Many people have been interested in the impact of solar panels on Advanced RV coaches. To help answer that question we conducted some measurements on the coach Gustav that is owned by Fred and Michelle Ahlgren. Fred is a retired engineer who does engineering projects for ARV so he was in an excellent position to make these measurements.
The day after the Summer Solstice was forecast to be a rare sunny day in Cleveland. Fred discharged the batteries in Gustav the night before so the batteries were able to accept solar charging. The van was parked with the front facing to the South in a driveway where it would get full sun exposure all day long.
Gustav is fitted with 3 of the ARV flexible solar panels, each of which is rated at 150 Watts. Each panel has a separate solar charge controller. So the total installed power is 450 watts.
A computer was set up to record the current (amps) that were generated by the panels once a minute. This data was then used to calculate the amp-hours generated during the day. The results are in Figure 1.
The blue line shows the amps generated by the three panels. The red line shows the amp-hours that were accumulated during the day.
This shows that for the daylight hours a little over 140 amp-hours were put into the batteries.
To put this in perspective we need to compare it to some other charging techniques. If the coach were being driven at 65 mph with the larger auxiliary Delco alternator that ARV is installing now, it would generate about 275 amps. So in one hour of driving the batteries could accumulate 275 amp-hours.
If the van were plugged into a 30 amp shore power station, the batteries would charge at about 100 amps. So in two hours the batteries would accumulate 200 amp-hours. Over night the batteries would be fully charged.
So solar is much less than either charging while driving or plugged into shore power.
The way to look at solar is to examine the impact it has on a parked coach that is not plugged into shore power. In this case the Silver Leaf, roof fan, and refrigerator will consume approximately 10 amps continuously. The van will need 240 amp-hours to operate for a 24 hour period.
The standard 800 amp-hour battery pack that ARV installs has a battery shutdown feature that is set prevent the batteries from being discharged below 20% of capacity. This is needed to protect the Lithium batteries. So the batteries can supply a total of 640 amp-hours if they are fully charged at the start.
If the coach is parked without any external charging it can sit for about 2.5 days before the batteries are depleted. With the addition of solar, the batteries would be charged an additional 140 amp-hours per day. Only a net of 100 amp-hours would need to be supplied by the batteries. So the van could sit for about 6 days and maintain the Silver Leaf, roof fan and refrigerator.
Of course this all depends on the weather and other factors. The data was taken in Cleveland where even on a sunny day the lighting is not as intense as in the southwest. So we could expect more solar charging in better locations. Also if the inside of the van gets very hot, the refrigerator will need to work harder and will consume more power.