Base load power plant
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Base load (also baseload) is the minimum level of demand on an electrical supply system over 24-hours: the load that exists 24 hours a day.
A base load power plant (or base load power station) is one that is best suited to serving this load because it takes a long time to start up and is relatively inefficient at less than full output. These plants run at all times through the year except in the case of repairs or scheduled maintenance.
Each base load power plant on a grid is allotted a specific amount of the baseload power demand to handle. The base load power is determined by the load duration curve of the system. For a typical power system, the rule of thumb is that the base load power is usually 35-40% of the maximum load during the year.[citation needed]
Peaks or spikes in customer power demand are handled by smaller and more responsive types of power plants.
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[edit] Base load power plant usage
Nuclear and coal power plants may take many hours, if not days, to achieve a steady state power output. On the other hand, they have low fuel costs. Since they require a long period of time to heat up to operating temperature, these plants typically handle large amounts of baseload demand. Different plants and technologies may have differing capacities to increase or decrease output on demand: nuclear plants are generally run at close to peak output continuously (apart from maintenance, refueling and periodic refurbishment), while coal-fired plants may be cycled over the course of a day to meet demand[citation needed]. Plants with multiple generating units may be used as a group to improve the "fit" with demand, by operating each unit as close to peak efficiency as possible.
[edit] Peaking power plant usage
Natural gas and oil power plants are much faster to start, but have much higher fuel costs. These plants are typically scheduled to handle peak power demands since they can be ready to supply power in 30 minutes or less. They are more expensive to operate than coal power plants, primarily due to higher fuel costs.
Hydroelectric power is the fastest to respond to increasing power demands, reaching full power in about two to three minutes. These plants can provide both base load and peak load demands for power at a relatively low cost, but are limited by the amount of water available and other considerations, such as water demand for municipal or irrigation sources, or the need to limit water discharge for flood control reasons.
A special case of hydroelectric power is pumped storage, where excess power from base load plants is used to drive pumps that fill an artificial or natural reservoir. When power demand exceeds base load capacity, the pumps become generators, feeding the stored energy of the stored water back into the grid, much like a very large storage battery.
Certain other types of plant may be intermittent or linked to other uses, which may limit cycling. For example, combined heat and power plants are typically most economical when used to produce both heat and electricity, and therefore represent base load electrical power only when the heat produced is in demand. Similarly, solar and wind power plants generally only produce useful amounts of electricity when conditions are right. When the sun sets or the wind calms, their output drops, regardless of the demand for electricity.
[edit] Load balancing
- See also: Load balancing (electrical power)
By moving peak loads to non-peak times, the output of base load power plants can be used more efficiently. Power companies use several techniques to shift demand and balance the load:
- Demand pricing - A power company installs special electric meters, particularly for its heaviest users, such as industry. These meters record not only how much electricity was consumed in all, but at what time the consumption took place. A higher price is assessed for power consumed during peak times than off-peak times, which encourages users to shift their operating patterns to demand the most electricity at off-peak times, if possible.
- Load shedding - In this case, it is remote-control switchgear that power companies use to remove large loads from the system. In ordinary usage, it is large industrial users who get their electricity on reduced tarrifs in return for agreeing to have their power cut during periods of exceptional demand. In emergencies, the power demand of large numbers of consumers can be shed from the system, either by planned rolling blackouts or by unplanned power cuts.
- Brownouts - Power companies can, in times of exceptional demand, deliberately reduce the line voltage on the power grid. Also, sudden spikes in demand can cause unplanned reductions in line voltage. Because of Ohm's law, reducing the voltage reduces the demand for power, lessening peak load. This is not an ideal method, however. Lowered voltage reduces the efficiency of electrical equipment and can, if lowered far enough, damage electric motors and other devices.
