Here’s a first: when someone called me last week and asked about solar generators, I didn’t know what to say.
But I couldn’t figure out if the man on the phone was using “solar generator” to describe a solar power system, or if he was just unclear on his terminology. Generators are what power your system during an outage or an extended period of weak sunlight.
Turns out, it was neither. He was asking about a line of small off-grid systems used to provide emergency power that are being sold as, yes, “solar generators.”
Now, in the course of the work I do, I’ve talked with hundreds of people who are interested in off-grid solar systems.
I understand how complex these systems are—and that many callers feel overwhelmed by too much talk about batteries, charging, and loads.
Most would simply prefer to be told what will work for them.
Apple Computers took advantage of this tendency in 1998 with their iMac computers. Instead of asking the public to understand storage, memory, or processors, they offered the iMac in a variety of colors. This allowed people to make a manageable decision, receive a product, and leave the technical details to the professionals.
Unfortunately, you can’t choose between a teal solar system and a red one. And even if you could, picking by color is not exactly a recipe for success with battery-based backup power systems.
The lifespan of a battery is based on the relationships among a number of complicated factors—depth of discharge, number of cycles (discharge/recharge), and your ability to return the battery to a full charge. Basic knowledge about watt hours and battery care is also critical to a successful experience with backup power systems.
Why does all this matter?
Because once you understand the basics, you’ll quickly come to see that anything that calls itself a “solar generator” has to be inadequate for most uses.
For just one example, let’s look at a refrigerator that uses 1200 watt hours per day.
This single load requires a 12 volt battery with 250 amp hours to support it. That means that each day, if you assume the battery works at only 80% efficiency, you’ll need to supply the battery with 1440 watts of energy to replace the 1200 watts used. And depending on the location and time of year, you would need two 270 watt solar panels to recharge the battery.
So far, so good—until you realize that one popular “solar generator” on the market indicates that it’s ideal for refrigerators, lights, phones, computers, and TVs.
The unit comes with a 100 amp hour, 12 volt battery and two 30 watt panels—which is sadly inadequate. A 100-amp hour battery is sufficient to supply 450 watt hours per day, and you’d need seven 30-watt panels to recharge that battery for the next day’s use.
Needless to say, this doesn’t appear to be a good match for a refrigerator. This particular “solar generator” is probably just using the phrase—which is something of a buzzword—to catch consumers’ eyes. The only thing it really generates is attention.
This particular “solar generator” is probably just using the phrase—which is something of a buzzword—to catch consumers’ eyes.
Ultimately, system design depends on your needs as an end-user. If you’re interested in supporting some critical loads during a power outage at your home, an appropriately sized battery bank can be used to take care of those loads for a predetermined period of time. And if you want to be able to support loads over an indefinite period of time, you’ll need to size a solar array that can charge the batteries in the sun hours that are available.
Which means—unfortunately—even the best “solar generator” just isn’t going to cut it.