Elon Musk has been in the spotlight a number of times on my blog now, and once again he succeeded in creating a good portion of buzz in the cleantech world which I cannot let go unnoticed. Yesterday the Silicon Valley entrepreneur announced that Tesla is now taking online orders worldwide for their latest disruptive technology: the solar roof. Seen by Elon as the third leg of the stool of a sustainable energy future, next to Tesla’s Powerwall and electric car, first installations in the US follow later this year, while worldwide rollout begins in 2018.

The solar roof promises a big step forward in residential solar energy. Imagine your house looking as it always did, except that now the roof is generating electricity to power your household and electric car. Instead of ugly solar panels mounted on your roof, solar tiles have cells incorporated. A special glass layer makes the tiles appear exactly as conventional tiles from the street level, but let sunlight through to reach the solar cell beneath. The roof is covered in a mix of active solar tiles and normal tiles, the ratio depending on the customer’s need for electricity generation as well as the amount of sunlight reaching the roof.

For Musk, the solar roof is the last cornerstone to reach a fossil-free powered household. The solar roof produces electricity during the day, powering the household and charging a Tesla Powerwall battery, that subsequently powers your Netflix session at night while your Tesla car gets charged up after coming home from work. Isn’t that beautiful?

Tesla’s solar roof: from the ground level it looks like a normal roof (photo: Tesla)

When Musk announced the solar roof for the first time at an event in L.A. in October last year, he didn’t give any hard number on its pricing. Hence, enthusiasts could only speculate whether the solar roof would turn out to be a niche product for the rich or an affordable option for the average household. Although yesterday’s announcement came with prices and estimated earnings that are better than most expected, I still have a lot of doubts whether a solar roof is a smart investment.

For an 186-square meters roof in New York state for which 40% of the tiles would be active solar tiles, the cost would be about 50 000 US dollars. This includes the purchase of a Tesla Powerwall to store part of the generated electricity during the day, but also takes into account US federal tax credits. According to Tesla, the roof would pay for itself over the lifetime of 30 years thanks to the produced energy.

Playing around with Tesla’s online calculator, it becomes clear that the tax credits are responsible for a large share of the positive outcome. This makes the solar roof’s value proposition very sensitive to the state or country you’re living in. Not to mention the difference in the number of active tiles you will need depending on your location and household electricity demand. Bottom line is that the economics of the solar roof depend very much from case to case. A solar industry expert told Reuters that a normal roof with a conventional rooftop solar installation would be more cost effective for most households.

(photo: Tesla)

Both during the event and on Tesla’s website, there is a lot of emphasis on the built quality of the solar roof tiles. It has the highest possible rating with respect to hail, wind, fire and glass coating standards possible. In typical Elon Musk style, the tile warranty is set on “infinity, or the lifetime of your house, whichever comes first”. Yes, great! The roof tile might survive a thousand years, the solar cell within will not. In fact, the power warranty is 30 years, which has become the standard for rooftop solar panels.

The solar roof has unlimited tile warranty, yet power warranty is only 30 years (source: Tesla)

In any way, Musk’s marketing tricks seemed to have worked.  Most of the news coverage I came across is full of praise for the solar roof. Surprisingly, no one seems to wonder what the efficiency of the solar roof cells is. At the event in October, Musk mentioned it would be somewhat lower than conventional solar panels and unfortunately no more information was given yesterday. Tesla is partnering up with Panasonic for the production of the solar cells and they can be expected to be of good quality. Nonetheless, I find it quite disturbing that Musk opens preorders, asking a deposit of 1000 US dollars, for a product of which even basic specifications are not revealed.

Don’t get me wrong. I think it is great that Tesla is pushing the boundaries of clean energy not only in transport but also in home electrification. A holistic approach is very valuable and is likely to improve earn back time of people’s investments. But the underlying idea that the package solar roof plus Powerwall plus Tesla car is the key to a sustainable planet doesn’t really work for me. “What is the future that we should have?” Musk asked on a call with reporters. “What do we think the world should look like?” According to Musk, it seems to be a world where everyone lives in a Silicon Vally-sized mansion with a Tesla parked on the driveway. But with the world’s population going towards a staggering 9 billion in a few decades, for the most part concentrated in million-cities, I fail to see how that’s supposed to work out.