A question that comes up a lot is: Is it worth tilting the PV panel(s) on my RV roof to increase the power output?
Tilting the PV
This page uses the NREL PVWatts calculator to estimate how much more energy you will get from a tilted pv panel than a flat PV panel. The answer varies with your location and with the time of year, so we look at a northern and a southern location for summer, fall, and winter.
PVWatts gives average energy produced for each month in KWH. I converted these to amp-hr of charging assuming a 12 volt battery system. So, the numbers in the table are the average amount of charge a 12 volt battery bank would receive in a day from a 300 watt PV panel at the tilt shown.
| July -- | --------------- | September | ------------ | December | ----------- | |||
|---|---|---|---|---|---|---|---|---|
| Location | Latitude | Flat | Tilted | Flat | Titled | Flat | Tilted | |
| Billings, MT | 46 | 133 | 121 | 85 | 110 | 29 | 67 | |
| Dallas, TX | 33 | 129 | 115 | 92 | 102 | 52 | 85 | |
The following assumptions are made for the table:
Size of solar panel is 300 watts
System Losses are 10%
The PV panel is either flat, or tilted at the local latitude
When tilted the panel faces south
The inverter efficiency is 96%
Conclusions
In mid summer, for both locations, the flat panel actually produces more energy than the tilted panel, so there is not much point in going to the effort of tilting. The reason for this is that the days are long and the sun is high in the sky for much of the day– so, it shines on the flat panel at a good angle for many hours. For the tilted panel, the sun is actually behind the panel for several hours near sunrise and sunset.
In mid winter, the tilted panel does quite a bit better than the flat panel, and the further north the location, the larger the difference Between tilted and flat. This is because the sun is low in the sky and does not make a good angle with the PV panel. For the Billings location, the tilted panel takes in 2.3 more energy per day than the flat panel!
For September (typical for Fall and Spring), there is some gain for tilting the panel, with a larger difference for the northern location. The tilting is worth an about 30% increase in energy per day for the Billings location.
So, maybe, the bottom line is that if you plan to use the camper in mid-winter its worth looking into finding a way to tilt the panels, but for other times of year maybe not.
Title Methods
The table gives the average output in KWH for a full day for a 300 watt PV panel either flat or tilted.
The table takes into account the weather at the location shown, so it includes some cloudy days with very little output along with sunny days with much more output.
If you want to look at other locations, PV panel sizes, times of year, or tilt angles, you can use PVWatts. Fill in your location, PV panel size, tilt, and Azimuth (180 deg is due south). Review the System Losses using the little calculator icon — I ended up using 10%. In looking at the results, the AC Energy produced is listed for each month — divide by 30 or 31 days per month to get the daily average energy output in KWH. To convert KWH to amp-hrs of charging for a 12 volt battery system, divide the watt-hrs per day by the charging voltage, so 1.5 KWH would be 1500 watt-hrs and dividing by 13 volt charging voltage would give 115 amp-hrs charge to the battery.