A Minimal Solar System for a RV

We have seen impressive solar systems on Roadtreks and read about others.  Campskunk's and Jim Lever's systems come to mind. Then there are the factory installed solar systems like on the eTrek. But most of us are not full-timers like Campskunk, nor do we have a compressor fridge to keep powered like Jim Lever, nor do we have banks of 8 batteries to keep charged like eTrek owners.  So what about the rest of us? Does solar make sense and how much solar do we need?

We addressed that question for ourselves a year ago. Your needs may be different, but we will discuss our thought process and what we did. We had already installed a battery monitor three years earlier, so we had a good idea of how much power we used on a daily basis. If you are considering solar, first buy a good battery monitor and learn how much power you are using (we use a Trimetric – see our post on how to install one).  Those idiot lights for battery level on the stock control panel are not quite worthless, but pretty close to it.  We had a couple of years of traveling with the battery monitor and enough experience with the other methods for recharging batteries (driving, shore power hookup and generator) to evaluate the benefits of solar for our situation.

Trimetric

Battery monitor show 0.3 amp draw

Several things influenced our decision.  Our existing equipment was one driving influence.  First, we had one house battery (a conventional deep cycle Group 24 Exide of 80 amp hours) and adding more would not be easy.  Second, we did not have an inverter.  Inverters convert 12 VDC to 120 VAC, but they use a lot of power doing it.  We originally ran our laptops off a small 150 watt inverter.  We discovered we could save a lot of power by buying 12 VDC car adapters for the laptops instead.  Our TV also ran off of 12 volts rather than through an inverter.  If you use an inverter (or inverters), you will likely need more than a single battery.   Many Roadtreks have a TV and sound system that runs off an inverter rather than 12 VDC – if you have this, be sure to account for the power it uses when you look at your daily needs. Third, we had an Onan generator and were happy to use it for the microwave, coffee maker, and of course air conditioner.  Installing an inverter large enough to run the Keurig coffee maker and the microwave was not something we wanted to do.  Plus having a generator was a backup for rainy day battery charging.

Assateague Campsite (Medium)

Assateague Island – No hookups

The second major influence was our camping style.  First, we don't often spend more than two nights in one spot with no hookups.  Since driving is the fastest way to charge your batteries (through the vehicle alternator) we seldom had a problem with the battery running low.  Second, our daily power usage was usually below 30 amp hours, which is likely lower than average.  Third, about twice a year we would attend an event or go to a place where we would sit for an entire week in one place (like our annual spring Assateague Island trip), seldom driving, and if we do it is not enough to charge the battery.  On those occasions we would have to run the generator to recharge the battery.

When we had to run the generator to recharge the battery, we would watch the battery monitor.  We would start the generator at breakfast to run the Keurig and the microwave.  We would watch the amps going into the battery.  It would start out high, but after an hour it would be down to about 2 amps (or less) and the generator was loafing along.   And the battery might  be up to 92%.  Batteries shouldn't go through lots of charge / discharge cycles without reaching a full charge.  We had lots better things to do than listen to a generator for 4-6 hours just to reach 100%.  True we didn't need to do that every day, but still it got old very fast.

Solar Panel instatlled (Medium)

Single 100 watt solar panel installed

The one thing solar is excellent for it topping off batteries, bringing them up to full charge.  The question was, did we need it often enough to be worth the cost?  Not being solar experts we read a bunch of online stuff and asked some of the experienced solar users on the Roadtrek Yahoo list.  AM Solar in Oregon came highly recommended by a number of Class B owners, so we initiated a discussion with them, outlining our requirements and desires.

Charge Controller (Medium)

SunSaver MPPT Installed near battery

Based on our needs they recommended their GS100 100 watt panel (21 inches x 41 inches), a Morningstar SunSaver MPPT controller, and we opted for the Morningstar remote monitor.  We already had a battery monitor.  They priced the package with all the wiring, connectors, mounting hardware and caulk for $695 (free shipping).  Should we ever add a second battery, adding another solar panel to the system would be simple.  We decided that was worth it not to have to listen to the Onan after the coffee was made and the bacon was cooked.

Wire Entering Coach (Medium)

Solar Panel wire runs through the pantry

Everything arrived well packaged and with detailed instructions.  The mounting hardware does not penetrate the roof.  The only roof penetration is the wiring from the solar panel to the controller.  We drilled a hole to run it down through the pantry cabinet.  The entire installation took the two of us two half days – roughly 8 hours.  The hardest and most time consuming part was running the wire from the panel through the interior of the Roadtrek.

Remote Meter

Morningstar Remote monitor between Progressive Industries power management remote display (for shore power only) and the Trimetric battery monitor

We mounted the Morningstar remote monitor next to the Trimetric battery monitor.  It is interesting to see how much more power the solar panel can put out beyond what is needed to charge the battery.  We find (if the sun is shining) our daytime power use is covered with plenty left to charge the battery.  We read somewhere that a good rule of thumb was to have 100 watts of solar for every 100 amp hours of battery.  Since our battery is only 80 amp hours, we have more than enough solar.  If you are using 2 batteries with about 200 amp hours total, you will likely want two 100 watt panels.  Solar Panels do come in various sizes.

Dry Camping at Meat Cove

Dry Camping at Meat Cove

Now that we have had nearly a year of use, and several week long boondocking trips we can say we are happy we added the system.  The cost was worth the benefit to us.  Another benefit is that we don't have to connect to shore power when at home to keep the battery charged (we have a constant 0.3 amp draw and no battery cut off switch).  We did recently encounter an unexpected issue that Jim Lever helped us sort through.  This extra cold winter had more snow that stuck around.  And it stayed on top of our solar panel too.  When we found the battery down to 70% we hooked up to shore power – and didn't bother to unhook when the snow melted.  Then result was that our Progressive Dynamics 4600 upgrade to the old Magnatek Converter did its job of keeping the battery fully charged, but every morning the solar system would wake up, see the float voltage on the battery and go through a full charging cycle on an already fully charged battery.  Oops!  We had gotten out of the habit of frequently checking the water level in the battery since the PD upgrade didn't seem to ever use any.  Although the battery compartment was clean, we sure “boiled” our battery.  We could see the tops of all the plates.  It seems to have recovered well, although we have undoubtedly shortened the life of our $85 battery.

Solar On Top (Medium)When you have multiple means of recharging your batteries, keep in mind that they might not play nicely together.   They have different charge profiles and voltage setpoints.  It takes a very sophisticated control system to balance out alternator (no smarts at all), shore power (through converter/charger or inverter/charger), solar input (through a solar controller) and if you add a second alternator or “engine generator” you are creating the complex control problem that the eTrek must tackle.  Get a battery monitor so you know what is happening.  Constant overcharging or undercharging will shorten the life of your house batteries – and you will not know it until you suddenly have to replace your batteries.  The more batteries you have and the more expensive they are, the more important it is.  Based on our experience, if you add solar to your existing system – put a cut off switch on your solar system.  If you are going to be plugged into shore power for awhile, turn it off.

 

 




Click to see all of our Roadtreking RV videos!


  • Cheryl

    Thanks!

  • Dennis and Stephanie

    We have a 210 Versatile with two house batteries. We installed a 100 watt solar panel last year because we prefer to dry camp almost exclusively and use our inverter to watch DVD’s, make coffee and charge our electronic devices. Our 100 watt panel has worked very well for us, consistently keeping the battery at a high level. The only concern we have faced is every once in awhile if the house batteries get too low, it takes longer for the solar panel to charge them fully. But since this rarely happens, it has not been a real problem. We plan to install a larger inverter so that we can run the microwave and toaster without powering up the generator.

    • D & S — if you use a larger inverter, won’t you need to increase other parts of your system? Seems like your two 6v would likely run down much faster than normal so maybe add more solar? I am so new to this I am sure this is a dumb question…sorry if it is.

  • Dave

    Nice article, thanks for sharing. You said that the mounting hardware does not penetrate the roof. Is the DiCor sealant used to secure the panel to the roof? Looking at the 35mm rocker foot mount set from AM Solar, there looks like mounting screws included – optional? You said it would take 4-6 hours to top off your battery with the generator. How have those times changed with the solar panel, given the same conditions? Thanks.

    • Dave – we had a long discussion with AM Solar about the mounting system. The brackets are held to the roof with a 3M adhesive tape. The connection is then covered with the DiCor caulk/sealant to prevent water intrusion. AM Solar says they have had no failures IF properly done.

      How long it take to recharge the battery is dependent on many factors. How discharged is the battery and how much sun are we getting being the main ones. Under ideal conditions the time to recharge is probably similar to the generator – but we are not burning fuel or listening to noise while doing it.

      For us, if the battery reached full charge during the day, we are likely at 92-94% charged at bedtime. In the morning we are often at 80-88% charged depending on furnace or fan use overnight. If the sun is good we may be fully charged by noon. If it is dreary and raining, the solar is probably not keeping up with our daytime load, let alone charging the battery.

  • Since serious offshore cruising sailboats share many of the same electrical challenges of a motorhome, here are a couple of follow-up comments to Roger’s/Lynn’s excellent summary we’ve learned over the years. MPPT controllers yield far greater panel output than non-MPPT types, so don’t be fooled by a lower price. House bank (deep discharge) batteries are rated by the number of discharge cycles before reaching 50% capacity. (So for a 100 amp/hr battery, that would mean it becomes unable to provide more than 50 amp/hrs when fully charged – quite a drop.) Given the importance of that one house bank battery in a system like Roger’s/Lynn’s set-up, I’d suggest shopping for such a battery by rating before price. Trojans are one example of an excellent capacity rating vs. price since you can find them at less than list price. But the best single piece of advice in this article – IMO at least – is the value of a battery monitor, and that’s applies to everyone using one or more house bank batteries. Not having one is a bit like ordering clothes without knowing their sizes and how they will fit.

    • I agree with you about the Trojan’s. When our previous battery died on the road (one the those dual purpose Interstate batteries) we did some research and found a Trojan 12 volt that would fit and provide a significant increase in amp hours. Unfortunately no Trojan dealer within range had one – and were were moving and needed a battery ASAP. Hence the 80 amp hour deep cycle Exide from Camping World. For an $85 battery we really can’t complain. But next time…