The Lowdown on Microgrids
Discover the ins and outs of renewable microgrids, how they work and what hydrogen storage is
29. novembre 2018
Microgrids offer complete energy independence and resilience to shock. Gone are the days of microgrids existing only in remote islands and rural communities, some of the most industrialised areas in the world run on microgrids. Find out why microgrids, especially renewable microgrids, are becoming an integral part of our future energy system below.
What are microgrids?
A microgrid is an electric power grid that runs on localised energy sources. It can operate as part of the traditional electricity grid or disconnect entirely from the grid to operate autonomously – this is known as off-grid. The infrastructure generally consists of a fusion of generation, storage and energy load management which makes them such a reliable and efficient power supply. Microgrid infrastructures have been implemented due to the remoteness of locations, lack of access to the national grid and economic reasons. Using local energy generation is a reliable alternative in times of crisis such as natural disasters and power outages.
Types of microgrids
A microgrid can be powered by a distribution of generators, batteries, and/or renewable resources like solar panels. Depending on how it’s fuelled, a microgrid can have zero emissions and provide electricity to communities with no carbon footprint. Energy sources such as steam/gas turbines and diesel generators have been the standard way of generating local power in a microgrid for many years. However, these have a negative impact on the environment as well as economic issues. The fossil fuels used to power these microgrids are expensive to purchase and transport, not to mention the transport has a carbon footprint in itself. This is a recurring issue for many communities that use diesel gensets. Given such consequences, microgrids are looking for cleaner alternatives.
Renewable microgrids are becoming increasingly popular and have been deployed across the world. They usually comprise photovoltaic (PV) solar panels, batteries, an electrolyser and a fuel cell. Such microgrids use the energy from solar panels to meet demand for electricity. When that has reached peak, solar panels charge the batteries (usually lead-acid or lithium-ion batteries). When the batteries are fully charged, excess solar from photovoltaic panels can power electrolysers/generators to produce green hydrogen. Hydrogen is an energy vector that can be stored for long periods of time without any losses. The hydrogen can be used by fuel cells to generate electricity, either to supply load or to recharge the lithium batteries. Hydrogen storage provides enough energy to satisfy demand for several days. To enhance the reliability of renewable microgrids, the use of built-in software, like the Enapter Energy Management System (EMS), is important. It unites the entire energy system, collecting and analysing data to make energy generation, storage and transmission much more predictable and balanced.
How a renewable microgrid works:
Microgrid energy storage
Energy storage is a flexible, versatile distributed energy resource that helps to stabilise a microgrid. The most common energy storage system (ESS) in a microgrid is a battery, however when used alone it lacks long term storage capabilities. Therefore, in a renewable microgrid, the battery ESS can be combined with hydrogen storage for a more resilient and efficient setup. Seasonal storage of green hydrogen is also an effective solution to replacing fossil fuels in a microgrid. It enables the transition to a completely clean and renewable microgrid. It accommodates yearly cycles in electricity demand and variable renewable energy sources, like solar and wind. During the winter months when there is less sun, green hydrogen that has been captured and stored during summer can be used to help meet electricity demand. Hydrogen storage is related to variations in weather which determine the heating and cooling demand as well as the generation of solar and wind power. It is therefore an instrumental part of a smart power system, bridging the gap between power generation and demand.
A renewable microgrid in action
Cirque de Mafate is a popular hiking destination located in the mountains of Réunion, a remote island in the Indian Ocean. As a classified UNESCO World Heritage site, it is home to 700 inhabitants. Due to the lack of
roads, Mafate is accessible only by foot. The microgrid on this island provides electricity through 100% renewable sources. The system is completely fossil free and comprises photovoltaic panels, lithium batteries, an Enapter AEM electrolyser for hydrogen production and storage, and a fuel cell. The electrolyser and fuel cell work together as a complete hydrogen system that generates and stores hydrogen. The power produced by solar panels is used first to satisfy demand. When that has reached peak, solar panels charge lithium-ion batteries, providing up to 5 days of autonomy for the local buildings. When the batteries are fully charged, excess solar from photovoltaic panels power AEM electrolysers to produce hydrogen. The hydrogen can be used by the fuel cells to generate electricity or to recharge the lithium batteries. Hydrogen storage provides a further 10 days of autonomy. In the case of a hurricane, the hybrid hydrogen setup has a total of 15 days autonomy. The system in Mafate services a school, several houses, a medical dispensary and a workshop. Since 2017, the community has benefited from electricity with no carbon footprint and entire energy independence. The hydrogen battery setup provides a very long term storage capacity. This guarantees continuous power for the residents and businesses, regardless of tropical climates and extreme weather conditions. Not to mention, it addresses the long term storage problem that batteries can’t live up to. With hydrogen production happening on-site, the remote island doesn’t pay for pollutant and expensive fossil fuels.
A microgrid not only provides backup for the grid in case of emergencies, but can also be used to cut costs or connect to a local resource that is too small or unreliable for traditional grid use. A microgrid allows communities to be more energy independent and, if powered by renewables, more environmentally friendly. Microgrids can manage energy supply efficiently and reduce costs or even provide local revenue streams. Hydrogen is the missing link, the final jigsaw piece, to complete renewable microgrids and provide the long-term seasonal storage needed.
For more information on microgrids, see our use cases.
by Aoibhin Quinn