Power capacity is the maximum amount of power that an electric line can transmit, and it varies with distance and voltage. The longer the distance, the lower the power capacity of the line due a drop in voltage. For example, a line with a 100-mile length has a maximum capacity of 3.8 GW. In contrast, a line with a 400-mile length has a maximum capacity of 2.0 GW (Amin & Stringer, 2008, p. 400). The higher the voltage, the higher the capacity of the lines since high voltages produce more heat that is likely to cause sagging of the lines. The amount of electricity flowing through a transmission line is, usually, less than its maximum capacity to ensure spare capacity during periods of unpredicted surges in consumer demand. Factors that limit the capacity of the lines include thermal limit and mechanical strength (Amin & Stringer, 2008, p. 401). Thermal limit is the temperature beyond which the line begins to sag. As electricity flows through the line, it begins to sag and may pose a danger to consumers. Mechanical strength refers to the conductor’s ability to support the weight of the line. Thus, a conductor with a higher strength-to-weight ratio for a specific current increases the line’s capacity.
Power capacity plays an important role in constructing an electric grid. Anderson (2014) defines an electric grid as “a network of transmission and distribution lines” that connects power sources with consumers. Transmission lines connect power plants to substations located near a group of consumers while distribution lines transmit power from substations to individual households. Usually, electric lines transmit high voltage electricity to minimize energy losses. The electric grid consists of lines of varying lengths such as short lines, intermediate lines and long-distance lines. Short lines transmitting high voltage currents require conductors with high capacity to prevent sagging or damage because of overheating. Intermediate and long-distance lines have lower capacities than short lines because of a drop in voltage as the distance gets longer. Consequently, the grid consists of transformers and capacitors that boost up the voltage, and maintain stability in power supply over long distances.
Despite the effectiveness of electric grid systems, many challenges exist that may interfere with their normal operations such as weather patterns, seasonal maintenance, emergency conditions and increased demand (Anderson, 2014). Weather patterns resulting in very high temperatures during the day heats up electric lines, therefore, contributing to sagging. Seasonal maintenance of power lines and other grid components, usually, result in power interruptions that cause losses since electricity cannot be stored once generated. Emergency conditions such as unexpected breakdown in several generators or transformers at once also cause power interruptions and losses. Finally, demand for electricity has increased greatly in recent years due to population growth, congestion in urban areas, and increase in disposable income. Favorable economic conditions have increased disposable income causing people to purchase electrical appliances and homes with additional lighting spaces. Such demand has strained the existing grid transmission capacity (Anderson, 2014).
A major limitation of electricity is that it cannot be stored. The pumped-hydro energy storage overcomes this weakness by pumping water uphill and releasing it when needed to generate electricity. During off-peak hours, low-cost electricity pumps water from a lower reservoir to a higher reservoir. The higher reservoir stores energy in the “form of gravitational potential energy of water” (International Electrotechnical Commission (IEC), 2012). The water flows down the hill during peak hours to generate electricity that consumers buy at a premium. The benefits of pumped-hydro storage include cost-effectiveness, compensates for variations in renewable energy sources, and maintains power reliability (IEC, 2012). Firstly, cost-effectiveness stems from the difference between the premium price during peak hours and the low-cost in off-peak hours. Hence, huge savings in operational costs result. Secondly, energy supply from renewable energy sources such as solar and wind is highly volatile due to changing weather patterns. The pumped-hydro storage fills this gap in periods when weather patterns do not favor energy generation from renewable sources. Thirdly, pumped-hydro storage system maintains reliability by running average load rather than peak load, thus, lessening the strain on electric grids. As a result, the lines transmit power that is below their capacity, thus minimizing overheating. In addition, the system can quickly respond to demand changes during emergencies.
Research into the integration of thermal/hydro energy systems is still underway. Thermal energy systems involve obtaining heat energy from a large body of water. The key benefit that would result from such integration is additional power capacity. During off-peak hours when electricity demand is low, thermal energy generated at full capacity can supplement power demand. The additional capacity will cut operational costs and minimize energy losses along the transmission lines.
Work cited
Amin, M., & Stringer, J. “The Electric Power Grid: Today and Tomorrow.” MRS Bulletin 33. (2008): 399-407. Available at: http://www.massoud-amin.umn.edu/publications/The_Grid_Amin_Stringer.pdf
International Electrotechnical Commission (IEC). “Pumped-Storage Key t Energy Storage.” (2012). Available at: http://www.iec.ch/etech/2012/etech_1112/tech-1.htm
Richard, Anderson. “Energy Storage: The Key to a Smaller Power Grid.” BBC News 23 April. 2014. Available at: http://www.bbc.com/news/business-27071303
