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ZEB
annual report 2014
Onsite electricity generation at the building
level is expected to increase systematically
and progressively in Europe and in Norway,
especially due to the requirement for all
new buildings to be nearly zero-energy by
the end of 2020. A large market uptake of
prosumers – buildings that both produce and
consume electricity – might have an impact
on the design and upgrade of distribution
grids. A distribution grid is traditionally
planned according to the expected peak load
, considering the grid as a one-way distributor
of power to the customers; while the advent
of a large number of prosumers will change
this paradigm. Buildings will, at times, be
net producers of electricity and will therefore
export it to the grid, potentially challenging the
grid’s capacity limits. In this study a bottom-up
approach is used to test if or when ZEB may
challenge the grid’s capacity.
The Norwegian case study (analyzed in
parallel to a Spanish case study) is based
on a neighbourhood of 200 single family
houses equipped with PV (solar cells) on
the roof. The building envelope satisfies the
requirements for the national definition of a
passive house, while space heating and hot
water are supplied by an air-source heat pump
as base system, with an electric resistance as
top-up heater to cover peak loads. Therefore,
the houses are all-electric, since also cooking
is electric. Hot water withdrawals and internal
gains, such as occupancy, lighting and plug
loads, are simulated with a stochastic user
behaviour model so that also the resulting
space heating need is different from house
to house, despite the identical envelope. The
average load for the entire neighbourhood is
approximately 5,200 kWh/y per household, or
33 kWh/(m2y). Each house has an installed
PV capacity of 6.0 kWp, with various tilts and
orientations. The average yearly yield from PV
is ca. 5,300 kWh/y per household, so that the
neighbourhood as a whole is a plus energy
neighbourhood.
At a single household level the peak load
might easily be as high as 10 or 15 kW, but at
aggregated level, e.g. for 200 households, the
average peak load per household is about 4
kW due to the time variability of loads in the
households.
The generation multiple (GM) relates the peak
of the generation system to the peak load. The
value of GM in a purely consumer building
– with no onsite generation – would be zero.
In ZEB or prosumer buildings a GM value
greater than one means that the generation
peak is higher than the load peak, and
therefore indicates that there might be stress
on the grid or that the distribution grid should
CAN ZEB CHALLENGE THE GRID CAPACITY?
|
KAN ZEB UTFORDRE KAPASITETEN I NETTET?
Perhaps building designers and
electric grid designers will have to sit
at the same table and work together
Igor Sartori (SINTEF)