Letter Re: Priority and Redundancy in Retreat Electric Power

In an attempt both to think through the issue and to stimulate other to do likewise, I present my personal analysis of our family’s current and future electric power usage. First some background: We live in a 2,400 square foot two-story home the suburbs of a southeastern city. Currently there are 3 of us, with one child away at school. Our summer temps are as high as 95F and winters can drop to the 20s. Currently is is between 50 and 80, which is great – windows often left open.  

We have grid power, for which we pay $150-300/month. Additionally, I have recently installed 720 Watts of solar photovoltaic on a south-facing roof which gets 6-8 hours/day of direct sunlight. This is tied through a charge controller to a bank of eight L-16 6 volt lead-acid batteries set up in a 24V configuration (4 in series, paralleled with 4 more in series). This system drives a Xantrex inverter and serves mostly as an emergency standby for absolute essentials. The batteries can also be recharged from the grid or from a generator. The generator (5 kilowatt diesel), when running, operates more systems, as well as charging the batteries in the solar system (if needed).  

So, we currently have three layers of electrical power:  

1) Solar running a few lights, television, radio, and the central heat blower motor (we have gas heat) and, most important, the controller for the on-demand gas hot water heater,

2) Generator (perhaps an hour a day) running more lights, computers, router/modem, one window heat/AC unit, refrigerator, freezer and microwave, and

3) Grid – running everything else (washer, dryer, range, central AC compressors).  

A separate system (three 12 Volt deep-cycle car batteries with float charger) powers the CB/ham communication gear.   

Although not nearly approaching off-grid, this arrangement lets us have essentials during a grid failure, with additional luxuries during brief generator runs. During the day, when we require little power, the solar system can run the house with energy to spare, leaving the batteries fully charged for evening use.  

We are overly dependant on piped natural gas; and, although we have reserves of propane for cooking, we would need to provide for heat and warm water in other ways if gas pumping stations were off-line.  Also of interest, our potable water drums are arranged to backfeed into the house’s plumbing after the water main is turned off.  We use a 24 volt DC water pump designed for boating (fed by the battery bank) with a built-in pressure sensor that actuates the pump when water pressure falls (from opening a spigot).  

I would welcome any readers’ comments on better optimizing our power use and prioritizing our demands during emergencies.   In closing, please get you final preparations ready soon – things are deteriorating faster than you think!   – J.B. in Tennessee