Many renewable sources of power, such as wind and solar, cannot provide steady energy output. New storage options would solve one of renewable energy’s greatest challenges.
Energy providers around the world are scrambling to develop storage for renewable energy in order to secure availability and improve profits. Supplies of wind and solar power fluctuate depending on the weather.
"A strorage unit helps to ensure a steady flow of energy from wind and sun, making it easier to respond to demand," said Martin Kleimaier of Germany's Association for Electrical, Electronic and Information Technologies (VDE). Last year, energy from sources like wind, biomass, hydroelectric plants, solar panels and waste incineration covered 20 percent of demand in Germany.
By 2050, Germany - which has the largest population of any EU country - is expected to draw as much as 80 percent of its power from green energy sources. That means new storage systems are needed to ensure reliability.
There are a number of new storage ideas already on the table. "There won't be one solution to for everything," said Claudia Kunz of the German Renewable Energy Agency. "There is a difference between short-term and long-term storage," Kunz explained. "Short-term storage unit capacity ranges from seconds and minutes up to a few hours. Long-term units can provide energy for weeks and months."
One solution is the pumped storage hydroelectric power station. These are short-term storage plants used primarily in mountainous regions. If there is excess electricity from wind or solar generation in the grid, it can be used to pump water from the valley, up the mountain to a subsidiary dam. When the water runs down the pipes again, it turns the turbine which is connected to a generator to produce electricity. The water isn't released until demand increases, so power facilities aren't as vulnerable to energy shortages caused by fluctuating supply and demand.
But a lot of energy - as much as one third - is lost as the water is pumped upwards. In Germany, pumped storage power plants need 7,500 megawatts of energy to run, which leaves the network with only four to eight hours of available power.
Turning to biogas
Researchers see chemical storage as a good solution for long-term energy storage. Jürgen Schmid of the Frauenhofer Institute for Wind Energy (IWES) in Germany explained that this system converts excess electricity into combustible gases. For example, wind tubines generate power. If there is too little demand for that power when the wind is blowing, the energy produced is used to split water into hydrogen and oxygen. The hydrogen is stored and used later to generate electricity. This releases no harmful emmissions and the only byproduct is water.
Hydrogen and methane are considered top choices for large scale energy storage. But, depending on how these gases are processed determines the size of their carbon footprint. Research is continuing as hydrogen storage is still considered largely inefficient.
Call for more grids
Availability of storage grids presents another challenge for energy providers. VDE's Wolfram Welßow told DW that expanding the electricity grid is a top priority in Germany.
Claudia Kunz of the German Renewable Energy Agency also wants to see the network infrastructure expanded as quickly as possible. But she says there are challenges ahead. "An enormous amount of research needs to be done in order to develop energy storage systems. A lot needs to be done to make them cost-effective," she said.
Experts say politicians should create a framework for use, so that the energy storage units can go online as soon as they are available. The German Environment Ministry expects demand for storage units to jump sometime between 2020 and 2030.
Author: Richard A. Fuchs / jw
Editor: Saroja Coelho