At critical junctures in their equipment upgrades, Lance and Jennifer had to examine the future of the system. They knew that most modern off-grid systems exclusively use AC appliances due to the wide selection of models available and to simplify home wiring during construction. But Lance says, “When we examined this carefully, we came to the conclusion that running DC loads for lights, refrigeration, and fans cuts the daily electric use significantly by eliminating the inverter losses, which may be 10 to 15 percent, or even more than 50 percent on a very small load like a single light.” Using DC loads instead of AC ones saves Lance and Jennifer more than 200 watt-hours per day. In a generator-free, off-grid PV system, every watt-hour counts. Minimizing the base load is essential to ensuring an adequate electricity supply through cloudy stretches of weather. Lance points out that “because straight AC systems are the ‘modern’ method of having an off-grid system, we call our system ‘post-modern,’ because we are aiming for the future, not the past.”
In his business as an RE consultant, Lance uses standard load analysis and sizing methods when he designs systems for off-grid customers. But his personal conclusions and lifestyle are different. “By setting limits to what Jennifer and I are able to consume, and living within these limits, we get a closer feel for what we are doing with our lives. It helps give our life purpose and meaning, and it helps make us happy. Our system is often called ‘pure’ or ‘purist.’ I see it as pure, all right—purely practical.”
Running a system like Lance and Jennifer’s takes tools. Lance says, “Our most important tools for making our system work are our brains! Sometimes visitors look at what we do and say, ‘I wouldn’t want to have to think about it.’ Well, we do want to have the opportunity to think about it and apply ourselves accordingly. Living without a generator gives us a close personal relationship with our energy use—how much energy is coming in and how much we are using.”
Another essential tool is a battery state-of-charge monitor (amp-hour meter), which provides cumulative and net battery charge data. It is installed where Lance can see it when sitting in his easy chair. Along with the amp-hour meter, they also have analog ammeters so they can see at a glance how the system is running throughout the day.
When Lance and Jennifer replaced their more than 20-year-old battery bank four years ago, they found that their battery sizing philosophy had changed because of their previous investment in increased PV capacity. As more modules are added to an array with maximum power point tracking (MPPT), more electricity is generated during low-light, overcast, or partly sunny weather. The result is that even with the sun’s limited availability on mostly cloudy days, the system’s batteries often still receive a full charge. By watching their battery monitor over the years, Lance and Jennifer determined that they really didn’t need the 800 amp-hour (AH) battery bank capacity they originally had (about 10 KWH of usable storage at 50 percent depth of discharge), and replaced it with a 640 AH bank, for about 8 KWH of storage (at 50 percent DOD).
The combination of a small base load, large PV array, and a very sunny location has enabled Lance and Jennifer to live off grid for close to three decades without any fossil-fuel-based backup energy source. During the winter months, this approach has continually provided them with ample electricity, when most off-grid system users would have to resort to firing up the engine generator to keep the batteries from being too deeply discharged. During the non-winter months, the PV array produces significant amounts of energy beyond what the base loads require.