Comment by Robotbeat | Hacker News Reader

Comment by Robotbeat | Hacker News Reader

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To make the system close for a single site (without any geographical diversity) is to produce about 3 times as much solar energy you need and install enough batteries to meet 48 hours of average demand. That's enough to deal with seasonality and with cloudy weather to provide a constant output for an entire year.

The 48 hours of battery would last a really long time as typically only about 12 hours will need to be used, thus you'd get very long cycle life. A battery used so lightly could get 10,000 effective full cycles, so probably would last multiples of 25 years from a cycle life perspective (calendar life may be another thing).

EDIT: If you add in geographical diversity and diversity in sources like wind, hydro, and geothermal, then you need to throw away a lot less energy and you need a lot less storage. IMHO, we should just bite the bullet and install a bunch of transmission lines (which could be done in 2 years, enabling us to decommission coal power within about 2 years in the US).

Haha lol.

Even in equatorial Africa 48h is not enough. Neither for actual usage, nor for battery life (and no one ever got marketing-leaflet-aka-datasheet-stated lifetime out of them batteries). Two years max, and hope either the project dies, or the company dies, or someone steals the batteries.

Source: been there maintaning solar offgrid.

And then --- geodiversity can only make it worse, never better.

Don't know why you are downvoted. I used to run solar powered sites that would have 5 rainy days in a row in which only about 10% of solar generation was delivered during daylight hours. We started with only enough batteries to last overnight and ended up with 10x that. Then we added 33% more when the first set of batteries had a short life due to getting so deeply discharged.

He’s downvoted because he’s bringing on-the-ground facts to a political discussion about solar and wind.

It may have more to do with the "haha lol", which is an antipattern for rational discussion.

Humans are irrational. And it’s hard not to laugh at wind and solar.

But you are right. I would downvote if I was wrong and laughed at.

Is 10x overnight demand close to 48h of average demand? If yes then original post was right.

My average day and night load was the same so I went from 12 hours to 120 hours worth of batteries and then could get through the 5 day storm, but with batteries depleted so badly they were essentially damaged. Now we have about 150 hours worth of stored energy for our loads.

we added a wind turbine as well which was great since some of the rainy stormy days had lots of wind. I don't understand my original posts parent's comment about (geo) diversity not helping.

FWIW, to arrive at my numbers, I used hourly sun data for a single site for a whole year and then optimized the amount of solar versus storage to minimize costs and prevent total depletion of the batteries while assuming a constant load for the whole year (and then iterating so that the amount of energy in the batteries at the beginning of the year is the same as that at the end). It turns out that even rainy days produce some solar power, which helps stretch the 48 hours of storage.

To make it work, it's cheaper to throw away about 2/3rds of your energy than to build 150 hours worth of storage. Some amount of "curtailment" is going to be optimal, and in my case, because solar is so cheap and my starting assumptions allowed no other energy sources, a LOT of curtailment is used. Literally most of the energy is unused.

If you ignore massive curtailment as a possibility, then yeah, haha, it's not going to work.

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