RVs – Grid Sub

Living in a camper van or an RV can be quite liberating. You are free to move around as you please, wake up in different regions and enjoy life to the fullest. All this freedom comes at a cost. You have to content with tons of compromises to make it work. The biggest issue people have to deal with (well, after the limited space compared to a house) is power. If you won’t be living in a parking lot with RV electrical hookups, you will have to go solar or run a generator constantly. Solar power is cleaner, less noisy and easier to manage that running a generator especially if you are a full time boondocker. This brings us to the big question: How many solar panels do I need for my RV? It Depends on a Couple of Things The biggest determinants of how many panels you need are: Your daily power consumptionThe wattage on each solar panelThe number of peak solar hours you expect to getThe size of the battery bankWhether you will install alternative chargers If you don’t feel like reading the whole explanation, you can download this free spreadsheet I made and just plug in some values to get your solar panel needs estimate! The number of panels you need depends on how much power you use per day. Figuring out your power needs is the first step to properly sizing a solar power system. It involves figuring out the gadgets you want to keep, how long you will be running them and their wattage. How Much Power Do You Need? If you are in the planning phase and don’t have the RV ready, you can create an appliance list to determine how much power you will need once you hit the road. I made a simple table you can use to collect the data you need to answer this question. The table is already populated with basic appliances an average RV will need to go offline for a month or so. You can download a Google Sheets version of the table. It has the formulas needed to handle the calculations and give you estimates off the bat. ApplianceQtyWattageHrs/DayTotal PowerLED Lights575175Smartphone15315Ventilation Fan115460Induction Cooktop110000.5500TV1373111 861 The above are just estimations, you can read actual values from the product sticker on your appliancesIf an appliance has Amps rating and no wattage, you can get the watts by using this formula: Watts= Amps x Voltage From the above data, my virtual RV will need 861 watts a day. This is the available power the camper needs. The figure doesn’t factor in power losses encountered during storage, conversion and transmission of the power. Pro Tip: If you already have the RV, get a power meter and log the total power you use in a day for a week or two. This will give you a more accurate figure of the overall electricity you need to go offgrid. Translating Your Energy Requirements to Solar Panel Sizing So, now that we have a rough figure in mind, we can go ahead and estimate how many solar panels we need to meet these requirements. Figure Out How Much Sun You’ll Receive The total energy your panels generate depends on how much sunlight hours they get in a day. Renogy Solar compiled an easy to use table showing solar peak hour estimations by state. You can find it here. Virginia quotes 3.5 to 4 hours average. We will go with the lower limit here when doing our estimations. To figure out the theoretical solar panel capacity we need, we will take the total watts needed and divide it by the solar peak hours Theoretical Solar Panel Power = 861/3.5 = 246 watts Theoretically, you will meet your energy requirements with around 250 watts of solar. This could be a single 250 watts panel or three 100 watts panels. (Note that I have rounded up. Rounding your power needs down always ends up in frustration!) In reality, the power you receive from your panels varies widely depending on: Solar Panel Inclination To hit the above 3.5 hour average, your panels should be inclined towards the sun. Most RV owners install their panels flat on the roof meaning that they get way less power than the estimate above. Transmission and Conversion Losses You are bound to lose some of the power you generate from your panels through resistance over wires, heat in the charge controller, battery inefficiency and your DC to AC inversion. Since the wire runs in an RV are relatively short and some appliances can run on DC skipping the DC to AC conversion step, let’s work with the assumption that we will lose 20 percent of the power our panels generate leaving us with 80%. This means that a 250W solar panel will deliver (250 x 0.8 =200) 200 Watts. Plugging it into our ideal solar peak hours formula, we get (200x3.5=700) 700 Watts a day which is less than our required 861 Watts. Conclusion #1: Your solar panels should produce at least 20% more power than your energy consumption needs. Always Oversize Your Array With this in mind, we can conclude that we need about (861x1.2=1033) 1033 watt rating per day to meet our 861 Watt load. This means our solar panel should be (1033/3.5= 295W) 295 watt. Rounding up to 300 watts won’t do any harm. Since the solar panels won’t be inclined to track the sun, you will have to look for additional ways to get more power (or slash your power consumption) to survive gloomy days. Doubling your solar panel array output is a good way to make through most of the days as long as you have enough batteries to store the generated power. Pro Tip: Surviving winter on RV mounted solar panels alone is next to impossible. At least for now Bringing Your Solar Panel Needs Down Sometimes, you might find out that your solar panel requirements are way higher than what you can fit on your RV. This and the fact that panels generate very little electricity in winter means that you still need to lower your power consumption or look for alternative ways to charge your batteries. Pro Tip: If possible, avoid the fancy RV curved panels and go for rigid solar panels as they have a longer life span and can produce decent power for longer compared to flexible panels Rethink Your Appliance List If you think your power consumption needs are higher than you can afford, cutting down on power hungry appliances is a good way to bring the wattage requirements down. For instance, you can slash out the induction cooker and opt to use a propane cooker or get rid of a coffee maker to give yourself some headroom. Always think of devices that consume bulk instantaneous power and look for ways to replace or use them less often. Find a Way to Charge from Your RV’s Alternator If you drive around a lot, you should consider tapping into your RV’s alternator for some extra juice. The additional power generated can boost your battery bank during winter or on cloudy days. There are different ways to do this without draining your starter battery or damaging the alternator. Some people use anything from a rudimentary switch they can flick when driving to an isolator. My favorite and perhaps safest approaching is using a DC to DC charger. A good DC-DC charge gives you granular control on the voltage and current you can push to your RV batteries making it a good idea if you own any form of lithium batteries. It is also gentle on your alternator hence reducing the chances of damaging your RV in the process. Most RVs have alternators that can pump out between 50 Amps and 110 Amps. You can always do an alternator upgrade to push the figure as high as 200 Amps. Choose your DC-DC charger such that it doesn’t exceed 90 percent of the alternator’s output to avoid overtasking it. Either way, a 1.5 hour drive on an RV running a 100 Amp alternator is more than enough to generate the 861 Watts our example RV dweller needs to survive a night. Here are some great DC to DC charges you can try out Renogy DCC50S 12V 50A DC Board Battery Charger with MPPTRenogy 40A DC to DC Battery Charger for Flooded, Gel, AGM, and Lithium Batteries Using Multi-stage ChargingVictron Energy Orion-Tr Smart 12/12-Volt 18 amp 220-Watt DC-DC Charger, Isolated (Bluetooth)REDARC BCDC1225D Dc-Dc Charger 12V25a Out Get a Backup Generator A backup generator gives you peace of mind especially if you live in your RV full time. Driving around aimlessly to charge your battery bank from the alternator isn’t as energy efficient as turning on a generator. There are also times when it won’t be practical to wait for the sun, plug to grid power or drive around. A generator gives you an instant solution in such cases. If you are really stocked on cutting the grid, get a solar array that produces double (or more) your power requirements and work on cutting your power consumption to match your energy generation. Having a generator at the standby can make you less frugal just because you know the consequence of depleted batteries isn’t that severe. Get a Bigger Battery Bank A big battery bank can help you coast through a couple of bad days using stored power. Going for something that can power you for two to three days without recharging will give your solar panels a lot of wiggle room reducing the number of times you run out of power. If you can, get Lithium batteries as they have a higher energy density and recharge faster. You can pack more of them and recharge them faster compared to AGM or other deep cycle lead acid batteries. Be ready for the initial high cost of lithium though – especially if you go for new cell batteries. The investment will pay back over time nonetheless since lithium batteries are more efficient and have a longer lifespan. Pro Tip: Your battery bank also determines how big your solar array should be especially if you use most of your electricity at night. A big array that generates most of its power in the day when you are not using it will be a total waste of money. You can learn more about batteries by going the through my sizing a battery bank guide. Plug in Every Now and Then If your battery bank is big enough, you can supplement your solar panels by plugging into the grid whenever possible to top them up. You will need an AC to DC charger for this. It is a little investment that could keep you going especially on those cold and tough winter days. Bottom Line The amount of solar panels you need varies depending on your energy needs, peak solar days and usage behavior. Living off grid is all about efficiency. The best way to meet your needs without blowing your budget is by auditing your energy needs and remaining with the essentials that you can afford to power for now.