The short version
- Solar covers 41% of electrical load, but electrical load is not our biggest energy use.
- The granulator is the single largest electrical load and runs well on daytime generation.
- Heat, not electricity, is the harder problem in a wash operation.
- We deliberately did not oversize the array — export rates made the last 20 kW uneconomic.
What we installed and why
Sixty-two kilowatts on the covered storage building roof, commissioned in the second quarter of 2022. The building was already there, the roof was structurally sound and largely unshaded, and the yard's load profile is strongly daytime — which is the combination that makes an industrial array work.
| Modelled | Actual, 3-year average | |
|---|---|---|
| Annual generation | 89,000 kWh | 93,400 kWh |
| Share of yard electrical load | 38% | 41% |
| Self-consumption | 84% | 91% |
| Payback period | 9.0 years | ≈ 7.1 years at current rates |
| Degradation | 0.5%/yr | ≈ 0.4%/yr |
Self-consumption running above model is the interesting line. We use more of what we generate than expected, which is a function of the granulator: it is our largest single electrical load, it runs during the day, and it turns out to be an excellent match for a solar profile.
Where the electricity actually goes
| Load | Share of electrical use | Time profile | Solar match |
|---|---|---|---|
| Granulator | 34% | Daytime, batch | Excellent |
| Wash bay pumps and circulation | 22% | Daytime, continuous | Good |
| Separator and filtration | 11% | Continuous | Moderate |
| Compressed air | 9% | Daytime | Good |
| Lighting | 8% | Early and late | Poor in winter |
| Fabrication shop | 7% | Daytime, intermittent | Good |
| Office and site services | 5% | Daytime | Good |
| Yard equipment charging | 4% | Overnight | None |
The one that will not move is overnight equipment charging. We run electric yard equipment specifically to reduce local emissions in Bayview, and it charges when the sun is down. A battery would fix that on paper; the arithmetic has not worked yet at our scale.
The load solar does not touch
Here is the honest limitation, and it is the reason I am cautious when people describe this yard as solar-powered. Electricity is not our largest energy use. Heat is.
The caustic circuit runs at 160 °F and the food line needs a potable hot rinse. That heat comes from a gas-fired plant, and 62 kW of photovoltaic panels do nothing for it. In energy terms the gas plant is comfortably larger than everything the array covers.
What has helped is heat recovery rather than generation. Spent rinse water passes through a plate heat exchanger on the way out, pre-heating incoming fresh water. That is worth roughly 9% off the gas bill, it cost less than a used flatbed, and it was a better investment per dollar than the panels were.
Which is the general lesson
Why we did not go bigger
The roof would take perhaps another 20 kW. We modelled it and did not proceed, for a reason worth stating plainly: the additional generation would have exceeded our self-consumption during the middle of the day, and export rates made the marginal panels a fifteen-year payback rather than a seven-year one.
That may change. If we electrify any part of the hot water plant, or if storage economics move, the calculation reopens and the roof is still there. For now, matching generation to load rather than maximising generation was the better decision and we would make it again.
One thing we would do differently: we should have specified more monitoring granularity at install. We know total generation and total consumption well; the per-circuit picture in the table above was reconstructed over two years with clamp meters rather than read off a dashboard. Sub-metering is cheap at install and expensive to retrofit.
Written by Priya Raghunathan, wash chemistry & compliance at IBC Totes San Francisco. Published November 27, 2025. Spotted something wrong? Tell us — we would rather fix it than defend it.