Functional Design of the mCCHP-RES System - Design for Micro-Combined Cooling, Heating and Power Systems - page 241

2.2.1 Electric Subsystem Components

Power generating need have two essential functions: first, the generating unit is

required to be equipped with a “ kilowatt function ” to generate suf cient power

when necessary, and second, must possess a ne-

tuning the output so as to follow minute-by-minute and second-by-second the

“ frequency control function, ”

if
necessary. Renewable energy facilities such as solar sources do not possess both a
kW function and a frequency control function, because they have DC current.
Electrical energy storage is expected to be able to compensate for such dif

fluctuations in demand, using the extra power from the “ kilowatt function ”

culties
with a kW function and a frequency control function. Stationary batteries are uti-
lized to support renewable energy output with their quick response capability. To
supply residence is needed AC power at the industrial frequency (50 Hz). The
switch from DC to AC is realized using mono-phase or three-phase inverter
depending on the installed power. The stand-alone micro CCHP supplies the
building (Fig. 3 ) with electricity by means of a battery and three- or one-phase
inverters to build up a supply network. If the batteries are charged, the power output
of the inverters has to guarantee electrical power supply of the building. When the
CHP unit is in operation, its power output must cover the residential consumption
and must charge the batteries (if the PV panel is not in operation). When the CHP
unit is not in operation, the total supply period is determined by the battery capacity
and depends on the total consumption. Additionally, a battery management system
is recommended to guarantee the special operation procedures of the batteries
resulting in improved lifetimes. In case that the produced electrical energy (espe-
cially photovoltaic energy) cannot be used by consumers or stored in the batteries,

PV
panels

CHP
Unit

S 1

L 1

PV charging
controller

Inverter1

S 2

L 2

Inverter 2

DC
distribution

Battery

S 3

L 3

Building

Inverter 3

N

Indication of
operation modes

Battery
management
system

Remote control

Fig. 3 Electric subsystem scheme