Intermittent Energy Source - Solving Intermittency

Solving Intermittency

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:

In 2009, 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 200 international studies, nor official studies for the eastern and western U.S. regions, nor the International Energy Agency, has found major costs or technical barriers to reliably integrating up to 30% variable renewable supplies into the grid, and in some studies much more.

Mark Z. Jacobson has studied how wind, water and solar technologies can be integrated to provide the majority of the world's energy needs. He advocates a "smart mix" of renewable energy sources to reliably meet electricity demand:

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.

Mark A. 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:

1. interconnect geographically dispersed naturally variable energy sources (e.g., wind, solar, wave, tidal), which smooths out electricity supply (and demand) significantly.
2. use complementary and non-variable energy sources (such as hydroelectric power) 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, (in batteries, hydrogen gas, compressed air, pumped hydroelectric power, and flywheels), for later use.
5. over-size 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 (winds, sunlight, waves, tides and precipitation) to better plan for energy supply needs.

Technological solutions to mitigate large-scale wind energy type intermittency exist such as increased interconnection (the European super grid), Demand response, load management, diesel generators (in the British National Grid, Frequency Response / National Grid Reserve Service type schemes, 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 (IEA) 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..."