Page 59 - Energize October 2022

TECHNICAL

find the best mix and sizing of each asset to achieve the project goals. dispatchable asset start-up events.
Through this energy model, a representative system can be evaluated for the Battery storage can also be used to
key metrics of the system such as levelised cost of energy (LCOE), system emissions, improve the transient response during
renewable penetration, energy shortfalls, fuel consumption, etc. The energy modelling large load changes.
begins with a detailed analysis of the site’s load profile at 15-to-60-minute intervals for As with PV panels, batteries are a
an entire year and a review of the exact site details to determine the wind availability, DC power source and use inverters to
solar radiation, etc. for the specific geographical location being considered. charge from, or discharge into, an AC
Finally, by investigating existing utility charges and/or on-site fuel consumption, electrical system
a variety of solutions can be measured against the baseline or status quo. Various Microgrids can also use other
assets can be considered in the energy model and the sizing of these assets can be power technologies such as wind
constrained based on site-specific information. For example, while solar panels are cost turbines and fuel cells.
competitive both from an initial investment and operating expense perspective, they
take up a significant amount of space. Wind turbines
Another common constraint is the availability of specific fuels for generator sets at Wind turbines, like PV panels, are
the project location. The energy model will determine how each of the chosen assets intermittent sources which produce
should be used to reduce the LCOE and maintain power to the microgrid. For example, power when there is adequate wind.
the energy model will find the best time to use grid power, when and how to charge Geographic location has a major impact
batteries, and when to use generator sets in the system. on the viability of using wind energy in
A system stability analysis will ensure adequate power quality (i.e., frequency, a microgrid but in the right location can
voltage deviation, etc.) and eliminate system disturbances. The stability analysis will be very beneficial.
confirm that the various energy assets being considered for the microgrid will maintain
the required electrical quality to sustain continued operation and prevent damage to Fuel cells
connected loads. Fuel cell technology has been steadily
Through these two analysis steps, the most efficient and stable integration of assets improving with higher efficiencies,
can be optimised for the specific drivers of the project, such as the lowest net present increased power density and reduced
cost or lowest system emissions. costs, leading to more microgrid
projects considering fuel cells. There
Components commonly found in microgrids inverter-based are different fuel cell technologies
technologies: available such as Proton Exchange
PV panels Membrane (PEM) fuel cells and Solid
Photovoltaic (PV), or solar, panels are made of silicon cells which, when exposed Oxide Fuel Cells (SOFC) which can
to sunlight change their electrical characteristics and generate electric current. PV accept and generate power from
panels are typically mounted on the rooftop of buildings, above parking garages, over different fuel sources.
carports, or in open space at ground level. They require a large amount of physical PEM fuel cells use very pure
space unobstructed by shade. PV panels provide a source of DC power and require an hydrogen (H 2) to produce power while
inverter to transform the DC power to AC for use in most common electrical devices. SOFC can use a variety of hydrocarbon-
Solar panel costs have recently fallen drastically, and they have an extremely low based fuels such as biogas, natural
or even non-existent marginal cost of generation, making them a valuable asset in a gas, propane and hydrogen. When
microgrid. They are, however, a highly intermittent power source – only producing considering a fuel cell for a microgrid
energy when solar radiation is available during the daytime. PV panels alone cannot it is important to understand the
provide uninterrupted electrical reliability and are increasingly being paired with performance characteristics of the
battery energy storage systems to ensure greater utilisation and reliability. chosen fuel cell as well as have a good
understanding of the supply chain and
Batteries costs of the required fuel.
Batteries are another common component found in microgrids as, when coupled
with intermittent energy sources such as PV panels, they can address the curtailment Inverters
and irregularity of renewable energy sources. During the day when solar energy is To connect the DC output of solar,
abundant, energy produced in excess of the load demand can be stored in batteries to storage and fuel cells to an AC network,
be discharged overnight rather than being curtailed. the DC output must be inverted to
Batteries can also be charged by utility power, if allowed by the utility, when utility AC power first. Inverters, which are
rates are lowest, and discharged during high-rate periods or to avoid costly demand semiconductor-based electronics, use
charges. Lithium-ion batteries are currently the most prevalent technology used in Insulated-Gate Bipolar Transistors
stationary storage applications due their high-power density, low costs and durability. (IGBTs) to “invert” the DC power to AC
Energy storage systems can be used in both off-grid and grid-connected systems power. In addition to inverters, filters
and can be used to supply near instantaneous power during grid outages or during and other electronic devices are used

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