|
|
| Fig. 1: Zoomed-in image of a 10 panel photovoltaic array for a 3 kW solar plus storage microgrid installation in village outside of Kuching, Sarawak, Malaysia. Image was taken August 10, 2018 about 11 am. (Source: C. Larios) |
Electricity in several areas of the world is distributed through centralized grids. However, as visions for decarbonizing carbon systems change, the demand for electricity has shifted toward distributed grids. [1] Decentralizing can come through microgrids. For this paper, a microgrid will be defined as a system that produces power locally and distributes it in the same geographic region. Microgrids can exist in various forms. The energy resources can include solar, wind, water, diesel, or more. Some include storage, and some include a grid management system to balance demand with supply. Some microgrids exist connected to a larger utility. [2] This paper will discuss various types and point out when and why variations have greater or worse success than others.
As power demand increases, development of network transmission is required, but due to the economic challenges, microgrids are being looked into as a viable alternative. [2] With the effort to increase energy equity, microgrids are being installed to help areas not connected to an electric grid and to provide energy security for areas in which the utilities are not reliable. [2,3] My mechanical engineering capstone was a project in partnership with NaturEdGrid, an organization providing renewable energy education and systems, to provide the Hang Lai Village in Hunan, China with a renewable energy plus storage microgrid system. Some team members visited the village and were told stories of how the extreme cold would freeze power lines and reduce overall availability of power. The village was secluded enough that repair would not come until several days later. In cases such as this village, where utility power was provided and insufficient, a microgrid can supply the demand. In a separate project I took part of with Engineers Without Borders Malaysia, the village we worked with was too secluded to be connected to utility power. The photovoltaic array for the installation can be seen in Fig. 1. With a solar plus storage microgrid, the community gained more reliable access to power. Therefore, a microgrid takes the place of utility when it fails to provide power equitably.
As smart technology develops, concern over energy security increases. Current centralized grids include high security levels because they face exposure to cyber attacks at various levels of the system, including generation, transmission and distribution. [4] In an attack like this, large geographic regions could be left without access to electricity and vulnerable to other power- related dangers. Regions with microgrids would be at lower risk, especially those with storage. [5] Although national security is one potential argument in favor of microgrids, I find other aspects more compelling.
Natural disaster and extreme weather events can result in blackouts and brownouts that leave communities without electricity, which has been seen time and time again. [6] Even excessive tree growth, combined with poorly maintained monitoring systems, can cause severe outage as was the case during the Northeast Blackout of 2003. [6] Power took up to 4 days to restore in some parts of the U.S. [6] In the United States, it is estimated that this outage cost between 4 and 10 billion US dollars. [6] The outage also affected Canada, costing them a loss of 0.7% in GDP for the month of August, a loss of 18.9 million work hours, and a reduction of 2.3 billion Canadian dollars in manufacturing shipments in Ontario. [6] With a decentralized grid, some of those 50 million people affected could have maintained power or have had the option to disconnect from the utility until power was restored. A microgrid has access to locally generated power and does not have to rely on a utility managing a large geographic region.
Renewable energy microgrids face the challenges of intermittency that come with wind and solar. A microgrid system without storage will be without power at night unless connected to an alternative source of energy. Even those with storage can go without electricity if the system is undersized or the system goes several days with inadequate generation. Utilities have the advantage of being connected to several energy resources. When solar generation decreases, natural gas or hydropower act as supply. Utilities have also developed agreements to share power. California has shared excess power generation with Arizona, Utah, and several other states, even paying them in an effort to reduce overloading power lines. [7] Thus, electricity from solar generation in California that is not in demand can be sent to other states to provide clean energy. Microgrids have been designed to be grid-connected or independent, and when renewable energy is intermittent, those that are independent must draw power another region, resulting in original issue of unreliability. However, local power generation does have advantages in reduced power losses. [2] Ultimately, while the rate of lost power does not change, shorter distances for transmission lines means less power is lost as the electricity reaches the end user.
One advantage a centralized grid has over a microgrid is the economics of scale. Though conflicting studies exist, microgrids are considered to be nonprofitable on a commercial level. [8] With renewable energy microgrids, a large investment cost reduces their adaptation, as well as their reduced savings in terms of unit of capacity. [8]
Despite the economies of scale, microgrids are being widely adapted to promote resiliency and reduce carbon emissions. The resilience is bolstered through the fact that microgrids do not have to be completely independent. [2] Some are connected to a centralized grid but have the capability to become a power island if the centralized grid loses power when a tree falls or during extreme weather events. [2] There are far more capabilities that can be discussed of microgrids beyond the contents of this paper. These include power control methods, load-side management, ability to have both direct and alternation current, and more. Ultimately, a variety a factors come into play when determining how beneficial a microgrid can truly be for a region, but as energy demand increases globally and natural events threaten the reliability of central grids, microgrids have an opportunity to step in.
© Celeste Larios. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] Y. Zhou and C. N.-M. Ho, "A Review on Microgrid Architectures and Control Methods," 2016 IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia) IEEE 7512799, 22 May 16.
[2] M. H. Andishgar, E. Gholipour, and R.-A. Hooshmand, "An Overview of Control Approaches of Inverter-based Microgrids in Islanding Mode of Operation," Renew. Sustain. Energy Rev. 80, 1043 (2017).
[3] A. Lopez-Gonzalez, B. Domenech, and L. Ferrer-Marti, "Sustainability and Design Assesment of Rural Hybrid Microgrids in Venezuela," Energy 159 229 (2018).
[4] S. Gholami, S. Saha, M. Aldeen, "A Cyber Attack Resilient Control for Distributed Energy Resources," 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), IEEE 8260213, 26 Sep 17.
[5] J. Nelson et al., "Statistical Development of Microgrid Resilience During Islanding Operations," Appl. Energy. 279 115724 (2020).
[6] "Final Report on the August 14, 2003 Blackout in the United States and Canada: Causes and Recommendations," U.S.-Canada Power System Outage Task Force, April 2004.
[7] I. Penn, "California Invested Heavily in Solar Power. Now There's So Much Other States Are Paid to Take it," Los Angeles Times, 22 Jun 17.
[8] R. Wang et al., "Renewable Energy Microgrids: Economic Evaluation and Decision Making for Government Policies to Contribute to Affordable and Clean Energy," Appl. Energy 274, 115287 (2020).