Comment by Hermel | Hacker News Reader

Comment by Hermel | Hacker News Reader

Great to see someone actually doing some calculations instead of just presenting a cosy vision. For example, they argue that - contrary to what Elon Musk implies with his illustrations - the solar cells on the roof of the gigafactory will only be able to generate a small fraction of the energy required to run it.

> The average solar insolation in Arizona is 1,964 kWh/m2/yr (in Phoenix). If we assume a solar PV efficiency of 15%, one m2 of solar panels would generate at most 295 kWh per year. Consequently, almost 68 square kilometers of solar panels (6,800 ha) would be required to power the factory -- a calculation that also relies on the assumption that solar energy is equally distributed throughout the days and the seasons (or stored in batteries), and that there's no open space between the panels. Remarkably, Tesla shows an illustration of the factory with solar panels on the roof. Knowing that the factory will occupy a surface of 1 ha, while 6,800 ha of solar panels is required to run it on renewable energy, Tesla's claim is an obvious example of greenwashing -- and everyone seems to buy it.

These are the kind of calculations that make me weep - somebody getting happy with numbers without engaging their brain as to the answer. Obviously the Tesla factory is not going to require 20,000,000 Megawatthours to operate - that is as much as the whole electricity production of the State of New Hampshire.

Assuming their input data is actually correct, I will speculate they are calculating the energy cost of the entire lithium battery production from raw materials, such as extracting lithium from mineral deposits, the majority of which would happen before the materials arrived at the Tesla factory.

I also expect Elon Musk knows what his electricity bill is. Given his investment in green technologies and his general success in delivering projects, I would be rather surprised if he advertised a solar factory if there was a chance he would be out by 4 orders of magnitude on how much power he would need.

Reportedly, the gigafactory will import ore from the mines directly, and process it. So, optimization might be possible, especially given that they can choose more expensive extraction processes because they don't have to compete on the cent.

Where has this been reported?

According to this study[0], it takes about 116 kWh of input energy to create a 100 kWh battery, given the materials. The majority of the total energy usage is in material production, not battery production. Assuming Tesla is not making their own materials, this deflates the required input energy substantially.

[0]: http://www.electrochem.org/dl/ma/202/pdfs/0068.PDF

> Assuming Tesla is not making their own materials, this deflates the required input energy substantially.

And also inflates that amount of greenwashing involved...... Why crow over renewable energy when your use of energy is irrelevant relative to your suppliers?

But their statement seems accurate and clear: they will operate the GigaFactory using renewable energy. They don't claim or imply that they will extract the materials using renewable's or that all their suppliers will use renewable's.

They should source their lithium from solar-powered contractors. Maybe even sell them some panels for a good price. (I realize the brine is already evaporated in the sun, but there's electrical separation after that.)

A 100Kw battery is used more than once. Making it 116kwh to store 116,000+ kWh.

So, your solar roof drops from 100% 'green' to 99.9% 'green' that's hardly a real issue.

So the statement "our factory will produce batteries while running solely on renewable power", though potentially factually accurate, is greenwashing?

They don't have any magical technology that allows them to dramatically reduce energy needed. The obvious conclusion is that they won't make anywhere near as many batteries as assumed.

It isn't magical technology, it is simple logistics.

South America to China to California vs Nevada to Nevada to Nevada.

Transportation uses very very little energy compared to everything else that needs to be done.

You will not find your magical technology in shipping.

Additionally ocean shipping is cheap enough that it can take less energy to ship something to the other side of the world than to the other side of Nevada.

I had a dig around, you are right that transport of lithium is relatively negligible in the energy budget (back of an envelope calculations suggest around 0.5 kwh for a 1 kwh capacity battery), transport of other material such as nickel is actually more important, but even when you add them all together it is only maybe a couple of percent or so of the energy involved.

It seems that the drying process is the one to target as it accounts for around 50% of the energy budget and uses big electric ovens. Electric ovens are something that respond very well to economies of scale though, given the losses are a function of the volume versus the surface area, so you could see significant reductions there with a factory this size.

>Assuming their input data is actually correct, I will speculate they are calculating the energy cost of the entire lithium battery production from raw materials, such as extracting lithium from mineral deposits, the majority of which would happen before the materials arrived at the Tesla factory.

If you look at one of their sources[1], it is clear that this is the case.

[1] http://www2.epa.gov/sites/production/files/2014-01/documents... p.65

>what Elon Musk implies with his illustrations

I think this is a very uncharitable interpretation of that 'illustration'. The illustration makes no explicit claim that the energy is produced by the solar panels on the roof, let alone solar power. And I think it goes without saying that heavy industry cannot be supported by a small cluster of panels. There are even wind turbines in the picture, which further discredits the idea that Musk is trying to imply the solar panels can do it alone.

The claim of "1 ha" stumped me, and I looked it up - the numbers you can find on the interwebs are conflicting, but it should take up about 200-500 ha. The assumption of 15% efficiency also seems quite conservative to me - I can imagine that they will use new cells fresh from the lab that are more in the 18-20% range. Another thing that Elon mentioned is that they might be able to drive energy consumption down because of synergy effects.

But yeah, they will probably not produce more than 20% of their needs with these solar panels.

Phoenix, Arizona is actually not the most sun-soaked part of the country. The Mojave desert gets a much greater amount of solar insolation[0]. Using those numbers, we can calculate ~511 kWh/m2/year, assuming 15% efficiency as well. That lessens the gap somewhat, but there's still quite a distance - perhaps wind and hydroelectric would account for the remainder?

It may just be flat-out wrong, which is unfortunate.

[0]: http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook...

This site is a bit easier to use: http://maps.nrel.gov/swera

Reno, NV is where the plant is being built. Not sure why that isn't being used as the location: (about 6.5kWh/m2/day = 2370kWh/m2/year)

Except his calculations seem all wrong. From the article picture above there's no way that factory only has ~100x100 sqm (1ha - a bit bigger than a soccer field). Maybe 100ha. And that seems to be the case:

http://cleantechnica.com/2014/09/12/tesla-gigafactory-huge-2...

If he got that wrong (which seemed obvious to me from the picture of the Gigafactory alone), who knows what else he got wrong.

An installation that has to provide power during clouds and night time has to be a multiple larger as well.

It's smart positioning by Tesla to show solar power for the factory but it certainly will still be connected to the grid.

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