Solar Thermal and Heat Pumps: Why Commercial Hot Water Needs a More Complete Energy Strategy

New research reinforces an important finding from earlier California modeling: commercial water-heating performance depends on more than equipment efficiency. Heat sources, thermal storage, electrical demand, and system design all matter.

As commercial buildings move toward electrification, heat-pump water heaters are becoming an increasingly important part of the conversation. Their ability to transfer heat using electricity makes them a valuable option for reducing reliance on fossil fuels.

But electrifying water heating introduces another question: How much electricity will a building need, and when will it need it?

For facilities with substantial hot-water demand, equipment selection affects more than annual energy consumption. It can influence peak electrical demand, utility costs, infrastructure requirements, and long-term system performance.

Solar thermal offers a different approach. By converting sunlight directly into useful heat, solar water-heating systems can contribute to a building's thermal demand without relying on electricity as the primary energy source for heat generation.

Research published in 2026, together with an extensive California analysis from 2020, highlights why these technologies deserve to be evaluated as components of a complete heating strategy rather than competing solutions.

What California Research Revealed About Water-Heating Electrification

In November 2020, J.R. Plaisted of Flagstaff Research published Assessment of GHG Reduction Technologies for Water Heating Electrification in California.

The analysis evaluated solar water heating, heat-pump water heaters, solar photovoltaics, and selected combinations of these technologies across all 16 California climate zones and 14 utility tariffs.

The study considered residential water heating, multifamily central hot-water systems, and commercial pool heating. Its objective was to evaluate greenhouse gas reductions, operating costs, electrical demand, and the economics of different approaches.

For multifamily water heating, the modeled statewide averages revealed meaningful differences between solar thermal and heat-pump configurations.

Source: Flagstaff Research, November 2020, Table 1. Results represent the study's modeled California configurations, utility rates, and emissions assumptions, not current operating guarantees.

The findings did not suggest that solar thermal was the appropriate choice for every project.

Solar water-heating systems carried higher initial installed costs in the modeled configurations. The economics also varied by climate, utility territory, and building application.

What the study demonstrated was that reducing greenhouse gas emissions and reducing electrical demand are related, but distinct, objectives.

A system can substantially reduce emissions while still introducing significant electrical consumption during periods when the grid is under pressure.

Direct solar heat can change that equation.

Why Peak Electrical Demand Matters

Water heating is often evaluated in terms of annual energy consumption. Yet commercial buildings must also account for when that energy is consumed.

A facility may have sufficient annual electrical capacity on paper while facing constraints during peak operating periods.

The 2020 California analysis examined electricity consumption during summer utility peak hours, generally between 4:00 and 9:00 p.m.

Its modeling showed that solar water-heating systems with thermal storage used substantially less electricity during those periods than the heat-pump configurations evaluated.

The reason is straightforward: solar thermal systems can collect heat during daylight hours and retain it in storage for later use.

This allows a properly designed system to meet some hot-water demand without requiring equivalent electrical input at the time the water is used.

The implications can extend beyond energy savings. For suitable projects, reducing peak electrical requirements may help limit additional infrastructure demands or exposure to certain utility charges.

These outcomes depend on the building's actual load, storage design, backup equipment, utility tariff, and operating strategy.

New Research Examines Solar-Assisted Heat-Pump Performance

More recent research is examining how solar energy and heat pumps can work together.

In October 2026, pv magazine reported on experimental research involving a 10 kW dual-source CO₂ heat pump developed by Italian researchers.

The system was designed to draw heat from either ambient air or photovoltaic-thermal (PVT) collectors, selecting its operating source according to environmental conditions.

Across 307 tests, the researchers evaluated how changing solar irradiance and other conditions affected system performance.

Under the reported test conditions, increasing solar irradiance from 322 to 904 W/m² produced a 21.1% increase in heating capacity and an 18.7% improvement in coefficient of performance.

The researchers also found that air-source operation could be preferable during periods of low solar availability.

These results apply to the specific experimental system and should not be interpreted as a universal efficiency improvement for solar-assisted heat pumps.

They also illustrate an important technological distinction.

PVT collectors combine photovoltaic electricity generation and thermal collection. In this experimental configuration, they served as an alternative heat source for the heat pump.

Conventional flat-plate solar thermal collectors operate differently, capturing sunlight to deliver useful heat through a solar thermal circuit.

The technologies are not interchangeable, and their integration requirements differ.

Nevertheless, the research reinforces a broader engineering principle: the performance of a heating system depends on how its energy sources are selected and managed under changing conditions.

Solar Thermal and Heat Pumps Can Serve Complementary Roles

The possibility of combining these technologies is not new.

The 2020 Flagstaff Research analysis examined solar water heating with heat-pump backup for commercial pool applications and discussed additional opportunities to integrate solar thermal, heat pumps, and storage.

In its modeled commercial pool-heating configurations, solar thermal paired with heat-pump backup achieved an 89% reduction in greenhouse gas emissions compared with the study's gas-heating baseline.

The report also identified the potential to use thermal storage and heat-pump operation strategically to improve system economics and manage electricity demand.

Not all of the proposed combinations were fully modeled, and their practical benefits require project-specific evaluation.

Still, the findings point toward a useful approach to commercial heating design.

Solar thermal can provide direct renewable heat when solar resources and thermal demand are suitable.

Heat pumps can supply heat under different operating conditions and may serve as primary or supplementary equipment.

Thermal storage can help manage differences between heat availability and demand.

Controls coordinate system operation according to temperatures, operating requirements, and available heat sources.

The goal is not necessarily to install every technology.

It is to determine which configuration best serves the application.

Start With the Building's Thermal Load

Before selecting equipment, engineers should establish how the building uses hot water.

That evaluation should include:

• Demand: How much hot water is required daily, and when do peak loads occur?

• Temperature: What supply and storage temperatures does the application require?

• Infrastructure: What electrical, mechanical, and rooftop capacity is available?

• Existing equipment: Can current water-heating equipment remain part of the system?

• Storage: How much useful thermal energy must be retained between generation and demand?

• Controls: How will the system respond to changing temperatures, heat availability, and operating conditions?

• Economics: How do installed cost, maintenance, energy rates, and long-term operation affect the decision?

A multifamily building with consistent domestic hot-water demand presents different design considerations than a school, hotel, aquatic facility, or industrial operation.

Even facilities with similar annual hot-water consumption may require substantially different system configurations.

Understanding the load is therefore more valuable than beginning with a predetermined equipment choice.

Thermal Storage Is Part of the Energy Strategy

Storage is particularly important when renewable heat is available at different times from the building's demand.

Solar thermal systems can collect energy during periods of sunlight and store useful heat for subsequent consumption.

The effectiveness of that storage depends on more than tank volume.

Engineers must consider operating temperatures, usable stored energy, heat losses, recovery requirements, heat-exchanger performance, and the interaction between generation and backup equipment.

The same principles become important when heat pumps and other heating technologies are integrated into a common system.

A properly engineered storage configuration can support reliable hot-water delivery while providing flexibility in when and how heat is generated.

Controls Help Connect Generation, Storage, and Delivery

As commercial hot-water systems incorporate multiple components, controls become increasingly important.

Temperature sensing, circulation management, and operating sequences influence how effectively available heat is captured, stored, and delivered.

Modern solar thermal controls support the management of solar collection and system operation.

More complex hybrid configurations may require additional equipment and supervisory control strategies to coordinate different heat sources.

Control capability should always be evaluated against the requirements of the actual system.

This is why a complete design approach matters.

Individual equipment specifications cannot, by themselves, determine how an integrated installation will perform.

A More Complete Approach to Commercial Renewable Heat

The 2020 California modeling and 2026 experimental research examine different technologies, applications, and performance measures.

They should not be treated as directly comparable studies.

Together, however, they support an important conclusion: commercial water-heating decisions benefit from evaluating the complete thermal system.

Electrification can reduce greenhouse gas emissions.

Direct solar heat can contribute renewable thermal energy while reducing dependence on electricity for suitable loads.

Thermal storage can help separate heat generation from the timing of demand.

And properly selected controls can support coordinated system operation.

For building owners and engineers, the opportunity is to evaluate these capabilities together rather than assuming a single technology will always provide the best outcome.

Manufactured. Engineered. Supported.

For more than 40 years, SunEarth has manufactured solar thermal equipment for residential and commercial applications.

Our approach considers the complete thermal system:

Generate. Store. Control. Deliver.

From solar thermal collectors and storage solutions to system controls and engineering support, SunEarth helps customers evaluate practical ways to incorporate direct renewable heat into their projects.

Whether designing a new commercial hot-water system, evaluating an existing installation, or exploring opportunities to integrate renewable heat with other technologies, the starting point remains the same:

Understand the load. Evaluate the available heat sources. Engineer the system around the application.

Planning a commercial hot-water project? Contact SunEarth to discuss your thermal requirements and system options.

Research References

1. Plaisted, J.R. (2020). Assessment of GHG Reduction Technologies for Water Heating Electrification in California. Flagstaff Research, November 2020. See especially the summary findings, multifamily analysis, commercial pool-heating analysis, and Section 8 on technology integration.

2. Applied Thermal Engineering (2026). Research on experimental dual-source air/PVT CO₂ heat-pump performance and operating-mode selection, reported by pv magazine, October 22, 2026.

Editorial note: The 2020 findings are historical modeling results. The 2026 findings concern an experimental PVT-assisted heat pump. Neither study establishes performance guarantees for SunEarth products or a particular commercial installation.