The one question every solar calculator forgets to ask

The arithmetic

Take an 800-watt system on a west-facing Irvine balcony, tilted, open sky. It produces about 1,050 kilowatt-hours a year.

Same panel. Same balcony. Same city. Same weather. A $105 spread, which is 40 percent of the return, decided entirely by whether anyone's in.

Now compare that to the things people actually agonise over. Choosing a premium panel over a budget one might get you 5 percent more output. Adding a third panel to a two-panel setup adds maybe $60. Neither is close.

Why it stopped mattering and started again

Under the old net metering rules, exported power was credited at close to the retail rate. Your meter effectively ran backwards. Whether you used your production at noon or bought it back at 8pm was very nearly a wash, so nobody modelled it and nobody asked.

The CPUC's net billing decision in December 2022 changed that for rooftop solar, cutting export compensation to avoided-cost rates. And SB 868 goes further: it's silent on export compensation entirely, which means for a plug-in device, exported power is worth zero.

So a kilowatt-hour you use is worth 33 cents and a kilowatt-hour you export is worth nothing. That's not a discount. That's the whole value of the thing, present or absent, depending on whether somebody happened to be running a dishwasher.

What you can do about it, free

This is the part that makes the question worth asking rather than just interesting.

Move one load into daylight. Set the dishwasher for 1pm rather than 8pm. Run the washing machine at lunchtime. If you have a timer on a water heater or a pool pump, move it. On a time-of-use plan you're shifting electricity from a 58-cent window to one where your panel covers it — worth roughly $60 a year for a single daily cycle, and it costs nothing.

Pre-cool in summer. Run the air conditioning harder at 2pm and let the house coast through the evening. Free, effective, and the house is more comfortable at 6pm.

Charge things at midday. Laptops, tools, an e-bike, a portable power station. Anything with a battery is a load you can move.

Think about it before you buy a battery. A battery is the equipment answer to this problem and it costs $800 to $1,500. Two timers cost nothing. Do the free things first, measure what changes, then decide. The battery decision.

Why we ask it in the wizard

Our calculator asks seven questions and this is the fourth. We phrase it as "is anyone usually home during the day" rather than "what's your self-consumption ratio," because those are the same question and only one of them can be answered by a person.

It's also the question that most often turns a yes into a marginal, and occasionally into a no. A west-facing balcony with good sun and an empty flat produces a figure low enough that we'd rather you knew before buying than after.

That's uncomfortable for a site that earns commission on kits. It's also the reason to trust the number when it comes back high.