Comment by toomuchtodo | Hacker News Reader

Comment by toomuchtodo | Hacker News Reader

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Yes, you can configure inverters to not dump excess current back to the utility. You either charge batteries or you dump the power into a load like an electric water heater.

In almost all grid-tied scenarios though, you want to sell the power back to the utility. I'm not familiar with commerical operations, as they would fall under power purchase agreements (PPAs), but with residential installations your meter quite literally does spin backwards or a separate meter is used to determine how much power you've sent back to the grid. This is dependent on how the utility compensates you for the power you generate (spin the meter back if its a credit or the same price as what your purchase it from them at, separate meter if the pricing paid to you is different than the retail rate).

As the article states, we don't have the issues in the US that Germany has yet, because Germany produces so much more solar energy than in the US. At some point though, questions will need to be answered about who is going to pay for the spinning capacity (likely natural gas generators) that isn't used except for those rare times when the wind isn't blowing, the sun isn't shinning, and you can't drag enough power in from another geographic region over HVDC transmission lines.

> who is going to pay for the spinning capacity (likely natural gas generators) that isn't used

That doesn't sound like a bad problem to have.

Fukushima showed us how hard it is to turn a nuke on and off quickly, but I would think most hydrocarbon burning and other generation systems could be throttled according to demand.

If you really have a problem with too much energy, well, smelt some aluminum or electrolyze water or something.

"Spinning Reserve is the on-line reserve capacity that is synchronized to the grid system and ready to meet electric demand within 10 minutes of a dispatch instruction by the ISO. Spinning Reserve is needed to maintain system frequency stability during emergency operating conditions and unforeseen load swings."

http://www.caiso.com/docs/2003/09/08/2003090815135425649.pdf

The poster isn't saying they're producing energy, just that they must be ready to do so at any time.

Correct. You're not paying for that field of gas turbines to run. You're paying for them to sit in the field warm until issued to run, because if they're not there, hello blackouts.

Spinning reserve ought to be replaced with batteries. I bet some of it could be replaced with batteries today with the utilities' customers saving money, aside from the sunk costs not then providing the proper return on capital to their investors.

LOL talk to an EE about the orders of magnitude involved, you're not going to like the answers.

The cheapest storage battery is simple lead acid figure a quarter per watthour installed. Or a KWh is $250. But with a 100% charge/discharge cycle the battery will be dead and need replacing in about 10 or so cycles. To get up to 1000 or so cycles (which is only 3 yrs daily cycles) means you only get to use about 10% of the capacity. Lets round up because rectifier/inverter gear, and buildings, and operators and their stuff, are not free. So you can guess about $3/watt of storage as an absolute best case, but probably more realistically a turn key battery storage facility would cost more like $4 and would depreciate fully in about half a decade.

Hydro turnkey is about $1/watt plus or minus massive corruption (what is the dollar value of the hetch hetchy valley of yosemite national park, etc?) Coal plants sell turnkey for a bit over $2/watt, natgas is arguably the most expensive around $6/watt. All of those last like 50 years, so divide those costs by about 10 to compare with a battery bank that only lasts at best 5 years.

Spinning capacity (well, sorta, in case of natgas) is around 10 times cheaper per KWH than batteries. You have to remember that power companies don't really care about pushing an agenda, more or less. There is no conspiracy, they just want to sell KWH. If they could install a battery bank instead of a natgas peaking plant, and keep huge profits, they most certainly would.

There are some interesting math problems too. If each stored utility grade battery costs $2500/KHW and the total overall worldwide battery industry is about $50B, that means if we abandon all other forms of battery use in the world and get rid of all laptops, cellphones, etc, we could build nothing but lead acid batteries at a pitiful rate of ... drum roll ... 20 megawatt hours of utility grade storage per year. Now since the batteries are scrap in 5 years, that means if in a Manhattan style worldwide project we focus the entire industry on utility grade storage, we can never store more than 100 megawatt-hours worldwide. Which if you assume a daily charge discharge cycle is about 10 MW continuous or about the capacity of ONE small gas turbine system. So its not as simple as going down to "batteries plus" and picking up a battery large enough to UPS a nuke plant.

The Fairbanks battery should provide some real world experience:

http://juneauempire.com/state/2011-04-17/fairbanks-battery-b...

http://www.gvea.com/energy/bess

They chose Ni-Cad (presumably for good reason).

Edit: Some numbers:

It's about 5 megawatt hours (varies somewhat based on draw, could stretch it to 6.5 MW-h for 15 minute runtime, less at higher draws).

Cost $35 million, so ~$7000 per KW-h of capacity.

Planning authorized in 1993, online in 2003.

Expected battery life of 20 years (maybe 30).

So a project that didn't seem to take up the entire manufacturing capacity of the battery industry managed to bring up 0.5 megawatt hours per year, with a lifetime of 20 years, half of your prediction of capacity production capacity (but at much higher cost than you started from).

Also, you are off by a factor of 1,000 on your capacity. $50 billion / $2500 implies 20 million kilowatt hours, which is 20 gigawatt hours.

Hmm yes good point.

Using the battery tech that is so cheap you can only 10% discharge sounds.. suboptimal.

You could probably store and recover more energy from those batteries by lifting them from a crane.

You just precisely described pumped-storage hydro and why it's used for 99% of bulk electricity storage :)

How come we don't hear about it more?

Instead we keep hearing the old "Wind and solar will never work because base load" garbage.

It sure could (in some places). Check out:

http://library.abb.com/GLOBAL/SCOT/scot271.nsf/VerityDisplay...

"An economically and ecologically more viable alternative to ‘spinning reserve’ – gas turbines kept running in case of an emergency – is battery back-up."

Do you have any idea how big and environmentally unfriendly those batteries would have to be? Ready reserve is generally provided by peaking generators (the aforementioned natural gas turbines) and by hydro dams. There aren't many batteries that can provide hundreds of megawatts for hours at a time.

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