How much solar should you get from 300W worth of panels of the Roof?

[booster]

I have always dreamed of implementing a "pointing" system by mounting the panel on four liner actuators. You see folks putting hinges on one side and actuators on the other. But, I am picturing using four actuators that lie flat under the panel and attached to the corners. The panel would be only attached to the actuators, so it could point in any direction. The geometry would be complex and probably only practical for 10-20 degrees or so off horizontal. Not sure if that is enough to make much difference.

It might not be as hard as it sounds, perhaps.


They have had such systems on satellite dish and other antennae for a long time.



There also have been solar panels done that way. The ones I have seen were usually in a ground based or building roof mounted setup and appeared to use two rotational actuators. It would probably be one to rotate the panel, either from the midpoint or one end, and they other rotate like a tank turret. Perhaps looking at like aiming the canon on the tank would be a good example.



I think the four corners might be pretty complex to control by comparison and definitely limited in range as you mention.


What I found interesting is that most of those systems went away and went fixed panels in a relatively short time. The ones on the old Honeywell headquarters in Minneapolis were put on to great fanfare, but a few years later was changed quietly. Linear actuators and weather don't get along very well in this part of the country. We constantly had trouble with roof mounted HVAC damper controls and such in the places I worked.

 

[GeorgeRad]

Tilting solar panels could at most increase the output by 20-30%. But doubling cells by 100%. This was discussed on the Sprinter forum; I have seen someone implementation and there was a fellow planning to sell 80/20 kits before Covid. Sliding panels could be easier to implement.

 

[phantomjock]

The first ground based, single axis trackers for solar panel tilting were developed in the early 1970s - quite a long time ago. Steve Bear (ZomeWorks) was the first. Met him in 1971-2.

The technology has been around a "while" and can be better optomized with todays tools and technology.

Best of luck.

Cheers - Jim

 

[JohnnyDanger]

This is my setup by the way.

In this picture, it does appear the TV antenna is casting a small shadow in this situation, however this was while traveling and not at the normal parking location.

 

[GeorgeRad]

With 36 cells panels you likely have 2 strings/panel, but could be none, only way to find out is to see the connector box on the back of the panel.

Pending on Sun angle your panels shading vulnerability could come from:
1. AC
2. Awning
3. Antenna
4. Vent

You are likely immune from shading with Sun directly to the left on the driver side. Check with discharge battery, low voltage on batteries if they are getting about 18A at sunny day, no tress.

https://knowledge-center.solaredge...._technical_bypass_diode_effect_in_shading.pdf

Do you know if your panels are connected in parallel or in series?
I assume you have MPPT (vs PWM) solar charge controller, which one?

 

[jakegw2]

One experience

I have two 170W monocrystalline panels that should generate 340W (or 23A @ 14.6v).

For complicated reasons I have two different solar controllers with a selector switch that lets me switch between them whenever I want.

With my MPPT controller I have seen as high as 19.7A peak (288W), with my PWM controller I don't get higher than 15A (219W) or so.

Time of year matters. I get my highest readings near noon in the mid-summer. output during other parts of the year is never as high, even at noon on a cloudless day.

 

[Davydd]

The rule of thumb when I bought my previous van in 2014 solar is a 100 watt solar panel produces an average of about 6 amps per peak sun hour, or about 30 amp-hours per day. We had solar panels of 420 watts total or equivalent to 126 amp-hours per day. Then time of year sun angle and daylight hours, shade, clouds, dirt could diminish it further.

I have an under hood second alternator that puts out 220 amps at idle. That means I can idle my engine less than a half hour (1/4 cup of diesel) to have the equivalent of 420 watts of solar panels at optimum performance or about 7 minutes per 100 amp panel. When you have 400ah plus of lithium batteries solar makes no sense but the second alternator does make sense. Solar might be beneficial in an outside storage situation. I garage my van when storing.

I had the 420 watts of solar panels with 800ah of batteries on my previous van with solar and now have 576ah on my current van with absolutely no solar. Both had the second alternator which I consider essential in lieu of Onan generator and propane. I now have a short Sprinter negating any solar panels on the roof anyway with what I feel are more essentials like two skylights, antenna, Maxxfan and of course an air conditioner. That's my opinion. Solar on a Class B is a feel good desire.

 

[Boxster1971]

Solar on a van is a mixed bag. My 2024 Airstream Interstate 19 came with 250W of solar panels. My van has the Volta 51V system and solar is useless for that battery because the three panels in series only max out at 65V on a battery that is at 55-57V.

I added a second Victron 12V SmartSolar controller to keep the Sprinter chassis battery charged while parked outside in my driveway. It works great at keeping the 12V battery float charged every day, even this winter with partial shading from my townhouse.

 

[MsNomer]

When we switched to LiFePO4 and alternator charging, I figured our 300W of solar had become obsolete. Wrong. Alternator charging only works when the engine is running. Solar works whenever the sun shines. Driving down the road in the daytime, we get both, cumulative. About 200W is the most I’ve seen from the panels, but it’s enough to more than sustain both fridge and freezer on a hot day, so our boondocking capability is significantly enhanced.

 

[avanti]

As I see it, the thing that prevents solar from being redundant with a capable lithium/charging system has little to do with faster charging. Rather, its importance lies in when the vehicle is parked and unoccupied. I do not accept the argument that "if you have lithium, you need shore power for storage". This is neither realistic nor correct. If I park for multiple days, say, to take the ferry to Isle Royale or Mackinaw Island, our single 200W panel can dramatically extend our ability to run the fridge and freezer. And, it can sustain the van's telecom and monitoring systems indefinitely, which permits remote monitoring and in extreme cases, remote engine charging. Thinking of solar as merely a tiny battery charger is oldthink.

 

[booster]

When we switched to LiFePO4 and alternator charging, I figured our 300W of solar had become obsolete. Wrong. Alternator charging only works when the engine is running. Solar works whenever the sun shines. Driving down the road in the daytime, we get both, cumulative. About 200W is the most I’ve seen from the panels, but it’s enough to more than sustain both fridge and freezer on a hot day, so our boondocking capability is significantly enhanced.

You bring up a an interesting point on the solar in it being on all the time.


Based on a lot of information I have read, there is getting to be a more consensus about not having LiFoPo4 batteries at the higher SOC levels. Usually mentioned as above 90% or 95% range.


If you are going to try to adhere to that and operate midrange, most or all the time the solar being on all the time could take it higher than you want unless you limit how far into state of charge it can go, and make sure it goes off or to a float level that stops charging as even at 13.3-13.4v charge level it will still eventually get to near 100% full.



If staying midrange is not a goal of your, it doesn't matter of course so it can run full time.


A secondary thing that might be of consideration to some is making sure you stay within the accepted charge rate of the batteries you are using. This could be an issue where you have a b to b charger that is limiting engine charging to the batteries at or very near the max allowable or desired. Slapping 15 amps from 300 watts of solar might put you over.


We will probably not use the solar on ours much now with the lithium swap. We have a panel disconnect switch so easy to turn off. We limit alternator charging to 120 amps which is right on the .2C battery recommendation for long battery life and capacity preservation. Solar will probably be set at 13.0 volts only and used when we are midrange and parked in one spot without driving for a long time, which will rarely happen as we have gone 6 days without charging already without issue with the solar off.


In good sun we can easily get 90+ah of recovery per day and we don't normally even use that much per day, so it is not a trivial amount of power from solar, just slow.

 

[avanti]

So, I haven't yet investigated the details of all this stuff on my new system, but don't modern solar chargers have a "disable" input? I would think that this feature would be necessary to protect agains low-temperature charging. If so, I would think it would be a fairly easy project to automatically shut-down the solar charger when the SOC rose above some target. No?

I am planning to implement a scheme in which there is a toggle switch to select between "use" and "store". In the former position, it would allow charging to 100%. In the latter, it would stop at 60% (or whatever). This looks pretty easy with the highly-integrated Victron system, but I would think it would be doable regardless.

 

[W9TR]

Two 100W panels in parallel, GoPower PWM controller. I’ve never seen more than 10A charge rate, AGM batteries @ <20% SOC, full sun, 35 degrees N latitude. So 130 W out of 200. 65%.

Normally I’ll see 6A to 8A on a sunny day. Our base load is 4A (fridge, controllers, etc). Our lake place @ 46 deg N latitude I get 6A max midsummer, partial shade. Hope this helps.

 

[booster]

So, I haven't yet investigated the details of all this stuff on my new system, but don't modern solar chargers have a "disable" input? I would think that this feature would be necessary to protect agains low-temperature charging. If so, I would think it would be a fairly easy project to automatically shut-down the solar charger when the SOC rose above some target. No?

I am planning to implement a scheme in which there is a toggle switch to select between "use" and "store". In the former position, it would allow charging to 100%. In the latter, it would stop at 60% (or whatever). This looks pretty easy with the highly-integrated Victron system, but I would think it would be doable regardless.

I can't speak to the newest controllers about full cutoff charging and how they would control it. Of course the ideal would be to have it controlled by a central controller like a Victron as that gives you complete control of stuff like that it appears. Older chargers would several shortcomings in general as many have temp compensation also that you don't want with lithium.


Are you going to be setting your "100%" at the actual 14.6v until near zero acceptance amps, or are you going to create an "in use" arbitrary 100% full point like we are doing to prevent repeatedly charging to the oft maligned full voltage for lithium? You have a huge system so using either way would work without you running out of power, I think.


Since I don't know how Victron does things in their approved system installs can't speak to that, but the very interesting thing about the Victron 700 series monitors is that it is very easy to setup the arbitrary less than rated 100% full point, and it also is used for the monitor's synchronization point, so you get double benefit from it, as it appears to me from the literature and what the limited testing has shown. You can then select a high and low SOC to control the built in limit switch in the monitor. I use the switch to shut off the engine charging regulator initiate wire. I also have added a bypass switch to monitor internal contacts so we can do a quick recovery of some charge before the monitor gets to 40% SOC and turns on the charging option. The bypass doesn't affect the monitor function it self so maintains accuracy.


I have been really surprised at how much very accurate control the $110 Victron monitor is giving compared to the other high priced items in the system. It basically has nearly all the SOC stuff taken care of. The Wakespeed regulator takes care of the current limiting during charging ans acts as a failsafe to terminate charging before overcharging can occur. The Magnum shore charger is used to charge to the arbitrary 100% point when the monitors are due for synchronization and also to go to full lithium voltage of 14.4v+ to activate balancing if needed. The Magnum equalization mode is used to do that part. The solar is around for the ride mostly.



For storage mode we will likely do like we did on our fall trip. I just turned off the coach charging 6 days before we were to get home when at the arbitrary full point and we didn't charge at all those days. We got home at about 50% SOC. If we are too full, the portable electric heater on the inverter is used to drop it to where we want.

 

[MsNomer]

I actively monitor and control the charge. I normally stay in the mid-range SOC, but do not hesitate to fully charge if we are headed into an extended boondock. Solar (Trimetric) is set to lower max voltage. B2B (Renogy) has a toggle on the dash.

 

[Bud-ClassB]

I actively monitor and control the charge. I normally stay in the mid-range SOC, but do not hesitate to fully charge if we are headed into an extended boondock. Solar (Trimetric) is set to lower max voltage. B2B (Renogy) has a toggle on the dash.

I'm starting to understand:

I've always maintained my marine deep cycle, then agm's well. attending to their curiosities. If I go with lithium, I won't need to. They will outlive me whether I do or not. Kinda nice.

Bud

 

[booster]

I'm starting to understand:

I've always maintained my marine deep cycle, then agm's well. attending to their curiosities. If I go with lithium, I won't need to. They will outlive me whether I do or not. Kinda nice.

Bud

I think you have hit on a real paradox and gap in the knowledge base on lithium batteries. EG, just how long will they last with various levels of "abuse" or "less than stellar" care.


In watching the ever changing use specifications of the various lithium batteries, it certainly appears to me that they have had some problems with early failures. This is based on the very much lower recommended charge rates, disappearance of the ability to use from 100% SOC all the way to zero, the charge to 14.6v and hold there is fine is no longer around, charge and then float is giving way to don't float use full cutoff charging. Etc, etc. None of these would have changed if they didn't have a problem, I think, because the original specs were good sales inducers.


Of course, none of them will ever own up to having problems or how much any given departure from the ever elusive "best practices" will shorten life. Original claims were often 10K or more cycles, but now we routinely see some at 2500 cycles, often with caveat that is at 80% discharge or such. I think we charged 6 times in our 30 day fall test trip so even fulltiming we would get less than 75 cycles per year and would not hit the 2500 even in 20 years.


But, what if the 2500 is really 1000 cycles due to a buildup of non maximized care? A full timer charging daily would hit that in 3 years. This kind of use may be what generated the changes in the recommendations from the manufacturers as there are many, it appears, one battery, under 200ah conversions done on top of systems that were for AGM batteries. The low capacity but heavier use like for electric cooking could make for many more charge cycles than the bigger systems see, and the AGM charging systems probably aren't great for the batteries either.


A lot of this may be moot in a very short time as the low end lithium, that is probably more prone to failure, is getting so inexpensive it won't even matter to many users if it fails in 1000 rather than 2500 cycles.


My built in nature, and my past profession, have made me unable to not try to take the best care I can on any and all our equipment, vehicles, house, you name it. Others will just accept the short life, and I think many with the high end expensive and large systems will trade for a new RV long before the batteries show any wear. For the manufacturers to maneuver in the market has to be a relatively tough thing because the have to sell enough to survive but also not get enough warranty issues to hurt them that way. Once it all settles and pricing and recommendations get more consistent, it will better for the customers and manufacturers, but now it is pretty much a shooting match.

 

[MsNomer]

I'm starting to understand:

I've always maintained my marine deep cycle, then agm's well. attending to their curiosities. If I go with lithium, I won't need to. They will outlive me whether I do or not. Kinda nice.

Bud

I doubt that is true. It’s just so much easier to take care of them. Life is sooooo much easier when you don’t need to get to 100% and voltage doesn’t crater at 80%, so it’s cool to run the microwave at 30%, etc.

 

[Boxster1971]

So, I haven't yet investigated the details of all this stuff on my new system, but don't modern solar chargers have a "disable" input? I would think that this feature would be necessary to protect agains low-temperature charging. If so, I would think it would be a fairly easy project to automatically shut-down the solar charger when the SOC rose above some target. No?

I am planning to implement a scheme in which there is a toggle switch to select between "use" and "store". In the former position, it would allow charging to 100%. In the latter, it would stop at 60% (or whatever). This looks pretty easy with the highly-integrated Victron system, but I would think it would be doable regardless.

Yes the Victron SmartSolar controllers have a disable input designed to be controlled by a BIM. The Volta system on my Interstate uses that feature to disable solar charging at 90-95% SOC and when battery is too cold to charge.

 

[avanti]

Yes the Victron SmartSolar controllers have a disable input designed to be controlled by a BIM. The Volta system on my Interstate uses that feature to disable solar charging at 90-95% SOC and when battery is too cold to charge.

Yeah, that's what I thought. But don't other modern units have this feature? Seems kind of obvious, but maybe it is unique to Victron?