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.