Community Forums

deputybubba · 08-28-2017, 09:22 AM

so for solar I thought the rule of thumb as at least the same amps solar as AH of battery...
I have a 300 AH battery bank and was going to put on 300 amp of solar or maybe 400 amp.
I 'only' have 3 group 27 AGM batteries and I could maybe go taller, but not wider or deeper.
Thoughts ?

Thanks
Bruce

Lv2Roam2 · 08-28-2017, 12:03 PM

I think you're off to a good start ... there's lots of add'l reading on posts throughout IRV2 and especially on the 'Going Green' tab. AM Solar's website [U]amsolar.com[U] can also be helpful. Share with us what you desire to operate from this system, how long, and what kind of camping you'll be doing and we can share some real-world experiences.

For instance - we use ~ 1400W of panels to operate everything in our coach except the A/C and electric heat/water. With good sun conditions we can sit almost indefinitely without generator use.

Searching_Ut · 08-28-2017, 12:52 PM

General rules of thumb are a starting point, but in my opinion not of much use really. You need to base your system on the locations, time of year, and other specific conditions under which you plan to use the system. Start with an energy audit so that you have a good understanding of how much energy you need to enable the type of camping you intend to do. I like to do a lot of camping in the shoulder seasons when daily solar harvest is a lot less than what you get in the summer. I can't be bothered to use tilting devices for my panels so that results in my needing more than I would need than if they could be tilted for better solar harvest.

Figure out how much energy you normally use in a day.

Determine the conditions you generally camp in, ie. forested areas vs. open areas. Mountains, deserts, northern areas vs. south, summer, winter, fall.

Knowing how much power you need, and having a better understanding of the conditions you'll be camping in will allow a much better designed system for your specific needs.

deputybubba · 08-28-2017, 01:21 PM

Quote:

Originally Posted by Lv2Roam2

For instance - we use ~ 1400W of panels to operate everything in our coach except the A/C and electric heat/water. With good sun conditions we can sit almost indefinitely without generator use.

Wow that seems like ALOT of solar.
I should have put in more info. So we almost exclusively boondock. and mostly in Az. so sun is usually present daily.
We have a res. fridge and currently no solar. The trips we have taken the batteries get to about 12.1 about every 8 - 10 hrs. which triggers the generator to start up. some light TV/blu ray use and all lights are LED, no satellite TV.

I'm looking to reduce that occurrence to hopefully once a day.
Thanks again.
Bruce

powercat_ras · 08-28-2017, 02:39 PM

A couple of things -

I still have flooded lead-acid deep cycle batteries that I am taking good care of that should last for years, I am not an expert on AGM or Lithium so I'll let others speak to those options.

1. Invest in a Smart Battery Monitor with Shunt , so you can track the state of your batteries and how fast they are charging or discharging. I found the Victron BMV-700 Battery Monitor to be a cost effective ( well under $ 200 ) fairly easy to self install retrofit for my Winnebago Vista RV.

2. If you have Deep Cycle Flooded Lead Acid Batteries, you want to operate them between 100 % charged and 50 % charged for them to have a decent life. OK to go down below 50 % occasionally but not regularly. So, you should consider your actual usable capacity only half of your batteries rated amp-hours.

3. If you have Deep Cycle Flooded Lead Acid Batteries, you can add a Battery Minder OBD-12 On-board de-sulfator to keep your batteries in good health so they can deliver heavy current to your DC-AC inverter when needed for more years. Under $ 80, also easy to self-install.

4. With your battery monitor you can see how many Amp-Hours you consume in a typical 24 hour day, with your RV off shore power. I suggest you want to have at least 2X that many Amp-hours of battery storage.

5. You can size how much solar it would take to put back the Amp-Hours consumed in #4. A reasonable conservative assumption to cover winter for un-shaded solar panels mounted flat on the RV roof is that you can put back 30 Amp-hours per day for each 100 watts of solar you add. Summer and south, you would do better. Tilt the panels and face them south, you would do better.

Some real #s. I have a 30' Winnebago Vista. Don't run the refrigerator on solar. Have 3,000 watt Windy Nation Pure Sine Wave Inverter so use battery for light cooking ( coffee pot, toaster, microwave ). Other loads for solar are lighting, fans, TVs, Sat Dish, computer and phone chargers. 320 Amp-hours of deep cycle lead acid batteries (4). 500 Watts Solar Panels on roof, parallel wired. Windy Nation TrakMax 30L LCD MPPT 30A Solar Charge Controller.

So far as the rule of thumb, I have found I needed to go a bit higher than 1 watt Solar per Amp-Hour of battery storage, so that I could just flat mount the panels on the roof of my RV . I also found that at least for the solar panels I installed, they NEVER put out what they were rated at, at best in the summer they do 75 or 80 % of rated output. I can't say that's is a general rule, but it's sure true for the Polycrystalline Solar Panels I used.

deputybubba · 08-28-2017, 03:18 PM

Quote:

Originally Posted by powercat_ras

A couple of things -

1. Invest in a Smart Battery Monitor with Shunt , so you can track the state of your batteries and how fast they are charging or discharging. I found the Victron BMV-700 Battery Monitor to be a cost effective ( well under $ 200 ) fairly easy to self install retrofit for my Winnebago Vista RV.

So far as the rule of thumb, I have found I needed to go a bit higher than 1 watt Solar per Amp-Hour of battery storage, so that I could just flat mount the panels on the roof of my RV . I also found that at least for the solar panels I installed, they NEVER put out what they were rated at, at best in the summer they do 75 or 80 % of rated output. I can't say that's is a general rule, but it's sure true for the Polycrystalline Solar Panels I used.

Randy thanks for all this info, I didn't quote the entire post but I read it all..
On the Victron I'm not sure how I woudl route the cable into the RV to be able to see the display.
If I went with the dongle thing I could just monitor from my smart phone without running wires into the RV ?

Again thanks for the info
Bruce

powercat_ras · 08-28-2017, 03:39 PM

Quote:

Originally Posted by deputybubba

Randy thanks for all this info, I didn't quote the entire post but I read it all..
On the Victron I'm not sure how I woudl route the cable into the RV to be able to see the display.
If I went with the dongle thing I could just monitor from my smart phone without running wires into the RV ?

Again thanks for the info
Bruce

I don't have the smart phone dongle so can't answer your question, but I think it attaches to the remote panel and not directly to the shunt. Think you have to have the remote panel with the Victron.

ByeTheWay · 08-28-2017, 03:52 PM

Here are some links to help: Here are some links to help you with your learning Journey RV Electrical
RV Solar Electric Store
http://www.starlightsolar.com/Home.html
solarseller.com alternative energy by John Drake Services, Inc.

I have 6-6v AGMs for a total of 672ah and 900watts of solar. Your calculation of 1ah of solar / watt is correct, but extra solar is nice too.

Gary RVRoamer · 08-29-2017, 07:26 AM

The amount of solar needed depends on your power consumption habits, not the battery bank size. Of course,the more power you use, the more battery amp-hours you would like to have as well.

The other factor is the available sunshine for solar charging. If you only get an hour per day of good sun, you need a lot of panels to take advantage of it, but if you have 16 hours of nice sunshine every day you can easily get by with a modest array.

If you use 1200 watt-hours/day of power (12v x 10A x 10 hours), then you need to put that much back into the battery bank every day. A 100W panel produces about 7 amps of charging (7A x 14.3v), so needs to have about 12 hours of full sun every day. Two 100W panels would be about half that time, and so on.

Since solar panels rarely produce their rated output except when the sun is high and directly above, you may need a lot of solar wattage to get maximum charging during the limited time when they are 100% effective. Solar charging in the SW desert is a lot more effective than solar in the NE woods.

Old Scout · 08-29-2017, 07:58 AM

Just did a "start-up" solar project on my 40ft DP. DIY-ed it so cost was about $800 for adding 400 watts--total now 500 watts with existing 660 amp/hrs of bat storage. Used mostly a Q-site in winter. Allows us to run resid. fridge all day and some propane heat at night. Reduced genset run time at evening to top off, but still need 2-3 hrs run time in mornings. So IMHO, 600 watts of panel and 660 amp/hrs of bats is about the minimum system to have an impact on RV life-style. Whether 600 or 1000 watts, solar is a significant "investment" and you still may not be "off the grid."
PS-- my 600 watt projects works fairly well but doesn't get us totally off generator. The irony with solar is with panels on the roof, you need to park in the sun to make then work; except in winter time, parking in full sun is the worst thing you can do to control interior heat in your rig????????