Reinventing the Wheel

A 2002 EU hydropower survey, found 100 GW, or 450 TW/h per year, of hydropower in Europe that was technically – but not economically - exploitable.

Much of the power that drove the first industrial revolution is available today, but is not exploited. In Germany in 1927 there were more than 35,000 water mills still in operation. A further 25,000 were registered in England and around 100,000 are estimated to have been in operation in France.

Outside Europe, there are many times more small scale unexploited hydropower sources. There are 63,000 km of large irrigation canals in Pakistan with heads of 0.3 to 2.5 meters every few kilometers, offering an unused potential somewhere between 5 GW and 15 GW. And there are thousands of kilometers of similar irrigation canals in India, Australia, the US, and other countries. A 2004 survey of the US estimated there is approximately 21 GW of low head, low power sites and 26 GW of high head low power sites that could be exploited – not necessarily economically.

Traditional waterwheels are still in production – at least two companies are building them in Germany. But their return on investment is probably close to 20 years.

However, there are some interesting innovations from European research teams and companies that are bringing more water sources into the ‘economical’ category.

A French company, MJ2 Technologies, has installed 15 of its innovative Very Low Head turbine systems (VLH) on larger rivers in France and Italy. A further two machines are about to go into operation in Belgium. The VLH turbine is designed for heads of 1.9 – 3.2 meters, but with at least 10m3 of water flowing past the turbine every second. It is not uncommon for MJ2 to install two or more VLH turbines together.

The VLH uses a Kaplan turbine that is much larger than the standard Kaplan. The units are between 3.15 and 5 meters in diameter. That results in some loss in turbine efficiency, but there also is a major advantage. The VLH turbine can generate its power from slower moving bodies of water. Therefore it does not need expensive largescale earthworks to channel and concentrate the waterflow. The VLH turbines deliver between 100kW and 500kW each. It is also built in a modular way, with a hinged lifting system to make installation and maintenance as easy and cheap as possible. The slow movement has ecological advantages as well. Following recent design modifications and scientific testing, fish can pass through the moving turbine blades completely unharmed.

The direct drive system and variable speed permanent magnet generator draws on technology that has been refined for the wind turbine industry. “Our project could not have been developed 15 years ago,” says MJ2 Director Marc LeClerc. “It is not so much that we are using advanced technologies as crossing existing technologies and putting them together in one unit.”

With European feed-in tariffs, the VLH is now economical for heads down to 1.9 meters and MJ2 Technologies have ambitions to lower that to around 1.6 meters. “In our field, 10cm can present a huge difference in costs,” say LeClerc. “For a location with a head of around 2 meters, costs would be somewhere around €2,200 per installed kW, with total costs varying from €1.5 million to €4 million, depending on the number of installed units.”

MJ2 Technologies has identified between 1,800 and 1,900 suitable sites for their technology on European rivers (300 to 400 or them are in France). There are bigger opportunities outside Europe.

Hydraulic Wheel

On a smaller scale, a new design of water wheel – the rotary hydraulic pressure machine (RHPM) is being built and tested as a retrofit at an old mill site in Germany and at a river site in Bulgaria.

The RHPM is different from the traditional undershot, breastshot and overshot waterwheels which were driven either by the impulse of a fast-flowing stream, or by potential energy – the weight of water in buckets on the wheel. Instead, the RHPM is driven by the pressure of water at two different heights - upstream and downstream of the machine.

Its advantage is its simplicity. The RHPM requires the construction of a concrete channel with a horizontal bed. But it can be installed by a local mechanical engineering company. The wheel is simpler to manufacture than a traditional water wheel. The RHPM does not rely on sophisticated power electronics. It maintains the upstream level at a more or less constant depth because when the water’s flow rate drops, the machine responds by moving more slowly, letting less water through.

Gerald Müller, who invented the RHPM and is coordinating the EU-funded project, reckons capital costs are around 60% less than the cost of an Archimedes screw generation system. He estimates a typical watermill retrofit generating between 5kW and 20kW would cost between €4,000 and €4500 per kW installed. At German feed-in tariff rates that would achieve a return on investment of between 7 and 8 years. “For a 100 kW unit we are talking more like €2,500 or €3,000 per kW installed,” Müller estimates.

A main area of cost and a focus for development in the RHPM is the power take-off. “Because the machine moves very slowly – somewhere between 3 and 12 rpm – you have high torque on the shaft and you need gearing to speed that up to 750 rpm for a generator. Those are not standard gearboxes and they are expensive, so we are looking at cheaper solutions, says Müller, who is now based in the Department of Civil Engineering at the University of Southampton in Southern England.

While the total potential power output may be dwarfed by other sources, these water courses often run very close to centres of population and industry. Müller’s German mill retrofit and Bulgarian river generation will be completed in April and he and his colleagues can start to generate some hard data – data that may signal the new life for some very old power systems.

“The hydropower is there,” he says. “It has just not been included in the equation.”