifi signal you have unlimited entertainment for very small wattage. We can use our fridge during the day with full sunlight on our solar panels but dont have enough storage from the battery bank to run it all night. I have found a good solution is to fill the small freezer full of blue ice blocks and set the freezer on its coldest setting. During the 6 hours or so that you run the fridge during the day they will freeze and you can then shut the fridge off entirely and move the blocks from your freezer to your fridge to keep it cool overnight.
We also have two solar lanterns and a few solar battery packs that we charge duriring the day so we can recharge our phones and use the lanterns for light at night. Installing a solar powered motion detector light outside your door is a great move as well. Not only does it enhance your security but makes it easy to find your key and get inside at night. If your motorhome is going to be in a fixed position you should consider a wind turbine. you can generate ampage at night rather than during the day with just solar. for $300 to $600 you can find a turbine that generates up to 1000 watts. as far as solar, consider getting polychromatic panels. they generate maximum wattage not just in direct sunlight but from dusk to dawn regardless of cloud cover.
In closing, you can build a workable off grid system that will cover most of your needs for anywhere from $500 to $5000. Just remember that you will have to sacrifice or rely on shorepower for the most power hungry of your appliances. You should view rationing your resources as not just frustrating limitations but a new opportunity to diversify your recreational and lifestyle choices. Reading, board games and writing all use 0 watts and will likely prove more rewarding than a steady stream of video games and reality TV.