Sunday, September 19, 2021
Sunday, September 19, 2021

How much solar power do you need?

The winter, snowbird season is upon us, and a parade of RVers is now underway south, many to boondock for months on end on public lands of the desert Southwest. If that’s you, then you probably already have enough solar panels to power your RV. But if you still need to get equipped, these “Rules of Thumb” from the folks at AM Solar will give you an idea of what you may need.

1. Use a minimum 65 watt solar panel for basic battery maintenance on trailers and fifth wheels.

2. Use a minimum 100 watt solar panel for basic battery maintenance on motorhomes.

3. For the more conservative consumers of electricity: Allow 200 amp-hours of battery storage capacity and 150 to 250 watts of solar panels.

4. For the more liberal consumers of electricity: Allow 400 amp-hours of battery storage capacity and 300 to 500 watts of solar panels.

5. For “hard core” boondockers with mobile offices: Allow 600 amp-hours of battery storage capacity and 500 to 800 watts of solar panels. AM Solar also encourages the use of an M.P.P.T. Current Boosting Controller.

Bear in mind that you can start with one or two solar panels and add more later if needed.

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David totten
9 months ago

Our present system comprises of two 100 amp lipro4 batteries and six hundred watts of solar in a series/parallel configuration. Our panels are flat mounted on our roof, witch makes installing much easier, but reduces power generation a lot. We use this to power everything in our trailer, including two 12 volt compressor refrigerators, but of course not AC’s. We have tons of electronics to keep charged also, such as phones, tablets, camera gear and laptops. On a typical sunny day, I can be done recharging my batteries by about 11 am. But if it’s even a little cloudy, or if the panels are partly shaded, we struggle to get a 100% charge all day. The best investment I made was going to lithium batteries. Yes they are expensive, but are an absolute game changer with solar.

Fred
9 months ago

All the tips in the article refer to use of standard flooded batteries which only allows you to use 50% of the rated amp hour capacity. If you choose to buy lithium batteries, then you can use almost 100& of the rated amp hour capacity, which will almost double the usable amp hours. Also, if you start with just one or two panels, & plan to add more later, be sure to size the wiring & solar charger to handle the maximum number of panels you plan to install.

Nanci Dixon
9 months ago

We have 1000w solar on roof, residential frig, 4 TVs (2 of which are 2 too many) satellite, and lots of lights and hardly ever need to start the generator when sunny. Boondocking in a snowstorm…not as good.

Tommy Molnar
9 months ago

We have 700 watts on the roof of our travel trailer and it runs through a Morningstar MPPT controller to two Trojan 145’s. This system powers everything except the a/c. The reason I kept upgrading the solar panels was so we could get a good charge rate even on days with clouds and even in some cases, rain. However, since we mostly boondock in NV and AZ, rain and trees are seldom the problem . . .

Graybyrd
2 years ago

“Interstate” is a battery brand in our area. We replaced the battery in our ‘new’ used truck camper with a Group 27 Interstate Deep Cycle battery. Oddly, Interstate provides no AH rating; only CCA, CA, and RC figures. After some search, I found a ham radio forum which gives an approximate conversion figure of 0.6 x RC to estimate AH of a given battery: in this case, Interstate Group 27 Deep Cycle with RC 160 is approx. 96 AH.

Our truck camper (an older model) has only the one battery compartment, which means we’re physically restricted to a little less than 100 AH capacity, half the “minimum” this article recommends. We can add more batteries in the empty pickup bed well area, forward of the rear wheels, but that would add extra cabling and significant weight increase (approx. 100 lb. per battery). So… needing only LED (conversion) lighting, the water pump, and occasional laptop/cell phone recharging, that’s our demand. Our 200 watts of auxiliary solar panels, somewhat limited by our Pac NW maritime sky conditions, is just enough for 96AH it seems.

Bill T
9 months ago
Reply to  Graybyrd

Agreed. We have a class c with a single group 27 100 A/H battery and 160 watts of portable solar and for powering our lights, water pump, fridge and laptops/phones. That provides us with enough for our power requirements to stay off the grid, in good weather. We don’t bring our stick and bricks with us to camp. We enjoy getting away from the sticks and bricks and all the associated routines and enjoy life.

Mark Sanders
2 years ago

We are likely in the conservative motorhome area of use. If we had 250W of solar, what could/would we be able to do throughout the day?

Wolfe
2 years ago
Reply to  Mark Sanders

Some bigger expert can correct me, but expect 50% of the solar rated capacity during daylight hours. Shade/rain/ non ideal pointing happen. So, 1KW solar panels deliver 500W X hours = daily KWh. Add up your expected KWh usage, and compare. I’d give yourself some surge margin as well.

A few months back, a solar supplier offered me semi-flexible panels for $1/W…I was VERY tempted to get 2KW or so, but finances are tight. Now more seriously looking at typical pricing, i’m kicking myself for not FINDING the money… 🙁

Cam
9 months ago
Reply to  Mark Sanders

The rule of thumb is ON AVERAGE you can expect to get watts divided by 4 as daily amp hours delivered to the battery in moderate to tropical latitudes provided you are not shading the panel at any time….SO you may expect daily availability of around 60-65 amp hours to run things from your battery daily. To find what that means… look on the product label…. a Mr. Coffee pot uses around 800 watts whch is amps x volts…so divide by 12 (volts) and you can see that you’ll use 66 amps of current to make a pot of coffee…now lets say that you leave it going for an hour…Well that would be 66 AMP HOURS or the entire daily output of your solar panels. But if we only brew for 10 minutes or 1/6 of an hour….you would use 1/6 of those amp hours or 11…leaving around 50 for other stuff. My 17″ laptop uses 45 watts so that is roughly 4 amps… so 4 hours of laptop time is roughly the same as 10 minutes of coffee pot time.
That’s how you do the math…but a real battery monitor is better!

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