IEEE Power & Energy Magazine - November/December 2019 - 75

include preheating, which involves warming the households
earlier than usual, while utilizing inherent heat storage in
the fabric of the houses and not compromising user comfort.
Furthermore, the smart control of HHPs can increase their
operating efficiency. It has been demonstrated that rolling
out smart control strategies would considerably improve
the value proposition of HHPs. Additional annual benefits
are between £5.1 and £15.2 billion/year, depending on the
availability of other operational flexibility sources in the
system (Figure 9).
The most significant value stream of this flexibility is
a reduced investment in low-carbon generation capacity,
including VREs and nuclear. This result is driven by the
operational flexibility of the HHPs with smart controllability to provide system-balancing services and related
increase of VRE utilization, thus meeting carbon targets
cost effectively.

Electricity and Water
There are three ways in which the interdependencies of
the electricity and water systems influence the provision of
operational flexibility.
1) Hydroelectric and pumped storage facilities: Run-of
river hydroelectric generation offers large amounts
of operational flexibility, depending on the available
water and environmental constraints. Pumped storage
is typically able to contribute to short-term regulation
and ramping services. Additionally, it can respond on
a diurnal basis by leveling the demand net of renewable production.

2) Water-related electric loads: Two types of waterrelated loads are large enough to represent flexibility opportunities: water treatment plants (WTPs)
and wastewater treatment plants (WWTPs). Both
represent a relatively large amount of load, offer
significant operational flexibility, and are available
throughout the year on a daily basis. In the region
of the United States operated by the Midcontinent
Independent System Operator (MISO), the total
nameplate capacity of WTPs and WWTPs is about
1,000 MW. Motors for pumping consume over 90%
of the load. If 30% of this load is on at any given
moment and available for the provision of f lexibility, this could contribute 270 MW of flexible
load. A typical weekday regulating reserve requirement in the MISO region is 400 MW, whereas 10min ramp-up requirements range between 10 and
1,300 MW and 10-min ramp-down requirements
range between 70 and 1,500 MW. Thus, a 270-MW
contribution to these requirements would be significant. WTPs often utilize water storage tanks, many
of which can gravity-feed water demand for hours
before being replenished. Both WTPs and WWTPs
have wait times built into their processes, offering
load-shifting abilities by minutes or hours. New
plant pumps with variable speed drives offer the
ability to modulate the load, which is an attractive
feature for frequency regulation. The investment
costs associated with initiating WTP and WWTP
as controllable demands are expected to be low, as
18

7.4

6
4.9

4
2
0
-2
-4

Low Flex

Distribution
Interconnection
Transmission
Generation (Other)

High Flex
Generation (Low Carbon)
OPEX: Electricity
OPEX: Gas
Total

figure 8. The annual cost savings attributed to the use of
HHPs instead of EHPs in a system with low and high flexibility. Positive values show benefits while negative values
show additional costs. The results show that transmission
adds neither costs nor benefits. (Source: Imperial College;
used with permission.)
november/december 2019

Benefits of Smart Control of HHP
(£billion/year)

Annual System Benefits of HHPs
(£billion/year)

16
14

15.2

12
10
8
6

5.1

4
2
0
-2

Low Flex

Distribution
Interconnection
Transmission
Storage
Generation (Other)

High Flex
Generation (Low Carbon)
OPEX: Electricity
OPEX: Gas
Total

figure 9. The system-level benefits of HHP smart control
strategies in a system with low and high flexibility. Positive
values show benefits while negative values show additional
costs. The results show that transmission adds neither costs
nor benefits. (Source: Imperial College; used with permission.)
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IEEE Power & Energy Magazine - November/December 2019

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