This is a good place to start if you're new to solar and would like to learn the basics of an Off The Grid RV solar system.
We are available 7 days a week if you have any questions, we would love to hear from you.
We get lots of customers asking about various size kits and what they will run, or I have a 30 amp RV will this 480 watt with 30 amp controller run everything in my new coach?
I have two batteries, so what size kit do I need?
So we are adding this section to shed some light, we hope it helps you better understand how an off grid solar system works.
We all have our own needs when it comes to dry camping or boon docking, some of us are power hogs and want the TV on all day, have residential refrigerators, while others needs are minimal using candles at night to conserve power. So for that reason, it's not a one size fits all type of deal. The amount of power usage "you" require is dependent on "your" RV and "your" camping style.
What the solar system does is charge your battery bank just like an off grid home or cabin, which on an RV is 12v like a car (not an electric car). The battery then stores that power so you have usable power at night also. That 12v battery or battery bank powers several things in your RV, even when you're on shore power via the "converter" (Fancy name for worthless battery charger). Your lights are 12v, the water pump is 12v, the furnace fan is 12v, while the fridge is running on propane (LP) it also uses a small amount of 12v to monitor the system, light the pilot etc. When your water heater is on, it also uses 12v like the fridge, if they have electronic ignition unlike the older systems you had to light manually while holding a button in. So with a larger battery bank and solar kit, we can use and store more usable power.
Most of the new RVs manufactured in the last several years have LED lights from the factory. This is a large amount of power savings, you can run 5-7 LED lights which is equal to 1 incandescent bulb. If you don't have them in your RV, get rid of the main area lights ASAP like the kitchen, bath and dining or living area. You don't have to change every single bulb in the RV, most people don't use half of them, so focus on the main ones.
Now, if this is all you require while dry camping then your needs are minimal, and in the southwest 1-2 batteries and our 160 watt kit will sustain that without ever running the generator. But you still don't have 120v household power for laptops, TVs etc. That's where the "Inverter" comes in, and more wattage is required in order to run and replenish that battery bank so you can repeat the cycle day after day.
Everyone gets confused when it comes to Converter or Inverter, so lets jump into that for a minute.
This worthless piece of equipment (unless you're in a $150K diesel pusher) is nothing more than an over priced, under performing battery charger. It's hidden out of sight like its name and usually plugged into a 120 volt outlet under a cabinet or behind the 120v breaker panel. So when your plugged into shore power, or out in the desert running off the generator, it powers up the Converter and starts attempting to charge the battery. So it takes the 120 volt, and "converts" it to 12v, then is hooked to the battery with a positive and a negative wire which is how it charges, just like a battery charger you can buy just about anywhere.
The biggest problem with this so called battery charger, is the charge voltage is preset to a safe zone voltage of 14.4v, and will only hold that voltage for a very short time at best. Then it will drop to a float charge (battery voltage maintainer) at 13.6v long long long before the battery is actually charged. If you have a flooded battery you add water to, they need to charge at 14.8v (check with your specific battery manufacture) in order to get fully charged, and usually that voltage will hold for 2-4 hours before it goes to a float charge of 13.6v. Even if you're plugged into shore power, or running the genset for 8-12 hours, or 6 months, you will NEVER EVER get your batteries 100% fully charged, and are slowly killing them. This is why Solar is far superior to your converter, and will actually charge your battery bank 100%. I will explain why after the inverter below.
This wonderful piece of equipment is what transforms 12v battery power, to 120v household power like your outlets at home for small appliances. Lets focus on these two types of inverters, one will be a stand alone or portable inverter with its own receptacles like this 2000 watt Cotek SP2000 This type of inverter has two battery cables to power it up, and a 120v receptacle you plug directly into.
The other 2000 watt will be a Magnum inverter/Converter which is a hardwired inverter designed to power your entire coach, which is what comes factory on a $150K plus diesel pushers. Hardwired. The built in 100 amp converter is actually adjustable per battery type and is capable of fully charging your batteries, but does come with a price tag that reflects the difference. These are both pure sine wave inverters producing clean power which is what you want. The price different is about $1500 more for good quality hardwired inverter like the Magnum USA made MS2012 including the required remote used for programing, operating and monitoring the inverter. Hard wired inverters are connected a little different, your shore power cord actually wires into the inverter (Pass Through), then out to the 120v sub panel (breaker panel) powering up all the receptacles in the RV when on shore or generator power. Or, if you have an on board generator your outlet side of the transfer switch will wire into the inverter instead of the shore power cord. So when your on shore power, or genset power, it passes through the inverter and activates the internal converter to also start charging the batteries. If you're dry camping, you push a button on the remote and all your receptacles are now powered up without the noise or fumes from generator.
Now back to the solar...
A quality solar controller will have adjustable battery type settings, which is critical to properly charge different batteries like Flooded, AGM, Gel, LiFePO4 (Lithium) etc. Check your specific battery specs on the manufactures website. In order to fully charge a battery, it must reach the voltage specified by the manufacture, and hold that voltage for a period of time until the battery becomes full and will not accept any more amps. Lets say we have a 400 amp hour flooded battery bank, this is total amp hour capacity and 50% is usable or 200 amp hours. Now, in order for this battery to become fully charged, it "must" reach 14.8v and hold that voltage until the incoming amperage drops down to 2% of the "total" battery bank capacity, which is 400 X 0.02= 8 amps. Even if we have 1000 watts on the roof, which would be charging at around 80 amps @12.6v, the amperage will drop down below 8 once the battery becomes fully charged. That is the only time your battery is considered fully charged, not when the little green dummy lights in the RV show good, or full.
This is the main reason 90% of all RV's out there can't make it through one single night without waking up to dead batteries. You're running your little Honda EU2000 for 8 hours wasting fuel, and don't even know your worthless converter has been in float mode (battery maintainer mode) for the last 7.5 hours at 13.6v. That's why you can't run your tiny little furnace for the night, its not because the furnace is a big power hog, they only draw 2.5 to 3.5 amps per hour when running! Did I mention worthless converter yet? Lol... Lets move on now.
True deep cycle batteries used for storing power will be rated in AH or amp hours, this is the total AH capacity of the battery. For most batteries you can use 50% of the total capacity, anything more will shorten the life of the battery/batteries. Lithium batteries can be drawn down 100%, charge 3 times faster, are light weight, and will hold a nominal voltage (under a heavy load) of 12.8v even with a 100 amp draw like this Lithionics battery which is 150 amp hours, and equivalent to 300.
So your average 6v flooded golf cart battery is 225AH, we need two of them wired in series (Positive from one battery to Negative on the other) to get 12v.Now we have two open post left (Nothing connected to them yet). If you were to measure the voltage there, you would get your 12v, and this is where our main positives and negatives go for every 12v wire that gets hooked up. Nothing else connects to the series (Positive to Negative) connection. When you wire anything in series like two batteries, or two solar panels the voltage doubles and the amperage stays the same.
Everything you plug in or turn on has a wattage rating or sticker which shows the wattage of that device. If you don't know what Ohm's Law is, this is how it works. Lets say you have a 32" flat screen TV, the sticker says its 90 watts and will also show the amps it consumes while on household power which is 120 volt. Ohms Law is watts divided by volts will equal the amp draw. So 90/120v= .75 of 1 amp per hour, so less than an amp per hour. This is where most people think they only need 1 amp to run the TV in their RV. So when running on solar and dry camping we are working with 12v to power everything. Now we take the 90/12v and are drawing 7.5 amps per hour instead of .75 because we are using a lower voltage to power it.
Now you want to run the TV 5 hours per night at 7.5 amps per hour = 37.5 AH (amp hours), run the furnace for 5 hours at 3.5 amps=17.5AH, laptop for 3 hours x 5 amps=15AH , plus the rest of our 12v usage we discussed earlier so we can repeat the cycle on a daily basis via solar without ever running the generator. Let just add another 30 AH for the rest of the 12v draws, now we are down 100 amp hours from full, or 50% of our 200 AH battery bank. Now we need enough solar to put back in 100 amp hours, and run the daily 12v draws. Our 360 watt kit will produce about 140 amp hours a day here in the southwest. More is always better when it comes to solar, if you're in cloudy weather, camping in December or January when the sun is at its lowest point etc.
200 watts/12.6v=15.87 amps per hour x 5 hours is 79.36, location and weather will vary results. Also as the battery becomes full and the voltage is rising trying to reach the set point voltage, our amperage will start to drop. The higher the voltage, the lower the amperage. 200/14.8=13.51A. Keep in mind, these ratings are at 77 degrees and angled towards the sun 45-55 deg depending on location.
The best way to determine your AH usage is a battery monitor which will calculate your exact AH usage at any given time. They will also show you what each and every device or light bulb draws down to 1/10th of an amp like this Victron BMV 702 with Bluetooth or Trimetric 2030A or 2030RV. what percentage from full you are, how many amps coming in or out of the battery bank, how many days its been since you were fully charged and met the criteria mentioned above ( Reached the set point voltage of 14.8v and dropped to 2% of AH capacity).
I hope your have a little more understanding of how an Off The Grid RV Solar system works, thanks for visiting.