Power Demand Variations and Balancing the power systems Electricity Demand varies and its not constant all the time.
There is some demand variation patterns discussed below: Daily patterns:Power demand in an hour of day varies, the peak demand occurs from 7am to 10pm. In working days. And in rest of the hours the demand is less. Seasonal patterns: Demand levels during the summer and winter months tend to be higher than demand levels during the fall and spring seasons when system demand for space conditioning (heating or cooling) is low. The annual peak of hourly, daily, and monthly demand typically occurs during the winter or summer.
In Norway, annual peak occurs during winter. To balance these variations in load, Load balancing is done. Load balancing refers to the use of various techniques by power stations to store excess power during low demand periods and release it when demand rises. (Loring Chien,(Jun 20117), ‘why there is load variation in power systems’)(https://www.quora.
com/Why-is-there-load-variation-in-a-power-system)Lecture Slide, Prof. Brian Glover, (Jan, 2018) Base load supplyBase load plant is an energy station which is used for the production of base load supply. Baseload plants are the production facilities used to meet some or all of a given region’s continuous energy demand, and produce energy at a constant rate, usually at a low cost relative to other production facilities available to the system. Nuclear plants, Coal fired plants, Oil fired steam generators, Thermal sources such as biogas, bagasse, combined heat and power, Gas fired combined cycle (gas turbines and steam turbine working in combination), Multi-purpose hydro e.g. combined with irrigation dams or water supply can be some of the base load plants. Baseload plants typically run at all times through the year except in the case of repairs or maintenance. These plants are often designed for relatively high efficiency, and may be combined cycle plants, but may take several days to start up and shut down.
(Energy Dictionary, energyvortex.com) Hydropower as a flexible Load following Power plantLoad following power plant is a power plant that adjusts its power output as demand for electricity fluctuates throughout the day. Load following power plants run during the day and early evening. They either shut down or greatly curtail output during the night and early morning, when the demand for electricity is the lowest. The exact hours of operation depend on numerous factors.
One of the most important factors for a particular plant is how efficiently it can convert fuel into electricity. The most efficient plants, which are almost invariably the least costly to run per kilowatt-hour produced, are brought online first. As demand increases, the next most efficient plants are brought on line and so on. Gas turbine power plants, Diesel and gas engine power plants, Hydropower with daily regulating reservoir pondage or larger reservoir, Pump storage plants, are the typical examples of load following power plants. Hydropower could be one of the most flexible power plant with the demand variation in load. Hydroelectric power plants can operate as base load, load following or peaking power plants. They have the ability to start within minutes, and in some cases seconds. Lakes and manmade reservoirs used for hydropower come in all sizes, holding enough water for as little as a one-day supply, or as much as a whole year’s supply.
A plant with a reservoir that holds less than the annual river flow may change its operating style depending on the season of the year. For example, the plant may operate as a peaking plant during the dry season, as a base load plant during the wet season and as a load following plant between seasons. A plant with a large reservoir may operate independently of wet and dry seasons, such as operating at maximum capacity during peak heating or cooling seasons.
(Renewable and Efficient Electric Power Systems By Gilbert M. Masters p. 140) Pump Storage Power Plants for supplying fluctuating energy demand The EU has agreed to undertake major cuts in greenhouse emissions and to increase power generations from renewable energy sources. Wind power will make up much of Europe’s future Power generation. Several major projects are already being constructed and planned on the continent in the north sea and along the UK coast line. Wind power can only be generated when the wind is blowing and variations are considered over time. These variations do not always correspond with the consumption.
A large share of wind power would represent a major challenge to stability of the transmission systems and the security of supply for the consumers. There is a need for backup capacity in order to generate power in days with no wind and high demand. There is also a need of storage capacity for surplus power on days with strong wind and low demand.
In Norway, with its long history of hydropower generation, we find half of Europe’s reservoir capacity. New pump storage power plants in connection with existing reservoir could be a part of solution in securing a reliable energy system. On windy days surplus power could be used to pump water from low to high altitude reservoir. This water could in turn be released to generate power on days when demand is high and wind levels are low. The cycle can be repeated over and over again. In order to use Norwegian Hydropower as rechargeable batteries for the European power supply more transmission capacity must be established between Norway and the major European consumption areas. Pump storage power solution must be developed in such a way that the environmental impacts are reduced to a minimum. The climate threat is a global challenge, the further development of Norwegian Hydropower can contribute a more reliable and a cleaner European energy supply.
(statkraft, pumped-storage-hydropower, statkraft.com/energy-sources/hydropower) Nordlink, The green link Nordlink is a proposed subsea cables between Norway and Germany over 500km which has a capacity of 1400 MW and an operational voltage of 500 KV. The new connection would be tested in late 2019, and operational in 2020. Different patterns of generation with large thermal and growing wind power on the Continent versus large hydro capacities in Northern Europe are expected to offer mutual benefits, however on the other hand there may be some risk of worsening existing bottlenecks in the grid.(Statnet, nord.link, “Status of transnational project”)Connecting Norwegian hydropower to German wind energy will be benefitial for both countries.
When for instance a surplus of wind energy is produced in Germany, this can be exported to Norway via NordLink. The water reservoirs in Norway will then function as natural storage for wind energy by retaining the water in the reservoirs. Likewise, Germany can import the renewable Norwegian hydropower when demand is high. (statnett,Feb-2015,”Green light for Nordlink”)