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Tesla Unveils Residential 'Solar Roof' With Updated Battery Storage System (theverge.com)
Tesla founder and CEO Elon Musk today unveiled the "residential roof" -- pegged as a roofing replacement -- with solar energy gathering powers. Unlike other solar systems which must be mounted on top of a traditional roof, these new panels are actually integrated within glass roof tiles, replacing a home's roof, Musk said. And because they're made of glass, Musk says they will last "quasi indefinitely," even in harsh conditions where snow and ice make short work of traditional asphalt shingles. Musk said that 50 years of lifespan should be no problem, and they offer efficiency that is 98 percent as good as a traditional, ugly photovoltaic panel. From a report on The Verge: There are a number of different versions of solar panels: Textured Glass Tile, Slate Glass Tile, Tuscan Glass Tile, and Smooth Glass Tile. Tesla says its glass tiles are much more durable than conventional roof tile -- something that's important in areas with risk of hail.The products are a "joint collaboration" between SolarCity and Tesla, according to SolarCity CEO Lyndon Rive. Tesla is attempting to acquire SolarCity for $2.6 billion and shareholders of both companies will vote on the proposed acquisition in the middle of November. The Powerwall 2 can store 14 kWh of energy, with a 5 kW continuous power draw, and 7 kW peak. The battery is warranted for unlimited power cycles for up to 10 years. It can be floor or wall mounted, inside or outside. It can be used for load shifting or back-up power. Musk says there are three parts to the solar energy solution: generation (solar panels), storage (batteries), and transportation (electric cars). Musk's plan is to sell all three of those products through Tesla.
Had a friend buy a hail-damaged car. He'd heard about hail sales and was looking to buy at the time. We walked the lot after a hail storm. The damaged cars had lots of dents in the metal, but not a single broken glass. The Texas dealership said that was common. Glass designed to take it is quite strong. Even bulletproof.
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Actually, it looks like Tesla has thought of that... apparently their "glass" tile is tougher than conventional tiles. See this CNET video for reference: https://youtu.be/uWcGRYT-aeE?t... If a conventional roof can withstand it, then so can theirs.
In other words, they've improved it from storing $1 worth of electricity to $1.40. But you still need to cycle it many thousands of times with FREE electricity before it breaks even.
A quick search shows that the average household electricity usage is about 10K kWh per year (900-ish per month), ranging from 14K in Louisiana to 6K in Hawaii.
Using your numbers, that would be roughly $1000/yr. The powerwall costs roughly $7000 installed with inverter and other extras, or you can lease it for 9 years for $5,000 which includes installation, a maintenance agreement, the electrical inverter and control systems.
Tesla is offering a ten year warranty on the batteries, and there's some discussion about how a battery can last for 3650 cycles (mostly because the 14K powerwall is a 20K battery pack that's discharged much more shallowly than if it was an actual 14K battery, and other tricks).
The total cost comes out to about 0.15/kWh.
"Tentative Conclusion: The battery is right on the verge of being cost effective to buy across most of the US for day/night arbitrage. And it’s even more valuable if outages come at a high economic cost."
Glass is tougher than most people think.
Irony: Agile development has too much intertia to be abandoned now.
That is actually quite irrelevant. Glass is weak and depends on it's structure to make it strong. The reason cars don't often suffer hail damage is due to the angle of incidence of the hail hitting the windows. Most damage is on the roof, bonnet, and boot (trunk for the America sedan owners), where the hail lands almost perpendicularly and can impart all of it's force into the thing it hits. By comparison window hits often happen at a very low incidence angle so only a tiny portion of the force is transferred into the glass. This is also why in a hail storm the most commonly damaged window by far is the front window despite also being the strongest of all windows in a car.
Strength comes from structure. The reason solar panels are strong is because they are supported underneath. Glass (especially tempered glass) performs very well under compression. The strength comes not only from the glass, but the substrate behind it and the metal backing of the panel. A typical solar panel is far more durable than a sheet of tempered glass alone.
Anecdote: I lived in a city with some ferocious hailstorms. Not just big round balls of hail, but irregular and sharp shaped blocks too. All of my solar panels survived. All of my neighbours' survived. All of our cars were completely written off and has massive amounts of damaged glass too (and in my case the inside turned into a bit of a swimming pool).
Glass is very, very strong - which is why it is used in glass fibre reinforced plastic. It is however normally very brittle as in it can't absorb a lot of impact energy without cracking.
If you add something to absorb the energy, such as a sandwich of plastic between layers of glass in a car's windscreen you end up with something that is tough enough to take some impacts without cracking.
For a first year engineering materials practical I used to get students to load up horizontal glass rods with a lot of weight until they bowed a lot. You need a very smooth surface so that cracks won't start from tiny scratches, so that meant preparing with Hydrofluoric acid (don't try it at home!). That gave the students a bit of an insight into the difference between strength (maximum load) and toughness (energy which is proportional to the area under a curve of load versus extension).
That is actually quite irrelevant. Glass is weak and depends on it's structure to make it strong.
Is hail that big a problem for most people? I'm sure for some people it is, just like some people have to deal with tornadoes, and others have to deal with heat waves, and others flooding. But most people don't have to worry about them, and for them, this is great.
BTW we get the odd hail storm here, in the lat 30 years we've had two big ones that were enough to break stuff, and even the it was only in some suburbs, not the entire city. So these rare cases would be covered by insurance. A small additional cost is still probably going to be cheaper than 30 years of paying electricity bills