Tesla must provide specs before roof tile claims can be verified, says roofing contractor

Tesla stated its solar roof tiles would cost less than a conventional roof when they were unveiled by Elon Musk earlier this year. However little is known about the generation capability or payback periods of the product, particularly in the UK.

More significant details regarding the generation profile of their solar roof tiles are needed before Tesla can substantiate claims that they are cheaper than conventional roofs.

That is the conclusion reached by major roofing contractor Bracknell Roofing, who said that without those details to hand Tesla’s roof tiles are likely to cost around double what a normal re-roofing project would.

However Tesla has moved to allay such concerns by arguing that any debate surrounding its pricing is "premature". 

When the solar roof tiles were unveiled by Musk in May, a key statement made during the presentation was the cost of the roof – said to be $42 (~£32) per square foot – would be mitigated over time by the generation potential of the install.

However, the company has yet to reveal these details, saying only that the electricity savings of the installed roof would be reflective of the households’ requirements. The efficiency and performance of the tiles has not been stated, leading UK contractor Bracknell Roofing to question the claim.

UK roofing jobs are defined in square meters, meaning the Tesla roof tiles would represent around £100/m2. According to managing director Simon Smith, this is considerably higher a low cost standard re-roofing job on a hipped property where all sides slope down to the walls.

“In terms of the overall cost of the roof and its lifetime performance, rather than an energy generator, it costs more - no doubt about it. At £32 [per] square foot which is £100 per square meter more or less, you're looking at an increase in cost of something like double,” he said.

Smith and his colleague, branch manager Ian Bladon, explained that the average cost for a re-roofing property with a 90m2 roof - erecting scaffolding, taking the whole roof off including the soffit, fascia and guttering, replacing it and refelting before completing with tile or slate – would cost around £75-80 per square meter, or ~£7,000 in total.

If the roofline elements are taken out of this costing, this drops to around £6,000-6,500 while for a straight ‘up and over’ or gable to gable home, this drops by a further ~£800.

Removing the cost of the soffit and fascia replacements lowers the cost the re-roofing further.

There is some variability due to the in-line nature of the Tesla product, which fits on the same plane as a standard roof construction. However, without any details on fixings, load profiles on the roof structure or accompanying tiles to fit around the system, it remains unclear how the company’s price claims can be matched in situ.

It therefore comes down the details of the product and its performance, as Smith explained: “You need to know things like; what's the energy generation and how many tiles do you need to generate a kW? That's really important because the efficiency of each unit is a big factor in the overall cost. Does it require any additional bracket systems to fit in-line? That's important because that's a cost.

“It tells you what extras you need over a conventional roof installation and what items from a conventional roof installation that you don't need, so you can offset one against the other and see what balances.

“Those are the kinds of simple things that you need to know so you can calculate a cost difference balance and then compare that to the cost of simply stripping and re-tile the roof, which is something like about £50-60 per square meter plus access, on average.”

When asked to comment on the pricing, Tesla responded by saying it would likely be “premature” to assess the claim made by its founder in May as no pricing information has been released for the UK yet. When pressed on when this information would be published, no answer was forthcoming despite Tesla roof tiles expected to ship to the UK in 2018.

It is also unclear if similar deals will be included for the UK market as they have in the US, such as inclusion of the Tesla Powerwall 2.0. However, prices here are generally higher after Tesla raised its UK pricing in December by 5% due to the currency fluctuations resulting from the Brexit vote.