Maui's largest solar project OK'd by PUC
http://www.mauinews.com/news/local-news/2019/03/mauis-largest-solar-project-okd-by-puc/Island’s other large-scale array, battery proposal awaits approval
Mar 30, 2019
Maui County’s largest solar project with battery storage, the 60-megawatt Kuihelani Solar, was approved by the state Public Utilities Commission, Hawaiian Electric Co. announced Tuesday.
AES Renewable Energy is developing the project to be built on as much as 500 acres of old sugar fields off Kuihelani Highway in Central Maui, the company said in November. It will include a 240-megawatt-hour battery storage system.
Maui Electric Co. will pay 8 cents a kilowatt hour for the power from the solar array and battery system, the lowest cost for renewable energy on the island and much lower than fossil-fuel-generated power.
“AES is excited about the PUC approval of its solar-plus-storage project in Central Maui, which is expected to provide enough clean energy for nearly 27,000 Maui homes per year, anticipated bill savings to Maui residents and offset nearly 2,000,000 barrels of fuel over the life of the contract,” said Rob Cooper, business development director of AES Renewable Energy, on Friday.
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i.e. dumping the wind when one already has enough other (usually thermal generation -- fossil, nuclear) on line but that can't be backed down further in order to take the wind because of their minimum loading constraint, and can't be shut down, because of operating constraints (minimum up time, minimum down time, and the high cost of a shutdown / startup cycle).
What worried me as a generation planner and system operation planner at an electric utility was meeting the load (total customer demand) at every hour, minute, and second of the day.
In other words I wasn't worried about the low load conditions when we had plenty online for the load conditions. We were worried about the morning and afternoon peaks. I don't know how a 4 hour battery helps much on a cloudy rainy day (solar) or calm wind day.
I get some of the "peaking" application -- as an Arizona utility described it, the solar did just fine in the early-mid afternoon, but in the late afternoon the sun is getting low in the sky and people are getting home from work and one has a peak when the factories and businesses haven't yet shut down and meanwhile the residential load is increasing ...
So that's when the 4 hours of battery power comes in handy, which, incidentally can be charged at night by any other generation that's online, wind, conventional, whatever....
But that seems kind of a limited application. And Arizona can count on sunshine during the days with high probability, not so many other places like Minnesota. So I'm hoping to get some insights reading the paper (and not just the executive summary 
)
Though the more I think about it, the more I like the idea of a 4 hour battery that can be charged at any time of the day or night, and then used during the 4 hours when it's most needed, which can be predicted in advance with a high degree of likelihood.
Or at half capacity for 8 hours. Or low capacity building up to full capacity and then tapering back down, all over several hours.
In other words, treat the battery as a total utility resource, not something that has to be operated as part of the solar farm to make the solar farm more useful. Operate both as separate entities in a way that is most useful to the system.
Back in my day at the utility (late 70's thru '92) was before wind and solar as a significant resource, but we did have deals with other utilities for non-firm energy that basically we couldn't really count on, but it's still -- if low cost -- useful to back down our more costly generation (search: equal incremental loading, incremental heat rate curve, incremental cost curve, power generator input output curve).
Somebody might object that a generator operating at say half capacity is not as efficient (on an overall MBTU/MWH basis or $/MWH basis) as one that is at full load, but still it's cheaper in dollars and consumes less fuel than operating it at some other higher load. (search: power generator input output curve, incremental cost curves).
Somebody might object that a battery wastes energy, but well, I can tell you that the cost of energy is several times higher during the daytime peak than at night (in my day it was like $30/Mwh during the day and $6 to $10/Mwh at night). So the issue of the "only" 80% round trip efficiency of a battery pales into insignificance compared to these kinds of cost spreads.
Thanks again
