Variable renewable energy


Variable renewable energy is a renewable energy source that is non-dispatchable due to its fluctuating nature, like wind power and solar power, as opposed to a controllable renewable energy source such as dammed hydroelectricity, or biomass, or a relatively constant source such as geothermal power.

Terminology

Several key terms are useful for understanding the issue of intermittent power sources. These terms are not standardized, and variations may be used. Most of these terms also apply to traditional power plants.
is the least accurate of all of the variable renewable energy sources. Grid operators use day ahead forecasting to determine which of the available power sources to use the next day, and weather forecasting is used to predict the likely wind power and solar power output available. Although wind power forecasts have been used operationally for decades, as of 2019 the IEA is organizing international collaboration to further improve their accuracy. The variability of wind power can be seen as one of its defining characteristics.
monthly output over a two-year period
, Tamil Nadu, India
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. If wind speed is too low then the wind turbines will not be able to make electricity, and if it is too high the turbines will have to be shut down to avoid damage. 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.
Wind generates about 16% of electric energy in Spain and Portugal, 9% in Ireland, and 7% in Germany. Wind provides around 40% of the annual electricity generated in Denmark ; to meet this percentage Denmark exports surpluses and imports during shortfalls to and from the EU grid, particularly Norwegian Hydro, to balance supply with demand.
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 and by daily temperature variations. During the 2006 California heat wave output from wind power in California significantly decreased to an average of 4% of capacity for seven days. A similar result was seen during the 2003 European heat wave, when the output of wind power in France, Germany, and Spain fell below 10% during peak demand times. Heat waves are partially caused by large amounts of solar radiation.
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."
In Ontario, Canada, the Independent Electricity System Operator has been experimenting with dispatchable wind power to meet peak demands. In this case a number of wind generators are deliberately not connected to the grid, but are turning and ready to generate, and when the need for more power arises, they are connected to the grid. IESO is trying this as wind generators respond to sudden power demands much faster than gas-powered generators or hydroelectricity generators.

Solar power

is more predictable than wind power and less variable – while there is never any solar power available during the night, and there is a reduction in winter, the only unknown factors in predicting solar output each day is cloud cover, frost and snow. Many days in a row in some locations are relatively cloud free, just as many days in a row in either the same or other locations are overcast – leading to relatively high predictability. Wind comes from the uneven heating of the earth's surface, and can provide about 1% of the potential energy that is available from solar power. 86,000 TW of solar energy reaches the surface of the world vs. 870 TW in all of the world's winds. Total world demand is roughly 12 TW, many times less than the amount that could be generated from potential wind and solar resources. From 40 to 85 TW could be provided from wind and about 580 TW from solar.
Intermittency inherently affects solar energy, as the production of renewable electricity from solar sources depends on the amount of sunlight at a given place and time. Solar output varies throughout the day and through the seasons, and is affected by dust, fog, cloud cover, frost or snow. Many of the seasonal factors are fairly predictable, and some solar thermal systems make use of heat storage to produce grid power for a full day.
The impact of intermittency of solar-generated electricity will depend on the correlation of generation with demand. For example, solar thermal power plants such as Nevada Solar One are somewhat matched to summer peak loads in areas with significant cooling demands, such as the south-western United States. Thermal energy storage systems like the small Spanish Gemasolar Thermosolar Plant can improve the match between solar supply and local consumption. The improved capacity factor using thermal storage represents a decrease in maximum capacity, and extends the total time the system generates power.

Run-of-the-river hydroelectricity

In many European counties and North America the environmental movement has eliminated the construction of dams with large reservoirs. Run of the river projects have continued to be built, such as the 695MW Keeyask Project in Canada which began construction in 2014. The absence of a reservoir results in both seasonal and annual variations in electricity generated.

Tidal power

is the most predictable of all the variable renewable energy sources. Twice a day the tides vary 100%, but they are never intermittent, on the contrary they are completely reliable. It is estimated that Britain could obtain 20% of energy from tidal power, only 20 sites in the world have yet been identified as possible tidal power stations.

Wave power

Waves are primarily created by wind, so the power available from waves tends to follow that available from wind, but due to the mass of the water is less variable than wind power. Wind power is proportional to the cube of the wind speed, while wave power is proportional to the square of the wave height.

Coping with variability

Historically grid operators use day ahead forecasting to choose which power stations to make up demand each hour of the next day, and adjust this forecast at intervals as short as hourly or even every fifteen minutes to accommodate any changes. Typically only a small fraction of the total demand is provided as spinning reserve.
Some projections suggest that by 2030 almost all energy could come from non-dispatchable sources – how much wind or solar power is available depends on the weather conditions, and instead of turning on and off available sources becomes one of either storing or transmission of those sources to when they can be used or to where they can be used. Some excess available energy can be diverted to hydrogen production for use in ships and airplanes, a relatively long term energy storage, in a world where almost all of our energy comes from wind, water, and solar. Hydrogen is not an energy source, but is a storage medium. A cost analysis will need to be made between long distance transmission and excess capacity. The sun is always shining somewhere, and the wind is always blowing somewhere on the Earth, and during the 2020s or 2030s it is predicted to become cost effective to bring solar power from Australia to Singapore.
If excess capacity is created, the cost is increased because not all of the available output is used. For example, ERCOT predicts that 8.7% of nameplate wind capacity will be reliably available in summer – so if Texas, which has a peak summer demand of 68,379 MW built wind farms of
786,000 MW, they would generate, at a 35% capacity factor, 2.4 million MWh per year – four times use, but might be sufficient to meet summer peaks. In practice it is likely that there are times with almost no wind in the entire region, making this not a practical solution. There were 54 days in 2002 when there was little wind power available in Denmark. The estimated wind power installed capacity potential for Texas, using 100 meter wind turbines at 35% capacity factor, is 1,757,355.6 MW. In locations like British Columbia, with abundant water power resources, water power can always make up any shortfall in wind power.
Wind and solar are somewhat complementary. A comparison of the output of the solar panels and the wind turbine at the Massachusetts Maritime Academy shows the effect. In winter there tends to be more wind and less solar, and in summer more solar and less wind, and during the day more solar and less wind. There is always no solar at night, and there is often more wind at night than during the day, so solar can be used somewhat to fill in the peak demand in the day, and wind can supply much of the demand during the night. There is however a substantial need for storage and transmission to fill in the gaps between demand and supply.
As physicist Amory Lovins has said:

The variability of sun, wind and so on, turns out to be a non-problem if you do several sensible things. One is to diversify your renewables by technology, so that weather conditions bad for one kind are good for another. Second, you diversify by site so they're not all subject to the same weather pattern at the same time because they're in the same place. Third, you use standard weather forecasting techniques to forecast wind, sun and rain, and of course hydro operators do this right now. Fourth, you integrate all your resources — supply side and demand side..."

The combination of diversifying variable renewables by type and location, forecasting their variation, and integrating them with despatchable renewables, flexible fueled generators, and demand response can create a power system that has the potential to meet our needs reliably. Integrating ever-higher levels of renewables is being successfully demonstrated in the real world:

Variability and reliability

Mark A. Delucchi and Mark Z. Jacobson identify seven ways to design and operate variable renewable energy systems so that they will reliably satisfy electricity demand:
  1. interconnect geographically dispersed, naturally variable energy sources, which smoothes out electricity supply significantly.
  2. use complementary and non-variable energy sources to fill temporary gaps between demand and wind or solar generation.
  3. use “smart” demand-response management to shift flexible loads to a time when more renewable energy is available.
  4. store electric power, at the site of generation,, for later use.
  5. oversize renewable peak generation capacity to minimize the times when available renewable power is less than demand and to provide spare power to produce hydrogen for flexible transportation and heat uses.
  6. store electric power in electric-vehicle batteries, known as "vehicle to grid" or V2G.
  7. forecast the weather to better plan for energy supply needs.
Jacobson and Delucchi say that wind, water and solar power can be scaled up in cost-effective ways to meet our energy demands, freeing us from dependence on both fossil fuels and nuclear power. In 2009 they published “A Plan to Power 100 Percent of the Planet With Renewables” in Scientific American. A more detailed and updated technical analysis has been published as a two-part article in the refereed journal Energy Policy.
An article by Kroposki, et al. discuses the technical challenges and solutions to operating electric power systems with extremely high levels of variable renewable energy in IEEE Power and Energy Magazine. This article explains that there are important physical differences between power grids that are dominated by power electronic based sources such as wind and solar and conventional power grids based on synchronous generators. These systems must be properly design to address grid stability and reliability.
Renewable energy is naturally replenished and renewable power technologies increase energy security because they reduce dependence on foreign sources of fuel. Unlike power stations relying on uranium and recycled plutonium for fuel, they are not subject to the volatility of global fuel markets. Renewable power decentralises electricity supply and so minimises the need to produce, transport and store hazardous fuels; reliability of power generation is improved by producing power close to the energy consumer. An accidental or intentional outage affects a smaller amount of capacity than an outage at a larger power station.

Future prospects

The International Energy Agency says that there has been too much attention on issue of the variability of renewable electricity production. The issue of intermittent supply applies to popular renewable technologies, mainly wind power and solar photovoltaics, and its significance depends on a range of factors which include the market penetration of the renewables concerned, the balance of plant and the wider connectivity of the system, as well as the demand side flexibility. Variability will rarely be a barrier to increased renewable energy deployment when dispatchable generation is also available. But at high levels of market penetration it requires careful analysis and management, and additional costs may be required for back-up or system modification. Renewable electricity supply in the 20-50+% penetration range has already been implemented in several European systems, albeit in the context of an integrated European grid system:
In 2011, the Intergovernmental Panel on Climate Change, the world's leading climate researchers selected by the United Nations, said "as infrastructure and energy systems develop, in spite of the complexities, there are few, if any, fundamental technological limits to integrating a portfolio of renewable energy technologies to meet a majority share of total energy demand in locations where suitable renewable resources exist or can be supplied". IPCC scenarios "generally indicate that growth in renewable energy will be widespread around the world". The IPCC said that if governments were supportive, and the full complement of renewable energy technologies were deployed, renewable energy supply could account for almost 80% of the world's energy use within forty years. Rajendra Pachauri, chairman of the IPCC, said the necessary investment in renewables would cost only about 1% of global GDP annually. This approach could contain greenhouse gas levels to less than 450 parts per million, the safe level beyond which climate change becomes catastrophic and irreversible.

Intermittent energy source

An intermittent energy source is any source of energy that is not continuously available for conversion into electricity and outside direct control because the used primary energy cannot be stored. Intermittent energy sources may be predictable but cannot be dispatched to meet the demand of an electric power system.
The use of intermittent sources in an electric power system usually displaces storable primary energy that would otherwise be consumed by other power stations. Another option is to store electricity generated by non-dispatchable energy sources for later use when needed, e.g. in the form of pumped storage, compressed air or in batteries. A third option is the sector coupling e.g. by electric heating for district heating schemes.
The use of small amounts of intermittent power has little effect on grid operations. Using larger amounts of intermittent power may require upgrades or even a redesign of the grid infrastructure.

Solving intermittency

The penetration of intermittent renewables in most power grids is low, global electricity production in 2014 was supplied by 3.1% wind, and 1% solar. Wind generates roughly 16% of electric energy in Spain and Portugal, 15.3% in Ireland, and 7% in Germany., wind provides 39% of the electricity generated in Denmark. To operate with this level of penetration, Denmark exports surpluses and imports during shortfalls to and from neighbouring countries, particularly hydroelectric power from Norway, to balance supply with demand. It also uses large numbers of combined heat and power stations which can rapidly adjust output.
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. Combining this with energy storage and demand response can create a power system that can reliably match real-time energy demand. The integration of ever-higher levels of renewables has already been successfully demonstrated:
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 variability of contributions from individual wind farms is determined mainly by locally generated small scale boundary layer. The low frequency variability 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. More than 95% of the remaining variability of the coupled system is concentrated at time scales longer than a day, allowing operators to take advantage of multi-day weather forecasts in scheduling projected contributions from wind.

Technological solutions to mitigate large-scale wind energy type intermittency exist such as increased interconnection, Demand response, load management, diesel generators, and use of existing power stations on standby. 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. For a hypothetical European-wide power grid, analysis has shown that wind energy penetration levels as high as 70% are viable, and that the cost of the extra transmission lines would be only around 10% of the turbine cost, yielding power at around present day prices. Smaller grids may be less tolerant to high levels of penetration.
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. The International Energy Agency states:
"In the case of wind power, operational reserve is the additional generating reserve needed to ensure that differences between forecast and actual volumes of generation and demand can be met. 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..."
With sufficient energy storage, highly variable and intermittent sources can supply all of a regions electrical power. For solar to provide half of all electricity and using a solar capacity factor of 20%, the total capacity for solar would be 250% of the grids average daily load. For wind to provide half of all electricity and using a wind capacity factor of 30% the total capacity for wind would be 160% of the grids average daily load.
A pumped storage facility would then store enough water for the grids weekly load, with a capacity for peak demand i.e.:200% of the grid average. 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.
interconnectors and hydrogen are predicted to be used much more for export of VRE.

Compensating for variability

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 used to meet regular and unanticipated supply demands. Additionally, the storage of energy to fill the shortfall intermittency or for emergencies can be part of a reliable power supply.

Operational reserve

All managed grids already have existing operational and "spinning" reserve to compensate for existing uncertainties in the power grid. The addition of intermittent resources such as wind does not require 100% "back-up" because operating reserves and balancing requirements are calculated on a system-wide basis, and not dedicated to a specific generating plant.
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.

Geographic diversity

The variability of production from a single wind turbine can be high. Combining any additional number of turbines 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. Wind output can be predicted with some degree of confidence using weather forecasts, especially from large numbers of turbines/farms. The ability to predict wind output is expected to increase over time as data is collected, especially from newer facilities.

Complementary power sources and matching demand

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. Ideally the capacity of the intermittents would grow to be larger than consumer demand for periods of time, creating excess low price electricity to displace heating fuels or be converted to mechanical or chemical storage for later use.
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 source in an electric power system, expressed as a percentage. There are several methods of calculation yielding different penetrations. The penetration can be calculated either as:
  1. the nominal capacity of a PE source divided by the peak load within an electric power system; or
  2. the nominal capacity of a PE source divided by the total capacity of the electric power system; or
  3. the electrical energy generated by a PE source in a given period, divided by the demand of the electric power system in this period.
The level of penetration of intermittent variable sources is significant for the following reasons:
Renewable electricity supply in the 20-50+% penetration range has already been implemented in several European systems, albeit in the context of an integrated European grid system:
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."

Maximum penetration limits

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.
High penetration scenarios may be feasible in certain circumstances:
Studies have been conducted to assess the viability of specific penetration levels in specific energy markets.

European super grid

A series of detailed modelling studies by Dr. Gregor Czisch, which looked at the European wide adoption of renewable energy and interlinking power grids the European super grid using HVDC cables, indicates that the entire European power usage could come from renewables, with 70% total energy from wind at the same sort of costs or lower than at present. This proposed large European power grid has been called a "super grid".
The model deals with intermittent power issues by using base-load renewables such as hydroelectric and biomass for a substantial portion of the remaining 30% and by heavy use of HVDC to shift power from windy areas to non-windy areas. The report states that "electricity transport proves to be one of the keys to an economical electricity supply" and underscores the importance of "international co-operation in the field of renewable energy use transmission".
Dr. Czisch described the concept in an interview, saying "For example, if we look at wind energy in Europe. We have a winter wind region where the maximum production is in winter and in the Sahara region in northern Africa the highest wind production is in the summer and if you combine both, you come quite close to the needs of the people living in the whole area - let's say from northern Russia down to the southern part of the Sahara."

Grid study in Ireland

A study of the grid in Ireland indicates that it would be feasible to accommodate 42% renewables
in the electricity mix. This acceptable level of renewable penetration was found in what the study called Scenario 5, provided 47% of electrical capacity with the following mix of renewable energies:
The study cautions that various assumptions were made that "may have understated dispatch restrictions, resulting in an underestimation of operational costs, required wind curtailment, and CO2 emissions" and that "The limitations of the study may overstate the technical feasibility of the portfolios analyzed..."
Scenario 6, which proposed renewables providing 59% of electrical capacity and 54% of demand had problems. Scenario 6 proposed the following mix of renewable energies:
The study found that for Scenario 6, "a significant number of hours characterized by extreme system situations occurred where load and reserve requirements could not be met. The results of the network study indicated that for such extreme renewable penetration scenarios, a system re-design is required, rather than a reinforcement exercise." The study declined to analyze the cost effectiveness of the required changes because "determination of costs and benefits had become extremely dependent on the assumptions made" and this uncertainty would have impacted the robustness of the results.

Canada

A study published in October 2006, by the Ontario Independent Electric System Operator found that "there would be minimal system operation impacts for levels of wind capacity up to 5,000 MW," which corresponds to a peak penetration of 17%

Denmark

A November 2006 analysis, found that "wind power may be able to cover more than 50% of the Danish electricity consumption in 2025" under conditions of high oil prices and higher costs for CO2 allowances. Denmark's two grids each incorporate high-capacity interconnectors to neighbouring grids where some of the variations from wind are absorbed. In 2012 the Danish government adopted a plan to increase the share of electricity production from wind to 50% by 2020, and to 84% in 2035.

Economic impacts of variability

Estimates of the cost of wind energy may include estimates of the "external" costs of wind variability, or be limited to the cost of production. All electrical plant has costs that are separate from the cost of production, including, for example, the cost of any necessary transmission capacity or reserve capacity in case of loss of generating capacity. Many types of generation, particularly fossil fuel derived, will also have cost externalities such as pollution, greenhouse gas emission, and habitat destruction which are generally not directly accounted for. The magnitude of the economic impacts is debated and will vary by location, but is expected to rise with higher penetration levels. At low penetration levels, costs such as operating reserve and balancing costs are believed to be insignificant.
Intermittency may introduce additional costs that are distinct from or of a different magnitude than for traditional generation types. These may include:
Studies have been performed to determine the costs of variability.

Britain

The British electricity system will be capable of operating zero-carbon by 2025, with only renewables and nuclear, and the company, National Grid Electricity System Operator, claims the overall cost of operating the system will be reduced.

Intermittency and renewable energy

There are differing views about some sources of renewable energy and intermittency. The World Nuclear Association argues that system costs escalate with increasing proportion of variable renewables. Proponents of renewable energy use argue that the issue of intermittency of renewables is over-stated, and that practical experience demonstrates this. In any case, geothermal renewable energy has, like nuclear, no intermittency.
The U.S. Federal Energy Regulatory Commission Chairman Jon Wellinghoff has stated that "baseload capacity is going to become an anachronism" and that no new nuclear or coal plants may ever be needed in the United States. Some renewable electricity sources have identical variability to coal-fired power stations, so they are base-load, and can be integrated into the electricity supply system without any additional back-up. Examples include:
Grid operators in countries like Denmark and Spain integrate large quantities of renewable energy into their electricity grids, with Denmark receiving 40% of its electricity from wind power. For the month of February 2020, the grid in eastern Germany had an average of 85% power from wind and solar.
Supporters say that the total electricity generated from a large-scale array of dispersed wind farms, located in different wind regimes, cannot be accurately described as intermittent, because it does not start up or switch off instantaneously at irregular intervals. With a small amount of supplementary peak-load plant, which operates infrequently, large-scale distributed wind power can substitute for some base-load power and be equally reliable.
Hydropower can be intermittent and/or dispatchable, depending on the configuration of the plant. Typical hydroelectric plants in the dam configuration may have substantial storage capacity, and be considered dispatchable. Run of the river hydroelectric generation will typically have limited or no storage capacity, and will be variable on a seasonal or annual basis.
Amory Lovins suggests a few basic strategies to deal with these issues:
Moreover, efficient energy use and energy conservation measures can reliably reduce demand for base-load and peak-load electricity.
International groups are studying much higher penetrations, and conclusions are that these levels are also technically feasible.
Methods to manage wind power integration range from those that are commonly used at present to potential new technologies for grid energy storage. Improved forecasting can also contribute as the daily and seasonal variations in wind and solar sources are to some extent predictable. The Pembina Institute and the World Wide Fund for Nature state in the Renewable is Doable plan that resilience is a feature of renewable energy: