Optimising energy storage to balance high levels of intermittent renewable generation

Paul E. DoddsUCL Energy Institute, University College

London

Presented at 33rd USAEE/IAEE North American conference in Pittsburgh27th October 2015

Thanks: Ed Sharp, Birgit Fais, Hannah Daly (all UCL)

The challenge20

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20,000

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160,000National Grid - Gone Green

Nuclear Coal Gas CHP CCS Interconnectors Onshore Wind

Offshore Wind Solar Biomass Other Renewables Other

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Baseload Flexible Intermittent

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The challenge

Storage technologiesMECHANICAL / THERMOMECHANICAL/ GRAVITATIONAL• Pumped Hydro• Heat Pumped Temperature Difference

System• Liquid Air Energy Storage (LAES)• Compressed Air Energy Storage (CAES)• CAES Undersea Bags• Pumped Hydro with Compressed Air• Flywheels• Advance Rail Energy Storage

ELECTRO-CHEMICAL• Rechargeable Batteries (e.g. Lead–acid,

Lithium–ion, Sodium–sulfur)• Vanadium Redox Flow Batteries• SupercapacitorsTHERMAL

• Phase Changes• Solar Ponds• Sensible Thermal Energy Storage: Diurnal

and Seasonal

CHEMICAL• Hydrogen from Water Electrolysis• Chemical Reactions (zeolites/water/

inorganic oxides)• Power to Gas• Large Scale Hydrogen Storage• Traditional Energy Storage (natural gas, oil

and coal)

OTHER• Superconducting Magnetic Energy Storage

Comparing technologies

• Specific (output) energy (J/kg)• Output energy density (J/m3)• Specific power (W/kg) (o/p & i/p)• Power density (W/m3) (o/p & i/p)• Minimum natural energy & power scales of a single device (J & W) • Optimum natural energy & power scales of a single device (J & W)• Nominal cost per unit energy & power at optimum scale (£/J & £/W)• Marginal cost per unit energy & power at optimum scale (£/J & £/W)• Lowest power slew rate at which performance degrades noticeably (W/s)• Effective turnaround efficiency• etc…

Energy system model: UK TIMES (UKTM)

Developed from the UK MARKAL energy systems model:• Bottom-up• Perfect foresight• Cost-optimisation – CAPEX, OPEX are model inputs; fuel prices

and the price of carbon each year are calculated

It helps us to understand:• Energy flows through the economy in the future• Impact of environmental and other constraints

UK high renewable scenario

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200UKTM - meeting the Climate Change Act (2008)

Baseload Flexible Renewable

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• No new nuclear• No CCS

Energy storage in 2050

Grid-scale Power-to-gasThermal

Thermal storage includes night storage heaters but excludes hot water tanks.

No demand-side response is assumed.

Analysing the future role for energy storage

Grid-scale electricity models

Only the electrical systemFixed electricity demand

Only grid-scale storage

High temporal resolution30 mins/1 hour

Several studies

Energy system models

Whole energy systemFlexible electricity demand

All types of energy storage

Low temporal resolution4 daily periods, 4 seasons

No studies

What is the impact of low temporal resolution?

1. Calculate excess generation from UKTM electricity portfolio in a high-resolution electricity model

2. Prevent UKTM from using the excess electricity to meet direct electricity demand

3. Check that UKTM is building the required technology capacity for the scenario

Energy storage in 2050

Low resolution High resolution0

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Grid-scale Power-to-gas Thermal

Ener

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ow in

to st

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0 (P

J/ye

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What is the impact of low temporal resolution?

Consequences:• Increases electricity consumption by 6%• Change mainly affects non-renewable generation:

– Renewable reduced by 1%– Baseload up by 10%, flexible up by 5%

• New investments in CAES and power-to-gas for hydrogen consumption in the wider energy system

Impact on hydrogen consumption

Low resolution High resolution0

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Standard Power-to-gas Imported

Hydr

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Conclusions• Low-resolution energy system models do not properly

represent the difficulties of using intermittent renewable generation.

• High-resolution electricity system models do not consider the wider types of energy storage in the energy system, which could be cheaper alternatives to grid-scale electrical storage.

• Several options – more networks, more storage, DSM/DSR• We don’t as yet know the most appropriate way to

integrate energy storage into the UK energy system in the future.

Thank you for listening