Solar Introduction

The ability to dry camp, or boondock, is inherently part of the capabilities of all RV’s. The amount of time one can live effectively “off-grid” is dependent on your water storage capabilities, and the size of your battery bank (or how much you want to run your generator). Most RV manufacturers do not provide advanced boondocking technology as a standard part of their RV’s, so you are usually limited to 2-4 days without hookups. Enhancing the standard RV’s capabilities can allow you to live indefinitely without hookups.

So what do you need to effectively live off grid indefinitely? The heart of your system is the battery bank. You will need enough battery capacity to supply your energy needs. That means translating some of the DC battery power to AC, so it can be used by your normal RV appliances. You do this with an inverter.

Next, you need a way to replenish the battery power you use. That can be either a generator in combination with a modern battery charger, or solar panels in combination with a solar regulator. Or a little of both, which is what most people use. Solar is really an option here. You can live effectively off grid with just a generator and a proper battery bank, but for long term use you will find it most convenient to combine this with some solar panels.

You also need a way to monitor the status of the system. Without monitoring the system you will not know how much energy is available for use, or when to use the generator to help recharge the battery bank. If the battery bank is the “heart” of your electrical system, then the monitors are the “brains’. You need them both.

Determining Your Needs

First, you need to be realistic about your expectations. If you expect to install a solar system and use power just as you did when hooked to shore power, then you will be disappointed. Despite what some may tell you, living with an alternative energy system in an RV requires conservation. This is because, unlike off-grid home applications, most RV’s cannot store enough batteries to allow a large enough system for unregulated energy consumption. You need to learn to minimize use of high-power-consumption devices, supplement your existing RV systems with more efficient devices (such as using a catalytic heater instead of your RV furnace, which uses great amounts of 12-volt power), and monitor your energy use so you know when you are in trouble. Running out of power when you really need it is not fun. Killing your battery bank because you drew it down too far is even less fun – batteries are expensive.

You also need to examine your motivations for wanting solar. Solar use is a lifestyle decision. Adding an effective solar system to an RV will rarely pay back the costs of installing it. Nor will you recoup your investment when selling the rig. The best (and really only) reason to add solar is so you have the option of boondocking for long periods of time without hookups. If you do not enjoy doing this, then you should reflect on why you want to install a solar system. One or two days of boondocking between sessions of hooking up to shore power does not require a solar system, and its auxiliary systems. You can get by for a couple of days on a reasonable size battery bank. If you need 120-volt power, consider adding an inverter/charger. If you then find you need to recharge the batteries without shore power, you can consider adding a generator – either a small portable one, like a Honda 2000, or a genset that is permanently installed. If you have a motor home, you likely have a genset already. Notice, there is no solar system here. You really don’t need one if you are just overnighting occasionally.

Need to run your air conditioning? Well, a solar system is not going to help you here. It is not realistic to expect to run an air conditioner on a battery bank. You need a properly sized generator to run air conditioning “off-grid”. (Note: small window units could be run for short periods of time off a large battery bank, but from a practical view, this is just not feasible for long periods.)

OK, so you like to boondock for long periods of time. You’ve decided that you can afford to invest $3000+ dollars to make your life more pleasant when boondocking. How big of a system do you need? Only you can answer that. You need to examine your lifestyle while boondocking (or your anticipated lifestyle – you don’t actually have to boondock) and figure out how much power you use. Figuring out power usage while connected to shore power won’t give you your answer, because you are using lots of electric devices you won’t use when you boondock. For example: electric hot water heater, refrigerator on electric, battery chargers plugged in, converter on, lots of lights on, cooking turkeys in the microwave (just kidding).

So, how do you figure your power use? Think about what you have to use and add it all up. You can figure in watts, or in amp hours. Watts is probably easier, but ultimately you will need to convert to amps so I suggest you do your figuring in amps to start with. Look on the electric plate on the various devices and it will tell you what the device uses power-wise. Add them all up for the amount of time you run them. Don’t count any 120-volt lights, because you will only use 12-volt lighting while boondocking. Remember, you can figure watts by knowing the voltage and the amperage that the device is rated at – both are on the electrical plate (and if you are lucky, the wattage is there) watts=volts x amps. Sometimes electric plates on devices list ratings as xxVA (e.g. 40 VA) – this is watts (VA means Volts x Amps). When you work with solar it is best to figure everything in DC voltage, because your battery bank is DC – that means converting all your AC measurements to DC. In electrical stuff, watts is the universal measure. If you have a watt rating on a 12-volt appliance, it can be directly added to the watt rating of a 120-volt appliance to get the total watts consumed. Amperatge ratings have to be converted, based on the voltage. Sounds complicated, but some simple math will allow you to get the total DC amps consumed from your battery.

Here are some 12 volt examples: 2 – 20 watt lights for 4 hrs= 40 x 4 = 160 watts DC, refrigerator 2 watts for 24 hrs = 48 watts DC. Now you have to figure your 120-volt loads: hairdryer 1500 watts for 12 minutes = 300 watts. You have to convert to DC – just multiply by 10 = 3000 watts DC. Microwave 1000watts x 5 minutes = 83 watts x 10 = 830. So all total we have (160+48+3000+830) 4038 watts in a 24 hr period. To convert to amps, divide by 12 or 120 – whichever voltage you are figuring watts for. (Getting complicated, right? That’s why you should just use amps to start with.) We did not count TV, satellite receiver, etc. You need to add up everything. Why did we count the refrigerator in our example when it is running on propane? Because, even when on propane, the refrigerator uses 12-volt power for its control circuits.

With an estimation of the number of DC watts you use on a daily basis you can calculate how many panels you need to supply that, and estimate how long you will have to run your generator to fill the “gap”, if generator use is part of your energy strategy. Don’t forget to add in “phantom” loads. For most RVs, these average around 1-2 amps DC (per hour). These are loads that occur when it seems everything is “off”. They come from battery chargers, electronic boards in your propane appliances, propane and CO alarms, etc. You also need to factor in the inefficiencies of converting/using power. There is energy lost when inverting, and energy lost in wire runs. The rule of thumb is 30% lost when inverting, and 20% lost in direct 12-volt battery use. It generally will not be more than this – it may actually be less, depending on your system.

Don’t get obsessed with figuring exactly what you need. Just get close and then usage will allow you to adjust. As a rule of thumb, the average RVer uses between 75 and 100 amps DC per “cycle” (partial day and overnight). Remember, when you are using power during the day (while charging) your instrumentation is not giving you a true count because power is being supplied while you are using it. The nice thing about a properly designed solar system is that you can easily expand it by adding panels (as long as you buy a large enough solar regulator initially). For an excellent discussion of sizing your system take a look at Mac McClellan's website http://www.bestfitrecruiting.com/ElectricalSystemSizing.htm