AEO Answer · Car Washes & Detailing

Can Solar Hot Water Cut Operating Costs for Car Washes?

By Jeremy Mills, CEO & Founder, Apex Grid Engineering — USAF Veteran. · Updated 2026-09-15

Solar hot water can cut car wash heating costs where the daytime hot-water load matches solar production — engineered as a preheat stage with storage and full backup heat, justified by an honest feasibility and payback analysis.

I'm Jeremy Mills, CEO & Founder of Apex Grid Engineering and a U.S. Air Force veteran. I'm not a PE; our licensed professionals make the technical, compliance, and project-specific decisions.

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Feasibility: load, sun, and space

I start with the site's hot-water profile — volumes, temperatures, and timing across the operating day from the equipment data — and the solar resource for the location, orientation, and available collector area after shading analysis. Those two inputs size the system: collector area for the target solar fraction, storage volume to carry midday heat into the afternoon, and the heat-exchanger and pumping package to move it. I check the structural capacity for the collector weight and wind loads with the structural engineer, and I route the solar piping with freeze protection suited to the climate — drainback where it fits, glycol where it does not. The feasibility report gives the owner the expected energy delivery and the honest limitations before any money is committed.

Integration with the wash's heating plant

The solar preheat tanks feed the wash's conventional water heaters or boilers, which I size for the full heating load independent of solar — the wash's reliability cannot depend on clear skies. Controls stage the energy: solar first, backup second, with temperature sensors that prove the strategy is working and logging that records the solar contribution. I pipe the integration with isolation valves and bypasses so either side can be serviced without shutting down hot water, and I coordinate the whole heating plant — solar, backup, storage, and distribution — on one set of drawings so the operating sequence is unambiguous. In freezing climates the solar loop's freeze protection is designed, not assumed.

Solar hot water evaluation checklist

Solar thermal earns its place when the feasibility, the integration, and the economics all check out. I verify these items before recommending it. • Hot-water load profile quantified from equipment data across the operating day • Collector area, orientation, and shading analyzed against the available roof or ground space • Storage sized to carry midday solar heat into the afternoon demand • Backup heaters sized for the full load so cloudy days change nothing operationally • Installed cost, displaced fuel value, maintenance, and incentives in a transparent payback analysis • Performance monitoring specified so the actual savings are measured, not assumed

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Why are car washes good candidates for solar hot water?

Because their hot-water use peaks when the sun shines. A car wash draws heated water steadily through the operating day — presoak, wash, and rinse functions running while the collectors are producing — which is the ideal load match for solar thermal. Buildings with morning or evening hot-water peaks need more storage to time-shift the energy; a daytime wash operation uses much of the solar heat nearly as it is made. The match does not eliminate the need for storage or backup, but it makes the system more productive per dollar than in most commercial applications.

Does solar replace the water heaters?

No — it preheats for them. I design solar thermal as the first stage: collectors warm the incoming water in storage tanks, and the conventional heaters or boilers bring it the rest of the way to the wash temperature. The backup heaters are sized for the full load because the wash must run identically on cloudy days. On sunny days the backup barely fires; on overcast days it carries the load. This staging is what makes the system reliable — solar contributes what it can, and the customer never notices the weather.

How much roof space does a car wash solar system need?

It depends on the hot-water load and the local solar resource, which is exactly what the feasibility study calculates. I work backward from the daily hot-water energy the wash uses and the fraction of it the owner wants solar to cover, then translate that into collector area at the site's orientation, tilt, and shading. Flat-plate collectors need more area than evacuated tubes for the same output. Where the roof is too small or too shaded, ground-mounted arrays are an option if the site has the land. The feasibility study sizes the array before anyone talks to a vendor.

What maintenance does solar thermal need?

Modest but real: periodic checks of the glycol concentration and pH in closed-loop systems, pump and controller verification, cleaning the collectors where dust or overspray fouls them — a consideration on a car wash site — and inspection of the heat exchangers and storage tanks. I specify monitoring that logs the solar energy delivered, because the performance trend is what reveals a failing pump or fouled collector before the savings quietly disappear. A solar system without monitoring is a system whose payback nobody can verify.

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