Page 54 - Energize May 2022

TECHNICAL

Microgrid with renewables, but no CHP/
CCHP
Microgrid systems can be enhanced by
adding bi- or tri-generation (i.e., either
combined heat and power (CHP) or
combined cooling, heat and power (CCHP)).
Those systems which do not include
CHP or CCHP, tend to operate with
emergency backup generators, which
would be used as a first line of defence
against an interruption of power from
the utility’s grid. Renewable energy
technologies can be used to supplement
the emergency backup generators to
preserve fuel consumption. Figure 1: Typical C&I microgrid configuration (Schneider)
Furthermore, if backup generators
operate reliably to supply critical circuits, Back-up generators
the microgrid could use DER to supply Data centres usually rely on diesel gensets for backup power supply. Diesel is a reliable
other circuits in the data centre to keep fuel source which can be easily stored onsite. However, diesel gensets have three potential
some services up and running during weaknesses:
a grid outage. This could be extremely • There are limits to how much fuel can be stored, and therefore the total runtime a facility
important in the event of a large-scale could expect is often limited to a few days.
natural disaster. • Environmental emission regulations restrict how long a diesel genset can run during the
year.
Microgrid with CHP/CCHP • Gensets have been known to fail. Even if they are serviced regularly, there is always a
The CHP/CCHP system would be running chance of the gensets failing to start up reliably. This can be the result of poor fuel quality,
continuously, serving the partial or full overloading or poor battery condition.
electrical needs of the facility. Typically,
CHP/CCHP is sized to meet the full CHP and CCHP
demand. Electricity demand can be grid These systems combine electrical generation with the production of heating or cooling.
augmented and if CHP/CCHP is sized large Combined heat and power (CHP) technology has been available for decades and typically
enough to supply the entire facility, backup uses a reciprocating engine or combustion turbine as the prime mover, fuelled most often
gensets would not be needed at all in the by natural gas. The prime mover produces heat at the same time as generating electricity.
case of a grid outage. A more advanced system solution, combining cooling, heat and power (CCHP) known as
trigeneration, provides cooling as well using absorption chillers.
Microgrid with CHP/CCHP and renewables A CCHP system would typically run continuously and would be better maintained than
When coupled with additional DER (i.e., standby generators, making it ready and able to provide power in the event of an outage. In
power from additional sources such as some cases, CCHP can be sized to provide primary power to the facility, with the utility acting
solar PV, wind, hydro, or some other source as backup. The microgrid system would need to continuously balance requirements against
of energy), a microgrid could achieve costs. This includes determining, at any given time, what the difference is between the cost
almost unlimited autonomy, depending of grid electricity and natural gas, and at what point to change between the grid and own
on fuel supply for the CHP/CCHP system. generation.
The additional renewable resources could
be used to augment the electrical energy Renewables
supply of the CHP/CCHP system to serve The availability and cost of renewables, together with local market factors such as electricity
loads throughout the facility. pricing and regulations, will determine whether the use of renewable energy makes sense
for a particular facility. In South Africa, solar PV is the renewable of choice; however, it takes
C&I microgrid components 1 about 2 Ha of space to generate 1 MW of electricity from solar. For sites which have the roof
The specific needs of C&I means that space or surrounding land available, the decreasing price of solar PV makes it a good choice.
microgrids need to offer generation,
storage and control. They therefore Fuel cells
require a range of components wider Fuel cells can provide primary power, backup power, or combined heat and power.
than that of the conventional microgrid. Fuel cells which operate on natural gas are available, but future trends will be towards
Figure 1 shows a typical C&I microgrid green hydrogen. Fuel cells have a much smaller footprint and weigh less than competing
configuration. alternatives.

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