Whether in offshore islands, remote uninhabited areas, or densely populated urban buildings, communities and factories, people are increasingly seeing distributed energy applications. For example, distributed photovoltaic, wind power and diesel generator micro-grid, to ensure all the energy needs of fishermen on remote islands; another example, natural gas cooling, heating and power (CCHP), distributed renewable energy technology is integrated into the urban community micro grid system, providing residents and enterprises with locally produced and cost-effective electricity, hot water and cooling services.
Thanks in large part to the rise of microgrids, the choice of energy services is no longer limited to the centralized supply of the municipal grid. This also allows for the establishment of distributed energy supply systems for remote islands and frontier areas outside the municipal grid, as well as for energy users with special requirements for economy, security, and environmental protection, according to their respective needs in a location close to the customer side.
Why Microgrids Are Needed?
"Microgrid" is a concept relative to the traditional "big grid", which refers to the use of advanced control technology and power electronic devices to connect distributed energy and its energy supply load and energy storage equipment to form a miniature complete grid. (For more information on microgrid, please read "What is a microgrid system?")
This "micro" grid is a complete power system from generation, transmission and transformation to the end-user, and can either form a fully functional local energy network on its own, operating "off-grid" without interfering with the transmission and distribution system, or it can be connected to the municipal grid through a common connection point. It can also be connected to the municipal grid through a common connection point: when the microgrid power supply is insufficient, it can supplement the shortage through the grid, and when the power generation is large, it can feed the excess power back to the grid. When necessary, the two modes can be switched, which fully maintains the safe and stable operation of the microgrid and the grid.
As a collection of various distributed energy sources, "microgrid" technology has a wide development space and application scenarios. In a complete micro-grid system, distributed energy sources are used as the main energy suppliers on the power generation side, and different types of energy sources can complement each other; on the power consumption side, the system monitors and controls the power load; at the control system level, the micro grid needs internal scheduling and external communication to achieve a high degree of autonomy; cooling, heat storage and electric energy storage make the micro-grid both safe and flexible.
Microgrids can be classified as off-grid or On-grid according to whether they are connected to the grid or not. Off-grid microgrids can be used to solve the problems of islands and remote areas, while grid-connected microgrids add security to customers' energy supply and improve the economic efficiency of the system.
Distributed Energy in Offshore Island Microgrid Application
The Isle of Eigg in Scotland, UK, is an example of a successful off-grid microgrid application on an island.
The local microgrid makes full use of local natural resources, with a power generation system consisting mainly of distributed photovoltaic, small wind and hydroelectric facilities with a total installed capacity of 184 kW. Excess renewable power is stored in battery arrays, which can provide a full day's power for the entire island in poor weather conditions. The microgrid also includes two 70 kW diesel generators for emergencies. The installed capacity of the system is not large, but it is enough to meet the power needs of nearly 100 residents, making it a "small but beautiful" island micro-grid.
In the microgrid, various energy sources operate together in different seasons and at different times of the year, and the multi-energy complementary system has become the best configuration of Ege Island's power system.
Thanks to the high latitude, Egger Island enjoys a long period of sunshine in summer, and with less rainfall in summer, the utilization rate of photovoltaic system is also increased. Due to the weather, the wind and hydroelectric power generation in summer is not very good, and the residents consume all the electricity throughout the day from PV and storage batteries, and only in a few cases, such as the increase of tourists, the backup diesel generator starts to supply electricity. In winter, when the island receives more rainfall, three small hydroelectric generators become the main source of power. The control system of the Egger Island microgrid monitors the operation of the power generation facilities, optimizes the charging and discharging cycle of the batteries, and automatically starts the diesel generators in case of power shortage.
The microgrid has greatly improved the quality of electricity consumption on Ege Island.
Before the microgrid was built, residents relied on their own diesel generators to supply electricity, paying high costs while enduring the noise and air pollution from the equipment. The island relied on ferries to transport diesel fuel, and households with limited reserves were at risk of losing power. Today, the microgrid ensures an uninterrupted power supply on Eger Island, where more than 90% of annual electricity consumption comes from renewable sources and CO2 emissions are reduced by nearly half.
On the other hand, the island's microgrid has demonstrated excellent economics. The design and construction cost of the whole project was about £1.66 million, while the cost of erecting the grid across the sea was more than 4 million; currently, the price of electricity on Eigg Island is still higher than the UK average, but it has been reduced by 60% compared to the past. The effective integration of wind, light, water and storage has freed residents from the constraints of fossil energy, and the experience of Eigg Island proves that off-grid island microgrids can meet the electricity needs of modern life.
Application of Distributed Energy in Microgrids in Remote Areas
In addition to improving the existing power supply system, off-grid microgrids are an important part of achieving universal access to electricity in areas without electricity.
According to the International Energy Agency (IEA), as of 2014, 1.2 billion people worldwide still lacked access to electricity. In India, the number of people without electricity reached 240 million, or about 20 percent of the country's population, the vast majority of whom live in remote rural areas, posing a significant technical and economic challenge to the Indian government's national electrification program. Bihar is one of the states with the largest power deficit in India, with 79% of rural households in the state without access to electricity and more than half of them not connected to the grid; other so-called "electrified" households rely on a single diesel generator, which makes the region particularly dependent on diesel, raising energy costs and contributing to air pollution.
A distributed energy system with photovoltaics as the primary and diesel generators as the backup could solve the electricity problem in these remote areas.
Researchers at the Indian Institute of Technology have developed a photovoltaic microgrid for rural households that includes a 125-watt solar panel, a 1-kilowatt-hour energy storage battery, a control box and DC appliances. Unlike ordinary AC electricity, this household micro-grid operates on DC power, avoiding the energy loss caused by AC/DC conversion between PV, batteries and appliances. The cost of the whole system is lower and the power supply is more reliable than the grid-based approach.
Homes already connected to the municipal grid can also use it as a high-quality backup power source, eliminating the hassle caused by frequent grid outages. The researchers have also developed 500-watt and 7.5-kilowatt microgrids covering multiple households. Currently, this system has provided electricity to more than 4,000 rural households.
In rural communities in Bihar, distributed PV, energy storage batteries and existing diesel generators form a microgrid system that provides reliable power to customers while reducing the cost of electricity, and the substitution of PV makes the system more economical at a time when diesel prices are high.
Currently, most microgrids and stand-alone power systems in India still use diesel generators, but the decreasing cost of distributed photovoltaic and locally adapted small-scale hydro and wind power facilities are emerging as economic and environmental benefits, which are particularly important in rural areas. Off-grid microgrids will play a key role in the electrification of India, and the technology is worth spreading to other unelectrified areas around the world.
Distributed Energy in Urban Community Microgrids
If off-grid microgrids are a must for islands and remote areas to achieve universal access to electricity, the development of microgrid systems in cities with reliable grid coverage will be the icing on the cake.
Grid-connected microgrids can switch between grid-connected and stand-alone operation. When the grid fails, the microgrid can choose to be disconnected from the grid to protect the energy supply of customers in the region; when it chooses to operate on the grid, the microgrid can also sell excess power and demand response to gain additional economic benefits.
The grid-connected microgrid meets the energy needs of Co-Op City, New York, the largest residential housing complex in the United States, and secures the system during extreme weather conditions. The core equipment of the project is a gas turbine, steam turbine, and control system capable of providing combined cooling, heating, and power (CCHP). With a total installed capacity of 40 megawatts, the station can meet the peak demand of 24 megawatts of electricity for all 60,000 residents, while the remaining 16 megawatts of capacity is sold to the larger grid.
During Hurricane Sandy, which swept through the East Coast of the United States in October 2012 and caused widespread power outages, United Apartment City's microgrid continued to provide power to 60,000 residents without being affected. In addition to Apartment City, New York University and Princeton University in the hurricane landfall area were equipped with microgrids based on natural gas distributed energy stations, and both universities were disconnected from the grid and switched to "island mode" to ensure energy supply to the campus during the municipal grid outage. These examples demonstrate the stability of microgrid systems.
Thanks to the advanced microgrid system, Algonquin College in Ottawa, Canada, has been able to significantly reduce its energy costs. It is worth mentioning that the microgrid system's distributed energy microgrid system management platform (MGMS), which integrates building automation and load management technologies, has a maximum capacity of over 10 million data points, monitors and records the energy consumption of the campus buildings, and remotely controls HVAC, lighting and other facilities to improve the energy efficiency of the buildings without affecting normal teaching and learning.
The on-campus microgrid is mainly powered by a natural gas CCHP unit with a capacity of 4 MW, as well as distributed photovoltaic, energy storage and electric vehicle charging stations, but the power generated is slightly below the peak load of the campus. When stand-alone operation is required, the control system will identify and curtail unnecessary loads, allowing the microgrid to transition smoothly to islanding mode.
On the other hand, the control system will also adjust the proportion of power supplied on campus based on price fluctuations in the energy market. As the price of electricity in the local market changes hourly, the algorithm of the control system can predict the load of the microgrid, compare the combined cost of CCHP units and grid power, and ultimately choose the most economical and reliable solution.
Through the microgrid and other energy-saving technologies, Algonquin College saves up to $3.2 million annually in operating costs. In addition, the independence of the microgrid allows the college to participate in the utility's demand response program, proactively increasing its energy self-sufficiency during periods of grid constraint and reducing the campus' demand for grid power, thereby receiving financial incentives from the utility. With the microgrid, Algonquin College will become more efficient, economical and clean.
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