Should you turn your solar on over winter?
Will solar panels keep my batteries charged over winter storage?
Dear Mike,
I’m trying to get used to solar, so my question is this… Should I shut off my RV solar system over winter while the RV is stored (Class C)? Or should I leave the solar panels on to keep the batteries charged? - Barry M
Dear Barry,
That’s a great question. If you have at least 100 watts of solar panels (more is better) and a properly set up MPPT solar charger, then it should easily keep your batteries charged and maintianed as long as you don’t have any heavy parasitic loads, like your CO detector turned on.
Many RVs (mine included) have a battery disconnect switch that turns off power to all RV systems, while leaving the solar charge controller connected to the batteries. So I always have fully charged batteries and all I have to do is turn the master battery switch and I’m ready for camping.
Does your battery disconnect switch turns off your solar panels?
The easiest way to know for sure is to measure your battery voltage on a sunny day with a digital meter, and turn off the battery disconnect switch. If you have a Lithium battery the solar charge controller should boost the battery voltage to between 13.5 to 14.5 volts. If the battery voltage is stable when you turn the battery disconnect switch to “OFF” then your solar system will continue to charge the batteries. Here’s a chart showing the resting voltage of a Lithium battery referenced to its SoC (State of Charge).
Now, if your solar charge controller is disconnected by the battery switch, then the battery voltage will drop a volt or so in a few minutes when it’s in the “OFF” position. If that’s the case, then your solar panels won’t be able to charge your batteries while the disconnect switch is in the “OFF” position.
Do you have to charge Lithium batteries during the winter?
One of the advantages of Lithium batteries is that they have a very slow self-discharge rate, as low as 1% of total charge per month. Many Lithium battery manufacturers recommend you simply charge them to 50% or 100% SoC (State of Charge) and store your battery over the winter without any type of charger. So check with your Lithium battery manufacturer for recommended storage procedures. If your Lithium battery is completely disconnected from your RV electrical system it might only lose 15% of its SoC in an entire year of storage!
What about Lead-Acid batteries?
On the other hand, a Lead-Acid battery can lose up to 10% of its SoC per month of storage. So they can lose 50% of their SoC over winter, which can seriously reduce the life of these batteries. So AGM and FLA (Flooded Lead Acid) batteries definitely need some sort of Battery-Tender/Maintenance charger over winter. You can do this with the batteries still in your RV, or bring them into your garage and connect them to a battery maintenance charger. Just be careful when disconnecting batteries and make sure you mark all your wiring.
That’s it for now…
Yes, unless you’re full-timing it’s time to get your RV ready for winter storage. If you do it properly then you’ll have a much easier time getting ready for spring camping.
Let’s play safe out there… Mike
I, too, have changed my RV off-season storage habits since switching to lithium coach batteries.
I now put the USE/STORE switch in STORE mode, rather than using shore power and the converter or an external charger to maintain the batteries. Even though our MH is parked in partial shade, the roof solar maintains the coach batteries daily (except when the solar panels are covered with snow or the cloudiest of days).
An added benefit: the LiBIM225 also, when sensing a sufficient voltage from the coach side, usually in late morning or about noon, also boosts the chassis battery (if it has self-discharged overnight below ~12.6V). If, by chance, the LiFePO4 BMS shuts down because of low temperature, the solar power is fully available for the chassis battery’s use.
My hypothesis: the daily solar cycle is beneficial to the longevity of both the lithium coach batteries and the almost 6-year-old OEM SLA chassis battery.
I have two 6 volt lead acid G.C. batteries with 150 watts of solar on the roof of our 5 th wheel connected to a victron mppt solar charge controller. The batteries remain in the trailer all year long and get very cold in the winter -40 C ~ and remain fully charged. I check for state of charge with a tri-metric battery monitor. Also there is a 4 position battery switch, 1 or 2, both or off.
The battery switch remains off for the winter but solar remains connected. The only hassle with this setup is occasionally sweeping off the snow that covers the panels! It all works very well!