Load Matching, Grid Interaction, and Advanced Control - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 310

6.3.1.1 Electric Energy Storage
In general, current battery technology does not allow storing an amount
of electric energy that would be significant for a building at a reasonable
cost, although efforts are being made in that direction (Lamonica, 2012).
In off-grid buildings, such as those located in very remote or inaccessible
locations, batteries can provide an economically attractive solution, but this
is more the exception rather than the rule. A possible alternative for
electricity storage is the use of fuel cells, but several practical shortcomings
(cost, efficiency, size) prevent its widespread adoption for the time being.
Batteries in electric vehicles (EVs) or plug-in hybrid electric vehicles
(PHEVs) provide an interesting potential for peak load shedding in
buildings. Car batteries can store an amount of energy in the order of tens
of kWh. With the electric installation commonly available in a household,
charging an electric car might take many hours (at a charging power of
about3kW).TochargeanEVbatterywithinareasonabletimeframe,special
electrical installations are required to supply significant charging power (up
to 50 kW). While such power requirements pose their own challenges for
load management, the car battery can also be used to supply power to the
building at a similar rate. For instance, in a “vehicle-to-home” scheme (V2
H) car batteries could supply some or all the power needed by appliances
when operated during peak hours. The charge/discharge cycles of the EV
battery will be scheduled considering factors such as the hours when the
vehicle is parked, the tariff structure of the utility, and occupant habits,
among others.
6.3.1.2 Thermal Energy Storage
The building thermal mass provides some energy storage capacity by
allowing moderate temperature fluctuations - the so-called passive energy
storage. This principle is used, for example, in night precooling strategies
(i.e., the building is cooled before occupancy hours). Likewise, the indoor
temperature of a passive solar house can be allowed to increase because
of solar gains, so that the building can “coast” for several hours without
heating. In practice, however, passive energy storage is limited by thermal
comfort constraints - for example, occupants might complain if the
temperature is too low in the morning - and other limitations (esthetic,
economical, functional, etc.), which limit the thermal inertia of the building.
As the increase of thermal inertia has mostly positive benefits, research and