Storage of renewable energy remains an enigma {writer: Staff reporter}

The global energy scene is currently dominated by two overriding concerns that strongly affect decisions on energy development priorities: security of supply, and
climate change.

While there is no shortage of ideas regarding possible sources of renewable energy and considerable progress has been made in the technology to exploit many of these, the major outstanding issue is storing the energy from most of these sources for later use.

Worldwide, renewable energy is still dominated by the ‘old’ renewables: hydropower and traditional biomass. They supply respectively 6% and 9% of global primary energy demand.

Only about 2% of the world’s primary energy is currently provided by ‘new’ renewable sources such as wind, photovoltaics and hydro.

But for these sources to become commonplace, they also need to satisfy the demand for security of supply. That is where the storage problem arises because all the sophisticated sustainable/renewable energy technologies – be it wind, solar, wave or something else – produce energy when it suits them.

The problem is to find ways of storing the energy for later use and also transporting it over greater distances with a minimum loss.

At least in theory, if science devise a major storage breakthrough, the world’s entire need for energy could be covered by renewable/sustainable energy.

Which are the current major renewable energy technologies, and what is the status of each?

Wind energy is a mature option with great potential and has enjoyed rapid development over the past 25 years at an average annual growth of 17.1%.

Insufficient international standards remain a problem, but it has a potential of providing in almost 30% of global energy needs. Not all impacts, such as potential interference with aviation communication, have been solved yet.

Solar cells or photovoltaics, which convert light directly into electricity, was the fastest growing renewable energy technology in recent years, with an average annual growth of 40%. Cost and lifetime of cells remain a problem with the lack of feed-in tariffs globally. It has potential to provide between 2% and 3% of global electricity needs.

Solar thermal, which is a long-established and mature technology for space heating and domestic hot water. New applications are emerging for industrial processes, to replace fossil fuels or electricity. Annual average growth is between 17% and 2%.

Biomass-based fuels for transport have several motivations as alternative transport fuels. They offer low carbon dioxide emissions, will reduce the dependence on fossil fuels, and it is possible to further develop a domestic industry based on liquid fuels. Annual average growth is 6.3% and total potential by 2030 is 10% of transport fuel, but competition with food for land use is problematic.

Thermal conversion of biomass and waste into power, heat and process energy is a mature technology and presently the world’s largest contributor of CO2 neutral energy and will also in the future provide a large share of CO2 neutral energy supplies.

The potential total share of global energy mix by 2030 is 25%. The competition with food for land is also a potential problem.

Geothermal energy, which is heat from within the earth and produces steam and hot water inside the earth, can be used to heat buildings or generate electricity. It is a mature technology with an average annual growth of 20%, with a potential of 2% of the global energy mix by 2030. The infrastructure required to exploit this source, however, is a major hurdle.

Hydro, ocean, wave and tidal, as a group of energy supply technologies, are at different stages of development. Hydro power and pumped hydro storage systems have for many years been fully commercially competitive in many parts of the world, but ocean energy is at an early stage of development. As a group, the average annual growth is 2% with a potential share of the global energy mix by 2030, 16% for hydro and ocean 10%.

Fuel cells are at the point of breakthrough as a versatile and efficient energy conversion technology. The major barrier is lack of testing and demonstration.

Hydrogen is an energy carrier, not an energy source, and realising it as such depends on low-cost, high-efficiency methods for production, transport and storage. Hydrogen can be produced by many technologies, based on fossil and sustainable fuels. In terms of maturity, it is still in the research phase with storing and infrastructure still unresolved problems.