PUMPED HYDRO AND NEW ENERGY

Wind-Hydro Integration: Pumped Storage to Support Wind
Fernando Perán Montero and Juan J. Pérez, June 1, 2010 (HydroWorld)

THE POINT
Back in the 1980s, before the variable New Energies – most notably wind and solar – commonly sent the electricity they generate to the grid, they were labeled “intermittent” and the perception developed that they are undependable because “the sun doesn’t always shine and the wind doesn’t always blow.” That is about as relevant a way to think about solar and wind today as is Madonna’s cone bra a way to think about today’s women’s lingerie.

Anybody who says wind and sun will not be substantial sources of power generation until there is adequate and economic storage for them is either uninformed or an adversary. The proof is what is happening with wind in Denmark, in Spain, in Iowa and in Texas.

A recent study from the U.S. Department of Energy (DOE) National Renewable Energy Laboratory (NREL) found that by 2017 the U.S. grid will be ready to utilize enough wind power to generate 30% of its electricity, along with enough solar energy to meet another 5% of the demand on it – WITHOUT any storage. In fact, the study found that under current circumstances no large scale storage – even pumped hydro storage (PHS), the most cost effective right now – would be economically advantageous. (See OVER A THIRD OF POWER FROM NEW ENERGY – STUDY)

One day last month, Texas got 14% of its power from wind energy-generated electricity, despite the fact that there is no storage. But that’s just the beginning. Last year, Iowa got a daily average of 14% of its power from wind for the whole year. Denmark got 20% of its power from wind last year. And one day this year Spain got over HALF of its electricity from wind power.

Spain’s New Energy installed capacity grew astonishingly fast in the 2005-to-2008 boom period. Its generation potential is so big that, when all factors are favorable, it tests the limits of what a system can do with New Energy and raises anew the question of storage. Even the NREL study suggests that the over-50%-levels of New Energy Spain is consuming might benefit from storage that is economically viable. Which is why – as detailed in Wind-Hydro Integration: Pumped Storage to Support Wind by Iberdrola engineers Fernando Perán Montero and Juan J. Pérez, Iberdrola - Spain’s biggest wind developer and one of the biggest in the world - has already built hundreds of megawatts of pumped storage and is committed to building thousands more.

Schematic of the concept (click to enlarge)

For pumped hydro storage, water is pumped uphill using excess electricity at low, off-peak prices. It is held in a reservoir. When there is an increase in energy demand, the water is released to flow downhill. The energy of the flowing water is recaptured to generate high-price, peak-demand electricity with a traditional hydroelectric mechanism that puts turbines into the water's flow.

According to the report, Iberdrola’s experience with its 635-megawatt La Muela pumped-storage plant in Spain has proven that, second to naturally occurring hydroelectric resources of which there are few remaining development opportunities, pumped storage is the most cost effective way to “firm” wind’s variability. Iberdrola is now building an 852-megawatt La Muela 2 facility in Spain and, by 2018, will have 1,750 megawatts of electricity storage in Spain and Portugal.

Interesting aside: At levels of New Energy up to 35%, the NREL report found grid operators only had to (1) expand the region from which they draw wind and solar power, (2) make power purchases more frequently than every hour, (3) utilize advanced forecasting capabilities, and (4) increase the use of demand response (DR) programs. Storage and new transmission would not cost effective.

The energy that would most benefit from more storage capacity (and new transmission) is nuclear, because it only has two speeds, full and off. Nuclear plants would therefore become significantly more cost effective if it could store power during off-peak hours when prices are low and do its planned servicing shutdowns during peak periods. Since the so-called “nuclear renaissance” has been most stymied by the skyrocketing costs of new plants, the availability of economically viable storage would dramatically lower nuclear's calculated levelized cost of electricity (LCOE) and thereby likely attract potential investors.

Iberdrola's 635-megawatt La Muela pumped storage facility (click to enlarge)

THE DETAILS
The accurate description of wind and solar is “stochastic.” That is much more precisely defined as “variable” than as “intermittent.” It is not accurate to say that wind and solar cannot be stored or even that electricity cannot be stored. It is true, though, that the energy from wind and solar is expensive to store in large quantities as heat or compressed air and that electricity is very expensive to store in large quantities in batteries, flywheels or comparable forms.

In the wake of rising European concerns about dependence on fossil fuels that (1) must be purchased from a hostile and dominating Russia or the Mid-East, and/or (2) are the source of greenhouse gas and other emissions that are unhealthy for the planet and its people, Europe has been building New Energy generating capacity as fast as it can.

World wind installed capacity at the end of 2009 was nearly 158,505 megawatts. More than 38,340 megawatts of this capacity was added in 2009.

Spain added 2,459 megawatts in 2009 and has 19,149 megawatts of installed wind power capacity that supplies, on average, well over 10% its electricity.

click to enlarge

Iberdrola is the largest producer of wind energy in the world. At the end of 2008, the company had an installed wind capacity of 9,302 megawatts globally, including 4,526 megawatts in Spain. Iberdrola has a further 54,000+ megawatts of new capacity in some developmental stage.

For Iberdrola, wind power presents challenges which they divide into long-term and short-term factors.

Long term factor: High demand can come when wind production (load level) is low, such as during the heat of the afternoon, and wind installation output is often at a high load level during off peak periods such as the very early morning. For Spain, the 2005-to-2007 average load level was 21% but the load factor (the part of the net output capacity that actually becomes electricity) ranged from 2.5% to 70%. This means that sometimes other types of generation must replace wind.

Short term factor: Because rate payer demand is variable, all sources must ramp up and down according to a weekly and daily schedule that is altered by real time demand. Every generation unit is scheduled for start up and shutdown times to meet demand using predicted weather and demand patterns and the lowest cost power source.

Storage is not needed in the U.S. at present. (click to enlarge)

Coal and gas plants take a relatively long time to come on and go off. While they are ramping up and down, energy is being wasted and cost grows. Conventional and pumped hydro and wind can come on and go off quickly, with little lost to fuel cost.

Power managers allot a 25% uncertainty factor for wind with a confidence of 70% accuracy. That means Spain’s 13,836 megawatts have an uncertainty level of ±3,460 megawatts in the weekly schedule. Nine 400-megawatt fossil fuel (usually combined cycle natural gas) plants would be needed to protect against (“firm”) this uncertainty.

For day-ahead purchases of the 13,836 megawatts of wind, planning uncertainty requires ±15%, or 2,075 megawatts (five 400-megawatt fossil fuel plants).

The final undetermined level of uncertainty is met with on-going (usually every 3-to-24 hours ahead) power purchases.

Spain uses a secondary reserve system and a tertiary reserve mechanism to handle these uncertainties, which put conventional hydro, pumped storage, conventional thermal, gas, and combined cycle plants through a series of start ups and shutdowns.

Iberdrola's La Muela 2 under construction. (click to enlarge)

To choose the wisest firming strategy, Iberdrola considered each type of power’s (1) Start-up and shutdown capacity, (2) Regulation velocity (in percent load per minute), and (3) Technical minimum load (in percent of maximum load).

Advantages of conventional hydro plants: (1) Greater flexibility in continuous start ups and shutdowns without significant harm to generating equipment; (2) higher speed changing of loads (up to 100% per minute); (3) minimum load of 10% or less; (4) zero fuel cost; (5) zero greenhouse gas emissions (GhGs).

Disadvantages of conventional hydro plants: (1) Potential environmental impacts on local river systems, (2) potential water supply impacts on local river system communities, and (3) potential water shortages leading to energy supply shortages associated with drought conditions.

The biggest problem: Most conventional hydro resources, especially those in developed economies, have already been exploited.

Pumped hydro storage have all the same advantages as conventional hydro but are not limited by the disadvantages and offer much opportunity for new development.

An Okinawa pumped storage facility that uses sea water (click to enlarge)

The only disadvantage is the cost. Energy must be used to pump water up to the reservoir. Iberdrola calculations put the efficiency of the system – in cost terms – at 75%. Perhaps the energy returned on the energy invested is not this efficient, but by pumping the water with off-peak price electricity and using it to generate peak price electricity, the return on the investment makes it cost-effective. There is a comparable saving of GhGs.

Conventional coal, open cycle and closed cycle natural gas plants have significantly slower start-up and shutdown capabilities that lead to significant fuel costs, making them significantly less advantageous as reserves.

Combined cycle natural gas plants are the most flexible and cost-effective of the “conventional thermal” fossil fuel options.

Iberdrola’s capacities and plans: (1) Iberdrola has ~10,000 megawatts of hydro capacity internationally, ~8,800 megawatts of it in Spain (almost half (47%) of that nation’s installed hydro capacity). 2,300+ megawatts of Iberdrola's hydro is pumped storage. This gives Iberdrola a great deal of practical experience with hydro and pumped storage.

Iberdrola is so favorable on pumped storage as a partner for wind that it is actively seeking sites. Choosing sites where costs can be kept down is the foremost challenge.

click to enlarge

The 635-megawatt La Muela 1 pumped storage facility is presently operational. Construction began on the 852-megawatt La Muela 2 pumped storage facility in 2006 and it is expected to be operational in 2012.

La Muela 2 will have four sets of Alstom generators and Voith Hydro pump-turbines. The contractor is Fomento de Construcciones y Contratas, S.A. (FCC) of Spain. A consortium (Alstom, Sacyr Vallehermoso, and Cavosa) will supply penstock. Ingenieria y Construccion S.A.U. (Iberinco) is doing the engineering.

Iberdrola is also planning to develop the Alto Tomega 1,200 megawatt hydroelectric complex in Portugal. Construction could begin as soon as this year and completion is scheduled for 2018. Alto Tomega will have four dams. Two power stations will be conventional hydro and two will be pumped storage. One pumped storage plant will be the 779-megawatt Gouvaes facility and the other will be the 112-megawatt Pradoselos facility. Iberdrola is also looking at other potential pumped storage sites, including the proposed 750-megawatt Santa Cristina facility in Spain.

Perán Montero and Pérez are electrical engineers in Iberdrola’s hydropower generating division and Perán Montero is in charge of electromechanical engineering for La Muela 2. Pérez was previously in Iberdrola’s energy management division.

$744 per kilowatt cost estimate for a 9GW proposal (click to enlarge)

QUOTES
- From Perán Montero and Juan J. Pérez, Wind-Hydro Integration: Pumped Storage: “Wind power is a generating technology that is included in many countries’ electrical systems and permits a substantial reduction in emissions of greenhouse gases. However, the increasing penetration of this technology in current electricity systems requires a substantial increase in the resources required to balance generation and demand, as well as additional investments to guarantee the continuity of electricity supply when wind intensity is low.”

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- From Perán Montero and Juan J. Pérez, Wind-Hydro Integration: Pumped Storage: “There are several existing generation technologies available to firm the variability of wind capacity. At Iberdrola, we believe the best operational option is pumped storage, which is always available and provides significant flexibility with regard to start ups and shutdowns. Iberdrola is building the 852-MW La Muela 2 pumped-storage plant for this purpose and is investigating construction of three additional pumped-storage plants with a total capacity of 1,640 MW.”