☀ The Solar Plumber

Water heating · PV · Solar thermal · Batteries

Solar Hot Water vs Solar Electric

Heating water is not the same problem as moving water. Pumps need motor power. Water heaters need heat energy. Solar can help both, but the design logic is different.

The first distinction

Solar hot water and solar electric are different tools.

“Solar hot water” usually refers to solar thermal equipment that uses sunlight to heat water or a heat-transfer fluid. “Solar electric” means photovoltaic panels that generate electricity. That electricity can then support household loads, including electric water heaters, heat pump water heaters, pumps, controls, and batteries.

TheSolarPlumber.com looks at this from the practical customer side: what is the existing water-heating equipment, what fuel does it use, how much hot water is needed, what does the roof allow, what does the electrical system allow, and what happens during outages or high-rate utility periods?

The right answer is not always the same. A home with gas water heating, a home with an electric resistance tank, a home with a heat pump water heater, and a home with a pool heater may all need different planning.

Heating is energy storage

A tank of hot water is already a kind of storage.

Batteries store electricity. Water tanks store thermal energy. A smart design may use solar production, timing, tank capacity, and equipment controls to reduce expensive grid use without pretending every hot-water problem needs the same solution.

Solar Thermal

Uses sunlight to produce heat. It can be effective, but it is a specialized plumbing and mechanical system with maintenance and installation requirements.

Solar Electric

Uses PV panels to produce electricity. That power can support many loads, including water heating, pumps, HVAC, lighting, appliances, and batteries.

Heat Pump Water Heaters

Use electricity to move heat instead of simply making heat by resistance. They can be efficient, but location, noise, air volume, drainage, and installation details matter.

Do not mix up the jobs

Moving water is a motor problem. Heating water is a heat problem.

A pump may need startup surge. A water heater may need long-duration energy. A heat pump water heater may need controls and space. A gas water heater may involve combustion safety, venting, fuel, and code requirements.

Solar planning gets sloppy when all water equipment is treated the same. The Solar Plumber approach separates water movement, water heating, storage, backup, and safety before making a recommendation.

Separate these questions

  • Are we moving water or heating water?
  • Is the load electric, gas, or both?
  • Can the load be shifted to solar hours?
  • Is hot water needed during a blackout?
  • Can the tank store enough heat?
  • What licensed trade owns the safety review?

Side-by-side

Solar thermal vs solar electric planning

Topic Solar Hot Water / Solar Thermal Solar Electric / PV
Primary output Heat for water or heat-transfer fluid Electricity for many household loads
Best fit Dedicated water-heating applications where thermal system design makes sense Whole-property electric offset, batteries, pumps, appliances, EVs, and electric water heating
Storage Hot water tank or thermal storage Battery storage or grid interaction; hot water tank can still store heat
Complexity Plumbing, roof penetrations, pumps, heat exchangers, valves, freeze/overheat protection Electrical design, inverter capacity, interconnection, battery controls, load panels
Maintenance Mechanical and plumbing maintenance may be more involved PV generally supports multiple loads; batteries and inverters require proper design and maintenance
Backup role Stored hot water may remain available after grid loss, depending on system and controls Battery-backed circuits may support selected electric water loads if designed for them
Manga comedy water heater dragon facing Solar Sensei in a utility room

The Water Heater Dragon

Water heating can look quiet until the bill arrives. Then the dragon wakes up and asks who scheduled hot water during expensive hours.

Load shifting

Sometimes the best hot-water move is timing.

With the right equipment and professional design, some electric water-heating loads may be shifted toward solar production hours. That does not mean every system should be forced into a complicated control scheme. It means timing deserves review.

  • Can water be heated during strong solar production?
  • Is the tank large enough to carry heat into evening use?
  • Does the utility rate punish evening electric use?
  • Will the customer run out of hot water?
  • Are manufacturer controls and warranties respected?
  • Is the installation code-compliant and safe?

Common homeowner situations

What the existing equipment tells us

Gas Water Heater

Solar PV may still offset other home loads, but gas water heating involves combustion safety, venting, fuel, and licensed trade review. Converting to electric is a larger design conversation.

Electric Resistance Tank

Electric resistance water heating can be a significant load. Solar production, tank timing, panel capacity, and battery expectations should be reviewed carefully.

Heat Pump Water Heater

A heat pump water heater may reduce electric consumption compared with resistance heating, but it needs suitable space, condensate drainage, air, noise review, and proper installation.

Pool Heating

Pool heating is a separate animal. Heating a large body of water can require serious energy. Solar pool pumping and pool heating should not be confused.

Solar pool pumps

Ranch or Remote Water

Remote properties may care more about pumping and storage than hot showers. The mission determines the design.

Livestock water and solar

Backup Hot Water

Backup water heating can consume a lot of stored energy. The battery plan should define whether hot water is essential, limited, or not included during outages.

Battery backup planning

Manga episode

Episode 2: The Water Heater Dragon

The water heater dragon sleeps in the garage, pretending to be harmless. Then the utility bill arrives. Smoke rises. Solar Sensei opens the panel, studies the schedule, and says, “This dragon does not need a sword. It needs a load plan.”

The Dragon

“I only wanted a little heat. All day. Every day. At the wrong time.”

The Homeowner

“I thought hot water was just... hot water.”

Solar Sensei

“A tank is storage. A schedule is strategy. A bill is a clue.”

Read Episode 2 See All Episodes

Important safety and licensing note

TheSolarPlumber.com is educational only. It is not plumbing advice, not water-heater installation advice, not gas-appliance advice, not electrical engineering advice, and not a substitute for licensed professionals. Water heaters, gas appliances, heat pump water heaters, solar thermal systems, PV systems, batteries, pumps, pressure systems, and backup-power systems require proper design, permits, inspections, and licensed professionals.

ABC Solar Incorporated

Need help comparing water-heating loads and solar?

ABC Solar can review the solar, battery, utility-rate, and electrical side of water-heating and water-moving loads, then help define what belongs in the solar scope.

Contact ABC Solar Call 1-310-373-3169 Visit ABCSolar.com