As an extension to the thread on keeping communications hardware running on battery power during power outages and other emergencies:
I have 10 kW of commercially installed photovoltaic panels on the roof of my house [1]. But when the grid goes down, this system goes down also, for reasons I think I understand [2].
Adding a full-bore battery setup to this installation to capture some or all the multiple kW that could be generated and used or stored even when the grid was out for multiple days, would clearly be a large and unreasonably expensive installation.
Seems to me, however, with a minor addition to the DC-to-AC inverter electronics one might be able to switch to a backup DC-to DC mode where the panels just trickle-charged a small set of low-voltage backup batteries of the kind used in lanterns, power tools, or electronics at say a few hundred watts charging rate. If we had a multi-day outage, we could at least charge up some of these batteries each day, and use some that charge for minimal purposes each night.
I've not gotten around to exploring the possibility of such a capability with the vendor who installed our system, and I'm aware of the existence of much smaller solar-to-battery units available at retail. I'm just wondering if anyone on this group has seen any mention of this kind of backup DC-to-DC trickle-charging capability built into any larger residential solar systems?
----------------- [1] If anyone is curious why this large a system on a single-family residence, it's a large old empty-nester house with half its area converted into three rental apartments, so more or less 4 households under one roof; PG&E will nonetheless only allow one meter; domestic rates are sharply tiered; the house layout is near optimal solar-wise; and we got in early on an good installation plan. So, it's saving us enough on my electric bills that it should pay for itself over a decade or so
[2] My understanding is the inverters need the grid AC to drive the inverter electronics and keep them synched and running properly.***** Moderator's Note *****
The only solar installation I've seen in person was a "standalone" design, with the arrays used to charge batteries that handle the house load at night or during cloudy days. The family has a generator to use when the batteries get too low, since they're too far from the pole line to have any outside feed.
I assume that it's possible to have both a battery-backup system, and to sell power back to the electric utility, although I now realize I've never seen such a system described.
The funny thing about solar is that a very small increase in cell efficiency would push it over the edge into "gotta have" status. I'll bet many major corporations are working on it right now.
Bill Horne Moderator