Thermal Storage and Demand Side Management

Professor NJ Hewitt

Director, Centre for Sustainable Technologies

This presentation……

UK’s energy challenges

Why demand side management as an option

DSM will need thermal storage

Energy efficient thermal DSM

The role & challenges of heat pumps

Role of solar thermal

THE UK CHALLENGE Wind and the “Perfect Storm”

UK and Ireland Wind Resource

Wind Energy Dynamics

Wind Energy Forecasting

Traditional Power Station Dynamics

Power Station Maintenance

Role of Thermal Storage?

Storing waste heat to ensure turbines etc. are always at warm/hot start condition

Storage waste heat from for example Compressed Air Energy Storage to use the air in an expander through an adiabatic system

What are the options?

Option 1: Build flexible generation and curtail excess supply

Option 2: Build expansive networks and enable spatial arbitrage

Option 3: Enable demand side flexibility to respond to supply

Option 4: Storage

DEMAND SIDE MANAGEMENT A panacea for wind turbine variability?

Why Demand Side Management?

Demand side

• 16% of demand moveable,

primarily thermal storage and EV

batteries.

• Dependency on deployment of

heat pumps and EVs; with smart

meter system capability.

UK Committee on Climate Change (2011)

‘Renewable Energy Review’

But the timelines don’t match

Wind Energy

Dynamic Electricity Generation

Wind forecasting is not sufficiently accurate

Existing Power Stations (coal, gas, nuclear) have substantially increased maintenance on steam sides

Differences in response times can be managed by Energy Storage and Demand Side Management (DSM)

DSM in the home

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Weekday Profile 1C Energy (kWh)

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Weekend Profile 1C Energy (kWh)

Weekend Profile 1C Energy (kWh)

Weekday Weekend Weekday Weekend Weekday Weekend Weekday Weekend Weekday Weekend

Energy (kwh) 15.18 17.37 15.18 17.37 15.18 17.37 15.18 17.37 15.18 17.37

Daily Cost (£) 2.28 2.61 2.60 2.11 1.88 2.12 2.21 2.50 2.27 2.57

Cost per kWH (£/kWh) 0.1503 0.1503 0.1713 0.1215 0.1238 0.1222 0.1453 0.1441 0.1495 0.1482

Tariff A Tariff B Tariff C Tariff D Tariff E

Effect of Load Shifting

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Shifted Demand Profile

Weekday Profile kWh Shifted Weekday Profile kWh

Original Profile Shifted Profile

Energy (kwh) £15.18 £15.18

Daily Cost (£) £2.60 £1.88

Cost per kWh (£/kWh) £0.17 £0.12

Tariff B

SPACE HEATING LOADS ARE LARGER!

Elephant in the Room Number 1

What can a heat pump do in 30 mins?

Residential test (7-8th Feb 06)

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WaterRet deg C

Air_left deg C

air_back deg C

air_righ deg C

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WaterRet deg C

10 minutes interval at

58.7°C

30 Minutes

System Marginal Price by Trading Period

01 Jan 2008 to 31st Aug 2008

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Trading Period

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Mean + 1σ Mean - 1σ Max SMP Mean SMP Min SMP

How to best operate a heat pump?

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Cond Water Temp 50°C

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Electrical Network Challenges

Bagdanavicius A, Jenkins N. Power requirements of ground source

heat pumps in a residential area. Appl Energy (2012)

Ulster’s Heat Pump Tests

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Residential test (06:00pm 4th Feb)

Heat Gain kW

Power kW

CoP

WHY THERMAL STORAGE? The elephant in the room!

Thermal Systems - Hot water

Hot water tanks and Legionella

Thermal Storage Performance

PCMs and Time

Heat Pumps and PCMs

Heat pump performance dependant on delivery temperature

Under-floor heating (Max. 40 deg C)

Radiators (Traditional Min 60 deg C, Smart Rads – lower)

Hot Water - 60 deg C

PCM storage for each temperature occasion?

Blends of PCMS?

Smart Radiators

y = -14.54ln(x) + 114.73 R² = 0.9995

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Air Flow m3/hour

y = 0.045x + 20.392 R² = 0.9876

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IS THE TIME-SHIFT FROM STORAGE SUFFICIENT?

The UK has a Single Phase Domestic Electricity Network

Heat Pumps

Full power is achieved for air source units (a likely retrofit DSM option) over a period of time

Status of the heat pump (warm/cold)

Condenser temperatures

Electrical load/DSM needs to take account of actual heat pump conditions!!

Residential test (7-8th Feb 06)

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Time

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pera

ture

(oC

) WaterIn deg C

WaterRet deg C

Air_left deg C

air_back deg C

air_righ deg C

Air-fron deg C

WaterRet deg C

10 minutes interval at

58.7°C

AND THE ROLE OF SOLAR THERMAL

A Brilliant Match?

Heat Pumps and Solar Thermal

The Perfect Combination!

Solar Thermal in summer for the reduced demands of hot water only

But what of winter?

Solar Thermal Performance

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kW

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Heat Pumps and Solar Thermal

In UK & Ireland conditions, winter solar gain can reduce heat pump demands by 5%.

To achieve this, quality storage is required (Low losses)

Traditional solar thermal controller must be allowed to float to some point above tank temperature to optimise energy capture

Or a separate winter storage tank acting as an intermittent smart controlled evaporator

The use of an adapted cascade system?

Modified Cascade Heat Pump

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R134a Evaporator Tempature and R410a Condenser Temperature °C

R134a COP

R410a COP

Conclusions

Heating is the big challenge for DSM

Heat Pumps raise fears over electricity network stability (as will electric cars)

Smart control through energy storage can time shift but magnitude is as yet unknown as heat pump/storage models are inadequate

Solar thermal can make a contribution

May need seasonal storage and modified cascade heat pumps