diy solar

diy solar

Trying to find the weak link in my solar system.

littlebunnyhead

New Member
Joined
Jun 8, 2021
Messages
2
I recently purchased an RV with a solar setup installed and am having trouble diagnosing what needs to be upgraded in order to solve the problem ihaving.

I have 500W of panels on my roof, and my 2x200ah deep cycle gel batteries are charging up to 12.7v+ most days if my daytime electrical use is moderate to low. However, even trying to keep our electrical consumption low, our battery monitor has been showing that the battery charge is pulled down below 12.1v overnight even running just a couple of small 12v fans and led lights.

Generally speaking, in a situation like this, would you add more panels (and upgrade the charge controller etc etc) so that the batteries are receiving more charge during the day, or add another battery or two to the bank to increase capacity? Or are both absolutely necessary?

Here are the components of my current system:
3x100w panels, 1x 200w panel
50a renogy mppt dc-dc battery charger/charge controller
2x 200ah renogy deep cycle hybrid gel batteries
1x 3000w inverter

thank you!
 
Welcome to the forum.

These typically symptoms indicate you are using more energy than the panels can deliver. The panels determine how much energy you collect per day, the batteries determine how long you can use energy without charging.

Your gel batteries should be hitting around 14V to attain something near full charge.

If you have an absorption fridge and are trying to run it on AC, then you need to run it on propane. I doubt you are, or things would be worse, but I'm mentioning it here just in case.

Shading/partial shading on the panels can severely decrease your panel output.

If your battery monitor can display current, do you ever see anything between 35 and 40A at high noon?
 
Having your panels flat on your roof cut down on charging all so , my buddy has a set of panels
That fold up and he slips them in his shower when he is traveling when he gets to camp he sets them up in the sun .
Your inverter is a large draw on your battery’s allso it could use all much as much power as a frig .
You need to see how much power you are getting from the sun .
This time of year you should get lots of power even with flat panels
 
Thanks Snoobler!

That’s what I suspected, that the issue was not enough incoming power. And wow, 14v? I don’t know that I’ve ever gotten the voltage that high but, admittedly, I’ve only just started really paying attention.

I’ve been keeping the bus parked pretty much in direct sunlight as part of my data collection trying to diagnose this problem, so I don’t think the issue is shading.

I’ve seen some amps in the 30s around midday I’m pretty sure, but I can check it out today and report back.

I’ve already got 300 more watts of panels (all that will fit on my roof without having to swap stuff out) and a new 100a renogy charge controller on order, but before that all arrives I wanted to make sure I wasn’t treating the wrong problem here.
 
Even partial shading can have a huge impact on a panel's output. If the panels are particularly hot from both sun and the metal roof, they will not perform as well.
 
Some thoughts - take a gander at Renogy's hybrid-gel OCV vs SOC chart at the bottom of their pdf (this one is for the 100ah)


Compared to agm, you might see gels to be *slightly* different, and as always, OCV voltage says nothing about the health of the battery (ie sulfated).

If you are being dragged down to 12.1v / 6 = 2.01v per cell. According to their chart, that is about 30% SOC. (if measured at rest/no load for 12 hours)

The big problem is that your load during the daytime is not letting the batteries charge properly. If you only hit 12.7v you are simply sulfating them from an inadequate charge. They should be reaching at least 13.8v if not 14.1 to 14.2v daily.

It is also possible that your bank is badly out of balance, if neither battery has ever received a full-charge once in it's lifetime.

Perhaps your moderate to light load during the day needs to be actually measured to see if that's the weak link!
 
Last edited:
Back
Top