Slashdot Mirror
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.
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.
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).
I think lead acid isn't terrible if you have the space, but really to get the most life out of a lead acid battery you have to look at max discharge as about 60% even using absorbed glass mat (AGM) batteries to get anything like long life cycles.
So your 1 kWh battery is only really useful for about 400 Wh which means you need 35 of them.
But it's more complicated than that, as you'd be better off driving an inverter at 48v and using something like 6v golf cart type batteries arranged in series/parallel strings to get to 48v and probably want some kind of more sophisticated charging/monitoring system to keep track of individual batteries and be able to isolate 48v groups if a unit failed. Usually more individual batteries gets you higher aggregate discharge rates since you pull less from any one battery.
I don't think it's impossible to built a decent setup, but doing it right will end up being more expensive than you'd think and will end up sucking a ton of space.
I think the half assed compromise is probably 4x 8D AGM 12v batteries in a 24v series/parallel combination, which would get you close to 14 kWh. But the batteries alone are $2k and then the inverter more yet.
Here's a video from Tesla showing the damage caused to various roof tiles from dropping a kettle bell on them.
I'm a leaf on the wind. Watch how I soar.
Bingo. I live on Colorado front range where we got golf ball size hail regularly. Thus summer our exposed hail resistant shingles failed with golf balls. Otoh, the Solar city panels? Not a scratch. Obviously the original poster has not a clue of what he is speaking.
I prefer the "u" in honour as it seems to be missing these days.
> but solar panel output drops to a level where you need to replace them after 20 or so years.
Citation? Solar panel output only drops about 0.5-7% a year. https://electrek.co/2016/07/04/solarcity-increase-useful-lifetime-of-solar-power-installations/
This isn't true. Even ten years ago an 18% efficient panel would be energy positive after about about 1.5 to 2.5 years anywhere in the lower 48 states. The Silevo polycrystalline cells used by SolarCity in this application are between 22 to 24% efficient. Then factor in that you don't need an underlying roof and the embodied energy goes down. Plus increased surface area of a tesla solar roof vs modules on the roof will mean that the embodied energy is amortized more rapidly as some tiles will be 'working' harder than others in areas that modules never would have been placed.
The only thing that might make this system better is liquid cooling heat exchange or phase change material and/or maybe aerogel blanket beneath. Then the cell efficiency would go way up as the cells are cooled and hot water is generated for the building. Aerogel would insulate the roof. But all of that would add cost, complexity, and liability. In meantime SolarCity must focus on profit and a sustainable business model.
The biggest problem for failure over the long term will be the framing, the racks, and the wiring. The cells themselves, absent stray rocks, will probably produces a useable amounts of power for over a hundred years. We are talking about he crystal/glass setups, not the plastic variety solar cells. Currently quite a few of the manufactures under promise the output of their cells so that they will still produce the rated amount of power for at least 20 years for their warranties. They seem to loose 5-10% of their output every decade or so.