Solar system status when not at property

[cbc58]

I have been researching building a small solar system for an off-grid getaway - and wonder what people do with their solar systems when they are not there.  Do you disconnect everything or just keep it hooked up with constant charging?

We would use the property sparingly and it could be vacant 4-5 months during the winter and maybe used on a weekend various times during the warmer months.

Any info appreciated.  Tks

[MountainDon]

A lot of what to do depends on what battery type is selected and how cold the winter is.

Lead-acid self-discharge enough that if left with solar disconnected from any incoming charge over a 4 to 5 month winter period they may discharge enough to cause sulfation damage to the plates. If it gets cold enough the electrolyte may also freeze and damage the batteries.

Lithium chemistry cells and batteries can be left at a partial charge state for months to years when not being discharged or being charged, even through a cold winter. However, lithium-based cells and batteries cannot be charged when they are colder than 0 C (32 F). They may be discharged colder than that but not charged. Once the batteries themselves, not just the ambient temperature, is above freezing they can be charged.

Lithium batteries are more costly but do last much longer when properly cared for. Being considerably more expensive to purchase it might not be desirable to use them in a remote location. Personal choice.

We have used lead-acid (golf cart) batteries at our cabin since the installation in 2009. We are on our second set, not bad for the length of time.

We have used only big-name brand hardware; charge controllers and inverters. During that whole time, I leave the solar charge system in operation. I do shorten the second (absorb) charge stage time a lot, as there are no loads being applied. I also reduce the float voltage slightly to possibly help keep the electrolyte level up by reducing the amount of gassing. So when the sun comes up there is a brief bulk charge, a short absorb charge and then the system remains in float charge till the sun goes down. The batteries stay charged and able to withstand the coldest winter. I change the CC settings when we return to use the system. 

In summer lightning season I do leave the solar disconnected by actually disconnecting the wires that come from the PV array to the charge controller. We lost an entire system to a big lightning strike when absent one summer. The batteries were the only hardware that survived.

If monthly access with enough time on site to give a charge was possible it would be fine to disconnect the charge system, IMO. But 5 months could be too long, IMO.

[cbc58]

Thank you MountainDon.  That's the kind of info I was looking for. 

[cbc58]

Thinking more about this... if you were to disconnect the batteries and store them for the winter at home, would you have to trickle-charge them every so often?  Once a month or something?  The area we would build will certainly hit 0 degrees during the winter so leaving them there would not make sense if they are at risk of getting damaged. 

[MountainDon]

Sure, removing the batteries to home where they can be monitored in a warmer place would be fine.  In our situation we wanted the batteries in place at the cabin as we snowshoed in several times a winter.   

Be careful handling the batteries when moving them. Acid burns are nasty.  It might also be a good idea to dedicate a few wrenches to what is needed to disconnect and reconnect the terminals. I have a few wrenches wrapped with thick PVC tape all over except the ends that are needed to turn the nuts. Also keep the plastic terminal covers the batteries are shipped with.