PREVIOUS: RV Electrical System: Sizing
Now that we have a good understanding of the intricacies of a well-designed electrical/solar system for an RV, it’s time to select the actual components for my upcoming Ford Transit cargo van conversion.
The goal I’m striving for, is a fully electrical, self-sufficient van/RV that can handle a minimum of 5-6 days off the grid. No other power sources such as propane for cooking & heating are considered and average consumption is calculated to be between 80-90 Amps per day.
The heart of the electrical system is the battery bank. Long dominated by lead-acid batteries (first flooded and more recently AGM’s), finally the more appealing Lithium technology is gaining a foothold. With the conversion likely to start towards the end of 2015 and an anticipated slow progress, there is still enough opportunity to delay a decision on the type of battery, until more is known about the sustainability of Lithium in the RV environment. I may decide to start with lead-acid and later convert to Lithium.
My sizing spreadsheet indicates an average use of approx. 80-90 Amps/day, with a 400 Ah lithium system, under rainy skies (with minimal solar recharge), will sustain me for 4-5 days (enough to get sick of the rain, humidity and cold), before you need to leave for more sunshine or a campground.
Rigid panels have a well-established performance history, are the most affordable and have the best efficiency ratings. I will choose the semi-flexible panels; a little less, but nearly the same efficiency, a third of the weight and very thin. The latter helps tremendously in maintaining the overall stealthiness of the van.
There are a few undesirable issues with these flexible panels; prices are currently on average twice as high as their rigid counterparts. Longevity is still undetermined and heat issues are unresolved (* see below).
Under ideal circumstances, three or four 100W panels should keep a 400 Ah battery bank fully charged. On smaller RV’s or vans, roof space often bottoms out at 3-4 panels, but the lightweight and thin semi-flexible panels make mobile use easier, by storing one or more extra panels under a mattress and placing them in the direct path of the sun, thus achieving higher efficiency rates at the same time.
The upcoming Ford Transit is equipped with a heavy duty alternator, that can recharge both car battery and house batteries with restricted amount of amps and that’s OK for lead-acid battery bank, that can’t handle lots of amps in an often short time period.
With the future use of Lithium batteries, a dual-alternator setup could be able to completely recharge the average system during a short trip to the store. The batteries ability to accept high charges and the lack of phased charging makes this an ideal combination. And a second unit keeps your house system completely separated from the car’s own electrical system.
You really need a large, dependable house bank to justify a second alternator. In addition to these after-market kits, that start at about $1,500.00, they very likely will cost you in lower MPG, noticeable over the length of the life of the van.
Solar Charge Controller
Maximum Power Point Tracking (MPPT) is the best method to regulating the charging of batteries from multiple solar panels. Their features are well-defined for use with lead-acid batteries, where temperature compensation and equalization are important.
An inverter is becoming less necessary to me, as nowadays many gadgets are charged through USB that ultimately comes from 12V outlets throughout the van. I’m not a big believer in microwaves, shave manually, use a 12V Danfoss fridge and plan a 12V computer/monitor setup. Only the short, but frequent use of a induction cook plate may make it a requirement.
- Four or more 100W Flexible panels.
- 400Ah Lithium batteries.
- MPPT Charge Controller.
- 1000W or 2000W Inverter.
- Dual-alternator option.
Flexible solar panels produced in Europe and China use the same SunPower cells, with those from Europe priced much higher, yet equal in performance.
- Operating Temperature
Panels that are glued to the roof of an RV have a higher operating temperature due to the lack of an air gap. Measurements on a hot day can detect a 25°F increase over those with an air gap.
Panels equipped with SunPower cells address this issue with lower temperature coefficients than other similar solar cells.
How long these panels will last, is still largely unknown and even the 25 year SunPower warranty on the cells doesn’t guaranty the operation of an assembled panel. On the other hand, as prices are continuously dropping and efficiencies increasing, and with more power needed all the time, the replacement cycle may override this implied life span.
Very nice coverage of the core system in the van. I’ve considered incorporating all of the options you highlight here in my project. My project is still in the distant future :(, but I considered each.
My thoughts/opions are: (I hope you were looking for this…)
Battery Bank: I agree with going lithium. 400 AH may be overkill. I recognize your desired 4-5 day use before recharging, but with solar your recharging all the time. add to that you can manage your usage to extend the up-time. If you get to empty on the bank, then it’s time to find that alternate charge. I look to have a plug in charger. Then you could spend a day in the RV park, or spend time with the sticks & bricks friend. An option is to get a small portable 1000W gas generator. I think you said the van was gas, so you could siphon gas from the van.
I think 100 to 200 AH on the Battery Bank is a good size. Lithium allows you to get to most of the charge in the bank; I like that. During the build, try to anticipate a retrofit of additional batteries by leaving space next to the bank that can be used by additional batteries.
Solar: I would go with 100 watt panel per battery, recognizing I might have to add on later. I like the thin flexible panels.
Alternator: Nope wouldn’t do that. I think that is extra cost that you wouldn’t utilize. it’s always reducing your MPG, and not needed if the solar is working. It’s also something you couldn’t readily sell off. The gas generator you could. The alternator would be the option instead of solar.
I’m not aware of the heat&solar panel issue.
Longevity… Yea, right now it’s a crap shoot on these newer technologies, but I think the risk is worth the reward.
Best Regards, -Dan
Lithium is still not ready for wide adoption in the RV environment, but that will hopefully change a bit in the coming year. I base the 400 Ah on worst case scenarios of little or no sun and as the major part of my electric use goes towards the fridge, I haven’t got much leeway either. In striving for a cleaner and simpler RV solution, a generator is a big No-No for me (same for anything propane). Size of the battery bank is really a personal choice and will clearly vary from user to user. Adding more batteries at a later time is a possibility, but that gets complicated if you include solar panels in that decision. I know that with lead-acid batteries, one should not add new batteries to an old setup, but don’t know whether the same restrictions apply to Lithium.
The general calculation is approximately 1 watt of solar for each 1 Ah of battery storage. The rigid solar panels are the best solution for anybody that has sufficient space to place them; they’re substantially cheaper, have longer warranties and slightly better efficiencies. The semi-flexible panels have a niche market in which they have certain advantages over the rigid ones. Absolutely the best choice in my case.
Some semi-flexibles come with a metal backing and can be installed in frames slightly above the roof, so they will receive extra cooling from air that flows under the panel. Such an installation defeats its purpose in my opinion, because when you do that, you can also use the cheaper rigid panels (except for the weight issue). Some tests of panels glued to the roof indicate an approx. increase in surface temperature of 25°F under high temperatures; that may mean a possible 10% decrease in efficiency. Instead of worrying about that too much, I’d rather add an extra ‘portable’ panel to make up the difference.
A dual alternator is a high expense and its viability is mostly determined by how someone uses his van/RV. Installation should be fairly simple and can be done at a later time.
I appreciate your input, but on the electrical issue, we’re mostly on the same wavelength, except for the generator….
What was your reason for not considering propane for heating or cooking?
I’m also doing a Transit conversion, and while I’ve got a ~560W solar/400AH AGM setup,
I decided that propane gave me the flexibility to avoid using gasoline or diesel for those heat energy functions. The reasons I went to propane are: solar electric is unlikely to cover those heating needs, propane doesn’t eat into gas tank reserves, and propane also should be a cleaner burning heat source than the heavier hydrocarbons.
In fact, I have always planned for propane in my next RV. Upon getting closer to realizing my plans, one gets to be a bit more critical and you start thinking about the details.
The main premise of the new van was my type of stealthiness. That shows in exterior upgrades to the van that are fairly standard: alloy wheels, color, mirrors, grille, etc.; nothing that would indicate the interior RV setting: no step, no awning and with the semi-flexible solar panels glued to the roof, no visible solar.
That leads to the propane issue. A tank added to the frame of the vehicle makes a loud statement that identifies the van as an RV. And during the last few years of planning that would have been inevitable, with the choice of a Propex propane heater and the virtual lack of heaters that worked on automotive gasoline, since most ‘professional’ heaters worked on diesel. Another similar issue was the cooking: don’t intend to cook much, so without propane I could go either with a Coleman stove or the power hungry induction cooktop. At home I have been using induction for 25 years and that peeked my interest, however than the lead-acid batteries are a limitation.
In the meantime, Lithium is gaining ground in the RV environment and that opened up the possibilities for a pure 12V Danfoss fridge and an induction cooktop and I found out that the diesel heaters also come in a gas variety. That leaves hot water for the shower (from propane) as the only unresolved matter.
For that, I get a cleaner van (on the outside), no propane safety trouble (used it for years, so not a big problem) and overall an electric only vehicle.
As for your questions:
In my travels, I will follow the sun and the need for a heater is often limited a bit of heat on cold winter desert mornings or after 5 days of rain, humidity and cold. May use the heater only for a couple of hours a year.
Despite the limited use of a heater, power from solar is always a limited resource, certainly if I add the 12V fridge. But that’s were Lithium changes things; more usable capacity, optimized for solar, chargeable by alternator, plus an option for a dual-alternator setup that can recharge your battery bank on your way to the grocery store.
Correct, but my heater use will be incidental.
I can beat that, if I can sustain on solar only.
All-in-all neither your or my choices are right or wrong; it’s mostly personal preferences, except for the heating requirements. If those are important to you, my setup may not work for you.
PS I have been following your conversion efforts on one of the forums for some time now.
Thanks for the answer Van, You are right, it all depends on planned needs. No right way or wrong way! Since I won’t be stealth camping, just boondocking in the boonies, and won’t be following the sun (even maybe avoiding it!), I can take advantage of propanes’s upsides without needing to be concerned as much about it’s downsides.
I’ve been following your build as well. Very nice work and thought process!
Just FYI, I’m primarily doing the boondocking too. I’m mostly concerned with the deed restrictions where I live. Being stealthy is just a bonus.