If you’re trying to use the sun to lower your energy bills, you have two fundamentally different technologies to consider: solar thermal, which uses the sun to heat water directly, and solar PV, which converts sunlight into electricity. They sound similar but work completely differently, have very different economics, and in 2026 the right answer for most California homeowners is more clear-cut than the solar industry would like you to believe.
The short version: for most people starting fresh today, neither solar thermal nor PV is the first move you should make. But if you’re specifically evaluating these two, read on — because the reasons matter and the details are worth understanding.
How each technology actually works
Solar thermal collectors are simple in principle. Panels on your roof absorb sunlight directly as heat. That heat is transferred — usually through a fluid loop — to a well-insulated storage tank inside the house, where it preheats your domestic hot water before it reaches your conventional water heater. No electricity conversion, no inverter, no grid interaction. Just heat moving from your roof to your tank.
The efficiency advantage of solar thermal over PV is real in theory: you’re capturing the sun’s energy as heat without the losses involved in converting it to electricity first. A good solar thermal collector can convert 60–70% of incident solar radiation into useful heat. A typical silicon PV panel converts 20–22% into electricity. On paper, solar thermal looks like the obvious winner for anything that needs heat.
Solar PV generates electricity. That electricity can power anything in your house: lights, appliances, your heat pump, your EV charger, your heat pump water heater. Under California’s old NEM 2.0 rules, excess electricity exported to the grid got close to retail credit. Under NEM 3.0 — in effect since April 2023 for new systems — that export rate dropped to roughly 6.5 cents per kilowatt-hour, versus the 32–44 cents you pay retail. The economics of PV changed significantly, pushing payback periods from the old 5–8 years out to more like 7–14 years for a typical system today.
Why solar thermal has become a hard sell
Here is the central problem for solar thermal in 2026: heat pump water heaters (HPWHs) exist, they work extremely well, and they are now very cheap to install in California thanks to aggressive rebates.
A heat pump water heater doesn’t generate heat — it moves heat. It pulls ambient heat from the air around it (your garage, utility room, basement) and concentrates it into your water tank. This process has a coefficient of performance (COP) of roughly 3.0–4.0, meaning for every unit of electricity it consumes, it delivers 3–4 units of heat to your water. Compare that to a resistance electric water heater (COP of 1.0) or a standard tank gas heater (efficiency around 0.65).
The TECH Clean California program — run by the state’s utilities — offers rebates of $500–$1,000 on HPWHs. After rebate, a quality unit installed typically runs $1,200–$2,200 all-in. That’s it. No glycol loop to maintain, no roof penetrations beyond a small line set, no freeze risk, no pump to replace, no collector glass to crack. The system can be serviced by any plumber or HVAC technician.
Solar thermal installed for domestic hot water typically runs $4,000–$8,000, requires annual inspections, glycol replacement every 5–10 years, and occasional pump or controller failures. The system is specialized enough that not every contractor can service it. When something breaks, you may be hunting for a solar thermal technician rather than calling your plumber.
The math is straightforward. A solar thermal system costs 2–5x more than a heat pump water heater, requires significantly more maintenance, and in California’s moderate climate, covers roughly the same need: your domestic hot water load. The HPWH runs on grid electricity, which means it will run on your future solar PV output if you add panels later. Solar thermal is a dedicated, inflexible system that only does one thing.
What the numbers look like side by side
| Category | Solar Thermal (DHW) | Heat Pump Water Heater | Solar PV System |
|---|---|---|---|
| Upfront cost | $4,000–$8,000 installed | $1,200–$2,200 after rebate | $15,000–$30,000 installed |
| Annual savings | $300–$600 | $300–$600 | $800–$2,000+ |
| Simple payback | 8–18 years | 2–5 years | 7–14 years (NEM 3.0) |
| Maintenance | Annual inspection, glycol every 5–10 yrs, pump/controller repairs | Minimal — anode rod every few years | Low — inverter may need replacement at 10–15 yrs |
| Flexibility | Hot water only. Cannot power EV, HVAC, or appliances. | Hot water only, but runs on any electricity source | Powers everything: EV, HVAC, water heater, appliances |
| Federal incentive (2026) | None — 25D credit expired Dec 31, 2025 | 30% tax credit (25C) still available | 30% ITC still available |
The Section 25D tax credit for solar water heating systems expired on December 31, 2025. As of 2026, there is no federal tax incentive for installing a new solar thermal system. This significantly changes the cost comparison. Heat pump water heaters (25C credit) and solar PV systems (ITC) still qualify for a 30% federal tax credit in 2026.
When solar thermal still makes sense
Solar thermal isn’t worthless. There are situations where it’s still a reasonable choice.
Very high hot water loads. Large families, households with a hot tub, or homes with high domestic hot water demand can push the savings up enough to make solar thermal competitive. If your household genuinely uses 100+ gallons of hot water per day, the economics get more interesting.
You already have a working system. If you have a solar thermal system that was installed 10 years ago and is still performing, there’s no obvious reason to rip it out. The capital is already spent. Maintain it, enjoy the offset, and think about what comes next when the system needs major repair.
Off-grid or grid-constrained situations. If you’re building off-grid or in a location with limited grid access, direct solar thermal for water heating avoids running an electric water heater off a battery system, which can be expensive. The direct heat approach has real advantages when electricity is scarce.
Very limited roof space. If your usable roof area is so constrained that you can only fit a small PV system, and your hot water load is large, dedicating a fraction of the roof to solar thermal while using the rest for PV could be reasonable. In practice, this is a rare situation in California where most single-family homes have enough south-facing roof for a meaningful PV system.
Why PV has become the one system to rule them all
The core argument for PV in 2026 isn’t that the economics are better than they were under NEM 2.0 — they aren’t. It’s that electricity is becoming the fuel for everything in your house, and one PV system can displace all of it.
If you have or plan to get an electric vehicle, a heat pump for space conditioning, and a heat pump water heater, the energy your house consumes is almost entirely electricity. A solar PV system generating that electricity is far more valuable than a dedicated solar thermal loop that can only offset your water heating. The PV system has no parallel in flexibility: every kilowatt-hour it generates can go toward the highest-value use at that moment.
Under NEM 3.0, the key shift is that self-consumption matters more than export. A system sized to cover your own usage — rather than to maximize export credits — is now the right design philosophy. That means pairing PV with batteries is more attractive than it used to be, and sizing the system appropriately to your actual load (including an EV) is more important than it was before.
The 30% federal investment tax credit still applies to PV systems through at least 2032 under the Inflation Reduction Act. At a $20,000 system cost, that’s $6,000 back at tax time. Combined with SCE, PG&E, and SDG&E rebates for batteries in some markets, the net cost of a well-designed PV system is meaningfully lower than the gross number suggests.
The maintenance reality of solar thermal
This is the part solar thermal installers tend to understate. Active solar thermal systems — the kind with a fluid loop and a pump, which is what most residential systems are — have real ongoing maintenance requirements.
The glycol antifreeze in the collector loop degrades over time and typically needs to be replaced every 5–10 years, depending on system type and operating conditions. If it isn’t replaced, it can turn acidic and corrode your collectors and heat exchanger. The circulating pump will eventually fail. Controllers and sensors need to be checked. In California, freeze risk is low in most of the state, but not zero in inland valleys and mountain areas.
Collector glass can crack from thermal cycling, impact, or hail. Most systems have roof penetrations that need to be maintained for weathertightness. Finding a technician who works on solar thermal is harder than it was a decade ago — the installed base is smaller, fewer contractors specialize in it, and parts availability for older systems can be a problem.
None of this is disqualifying on its own, but it’s a real contrast to a heat pump water heater, which has no outdoor components, no fluid loops, no pumps to service, and can be repaired by any HVAC technician with standard parts from a supply house.
For most California homeowners starting fresh in 2026: get a heat pump water heater first. It costs $1,200–$2,200 after rebates, has a 2–5 year payback, and requires almost no maintenance. It’s the best bang-for-buck hot water move you can make. Then evaluate PV on its own merits for your situation — roof orientation, shading, electricity usage, and whether an EV is in your future. Solar thermal is rarely the right first move, and with the 25D credit gone, it’s an even harder case to make.
How to think about sequencing your investments
The frame that makes this clearest is: what do you want your house to look like in ten years, and what order do you get there?
The direction California is heading — and the direction that makes financial sense — is full electrification. Replace your gas appliances with efficient electric ones, add PV to offset the load, add a battery if storage pencils out. In that sequence:
- First: Air seal and insulate. Reduces the load you’re trying to offset. (See our air sealing guide.)
- Second: Heat pump water heater. Cheap, rebated, high-ROI, fits your eventual all-electric home.
- Third: Heat pump for space heating and cooling, if you’re replacing aging HVAC.
- Fourth: Solar PV, sized to cover your actual electrified load. The 30% ITC is available through 2032 — no rush, but the incentive is real.
- Fifth: Battery storage, if you’re in a fire risk area with outages, have a time-of-use rate where afternoon storage adds value, or want resilience.
Solar thermal doesn’t fit neatly into this sequence. It’s a parallel track that does one specific thing and doesn’t integrate with the rest of your electrification journey. That’s the fundamental problem with recommending it in 2026: it’s a good technology solving a problem that a better, cheaper, more integrated technology now handles.
Use our home energy tools to estimate your savings from a heat pump water heater or solar PV system based on your actual utility rate and usage.