Electricity isn't just used to keep the lights on; it powers household appliances, public and private services facilities, complex industrial processes and much more. Regardless of what its used for, the quality of electricity matters just as much as quantity. Getting a clean and stable power flow can make the difference between success or failure for a business: power quality affects machine down-time, clean-up costs, product quality and equipment failure. It can also make the difference between life and death in mission critical applications.

Delivering power with a pure sinusoidal wave form that remains within specified voltage and frequency is the obsession of experts working with the power grid, and something hydropower operators have been called on to do for decades. Because they can produce electricity if and when needed, hydropower plants can also make micro adjustments to compensate for quality losses elsewhere in the grid. This benefit of hydropower is often undervalued.

Unfortunately, micro-adjustments can be costly for the equipment. Changing the amount of water flowing through the turbines at short notice to change the power output or changing the angle of the blades can result in premature wear and tear of the turbines.

The solution presented here is the product of a collaboration between EDF, Andritz, CEA, EPFL, UPC, Armines and Power Vision Engineering as part of the XFLEX HYDRO project, supported by the European Union.

It relies on a simple observation: both batteries and hydropower plants can provide grid services to improve the quality of power on the grid. They have advantages and disadvantages, which can be combined to provide a more efficient and all-round cost-effective solution. Batteries are fast to respond but generally do not last long, whereas run-of-river hydro has opposite qualities: providing a somewhat slower response but with indefinite available energy.

The hybrid arrangement tested at the Vogelgrun run-of-river plant (France) allows the short-period response of a battery unit to complement the longer-period ramping capabilities of hydro turbines, at a single site. What is particularly new is the size of the battery used for grid support services. Thanks to the hydro complement, the battery is ten times smaller than what it would be as a standalone. Moreover, installing a battery at an existing hydro plant can also achieve cost savings through shared infrastructure.

Another rationale for this innovation is that a hybrid arrangement will likely lead to cost savings for operation and maintenance, by reducing ramping requirements and wear and tear on the hydro turbines.

Implementing the technology requires the development of hybrid control strategies to manage smart operation between the battery unit and the hydro plant. Such a master controller can ensure optimal power dispatch, grid services, and potential savings to be achieved across the hybrid installation. Further research is ongoing about the control algorithm; the actual efficacy is being checked live using a hybrid demonstrator unit, as part of the XFLEX HYDRO research project. With the data collected through the demonstration, the reduction in wear and tear will be checked, which here also will be a world first.

With the addition of variable renewable energy to the electricity grid, deviations in the ideal flow of power are frequent. The ability to compensate for these variations is an asset for power plants connected to the grid. Hydropower already provides flexible generation to help balance supply and demand on the system and improve power quality, but with energy storage and faster response time, electrochemical batteries can enhance this service.

Innovation overview

• Vogelgrun,France: 142-MW run-of-river hydropower plant
• Under development: smart power plant supervisor
• Currently ongoing: wear and tear assessment

Battery characteristics

• Type : Li Ion
• Capacity: 300 kWh of useful energy
• Inverter power: 650 kW