IEEE Power & Energy Magazine - January/February 2017 - 32

The parallel deployment of wind and solar power,
in combination with relatively inflexible nuclear generation,
could exacerbate flexibility demand.
storages or peak shaving-demand response. Buildings with
local heating and the transport sector were not included in
the study.
Heat Loads in Primary-Frequency Reserves

When a power system is running mainly with nonsynchronous generation, one option in providing upward primaryfrequency reserve is to curtail wind or solar power plants to
get the necessary headroom for reserve operation. However,
flexible heating and cooling loads can also provide a fast
response, typically in the order of 100-400 ms, when using
local frequency detection. Consequently, some generation
curtailments could be avoided, and system-wide fuel use
could be decreased.
In one case study, system-wide operating cost savings
ranged €8.5-500 per heating appliance, depending on various factors (fuel costs, wind penetration, etc.), for Great
Britain's power system. The cost savings from the activation
of flexible heating loads improve with increasing shares of
wind power and with increases in reserve requirements. In
addition to direct economic benefits, using flexible loads in
primary reserve reduces the number of conventional plant
startups, enables higher levels of wind penetration, and
improves frequency stability.
When implementing heating- or cooling-based reserves,
one needs to consider the load pickup that takes place after the
load has been curtailed for reserve provision. The magnitude
of the pickup varies with the thermal inertia characteristics
of the heating/cooling load, the duration of the response, and
the control mechanism. For example, activation of 60 MW
of primary reserve from a domestic cold load (refrigerator/
freezer) for 90 s (5-min recovery duration) requires the addition of 20 MW (35% of activated flexible load) to subsequent
reserve categories to allow for the load pickup.
Residential Heat-Electricity Integration
Using Hybrid Heaters in Ireland

Hybrid heating systems, such as a combination of a heat pump
and a gas boiler, enable shifting between the two different
sources of heat. If equipped with smart controls, it is possible
to shift in real time, depending on electricity market conditions.
An investment study of the Irish 2030 system, with 40%
electricity from wind power, found that the large-scale
deployment of such systems can provide electricity system
benefits. An optimization model was used to find the leastcost heater capacities and operation schedule. If a gas boiler
is combined with a resistance heater, those hybrids will
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operate primarily on gas but will shift to electricity whenever low-price electricity is available. When compared to a
gas boiler alone, the results showed annual system-wide savings of €18-65 per household, depending on the gas price.
If a gas boiler is combined with a heat pump, they will operate mainly on electricity and shift to gas during periods of
low wind-power supply or high demand. Then, the annual
savings were €46-159 per household. The flexibility from
hybrid heaters enabled the lowest-cost energy system.
Benefits of Electric Boilers in Reducing Wind-Power
Curtailment in Northern China

In the northern provinces of China, 20~40% of wind energy
was curtailed in 2015 due to inflexible operation of coal-fired
CHP plants. In winter, these plants must operate at nearly full
capacity to meet the demand for building heat (delivered as
hot water through district heating systems) and must produce
electricity at the same time. Combined with a high output from
wind power plants, this often causes an oversupply of electricity, and wind power plants need to be curtailed. A series of
numerical studies tested the use of thermal storage and/or heat
pumps to increase the flexibility of the system. The results
demonstrated a significant reduction in wind-power curtailments. On the other hand, air-source heat pumps suffer from
low efficiency in the cold winter conditions of Northern China
and may not be an economic choice.

Some Real-World Experience
and Applications
Denmark is one of the leading countries in the integration of
large amounts of wind power. In 2015, 42% of its electricity
was generated by wind turbines. Apart from its large interconnectors to neighboring countries, the integration of wind
power was enabled by its district heating networks. These
networks can store excess wind power generation through
a combination of electric heaters and heat storages. Meanwhile CHP plants can be operated when there is not enough
low-price electricity available.
In residential buildings, smart thermostats can give functionality beyond temperature and time-of-use control. Communication with the Internet or an aggregator enables the utilization
of power prices and weather forecasts. Meanwhile, occupantmodeling intelligence can consider the actual needs of the occupants in the control scheme. For example, the model predictive
control (MPC) algorithm can make use of the additional information to better utilize lower power prices and improve energy
efficiency. From a power system perspective, this appears as
january/february 2017

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - January/February 2017