Hacker News Reader

Comment by jws | Hacker News Reader

3. It's solar-powered. I wonder if they have a electricity backup...

It's grid electric powered. The canopy doesn't do much.

Let's calculate:

  Guess that the canopy for each bay is 7 by 4 meters, 28m^2

  Sunny spots receive about 4kWhr of solar power per square meter per day.

  Solar panels might be 25% efficient.

  Total daily power: 28m^2 * 4kWhr/m^2/day * 0.25 = 28kWhr/day

  Model S has an 85kWhr battery, half charge is 42kWhr.

It is going to take about two days to charge off the solar.

View on HN

Right, so if you think of it as a grid tied system it will generate power when ever it can, and people will charge on it. I've got 5.2kW of panels on my roof and can verify attest to the fact that even though I might use 28kWh in a day I can generate 34kWhr (during the summer, during the winter my best days are about 20kWhr) I would guess that as long as the duty cycle on the fill up is small they will consume net zero power.

The SunTech panels [1] produce a nominal 295W and are 2 x 1M so in your 6 x 4M square you can put 12 panels, nominal output 3.5Kw, my system is 90% "efficient" (5.2 kW Panel rating, 4.7kW delivered to the grid) assuming the same that is 3.15kW delivered to the grid. over a nominal 6 hr solar 'day' that is about 18kWhr/day. So the duty cycle on a power station would need to be one fill up every 3 days. If the travelling is mostly on weekends I could see the stations getting a couple of fillups on the weekend and having 5 days of no visitors. Time will tell. It is handy that Elon's the primary stockholder of Solar City :-) Good discount on panels.

[1] http://www.solarsystemsusa.net/solar-panels/by-brand/suntech...

I support your figures. However, my efficiency of my inverter is 98% rather than 90%. I'd also clarify that the average during winter is a lot less than 20kWhr/day ... I know you said it was a maxinum :) It's most probably about 14kWh for me.

>It's grid electric powered. The canopy doesn't do much.

They're sizing the installations in partnership with SolarCity, one of Musk's other start-ups. They claim they'll be sized such that it will generate as much energy over the course of the year as the vehicles consume. Meanwhile, you're estimating power output from a CG rendering on a marketing page.

You could argue whether or not they're lying, but they're certainly not incompetent. SolarCity's sizing calculators take these (and many more) variables into account.

  generate as much energy over the course of the year as the 
  vehicles consume

Yeah right. At what utilization rate? A single charge is ~90KWh, and takes half an hour. Two charges back to back are 180KWh.

jws guesses that each slot generates 28KWh/day. A ten slot charging station would only be able to charge three cars without going into the red. Tesla would have to build a lot of very oversized installations in a lot of sunny, rural locations to hit breakeven.

They could have solar only at some locations and excess capacity to make up for the locations without solar.

Ok, but prob with solar is it does you no good if its not connected to anything. And if they are just putting it into the grid what is the point other than PR?

Well for one, you presumably get paid to put power back into the grid. Secondly, is there not value in putting as much power into the grid as you consume anyway?

The problem is, in the case you propose, Tesla would be creating installations in urban environments. This type of "development" kills their credibility on "green" or environmentalism, etc. Is this kind of thing better than hydropower?

Hydropower is pretty gnarly from an environmental standpoint. And I doubt the land they are using would otherwise remain undeveloped.. it is an urban area after all.

Perhaps solar in previously undeveloped areas would be better? I doubt that. Developing solar plants in undeveloped areas only to put the charging stations in urban areas (that is where the market demands them after all) hardly seems better than putting charging stations in urban areas and sticking some solar there too. What is there to be gained from not putting solar wherever you can?

Hydropower is clean and renewable. Dams are already built, etc. Everything has its tradeoffs, though. Remote solar and wind take up lost of room and are eyesores. Grid connects require large-scale duplication/new assets. But, I think we need less sprawl generally, so I find it hard to support, in particular, urban development where better use could be made of the land.

If there is anything this continent (or world, for that matter) is lacking, it is space.

That said, I think we should be plastering the land we already use with solar panels. Might as well put all those rooftops to use.

I also think there is likely a lot to see in the future of non-panel-type solar. That generally involves a much larger or smaller scope than panels though, "medium" sized doesn't work well.

What I would be cool with is solar on top of wall mart and home depot and costco...and the like...those are good size square footages. and the assets are already in place. wonder if the roofs would hold =D !

Absolutely. For that matter, get some solar-panel covered parking lots at those places too so my car doesn't melt in the summer!

If there is anything this continent (or world, for that matter) is lacking, it is space.

Have you ever looked at satellite views of the US? There are massive deserts just begging for the shade of some solar panels or mirrors. No use in heating up all that sand.

It's not so hard to move the energy out of the desert either. Just run wires, or better, relocate an aluminum smelter from the grid to out near the solar array.

>> If there is anything this continent (or world, for that matter) is lacking, it is space.

> Have you ever looked at satellite views of the US?

My thoughts exactly. I think looking at Europe could bring a new perspective into what does 'lacking space' mean.

Whoops, left out a "not" there somewhere. We most certainly are not lacking space.

> It's not so hard to move the energy out of the desert either.

It's tougher than you realise. Energy is lost when transmitting power over long distances - like from a desert to an urban area. I'm not an expert but as I understand it there are major challenges. A lot of solar installations tend to be located where the power is used (next to data centres, on people's roofs).

A lot of data centers and aluminum smelters tend to be located next to where the power is. If you build it they will come.

Considering all the infrastructure that goes into keeping a fossil or nuke plant fed and cleaned and its power output distributed, I think if a solar installation has a net payback time of similar period we ought to be willing to invest a little in the distribution as well.

> aluminum smelters

Why aluminium smelters? I haven't heard this before.

> we ought to be willing to invest a little in the distribution as well.

I agree. I've read that's it's a huge challenge though, which is one of the factors holding up the development of large scale solar installations in the desert. Another challenge is the variance and relative unpredictability of power generation which means batteries are needed to smooth out the peaks and troughs to balance supply and demand.

>jws guesses that each slot generates 28KWh/day

Again, this is a guess based on a CG rendering on their website. That drawing doesn't constrain Tesla's engineering talent in any way – even without using extra land they could put up solar shade structures over adjacent parking spaces.

Adjacent parking spaces, eh? To go from 3 charges a day to 6, right?

Assume you've got a couple dozen slots, charging 100 cars a day. (Far, far fewer than an equivalently-sized gas station. If we're going to transition to an electric-only transportation infrastructure, then car changing stations are going to become a common sight)

That's 9 megawatt-hours a day. A random solar panel calculator I found guesses that would need ~2000KW of solar panel capacity. So you'll need 8,000 250 watt panels. That'll cover 9,600 square metres, (2.6 acres-- if you're lying them flat, which you won't. A big dedicated solar generation station will use tilted one-axis tracking, which will use a lot more ground space) and cost you (at $410 a panel) a cool $2.4 million.

(Google's big solar installation at Mountain View, the one that got so much press, was only 1700KW. Our tiny electric car charging station has to be 17% bigger than it.)

Electric car charging uses a lot of power. Solar is great, I love solar, but it's not space-efficient, or cheap. Either Tesla is going to build a national solar generation network on the scale of Germany's move into solar power, all on their own dime, or they're lying through their teeth about charging draw/solar production breakeven.

Yes, in a couple years there will be more electric cars, but solar power installations are getting less expensive every year. I don't know how long until there are enough electric cars to need "Germany-sized" solar installations, but when they do they'll pay a lot less than Germany did.

I don't think Elon Musk would green-light the "100% solar power" line without doing the math. Again: you can argue about whether he's lying, but I can guarantee you he knew exactly the scale of what he was promising. That makes it all the more impressive, imo.

Re:lying, I'm imagining at some point they'll transition over to "we buy 100% solar power for SuperChargers", which is fine by me since it's functionally equivalent to what they're doing now.

So you are basically saying that Musk is lying. This doesn't sound too much like him, does it?

A simpler explanation would be that he's not telling the whole story, and that perhaps they have dedicated solar farms in development/deployment or something to that effect. Don't afraid to dream a little bigger, darling.

Sure doesn't sound like him. He's headed up the first company to commercially resupply the International Space Station, for pete's sake.

You bet your ass he quadruple checked those numbers.

I'm guessing that the supply at these stations will be much higher than the demand for charging, so they'll make up the cost of "free" by selling wh's back to the grid.

The source I worked from, http://www.teslamotors.com/supercharger , contains only this about solar power…

And, at many locations, solar cells mounted on the weather canopy charge your Model S with solar energy.

I'm sure SolarCity projects will be supplying more power than Teslas use, but not from these charging stations. (Unless virtually no one uses the stations, which is probably not the plan. There'd be no reason to install 4 parallel charging stations if you were charging less than one car a day. Another possibility is that they build car ports that cover many parking spaces in a lot to support each charging bay. That's not what the picture shows, but it would work.)

I can't find an original source for the idea that the stations will produce more power than they consume, but it appears, attributed to Musk, in both Engadget and Huffington post. Most other articles on the event don't have it. It seems to have come from an oral presentation.

The good news is, if a Tesla S goes about 2 miles on 1 kWhr of power and if an average person drives about 10k miles per year, that is only 14kWhr/day. Each bay would supply the typical power requirements of two Tesla S cars.

Update: The press release is out now, http://finance.yahoo.com/news/tesla-motors-launches-revoluti...

It clearly says the stations will make more power than they consume. So either they are huge compared to the picture, or Tesla S drivers aren't much for road tripping.

You'll only collect the total insolation if you use two-axis solar panel pointing. Fixed panels are less efficient. Depending on latitude, sometimes much less efficient:

http://physics.ucsd.edu/do-the-math/2012/08/solar-data-treas...

The press release makes a seemingly absurd claim:

Each solar power system is designed to generate more energy from the sun over the course of a year than is consumed by Tesla vehicles using the Supercharger.

wtf?

They're presumably assuming that the station will not constantly be charging a car. ChuckMcM (your sibling) explains in greater detail.

Reply on news.ycombinator.com