Solarp

I have a Mercedes Sprinter Villagio and would like to add solar.  I would like guidance about wattage and placement t of panels. I have a diesel generator but don?t want to run it overnight. My present batteries are good for me night if I watch tv. If I didn?t need air conditioning, how much wattage would I need

How many amp hours are your batteries?

There is a general rule of thumb that you need a minimum of 100 watts of solar panels for every 100 amp hours of battery bank capacity.  If you're mostly operating someplace like the Pacific Nortwest - lots of cloudy and rainy days - then you will need more.

The Villagio specs indicate it has 2x 12v house batteries, but doesn't give a size. That's anywhere from 170-240 Amp-hours (AH).  If you use half of that overnight, you need to replace somewhere between 85 and 120 AH the following day.  A 100W panel in full sun will produce around 7 amps at charging voltage (14+) for however many hours of sun it receives.  I would suggest at least 200 watts of panels, maybe even 250-300 if you have room.

If you don't use half the battery charge overnight, you can do with less. You really need to get a better handle on your amp-hour usage before you decide on solar capacity.  Install a battery monitoring system first, then you will know what you need.  Maybe start with a 100W system and monitor, but plan it so that more panels can be added.

If you don't always camp in full sun, solar may not be for you. Even a tiny bit of shade on a panel can have a huge impact on its power output.

If your goal is to fully recharge your batteries with solar power, you need to know how much power you typically consume in a 24 hour period. The best way to do that is with a good battery monitor, as Gary mentioned. The Trimetric RV 2030 and the Victron are probably the most common, and both get good reviews from RVers.

Make sure your batteries are fully charged, then camp somewhere for 24 hours (even in your driveway.) Do everything you would normally do - watch TV, turn on lights, charge your phones/tablets etc. After 24 hours, look at the battery monitor and see how far your batteries have discharged - in percentage. Both the Trimetric and Victron will display that information.

Look at your batteries to determine their amp hour capacity, or look them up online. Let's say your batteries (combined) have a total AH capacity of 240 AH, and after 24 hours, your battery monitor is indicating 50%. That means you've consumed 120 amps in 24 hours. That's how many amps your solar panels are going to have to generate to fully recharge your batteries.

A single 100 watt solar panel will generate about 7.5 amps per hour under ideal conditions (which rarely exists.) Most experienced solar users will build in a "fudge-factor" to help compensate for cloudy days and installation inefficiencies.  Depending on what part of the country you're in, the solar charging window is about 5 hours per day in the winter (when RV solar is usually more relied upon) and roughly 8 hours in the summer. The average cloud cover in different regions will also have a significant impact on how much charging you can expect to get out of your panels. Keeping your panels tilted toward the sun will also have a significant impact on how much power they generate - especially in the winter.

So to best ensure that you get what you want out of your solar setup, there are some things you have to know first. On the other hand, a lot of folks just slap some solar panels on their RV's roof and hope for the best. Good luck, and let us know if we can help.

Kev