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Believe it or not, solar panels aren’t exactly pros at handling the sun. Sounds backward, right? But it’s true — excess heat can be a big problem for solar panels. It drags down their efficiency and can even shorten their lifespan. So, how do you keep something that’s basking in the sun all day from overheating?

One clever solution: combine solar panels with a heat pump. The heat pump swoops in, grabs the excess heat from the panels, and repurposes it to warm your home or water. This dynamic duo keeps the panels cooler, helps the heat pump work more efficiently, and saves you money. They’re the Batman and Robin of renewable energy.

But if this combo is such a great idea, why haven’t we been doing it all along? And do the potential energy savings really make up for the hefty upfront costs?

PaXos & LONGi

So, what’s the big idea? It’s called a Solar Assisted Heat Pump, or SAHP. German company, paXos Solar GmbH, thinks its sleek, stylish solar roof SAHP in particular could revolutionize residential solar and heat pump systems.

This is paXos’ new SAHP: a two-in-one system that combines heating and solar power generation. Instead of mounting traditional solar panels on your roof, it uses PV tiles that become your roof, much like Tesla’s Solar Roof.12 Perfect for anyone who loves the idea of solar energy, but isn’t thrilled about the aesthetics of standard panels.

Don’t let the sleek design fool you, though. These tiles are more than just eye candy. They’re installed over a water-bearing layer with enough space underneath for airflow…and that’s where the magic happens.3

Solar panels are great at absorbing light, but sunlight doesn’t just bring light. It also brings heat. If you’ve ever baked in a kitchen flooded with summer sun (and I hope you’ve treated yourself to some lemonade while doing it), you know how intense that can be. As I mentioned before, too much heat actually hurts solar panels performance. For instance, if a panel has a temperature coefficient of -0.5%, that means for every 1°C increase in temperature, a solar panel’s efficiency can drop by about 0.5%.4 The specifics vary panel to panel.

Cooling solar panels while they’re hard at work can dramatically improve their performance. And when it comes to cooling, water is hard to beat. (Ask anyone with a water-cooled PC. They’ll back me up.)

Heat pumps, on the other hand, face a whole different challenge. If you’ve been here before, you know I’m a heat pump enthusiast. (And if you own one, you probably are too!) These systems can achieve a Coefficient of Performance (COP) greater than 1, meaning they output more heat energy than the electricity they consume. Some even hit a COP of 3 or higher (3 units of heat for every unit of electricity). That’s something no traditional space heater can match because… physics.5

How do they pull off this magic trick? Heat pumps don’t create heat, they move it. They capture warmth from outside air and transfer it into your home, keeping you cozy without guzzling energy. But — and there’s always a but — when temperatures drop, heat pumps have to work harder. The colder it gets, the lower their COP. In extreme conditions, some models rely on backup heaters, which can eat into your energy savings.6

Air-source heat pumps are particularly prone to this. In colder climates, they often include heating elements to defrost their heat exchangers. Handy, yes, but it’s an energy hog that takes a bite out of the energy and cost savings.7 But before you start typing frantically in the comments, there are more and more cold climate heat pumps hitting the market making this better and better.

To summarize, heat pumps need extra warmth sometimes, while solar panels often need to cool down. The symbiotic relationship between them is what makes paXos a potential solution to both problems. By tackling the downsides of both solar panels and heat pumps, this system combines the best of both worlds. It’s a smart, elegant solution that boosts efficiency and reduces energy waste.

Here’s how it works: warm air from under the tiles is piped to the heat pump’s heat exchanger. When the air is at least 1 Kelvin warmer than ambient, a fan switches on, cooling the tiles while warming the heat pump.8 This keeps the heat pump efficient in winter. In summer, the tiles generate energy to power the pump, keeping your home comfortable year-round.13

PaXos says this setup cuts the heat pump’s energy use by 20% annually compared to a similar device without the additional heat generation.3 A claim tested by the Technical University of Cologne. A preliminary study concluded that this boosted the heat pump’s coefficient of performance by nearly 25%, weather permitting.8

That’s a lot from a device that doesn’t look very flashy…by design. The tiles are sleek, made to look like regular roofing to appeal to those who dislike traditional panels.9 They use LONGi’s back-contact cells, which capture angled light for extra efficiency.3 Larger tiles (~59 cm x ~42 cm) also make installation faster, as fewer tiles cover the same area. Just five tiles over 10 square feet can generate 1 kilowatt-peak of power, worth about €1,400 ($1,487).3

With all these advantages, why aren’t SAHPs everywhere yet?

Let’s explore where they came from.

Quick SAHP History

The concept of combining solar energy with heat pumps isn’t new. In 1955, researchers E.R. Ambrose and Philip Sporn explored using solar collectors to boost a heat pump’s efficiency.10 However, the first recognizable solar-assisted heat pump came from NASA in 1973 in the form of a solar-powered absorption-cycle heat pump.11 NASA made the design available to private industry, just as the energy crisis ramped up interest in alternatives to fossil fuels.1112

SAHPs gained traction because heating and cooling are massive energy hogs. In 2022, they accounted for 45% of residential energy use, with water heating adding another 12.9%, according to the University of Michigan.13 That’s a lot of potential savings. (And SAHPs can handle water heating too, but that’s a topic for another day.)14

For commercial buildings, the stakes are even higher. In 2018, U.S. commercial buildings spent $140 billion on energy, with space heating taking up nearly a third of that.15 Cutting those costs with clean energy isn’t just good for the planet; it’s great for the budget, too.

Interest in SAHPs faded after the oil crisis ended, but incremental improvements kept coming through the ’70s, ’80s, and beyond.1011 So, with decades of progress, we must all be enjoying cutting-edge SAHPs on all of our homes right now, right? Right?

Obviously… not exactly.

Drawbacks

So, why doesn’t every house in your neighborhood have a SAHP? The answer lies in their shared weaknesses — and the cost.

Like heat pumps, SAHPs struggle in cold weather. And cold weather is often cloudy, meaning the solar panels can’t provide as much help when the heat pump needs it most.16

Another hurdle is integrating the solar and heat pump components. This requires what one paper calls “precise calibration,”17 or the balancing changing air temperatures, sunlight levels, and the building’s heating or cooling needs. It’s a complex juggling act, especially in real time. Some research suggests this complexity might even be a drawback. A 2021 study by the University of Hull and North China Electrical Power University found that combining solar thermal panels with heat pumps can lead to constant operation, increasing electrical use and inefficiency.16

Cost, however, is the biggest barrier. Solar roofs are notoriously expensive as they replace your actual roof, and heat pumps aren’t exactly super cheap either. Combine the two, and it’s no surprise the price adds up. According to Eco-$mart, a U.S.-based green construction company, an SAHP system costs between $2,000 and $6,000, depending on the model and manufacturer.18 Over in the UK, Homebuilding & Renovating magazine estimates material costs at up to £2,000 ($2,540).19 Installation adds even more. SAHPs are specialized, the technology is relatively new, and there aren’t many trained installers yet…all of which drive up costs further.

SAHP vs Solar Roof

How does a SAHP like paXos’ system stack up against a solar tile technology like Tesla’s Solar Roof? Let’s break it down. But first, a few caveats.

This comparison is apples to oranges because Tesla’s Solar Roof doesn’t include a heat pump, which is a major part of paXos’ appeal. Unfortunately, we don’t have solid data yet on what that extra functionality means in dollars and cents. Even if we did, solar pricing depends on countless variables, like where you live, your roof size, and local labor costs. So, take this analysis with a grain of salt.

I’m using real-world data from resources like EnergySage and Roofingcalc.com for Tesla’s Solar Roof. For paXos, we only have company-provided numbers, which could tilt things in its favor. When (and if) real-world data for paXos becomes available, we’ll revisit this comparison.

Because rooftops vary, cost per square meter is a fair starting point. According to EnergySage Tesla Solar Roof starts at about $3.90 per Watt,20 which means it averages about $461.50 per square meter. PaXos claims €260 ($271) per square meter3, giving it a clear edge in affordability.

Tesla’s Solar Roof has improved to 165 W/m², up from 118 W/m² in earlier versions.21 For paXos, things are murkier. Its claimed output is around 189 W/m², but when calculated based on tile dimensions from the spec sheet (59.5 cm x 42.2 cm), we get 175.3 W/m². 3 22 This discrepancy may be due to tile overlaps, as noted by PV Magazine, but it’s a little confusing.

As I mentioned, Tesla’s Solar Roof starts around $3.90 per watt, while paXos reports €1.4 per watt, or $1.47 at current exchange rates3. That gives paXos a significant advantage in cost-efficiency, but that could just be regional costs at play to explain the difference. So numbers don’t tell the whole story. There are important factors to consider here that don’t neatly fit on a spreadsheet.

As you can see in my video where I teamed up with Paul Braren to compare our experiences between traditional solar and a Tesla Solar Roof, Tesla has faced challenges, like installer shortages that have delayed installations. However, the company has built a reputation for offering “turnkey” solar solutions — in other words, handling everything from design to activation — which is a big plus, even if customer service post-installation gets mixed reviews.21

PaXos, meanwhile, faces uncertainty. The company sold its solar tile rights to Swiss manufacturer Meyer Burger, which is now handling production and distribution. However, Meyer Burger recently lost a major U.S. contract, causing its stock to drop 72% and raising questions about its future, and by extension, paXos’.232425

So, which is better? It’s complicated. Solar is a deeply personal choice, influenced by factors like location, budget, and roof size. For now, paXos holds promise on paper but lacks Tesla’s established infrastructure and brand reputation (however you feel about that).

The true test will come when paXos installs 200 systems in Germany next year.3 Will its system deliver the efficiency and savings it claims? Can it avoid Tesla’s installer bottlenecks? And how many people are willing to replace their entire roof to avoid the look of traditional panels?

Germany’s 12.3% solar adoption rate dwarfs the U.S.’s 3.4%26, so aesthetics may not be a major barrier there. Historically, countries like Germany, Japan, and Nordic nations have embraced solar and heat pumps individually2728. Combining them could be the next logical step.

Where does that leave us when it comes to this technology’s maturity? What kind of Technological Readiness Level (or TRL) are SAHPs currently at? Answering that question is a little tricky. SAHPs have been quietly working away in some parts of the world for half a century. They’re on the market, and you can likely go and buy one right now. Per researcher Christian Dick of TH Köln, paXos’ system is “ready for continuous use under real conditions.9 That certainly sounds like a 7 or higher on the ol’ TRL scale. At the same time, there’s still a lot of room for improvement. The nice thing is that as a fusion of solar panel and heat pump tech, breakthroughs for either of its components can improve a SAHP.

Ultimately, SAHPs are a clever piece of technology that help you squeeze every last drop of efficiency out of your system. The downside of having the strengths and weaknesses of both a heat pump and a PV system means there’s added complexity. But just because SAHPs aren’t great everywhere doesn’t mean we should drop them all together. For places where the weather does support them, combining PVs and heat pumps seems like a great way to kill two birds with one…shingle.


  1. Wikipedia, Solar-assisted heat pump ↩︎
  2. Tesla, Why Solar Roof ↩︎
  3. PV Magazine, paXos Solar unveils glass-glass PV tile with heat pump integration ↩︎
  4. 8MSolar – Solar Panel Efficiency vs. Temperature ↩︎
  5. MIT Technology Reviews, Everything you need to know about the wild world of heat pumps ↩︎
  6. Bloc Power, Heat Pumps In Cold Climates: 2024 Edition ↩︎
  7. Consumer Reports, Can Heat Pumps Actually Work in Cold Climates? ↩︎
  8. Interesting Engineering,Germany unveils solar roof tile that powers heat pumps as well as homes ↩︎
  9. PV Magazine, Solar tiles connected to an air heat pump ↩︎
  10. Krockenberger, Kyle G.; DeGrove, John M.; Hutzel, William J.; and Foreman, J. Christopher, “Design of a Heat Pump Assisted Solar Thermal System” (2014). International High Performance Buildings Conference. Paper 146. ↩︎
  11. Air Conditioning, Heating, Refrigeration News, The 1970s: Heat Pumps Return, Solar Heats It Up In ↩︎
  12. Harvard, The Geopolitics of Energy: The 1970s Oil Crisis) ↩︎
  13. University of Michigan Center for Sustainable Systems, Residential Buildings Factsheet ↩︎
  14. SAHP Technology ↩︎
  15. University of Michigan Center for Sustainable Systems, Commercial Buildings Factsheet ↩︎
  16. Yi Fan, Xudong Zhao, Zhonghe Han, Jing Li, Ali Badiei, Yousef Golizadeh Akhlaghi, Zhijian Liu, Scientific and technological progress and future perspectives of the solar assisted heat pump (SAHP) system, Energy, Volume 229, 2021,120719, ISSN 0360-5442 ↩︎
  17. Herzallah, L. and Hermanucz, P. (2023) Energy Study of a Solar Assisted Heat Pump (SAHP). Hungarian Agricultural Engineering : Periodical of the Committee of Agricultural and Biosystem Engineering of the Hungarian Academy of Sciences Hungarian University of Agriculture and Life Sciences Institute of Technology(42). pp. 65-73. ISSN 0864-7410 (print); 2415-9751 (online) ↩︎
  18. Ecosmart, Solar Assisted Heat Pumps: Everything You Need To Know About ↩︎
  19. Homebuilding UK, Solar assisted heat pumps: What are they and are they a good idea? ↩︎
  20. EnergySage – Tesla Solar Roof review: As expensive as it looks ↩︎
  21. Tesla, Tesla Solar Roof ↩︎
  22. Paxos data sheet SFZ-H-BK-44W ↩︎
  23. paXos, Solar Innovations ↩︎
  24. PV Magazine, Meyer Burger loses biggest customer, questions business viability ↩︎
  25. Reuters, Swiss solar panel maker Meyer Burger’s future in doubt after key client quits ↩︎
  26. Tigo Energy, ​​A Solar Powered Future: Residential Adoption on a Global Scale ↩︎
  27. Wikipedia, Growth of photovoltaics ↩︎
  28. Carbon Brief, How heat pumps became a Nordic success story ↩︎

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