IEEE Power & Energy Magazine - July/August 2018 - 73

Electricity is also widely used in the residential sector
for water heating, which is typically combined with
thermal storage (a water cylinder).

Ireland, the united Kingdom, germany, france, and new
Zealand. traditional nighttime storage heaters were used to
reduce systemwide peak loads and fill in the night "valley"
and allowed customers to use less-expensive off-peak electricity tariffs to meet their heating demand. storage heaters
contain a core of high thermal capacity bricks, heated
by a resistive heating element and surrounded by a highly
insulated enclosure. they are designed to be used on a 24-h
cycle (i.e., charged at night and heat released during the day),
although older storage heaters could not always keep sufficient charge levels to maintain thermal comfort on colder
winter days. Modern storage heaters, through improved insulation and controls (the release of the heat during a 24-h cycle
can be more accurately controlled with the use of a variable
speed circulation fan), offer a higher degree of comfort to end
users. Moreover, with adequate controls and communication,
smart electrical thermal storage (sets) can participate in
active demand-side management (DsM) and enhance power
system flexibility. the eu-funded Horizon 2020 realValue
project is trialing sets systems at a household level, providing a range of system services while maintaining the thermal
comfort of customers.
electricity is also widely used in the residential sector
for water heating, which is typically combined with thermal
storage (a water cylinder). as with space heating, this storage capacity decouples the power demand from the heating
demand, and when equipped with communication and control architecture, electrical water heaters can also participate
in DsM.
the building envelope itself also provides thermal inertia
depending on the insulation level. In a well-insulated house,
electric load can be shifted (around 5-12 h), depending on
the building insulation level, while consumer comfort is still
met. preheating increases flexibility but typically increases
energy usage, depending on the insulation level. thermal
storage and building preheating enables large demand shifting potential at very low cost, especially when compared to
electricity storage.

Hybridization
Hybrid heaters combine different heating appliances in one system and can switch between those appliances during operation, providing a very flexible demand. possible configurations include Hp-gas boiler (Hp-B) and gas boiler-resistance
heaters. Hp-B systems have been available commercially
for several years and were developed to lower investment
july/august 2018

compared to stand-alone Hp systems. However, hybrid heaters could offer electricity system benefits if connected in a
smart manner that enables the electricity system to access
the flexibility of the gas system by switching from the Hp to
the gas boiler whenever the electricity system is under stress,
which can include an extended period over several days.
Hybrid gas boiler-resistance heater systems could also provide the option to use excess renewable electricity by switching from gas to electricity.

System Integration
Widespread electrical heating can have a significant impact
on the overall system energy demand as well as on the shape
of that demand. High shares of direct electrical space heating
increase the winter system peak demand. on the other hand,
when combined with thermal storage, the electrical demand
can be shifted to off-peak hours, with minimal impact on
the peak, and with the additional advantage of increasing
baseload plant utilization in the off-peak hours. However,
as shares of variable renewable energy increase and the net
load becomes more variable and harder to forecast, smarter
controls and two-way communication are required to fully
take advantage of the thermal energy storage capacity.

Coupling Small-Scale Electric Heating
and Thermal Storage
Cooptimizing heating (combined with storage) and power
system scheduling could reduce overall system costs and
increase shares of variable renewable generation that can
be integrated. as discussed earlier, sets for both space
and water heating (i.e., resistive electrical heating combined with thermal storage) is currently being trialed in
the eu Horizon 2020 realValue project. a combination of
physical demonstrations in three winter peaking systems
(Ireland, germany, and latvia) along with detailed building and power system modeling will demonstrate how local
small-scale energy storage with advanced ICt, optimized
across the eu energy system, could bring benefits to all
market participants.
enormous benefits can be realized from the integration
of the power and heat energy systems. However, to adequately assess the scale and value of the flexibility that can be
accessed from the heat sector, detailed modeling is required
to consider the impact of any load shifting and demand
response activities on the end users. Cooptimized buildingto-grid models have been developed and refined as part of
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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2018