Crunching The Numbers On The Tesla Solar Roof

Last week, Tesla announced Australian pre-orders for its solar roof, with installations starting in 2018. The idea is fantastic – replace your house roof with solar tiles that look good, generate power and are even more durable than existing options. But in the real world, is it worth the price? We crunch the numbers to find out.

For now, Tesla has not announced any specific Australian pricing, aside from the $1310 reservation cost. That makes it hard to accurately compare — so we will need to use the US pricing, as well as some reasonable assumptions about use in Australia.

Once we get firm pricing in the future, we will re-visit our calculations (And we have not included opportunity cost, any maintenance costs etc), but this is a good place to start.

The concept of solar roof tiles is not exactly a new one either — many companies have tried to bring them to market, but the cost to benefit ratio was just not there. But as we have seen with the Powerwall, not everyone is worried about economics, and will happily jump on board as early adopters.

Solar Roof Pricing

In the US, Tesla has a calculator that helps homeowners estimate the size and cost of replacing their roof. We Aussies don’t get access, but Tesla has suggested that homeowners can expect to pay around $US21.85 per square foot for the solar roof, fully installed. There are two types of tile – one with solar, and ones without, and the price includes 35% of the tiles as the active power generating type.

Australian and American roofing can be quite different, with variable build methods, regulations and environment – such as snow. But it’s a good place to start. Keep in mind that Tesla is targeting high end roof tiles, not the budget variety or steel roofing.

$21.85 US per square foot equates to $US235 per square metre, or $318 per square metre at current exchange rates to the Australian dollar.

The tiles are backed by a 30-year warranty, which is more about the solar — which degrades in output over time — than the panels themselves, which are tough glass.

Tesla suggest that at the $21.85 US price, the ongoing solar generation over 30 years makes the roof cost competitive with a normal roof.

Aussie Roofing

We enjoy a wide range of roofing materials in Australia — many of which can be comparatively affordable. Depending on the area, common materials such as concrete tiles can be very cheap, guaranteed for 50 years or more, and last even longer without issue.

Pricing depends on a huge number of factors, but an average roof, fully installed, ranges from around $80 per square metre on the low end, to $130 per square metre for higher end products such as terracotta tiles. For speciality roofs like slate, it can be even more. If other repairs aside from tiles are needed, the costs can also be a lot higher. Likewise, the costs when building a new house can be cheaper, as the old roofing does not need to be removed.

Still, Tesla is targeting the higher end, so let’s use the $130 per square metre figure. That means the Tesla solar roof is about 2.5 times more expensive than a comparable — but not solar — roof.

Using a large single Aussie home as an example, it could have a 300-square metre roof — similar sizes are used for the Tesla price example. That’s $39,000 worth to replace with a normal roof, or $95,400 if installing a Tesla Solar roof. That means the Tesla roof is $56,400 more expensive.

Solar Generation

Tesla have not given numbers on the exact size of each tile, compared to how much solar power it generates. Comparing numbers from other users, playing with the Tesla calculator and some back of the napkin math gives around 100 watts per square metre. [related title=”More on Tesla Powerwall” tag=”powerwall” items=”5″]

So 35 per cent solar on an a large Aussie home with a 300 square metre roof is about equivalent to a 10 kW solar array. According to Solar Choice, that will net us at least 40 kWh or so a day, depending on location. Solar output drops over time, but the house should generate 400,000 kWh or so over its life.

That means that each kWh produced needs to be sold for, or save the household, around $0.14 per kWh for the cost to break even. Houses with high direct solar use might achieve the savings, but it’s well above the $0.08 or so per kWh from feed-in credits.

Two-storey houses or small houses will either need to increase the percentage of actual solar tiles, or simply generate less power. 10 kW is actually a very large array, and only about one third of that is needed to charge a Powerwall 2 each day. Since we are just comparing prices, it’s a good starting point — though smaller installs will be a bit more expensive per square metre, and very large ones a bit cheaper per square metre.

Traditional Solar Comparison

Tesla likes to give numbers based on subtracting the value of the solar power from the cost of the roof. But that’s comparing to a roof with no solar – what if we get traditional panels installed?

An array to generate the same 10 kWh as the example tesla roof above costs an average of $14,675 in Australia, according to Solar Choice. Darwin actually bumps that average up a lot, so $14,000 is closer for most of us.

So a normal roof plus normal solar on the example home from above costs about $53,000, vs the $95,000 for the Tesla roof. That means the Tesla Solar Roof isn’t double the cost, but is a lot more expensive for the same solar capabilities.

As a comparison, over a 25-year life (Australian solar panels typically have a shorter warranty), the solar panels should make at least 333,000 kWh. That gives a break even saved cost per kWh of about $0.04 – half most grid feed ins.

In A Nutshell

It’s worth noting there is a significant fudge factor, as the number released are incomplete, and every roof and install is different.

But compared to a normal roof of comparable quality plus normal solar, the Tesla Solar Roof is between 1.5x to 2x more expensive for the same capabilities.

The economics are not the whole story, of course, as aesthetics and other factors play a role too.

But for now, the Tesla Solar roof is not a solid investment compared to normal solar. It probably will be around the third generation, as prices are driven down by scale.

Adding a Powerwall 2 or other battery storage into the mix does not help either — in Australia that still makes the economics worse. But once again, in the future, battery storage will be well worth the money.

Update: From Tesla: “Calculations have shown that it is likely to within the warranty period of the product. Futhermore, it will 100 per cent help the economics, as with high feed in tariffs ending, the only benefit is a small tariff. Powerwall far outweighs that tariff in its value to the customer.”

Don’t care about the economics over the cool factor? Head over to Tesla and make us all envious.

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