The improved capacity factor using thermal storage represents a decrease in maximum capacity, and extends the total time the system generates power. Wind-generated power is a variable resource, and the amount of electricity produced at any given point in time by a given plant will depend on wind speeds, air density, and turbine characteristics among other factors.
If wind speed is too low less than about 2. While the output from a single turbine can vary greatly and rapidly as local wind speeds vary, as more turbines are connected over larger and larger areas the average power output becomes less variable. Because wind power is generated by large numbers of small generators, individual failures do not have large impacts on power grids.
This feature of wind has been referred to as resiliency. Wind power is affected by air temperature because colder air is more dense and therefore more effective at producing wind power. As a result, wind power is affected seasonally more output in winter than summer and by daily temperature variations. According to an article in EnergyPulse, "the development and expansion of well-functioning day-ahead and real time markets will provide an effective means of dealing with the variability of wind generation.
Several authors have said that no energy resource is totally reliable. Amory Lovins says that nuclear power plants are intermittent in that they will sometimes fail unexpectedly, often for long periods of time. The penetration of intermittent renewables in most power grids is low, global electricity production in was supplied by 3. The intermittency and variability of renewable energy sources can be reduced and accommodated by diversifying their technology type and geographical location, forecasting their variation, and integrating them with dispatchable renewables such as hydropower, geothermal, and biomass.
Combining this with energy storage and demand response can create a power system that can reliably match real-time energy demand. In , eight American and three European authorities, writing in the leading electrical engineers' professional journal, didn't find "a credible and firm technical limit to the amount of wind energy that can be accommodated by electricity grids".
In Fact, not one of more than international studies, nor official studies for the eastern and western U. A research group at Harvard University quantified the meteorologically defined limits to reduction in the variability of outputs from a coupled wind farm system in the Central US:. The problem with the output from a single wind farm located in any particular region is that it is variable on time scales ranging from minutes to days posing difficulties for incorporating relevant outputs into an integrated power system.
The high frequency shorter than once per day variability of contributions from individual wind farms is determined mainly by locally generated small scale boundary layer.
The low frequency variability longer than once per day is associated with the passage of transient waves in the atmosphere with a characteristic time scale of several days.
The high frequency variability of wind-generated power can be significantly reduced by coupling outputs from 5 to 10 wind farms distributed uniformly over a ten state region of the Central US. Jacobson has studied how wind, water and solar technologies can be integrated to provide the majority of the world's energy needs.
Because the wind blows during stormy conditions when the sun does not shine and the sun often shines on calm days with little wind, combining wind and solar can go a long way toward meeting demand, especially when geothermal provides a steady base and hydroelectric can be called on to fill in the gaps. Delucchi and Mark Z. Jacobson argue that there are at least seven ways to design and operate renewable energy systems so that they will reliably satisfy electricity demand: Studies by academics and grid operators indicate that the cost of compensating for intermittency is expected to be high at levels of penetration above the low levels currently in use today    Large, distributed power grids are better able to deal with high levels of penetration than small, isolated grids.
Matching power demand to supply is not a problem specific to intermittent power sources. Existing power grids already contain elements of uncertainty including sudden and large changes in demand and unforeseen power plant failures. Though power grids are already designed to have some capacity in excess of projected peak demand to deal with these problems, significant upgrades may be required to accommodate large amounts of intermittent power. Again, it has to be noted that already significant amounts of this reserve are operating on the grid due to the general safety and quality demands of the grid.
Wind imposes additional demands only inasmuch as it increases variability and unpredictability. However, these factors are nothing completely new to system operators.
By adding another variable, wind power changes the degree of uncertainty, but not the kind A pumped storage facility would then store enough water for the grids weekly load, with a capacity for peak demand i. This would allow for one week of overcast and windless conditions. There are unusual costs associated with building storage and total generating capacity being six times the grid average.
All sources of electrical power have some degree of variability, as do demand patterns which routinely drive large swings in the amount of electricity that suppliers feed into the grid. Wherever possible, grid operations procedures are designed to match supply with demand at high levels of reliability, and the tools to influence supply and demand are well-developed.
The introduction of large amounts of highly variable power generation may require changes to existing procedures and additional investments. The capacity of a reliable renewable power supply, can be fulfilled by the use of backup or extra infrastructure and technology , using mixed renewables to produce electricity above the intermittent average , which may be utilised to meet regular and unanticipated supply demands.
All managed grids already have existing operational and "spinning" reserve to compensate for existing uncertainties in the power grid. At times of low load where non-dispatchable output from wind and solar may be high, grid stability requires lowering the output of various dispatchable generating sources or even increasing controllable loads, possibly by using energy storage to time-shift output to times of higher demand. Such mechanisms can include:.
Storage of electrical energy results in some lost energy because storage and retrieval are not perfectly efficient. Storage may also require substantial capital investment and space for storage facilities. The variability of production from a single wind turbine can be high. Combining any additional number of turbines for example, in a wind farm results in lower statistical variation, as long as the correlation between the output of each turbine is imperfect, and the correlations are always imperfect due to the distance between each turbine.
Similarly, geographically distant wind turbines or wind farms have lower correlations, reducing overall variability. Since wind power is dependent on weather systems, there is a limit to the benefit of this geographic diversity for any power system. Multiple wind farms spread over a wide geographic area and gridded together produce power more constantly and with less variability than smaller installations.
The ability to predict wind output is expected to increase over time as data is collected, especially from newer facilities. In the past electrical generation was mostly dispatchable and consumer demand led how much and when to dispatch power. The trend in adding intermittent sources such as wind, solar, and run-of-river hydro means the grid is beginning to be led by the intermittent supply. The use of intermittent sources relies on electric power grids that are carefully managed, for instance using highly dispatchable generation that is able to shut itself down whenever an intermittent source starts to generate power, and to successfully startup without warning when the intermittents stop generating.
The displaced dispatchable generation could be coal, natural gas, biomass, nuclear, geothermal or storage hydro. Rather than starting and stopping nuclear or geothermal it is cheaper to use them as constant base load power. Any power generated in excess of demand can displace heating fuels, be converted to storage or sold to another grid. Biofuels and conventional hydro can be saved for later when intermittents are not generating power.
Alternatives to burning coal and natural gas which produce fewer greenhouse gases may eventually make fossil fuels a stranded asset that is left in the ground. Highly integrated grids favor flexibility and performance over cost, resulting in more plants that operate for fewer hours and lower capacity factors.
Penetration refers to the proportion of a primary energy PE source in an electric power system, expressed as a percentage. The penetration can be calculated either as: The level of penetration of intermittent variable sources is significant for the following reasons:. There is no generally accepted maximum level of penetration, as each system's capacity to compensate for intermittency differs, and the systems themselves will change over time.
Discussion of acceptable or unacceptable penetration figures should be treated and used with caution, as the relevance or significance will be highly dependent on local factors, grid structure and management, and existing generation capacity. For most systems worldwide, existing penetration levels are significantly lower than practical or theoretical maximums; for example, a UK study found that "it is clear that intermittent generation need not compromise electricity system reliability at any level of penetration foreseeable in Britain over the next 20 years, although it may increase costs.
There is no generally accepted maximum penetration of wind energy that would be feasible in any given grid. Rather, economic efficiency and cost considerations are more likely to dominate as critical factors; technical solutions may allow higher penetration levels to be considered in future, particularly if cost considerations are secondary. Manufacturing A guide to manufacturing.
What is Batch Production? The difference between batch production and mass production. The difference between a production line and assembly line. A definition of continuous process with examples. What is Takt Time? The definition of make to stock with examples.
The common types of production process. A definition of production run with examples. A definition of continuous production with examples. The definition of cell production with examples. In continuous production system, production process is not flexible. The same product is manufactured continuously.
In intermittent production system, goods are produced on a small scale, so there is no economies of scale. In continuous Production System, goods are produced on a large scale, so there are economies of large-scale production. In intermittent production system, cost per unit may be higher because production is done on a small-scale.
In continuous production system, cost per unit may be lower because production is done on large-scale. In intermittent production system, wide ranges of products are manufactured. In continuous production system, normally one particular type of product is manufactured.
In an intermittent production system, many detailed instructions must be provided depending upon the customer's specification. In continuous production system, single set of instructions is sufficient for operation.
A manufacturing method of producing several different products using the same production line. Once an initial production line has run, a second product will be produced which increases the amount of productivity a company is capable of at one time.
In continuous Production System, goods are produced on a large scale, so there are economies of large-scale production. Per unit cost: In intermittent production system, cost per unit may be higher because production is done on a small-scale.
Intermittent production system Intermittent means something that starts (initiates) and stops (halts) at irregular (unfixed) intervals (time gaps). In the intermittent production system, goods are produced based on customer's orders. Intermittent production is the common practice of using the same production line to produce different types of goods. The following are illustrative examples.
A intermittent production process a production process in which the production run is short and machines are changed frequently to make different products. Intermittent Production System According to E.S Buffa, intermittent production situations are those where the facilities must be flexible enough to handle a variety of products and sizes, or where the basic nature of the activity imposes change of important characteristics of the input (e.g., change in .