Some people in the US "still hate the look of solar", Kate Collardson acknowledges.

She would know. Collardson handles operations for the Solar Service of Colorado, a solar maintenance and inspection company. She's also held just about every other job in the industry, from installer to instructor.

For those that hate the look of solar panels, an alternative is a solar roof, where the tiles (or shingles) house solar cells, but look much the same as regular tiles.

This is especially important for historic buildings, where heritage rules limit changes to their appearance.

For many people, the first time they'd heard of this product category was in August, when Tesla's website stopped offering solar roofs This followed disappointing sales and a lawsuit over sudden price hikes Other companies have also pulled out, but Tesla's decision in particular sent shockwaves through the solar roof industry. Some see it as a death knell for solar tiles; others, as an opportunity. For instance, the small Swiss company Freesuns is considering expanding to the US.

Deborah Learoyd, Freesuns' CEO and managing director, estimates that the company's sales have grown 20–30% since it was established in 2019.

In general, solar roof components continue to be manufactured in smaller batches. This limits the economies of scale and standardisation, though flexible manufacturing could help somewhat.

Learoyd says that while the unit costs for Freesuns' products are slowly decreasing, "a lot of the cost is actually the fact that every roof is a little bit different. And so it has to be engineered a little bit differently, installed a little bit differently".

Solar roofs typically require collaboration among roofers, solar installers and electricians. And building regulations tend to be more complex than for solar panels.

The additional time and paperwork can take a toll on a roofing business, Collardson explains. "You try to put a roofer into the equation and they're going, 'This is taking forever. I'm losing money. I could have sold 10 roofing jobs in the time that it takes me to sell this one'." Collardson has to charge more for repair of solar shingles, compared to a standard photovoltaic (PV) setup.

She explains, "With traditional solar, we generally have electronics on the panel and a map that shows us exactly how much each panel is producing." So when something goes wrong, it's easy to spot where.

"With solar shingles, we don't really have the benefit of that mapping; there's no room underneath the shingle for the electronics." Thermal cameras can identify the trouble spots, however.

But then there's the matter of accessing them. "You can remove the one in the middle of the array, but you have to walk on the others, and you really shouldn't walk on them because you're going to create micro-fractures and that's going to cause issues down the road." Before repair costs are factored in, a solar roof might cost twice as much as a system of solar panels mounted on a roof. Solar roofs are also less efficient - one reason is that the tiles are just smaller.

Another factor is the energy lost as heat. Since the tiles sit close to the roof, there's less airflow than with standard solar panels mounted on a roof. Heat impairs solar performance.

Coloured tiles are even less efficient, comments Ben Graves, co-founder of UK solar company Sunsave. "The reason why all solar cells are black, and increasingly the whole panel is now black, is because black is the best absorbing colour." Overall, much more space would need to be devoted to solar roof tiles to produce the same amount of energy.

Sunsave does not offer solar roofs. "Most people in the UK just don't have enough money to pay for it," Graves believes.

While appearance was a bigger factor five years ago, now "the vast majority of consumers are most interested in how much they can save".

But supporters of solar roofs argue that they should not be pitted against standard solar modules on roofs.

"Let's not compare PV roof tiles to a standard PV system, but look at PV roof tiles as generating additional electricity from our roofs instead of just having the roof sit there," urges Martin Heinrich who leads a research group at the Fraunhofer Institute for Solar Energy Systems in Germany.

While standard solar panels have gone from strength to strength, solar roofs have not advanced to the same extent. One advancement that could especially help solar roofs is matrix shingling technology.

This is a different way of connecting solar cells. The solar cells are cut into narrow strips, layered like overlapping shingles, and connected to each other using electrically conductive adhesive, rather than metal wires.

This means that the electrical current can flow around shaded areas, unlike with standard modules. "If you get like a bird pooping on a part of the cell, the current can go around it," Learoyd explains.

In addition to increasing energy output, this improves the appearance as the silver wires aren't visible.

Another advantage, Heinrich says, is that "since we cut the cells into smaller areas, we can fill out special sizes more easily. You don't have to adhere to the regular pattern size." Freesuns is an early adopter of matrix shingling technology in building-integrated PV. "We see it as a big opportunity for the future in terms of how we would make our tiles," Learoyd says.

What would also help the company is better software for automated design. This would speed up the design process, since each roofing job is unique.

Learoyd believes this would lower costs and give "the whole construction industry much more confidence in using the product".

Ten years after her own solar roof was installed, and despite the sector's setbacks, Learoyd remains optimistic.

She believes that for people with the means, it will eventually become standard to install a new roof with some sort of embedded solar. "It's just a no-brainer."