Red In The Water

A Year Off Grid - Solar System Components, Design, and First Hand Experience (Nerd Out Warning!)

Hi folks! Our Westfalia has been completely solar powered for one full year now! In light of (literally and figuratively) this recent celebration, I wanted to share our system design and first hand experience with all of you aspiring off-gridders out there!

First off, a well designed solar power system truly runs like clockwork with minimal effort. No utility bills to pay, no worry about plugging into a generator, everything runs by itself. Your food and drinks (beer!) remain cold and all your kitchen appliances work as though you were in your own kitchen at home. There have only been two times over the past year that we have ran out of power; once in hurricane Matthew (when it rained for two weeks straight!), and after starting with a nearly empty battery in the freezing cold of a Michigan winter.

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Here is some basic information that you will need to know to design your solar system:

  1. Watts (W) : Watts are a measure of electrical energy. That could be energy being used or energy being collected by your solar system. The standard definition of a watt is one amp of current at one volt. That means you take the current multiplied by the voltage to get watts (1v * 1A = 1W). You can think of current as the amount of electricity flowing though a wire and volts as the pressure of the electricity in that wire. But nothing's ever that easy, right?! Of course not! You will commonly have two major voltages in a solar system: the low side (solar panels and battery), and the high side (where you run all your regular appliances). One amp of current is a vastly different amount of watts on the low vs. high side of your system. For example, one amp of current at 12 volts is 12 watts (1A * 12v = 12W), but one amp of current at 120 volts is 120 watts (1A * 120v = 120W)! Hopefully you're still with me, if not head over to youtube and watch a video or two on watts.
  2. Watt-hours (Wh) : The most common way of measuring the electricity that you will consume and collect is in watt-hours. If you used one watt for one hour, you just used one watt-hour! 500 watts for an hour is 500 watt-hours. 500 watts for half an hour is 250 watt-hours. You get the idea. When your solar panels are in the sun you get the same watt hours, but this time you're collecting it! If you collect 100 watts for 5 hours, you just collected 500 watt-hours!
  3. Kilowatt-hours (KWh) : A kilowatt-hour is just a 1000 watt-hours. Kilowatt-hours multiplied by 1000 will give your watt-hours and inversely, watt-hours divided by 1000 will give you kilowatt-hours. For example, 1.3 KWh is equal to 1300 Wh.
  4. Amp-hours (Ah) : Amp-hours are used to rate a batterie's storage capacity. One amp-hour is defined as one amp for one hour. It's that simple! 100 amp-hours could be one amp for 100 hours, 100 amps for one hour, 50 amps for two hours, etc.

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Ok, now that we have the boring stuff out of the way, I'm going to walk you through how I designed my solar system and what components I chose. You can use this exact same process to design your solar system or, if you happen to be designing a system for a van sized RV, you could just copy it :)

  1. First things first, you absolutely have to figure out how many watt-hours you're going to use on a daily basis! I cannot stress this enough. I know it's boring and takes some digging to figure out exactly which appliances you will use and for how long they will run, but it's vital that you DON'T SKIP THIS STEP! Luckily, most appliances these days spell out exactly how many KWhs they use right on the energy saver tag. If that doesn't work, Google it and the appliance manufactures phone numbers are your friends.
    • Here's list of what I run in my van and how many watt-hours they consume on a daily basis:
      • 550 Wh - Electric bike. 550 Wh is a worst case scenario in which I've drained the bike battery fully. On an average day it's probably more like 200-300 Wh. In addition, I only charge my bike during the day to save my van battery for at night. I just acquired the electric bike and didn't plan for it in my original design, but my system has been keeping up with it without an issue :)
      • 12 Wh - Led lighting
      • 160 Wh - Fan for hot weather at night. The fan pulls 20 watts and I'm estimating 8 hours of runtime per night.
      • 250 Wh - Control relays idle drain. This one I had to figure out the hard way! The battery controller I bought required three relays to run all the time in order to be able to disconnect and therefore protect the battery in case anything went wrong. Basically I'm losing .8 amps at about 13.5 volts all the time! This is an area that could use some major improvement and I've read that my battery manufacturer has now improved their controller design and only requires one relay.
      • 200 Wh - Misc. kitchen appliances. Blender, toaster, electric kettle, etc. All the stuff you use for a few minutes randomly on a given day.
    • That totals up to 1722 Wh's on a high usage day
  1. Alright, now that we know the max of what we plan to use we have to figure out how to collect at least that much power every day! As you may know, solar panels are rated in watts. We all know that solar panels only work during the day, but you may not know that you only get the full wattage out of a solar panel when its super sunny outside (think middle of summer on a clear day) and the sun is right overhead (solar noon). On a cloudy day, you may only get 1/3rd of the rated wattage. On a rainy day you, may only get 1/10th! So you have to plan for the weather conditions you're going to be living in. If it's often cloudy where you live (Ohio!), you'll want to get lots and lots of panels to make up for it. If you're going to be living in the awesome gorgeous sunshine every day (the beach!), you won't need as many panels. On a good day, you can estimate 5-6 hours of proper sunlight for your panels. To estimate the number of watt-hours you will collect from your solar panels, multiply your panel wattage by 5-6. For my system, I installed two 150 watt Renology panels (300 watts total). So my system is estimate to collect 1500-1800 watt-hours every sunny day. If you look at the number of watt-hours I can use on single day, you can see I'm cutting it close now! Luckily we live in a very sunny location! In Ohio we'd never be able to keep up with our current usage due to constant overcast conditions. In general, it's best to over- build your system. Solar panels are so inexpensive these days that it makes sense to install as many as will fit on your RV. You will never regret having more power than you can use, but running out is quite the inconvenience! You can use your extra power to charge your neighbors improperly designed system! (We charged our neighbors in Mexico for two months :)
  2. Ok, we're almost done! Now we have to store all that power! Of course, just to make it difficult, battery manufacturers rarely rate their batteries in watt-hours. Batteries are usually rated in amp-hours. To figure out how much power you can get store in your batteries, just take the amp hour rating multiplied by the voltage of the battery. For example a 100 amp-hour 12v battery is rated for 1200 watt-hours. That sounds easy enough, right?! But, of course, there's more to consider! For lead acid batteries (the most common type), you're only supposed to use the top third of the batterie's capacity in order to maximize battery life. So that 1200 watt-hours gets cut down to 400 useable watt-hours! Lithium batteries have no such restrictions! You can run them all the way down. So a 1200 watt-hour lithium battery actually gives you 1200 watt-hours of usable storage. The general rule is you should have enough stored power to run for three to five days without any sun. In my original design, with only the fridge and lights, I was doing alright. I have a 1300 watt-hour (1.3 KWh) lithium ion battery from Elite Power Solutions that can run my fridge for almost three days. Since my van has the horsepower of a sick baby goat and all the storage capacity of a hoarder's closet, I had no real choice other than to go with the lightest and smallest battery that I could find. There are some other advantages to lithium batteries, mostly life span. My battery is rated for about 7000 complete cycles (drained and charged all the way). That's a lot. Lead acid batteries only go for about 500 cycles. By my estimate, my lithium battery should last at least ten years and then still have 80% of it's rated capacity. Lithium batteries are also much more efficient the lead acid. What that means for us is that we aren't losing energy when charging and discharging the battery. Lead acid batteries heat up when charged or discharged. That heat is wasted solar power.
  3. Last step! Install a proper panel or set of panels to monitor your system. A proper panel will show detailed battery charge status, incoming solar power, and real time current drain going out of the battery. Without this information, how will you know if you should conserve power or if you can string up that set of tiki lights, blast your stereo, and party?! How will you know that your newly acquired toaster consumes 80 amps and that you really shouldn't run it very much?! This information is crucial and usually doesn't cost very much when compared to the rest of your system. I think I spent $200 for this information. It was worth absolutely every penny. Your extended battery life will repay you in the future anyway :) Below you can see the video output from my Elite Power Solutions battery monitor and my remote solar charge controller interface from Rogue Engineering.

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I hope this blog guide was helpful and that whomever reads this feels less intimidated by the idea of installing a solar design system.

Living off the grid is entirely rewarding, and with a little bit of effort, you'll be drinking a beer cooled by the rays of the sun in no time.

Cheers!
-Rick

My System:
2 150W Renology 12v Solar Panels
Rogue MPT 2024 Charge Controller (Made in the USA!)
Rogue COM-4850 Remote Display and Interface (Made in the USA!)
Battery - 12V 100Ah 1.3KWh iBCS System - LiFeMnPO4 Battery Chemistry
Xantrex ProWatt SW 1000 Inverter
Truck Fridge TF-65 - Compressor Based Fridge