Energy Storage & RenewablesJim McDowall, ESSB SM2019

Renewables integration

– Rule of thumb for percentage of load supplied by renewables– Up to 25%

• No special requirements– 30% to 50%

• Special controls needed– 50% to 100%

• Energy storage needed for stability– Over ~120%

• Energy storage for shifting starts to make sense

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Renewables integration – 3 solution levels

– Make it compatible– Make it predictable– Make it dispatchable when needed

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Seconds Minutes Hours

Power-to-energy ratio

Ancillary services

Energy servicesNon-

Renewables

SmoothingShaping

Shifting

Renewables

Storage and renewables

– Compatibility• Ramp-rate control & frequency response• Low energy requirement• Important for weak grids

– Predictability• Firming to forecast• Moderate energy requirement• Weak grids and grid management

– Dispatchability• Shifting to grid peak• Hours of energy• Competition with conventional generation

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Compatibility with island networks

– Variability of renewable generation can affect grid frequency

– One solution is to implement grid interconnection requirements• E.g. PREPA Minimum Technical

Requirements (MTRs)

• Ramp-rate control – 10% per minute

• Frequency response – 10% of facility power; 5% droop

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0 100 200 300 400 500 600 700 8000

5

10

15

20

25

30

Time(min)

Pow

er(M

W)

0 100 200 300 400 500 600 700 80059.4

59.6

59.8

60

60.2

Time(min)

Freq

uenc

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z)

PREPA MTR philosophy

– Minimum ESS output• Peak power at 45% of facility rating

• Sufficient to control most (but not all) ramps

– When one facility falls short…

• Frequency response ofother facilities kicks in

• Portfolio effect

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Ramp control pros and cons

– Pros• Makes sure each facility is a ‘good

citizen’• Addresses grid disturbances caused by a

single facility

– Cons• Not always necessary

○ One facility ramping up while another ramps down

• Can be counter-productive○ Controlling up-ramps while frequency is low○ Controlling down-ramps while frequency is

high

• ESS in Puerto Rico operates only when the PV is in production○ US investment tax credit

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Frequency response is generally a better solution for non-US grids

PV shifting example – Kauai

– Aggressive renewable energy targets – 70% by 2030– Reached ~50% renewables in early 2019

• Solar PV, hydro and biomass– 2017 and 2018 deployments of solar plus storage

• Combined 41 MW of PV with 152 MWh of storage– First evaluation of storage for PV shifting back in 2014

• No purchase resulted, but interesting case study• Saft offered a 7 MW / 20 MWh ESS

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KIUC projected load curves (duck curve)

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With storage:Curtailment reduced 98%System ramp reduced 21%Peak reduced 11%

Market status

– Energy storage for system stability will continue to be important for island networks

– Solar and storage deployments growing• Storage is now competitive with peaking generation in many areas

– Storage systems shifting to longer run times• Battery development work will concentrate on lowest cost for multi-

hour storage

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Questions?

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