#64 -
Renewable Energy > Technical Discussion: Other > Re: Solar for RV
I don’t see why Fred thinks that Handy Bob’s articles would be “persona non grata around these parts”. There is a lot of good info in them, but it has the danger of being mis-used.
Handy Bob has a disrespect of RV dealers/solar sellers around Quartzsite AZ, not of all people in the solar business. Fred seems to apply a similar disrespect to everyone in the solar business.
Solar systems in RV’s while being similar to residential systems, do have different aspects that you need to consider. And conversely, you cannot apply “what works best for RV’s” to all PV systems.
Golf cart batteries are the entry level batteries of the solar business. They could even be called the bread and butter of the small system. But for larger systems, they are just training batteries. There are a lot better batteries out there, particularly for larger stationary systems.
Charging at 14.8 is Trojan’s recommendation; it is not the gospel for every wet cell batteries. Interstate recommends a bulk charge setting of 14.4.
Note that Handy Bob mentioned a battery temp sensor. While I like them for all installations, they are even more important in RV’s. And, if you are charging above 14.4 volts without one, you are living dangerously. The warmer the ambient conditions, the more important the sensor is. I’ve gotten to the point where I no longer consider them optional.
Wire sizing is important. I generally aim for 3 percent drop or less. It is also important to consider future upsizing of the system. I weigh the cost of going larger now vs. the cost of future rewiring. But “bigger is not always better”. #6 and #8 are SMALL wires with a marginal cost difference. Look at the price difference in a 1/0 and a 3/0 before saying bigger is better. Carte blanche oversizing wires can be a huge waste of money.
But the point that I really differ with these gentlemen on, is the value of the MPPT controller. If you live (or RV) in an area with great solar conditions, you may not see great value in it. But, where you will see the value of it is in less than optimal conditions. It shows gains in the hours before and after the peak sun period. If you have any type of overcast, marine layer, smoke, smog, dust, etc, that reduces the solar insolation, you can have a boost even during the peak sun hours.
In my area, I usually see a summertime increase in production that is close to 10%. Over in the fog belt (closer to the coast) it is closer to 15%. We never get the 30% boost that the mfgs claim for wintertime, primarily because we don’t have subfreezing, crystal clear winter days. You can count the days below 40 degrees on one hand. MPPT is not “only useful in winter”.
You do have to try to quantify what this increase is for a particular microclimate, and weigh the value of it. The best way to do that is install one on an existing system with known production and then compare the difference in monthly production. In my area, it is a no brainer. Yes, it costs more. But it is a lot cheaper than increasing your array by 10%.