As the world makes technological advancements, every sector is being carried along and the energy sector isn’t any different. With recent developments, the earth may be able to go greener with energy generation sooner than expected. Scientists have done plenty of research on renewable energy and have made amazing breakthroughs. They are finding simpler and cheaper ways to generate, distribute and store power. Most of these ways involve renewable energy sources.
For over 100 years, fossil fuels have been used to generate power. In the past, energy demand per house was low, energy generation was localized and grids were built to support power distribution and supply.
As global energy demand increases (by about 2%) each year, the present grid needs upgrading as it’s running at full capacity. Outages occur when power lines break or when power plants can’t produce enough electricity. Also, there’s the problem of relying on a single power source without detailed knowledge of energy usage, this makes electricity difficult to manage. In the past, more plants were built but now, we can work towards sustainability by using microgrids and smartgrids.
What is a Microgrid?
Traditionally, an electrical grid is an interconnected network for delivering electricity from producers to consumers. It consists of generating stations that produce electricity, high voltage transmission & distribution lines that carry power from the generated source to individual customers and a few control centers for monitoring and control.
A microgrid is a small-scale electrical grid that can operate independently or in conjunction with an area’s main electrical grid. Basically, any small-scale localized station with its own power resources, generation and loads within a definable boundary qualifies as a microgrid.
Microgrids can serve as backup power to the main electrical grid or bolster it during periods of high energy demand. Microgrids can also run independent of the main electrical grid and in this way integrate other sources of distributed generation like renewable energy.
Components of a Microgrid
- Distributed generation
This represents the various types of generation source that feed electricity to consumers. These sources are usually categorized into two groups: thermal energy sources (e.g. Diesel generators) and renewable generation sources (e.g. Solar, wind, etc.).
These are the various elements that consume electricity. They range from single devices to lighting, heating system of buildings, etc.
- Energy Storage
In a microgrid, energy storage is able to perform multiple functions, such as ensuring power quality, including frequency and voltage regulation, smoothing the output of renewable energy sources, providing backup power for the system and playing a crucial role in cost optimization. It includes all of electrical, pressure, gravitational, flywheel, and heat storage technologies.
- Point of common coupling (PCC)
It’s the point on the electrical circuit where the microgrid is connected to an area’s main electrical grid. Microgrids may be without a PCC, those like this are called isolated microgrids (island modes). Isolated microgrids are usually present in cases of remote sites where an interconnection with the main area grid isn’t feasible due to technical or economic reasons.
Advantages of the Microgrid
A major advantage of the microgrid is its ability to operate alone as an island mode or interconnected to an area’s main electrical grid. A microgrid can also transition between both. When connected to the grid, a microgrid provides ancillary services by trading activities between the microgrid and the main electrical grid.
Other advantages are:
- Microgrids facilitate the integration of renewable energy by its ability to modify energy flow through its components without requiring a redesign of the national distribution system.
- Modern optimization methods can also be incorporated into the microgrid energy management system to improve efficiency, economics, and resiliency.
- Microgrids can provide substantial savings and reduce carbon emissions.
- Microgrids can provide high quality and reliable energy supply to critical loads.
- Large transmission build outs and transmission losses can be reduced.
- Microgrids enable smart grid technology integration.
Challenges faced by the Microgrid
Microgrids and integration of Distributed Energy Resources (DER) units introduce a number of operational challenges that must be addressed in their design of control and protection systems to ensure reliability. Addressing this will also ensure potential benefits of Distributed Generation (DG) are fully harnessed. Some challenges arise from invalid assumptions typically applied to conventional distribution systems, while others are the result of stability issues formerly observed only at transmission system level. The most relevant challenges include:
- Bidirectional power flows:
The presence of DG units in the network at low voltage levels can cause reverse power flows that may lead to complications in protection coordination, undesirable power flow patterns, fault current distribution and voltage control.
- Stability issues:
Interaction of control system DG units may create local oscillations, this requires a thorough small-disturbance stability analysis. Moreover, transition activities between the grid-connected and island modes of operation in a microgrid can create transient stability.
Operating microgrids has some level of uncertainties in which economic and reliable operation of microgrids rely on. Load profile and weather forecasts are two of them that make coordination become very challenging in isolated microgrids.
Some characteristics of the traditional scheme such as prevalence of three-phase balanced conditions, primarily inductive transmission lines and constant-power loads do not necessarily hold validity for microgrids. This means models for microgrids need to be revised.
- Low inertia:
Microgrids show low inertia characteristics that are different to bulk power systems where a high number of synchronous generators ensure a relatively large inertia. Low inertia in the system can lead to severe frequency deviations in island modes if a proper control mechanism isn’t implemented.