Underground pumped hydro storage to increase renewables and the efficiency of thermal power plants

Illustration - Principle of the underground pumped hydro storage proposed by Pierre Couture. It can store power and regulate variations in renewable energy, among others, and is an essential component of intelligent electricity networks of tomorrow. (Illustration: Paul Berryman, from my book Driving Without Oil)

On 5 March 2009, Steven Chu, the United States Secretary of State for Energy, stated before a Senate committee his government's priorities in research and development. Five areas were identified and the storage of energy on a large scale is one of them. Storage units of appropriate size would compensate for daily variations of solar and wind, and increase the efficiency of thermal power plants. Energy storage is a key element to reduce greenhouse gas emissions as well of toxic emissions associated with electricity production.

Currently, the most used technology for large-scale storage of energy is pumped hydro. In its traditional version, there are two water tanks located one above the other, connected by an underground tunnel which houses a turbine that can operate in both directions. During periods of low electricity demand (eg at night) the electric motor-generator coupled to the turbine pump water from the lower reservoir to upper reservoir. In periods of high demand, we let the water flow from upper to the lower reservoir, which causes the turbine to generate electricity. In a well designed power plant, the movements of water between the two reservoirs cause a loss of about 20% of stored energy.

But to regulate the daily fluctuations of wind and solar power or to control the variations in demand throughout the day, we do not need to store more than 25% of the energy produced. Hence, regulation leads to a loss of only 5% of the total energy produced.


Illustration - Principle of a traditional pumped hydro storage facility. (source: Wikimedia Commons)

There are currently about 200 pumped storage facilities on the planet, totaling 90 GW of power, or about 3% of the installed capacity at the global level, according to the ESA (Electricity Storage Association).

The obligation to have a significant height difference between the two water tanks has brought many people to say that pumped hydro storage is a technology that could not operate on a large scale. As proof, the following statement

"Expanded use of this technology depends on the availability of suitable geography"

found in the "National Energy Policy Recommendations" of the IEEE-USA (Institute of Electrical and Electronics Engineers), dated 15 January 2009 (download HERE under the heading Energy and Environment).

But it seems that such an assertion is a lack of imagination, because one can very well build pumped hydro storage in the midst of vast plains or in the heart of a city. Just dig a deep well in the rock and build galleries at the bottom to get the second tank.

This is the concept which was proposed by Pierre Couture, a researcher for Hydro-Quebec and inventor of the modern wheel motor (previous post). Louis-Gilles Francoeur, journalist at Le Devoir has unveiled the project in an article dated 22 January 2004.

To avoid too large excavation for the galleries, it is expedient to settle at a greater depth. Pierre Couture recommended digging a well about 2 meters in diameter and three kilometers deep. Turbines that can be reversed and also act as pumps are placed at every kilometer going down, with a buffer cave behind each group of turbine-generators assembly (see illustration at the top of the post).

Calculations show that for a 1 GW of power lasting 10 hours, one must have 3 kilometers (1.9 miles) of galleries with a 20 meters x 20 meters (65 feet x 65 feet) opening, that is 1.2 million cubic meters, to store water at the bottom. The cost of such a plant would be in the range of $ 700 million to $1,000 million, and could regulate power plants with nameplate power of 3 to 4 GW.

If the facility lasts 50 years, we arrive ultimately at a cost below 0.2 cents / kWh of energy produced and regulated, which is only a few percent of the production cost.

Such pumped hydro storage facilities can be used in multiple ways. One can, of course, increase the percentage of renewable energies on a grid by regulating their inherent fluctuations. To reduce the need for too large storage facilities, we need to set up power lines to connect wind farms over thousands of kilometers, because there is always wind somewhere. The high voltage DC power lines are particularly interesting in this regard since they generate only 3% loss per 1000 km (600 miles). As for the solar power plants, they follow quite well the daily demand for electricity (more sun at noon). By placing them in desert areas, one ensures a minimum of cloud cover, which requires less storage of energy for the fluctuations. Most of the storage would be used to postpone to the night a part of the energy produced in the day.

Furthermore, pumped hydro is also interesting to increase the efficiency of thermal power plants. We know, for example, that gas-fired combined cycle plants can achieve an efficiency of 60%. Unfortunately we can not vary significantly the power of such plants to follow daily demand. We must use for that gas power plants whose efficiency is less than 40%. Thus we see all the benefits of coupling a pumped hydro storage to one or more gas-fired power plants. We could then use the most efficient combined cycle gas-fired power plants operating at constant optimal conditions. The daily fluctuations would be managed by the pumped hydro facility. In doing so, we would obtain 50% more electricity with the same natural gas!

With the additional electricity recovered one could close much dirtier coal power plants, waiting to close also, over time, the gas power plants and replace them with renewable energy.

Pumped hydro storage is an essential element of any smart energy policy! And with the underground concept proposed by Pierre Couture, it will become more and more interesting.

The great importance of wheel-motors

Illustration - Representation of a wheel-motor similar to those developed by the team of Pierre Couture at Hydro-Québec and presented to the public in 1994. The author of this blog has drawn it from public information contained in the promotional materials and patents.

Quebecers over 30 years old remember seeing on television in 1994 and 1995 a revolutionary experimental car equipped with high performance electric wheel-motors. It was a Chrysler Intrepid transformed by researchers from Hydro-Quebec, under the direction of Dr. Pierre Couture, a brilliant physicist ahead of its time, the main inventor of this power train, unmatched so far. The press conference to announce this brilliant technology took place on December 1st, 1994. To see the flyer distributed on that occasion click HERE, and to read the transcription in english of Pierre Couture’s speech explainaing the technology ckick HERE.

The basic idea was to convert the Intrepid in a plug-in hybrid car. By recharging the battery during the night at home, the owner of the car could travel 65 km (40 miles) in electric mode for each day without consuming fuel. For journeys longer than 65 km (40 miles), a small fuel engine activates a generator to recharge the battery while driving, giving the car a range similar to that of a traditional car. This is what we call today a series hybrid vehicle, whose fuel engine is not mechanically connected to the wheels. Furthermore, since 80% of people drive less than 65 km (miles) per day with their car, on average, the vast majority of their mileage would be done with electricity.

It is this concept that is used by GM in its Chevy Volt, which should be commercialized in 2011. However, the Chevy Volt is not equipped with wheel-motors, but with a central electric motor under the hood. This makes the car heavier and more expensive, while consuming more electricity and leaving less space available for the passengers and the trunk.

Unfortunately, in 1995 Hydro-Quebec has taken a completely incomprehensible decision to significantly reduce its proposed development of Couture’s power train, which led to the resignation of its inventor in 1995. Pierre Couture has never worked on this project since. The TM4 company, a subsidiary of Hydro-Québec, which was set up to commercialize the Couture power train with 4 wheel-motors, hence its name (Technology Motor 4 “wheels”), has stopped working on the high power wheel-motor for all practical purposes and works now mainly on central electric motors, like everyone else.

The author of this blog is absolutely convinced that the wheel-motor power trains, similar to the one developed by Pierre Couture, are the best and will be the power trains of the future. Here's why.

First, looking at the illustration above, we find that the permanent magnets (green and orange) are fixed near the rim of the wheel, giving the motor a large diameter, which increases its torque and power. There are of course other innovations designed by Pierre Couture that contribute to its high efficiency (above 96%), with a power greater than 100 kW (134 hp) and a torque of 1200 N.m (885 lbs-ft) for each motor, which was 2.5 times more than a Corvette engine of the time! The total power with 4 wheel-motors would have exceed 400 kW and the total torque 4800 N.m, which would have propel the Chrysler Intrepid from 0 to 100 km / h (0-60 mph) in 3 seconds, according to calculations by Pierre Couture!

The performance of these wheel-motors have been tested in the laboratory, but at the time of the resignation of Dr. Couture, only 2 wheel-motors were installed on the Intrepid and the power electronics was not yet complete, hence the impossibility to have full testing on the road. However, the illustration below shows a field test where the two motorized wheels were spinning while remaining on the spot and burning rubber. This performance was simply not possible with the V8 engine of the original Chrysler Intrepid.


Illustration - Images from the TV program Découverte broadcasted by Radio-Canada in 1997. (Photo: Archives of Radio-Canada)

The goal of having such powerful motors was not to race but to recover more of the car kinetic energy when braking, even suddenly. With four wheel-motors and good batteries we can recover nearly 90% of the kinetic energy since the four motors act as four powerful electromagnetic brakes that produce electricity to recharge the battery. This is called regenerative braking. In traditional cars, the kinetic energy is lost in heat in the mechanical brakes. Now, in an electric car with a central motor, we can only recover 20% to 25% of the kinetic energy when braking. This is because the electric motor is connected to two wheels only, while we must have four brakes, and because the motor being located behind a differential we must have mechanical brakes even on the two motorized wheels. Otherwise if one wheel is on ice, the driver could lose control of the car.

Moreover, with four wheel-motors, there is no differential neither transmission. It is a direct drive, and there is no energy loss between the motor and wheels, as in a car with central engine. This is a second reason why wheel-motors consume less energy, particularly during cold winters.

Moreover, since energy consumption is lower, we can reduce the size of the battery, engine-generator and fuel tank. Besides the wheel-motors themselves are lighter than a central electric motor of equivalent power, since their external structures fulfill a dual function, serving also to support structure to the wheels. The reduction of the car weight is therefore a third cause of reduction in energy consumption.

Now, the fact that with wheel-motors there is no motor under the hood allows us to taper the front of the car and close the underside. These changes improve aerodynamics and provide a fourth contribution to reducing its energy consumption.

These four factors combine to give an energy consumption in urban driving about 35% less than a car having a central electric motor, and about 15% lower when driving on the highway. In mixed driving, we obtain a reduction in consumption of around 25% with four wheel-motors. THIS IS A BIG DIFFERENCE, ESPECIALLY FOR URBAN CARS, TRUCKS AND BUSES! This reduced energy consumption affects not only the operating cost of vehicles but also the purchase cost, since the battery (very expensive) and the engine (for plug-in hybrids) can be scaled down considerably. Moreover the wheel-motor vehicles have significantly less parts (no differential, no transmission, no cardans, no ABS braking hardware).

BESIDES, NOT ONLY THE WHEEL-MOTOR CARS ARE THE MOST ENERGY-EFFICIENT BUT THEY ARE ALSO THE MORE POWERFUL, WHICH IS REALLY A PARADIGM SHIFT. James Bond and Al Gore could carpool together in a wheel-motor car and the two would be very happy!

In closing, it would be good to mention four other advantages of wheel-motors that are not related to energy consumption or power. The fact that there is no engine under the hood increases the crush zone of the metal during a frontal impact, improving the safety of passengers. Furthermore, the lack of engine under the hood gives more flexibility to the car designers. Also, with four wheel-motors, we can incorporate an anti-skidding system and an ABS braking system only by software. Finally, the driver has a four-wheel drive vehicle, which is quite popular in winter in the nordic countries, and well appreciated by those who drive off-road.

High speed monorails instead of high speed trains

ILLUSTRATION - Artistic View of a high speed monorail equipped with wheel-motors, as designed by Pierre Couture at the beginning of the years 1990s. Illustration taken from my latest book «Rouler sans pétrole»(Driving without oil). (Drawing: Paul Berryman)

The author of this blog who has lived in France for two years knows how much the TGV (from the French expression «Train à Grande Vitesse», High Speed Train) are comfortable and faster than the plane for travels of less than 1000 km, taking into account the loss of time at airports and between airports and city centers.

But the establishment of a high speed railroad line costs around 15 million euros/km (15 M€/km) in France, or 23 M CDN $/km (29 M US $/mile). In the Nordic countries such as Canada, it is necessary to have deeper foundations for the railroads in the event of freezing and thawing, and the bill could climb to more than 30 M CDN $/km (37 M US $/mile). The cost of a high-speed train between two cities 250 km (156 miles) apart could very well exceed 7.5 billion CDN $ (5.8 billion US $). To make such infrastructures worth it requires a high population density, while in countries like Canada there are few populous cities far apart.

This problem of fast interurban transportation was the subject of much thoughts from Pierre Couture, the inventor of modern wheel-motor (with the Institut de Recherche d'Hydro-Quebec in 1994). It led him to a concept quite revolutionary. Judge for yourself.

To minimize the foundation works for the tracks which must be resistant to frost, the solution proposed by Pierre Couture is to build a lightweight monorail with two lanes suspended to the same structure, itself supported by poles every 60 meters (180 feet) or so. The self-propelling cars, suspended and powered by 16 wheel-motors, are capable of carrying sixty passengers and travel apart from each other at a speed of 250 km/hour (155 miles/hour).

To avoid having to expropriate land for the lines, the monorails are constructed between the two lines of a highway. The surfaces used on the ground are just a few square meters every sixty meters. For tight turns, it would suffice to overflow slightly plots and tilt the rails. Since the wheels are equipped with rubber tires, they offer a better grip than the iron wheels of trains, allowing the monorail to climb the slopes of highways and step over crossing bridges. The I beam on which the motorized wheels roll is embodyed from the top by a light enclosure, that protects the rail-beam from snow falls.

When you think of it, this light and fast monorail would greatly benefit all over the world, not only in cold countries. Especially as the cost of infrastructure is at least 3 times lower than that of a TGV (High Speed Train), given the little work done with the ground, the absence of expropriation, and construction of structures in automated factories, 12 months a year ! We could develop these monorails only with the money saved by introducing a line of 250 km, since this line would cost about $ 5 billion less than a TGV! Thereafter, the commercialization of this technology would quickly recover the investment.

These light and fast monorails would also be ideal for connecting downtowns to airports, or for people transit across a river to reduce the traffic congestions on bridges at rush hour. We only have to hang the monorail guiding lines on the side structures of bridges. Such a service of public transportation is much less expensive than a subway under the river.

Who will do it?