Increasing power generation from wind farms and solar panels coupled, in many countries, with high electricity prices and declining feed-in tariffs, will trigger a five-fold increase in demand for energy storage systems by 2020, analysts predict. BCG forecasts that annual sales of storage technologies will reach €6 billion ($7.9 billion) in 2015 and €15 billion in 2020, from less than €3 billion last year.  Recently one New York-based energy-storage device maker, Ioxus Inc., received $15 million in an equity offering. Ioxus is backed by Braemar Energy Ventures, Northwater Capital Management Inc., Aster Capital and Energy Technology Ventures, a joint venture between General Electric Co., ConocoPhillips and NRG Energy Inc. The company makes ultracapacitors that rapidly absorb and release high-voltage power, according to its website. The devices can store power generated by solar and wind farms or be paired with batteries in electric vehicles to capture energy from braking. 
In weather conditions when there is an abundance of wind and sun, wind and solar photovoltaic systems produce more power than can be used. Energy storage systems smooth out the resulting peaks and troughs, by holding the excess energy when supply is high and releasing it when supply is low. Storage technologies include a variety of battery designs along with systems based on compressed air, water and hydrogen. At present, most of them face problems with reliability, durability and, above all, cost, said Reza Shaybani, chairman of the BESIA. But solar PV installations with battery storage are close to economic viability in several regions, the BCG report said. The economics are particularly attractive in off-grid residential applications, it noted – in rural areas of South Africa and Australia, for example. In Germany, the country with the most solar capacity in Europe, energy storage for PV systems does not yet make economic sense, but perhaps in the future, IHS said. By 2017, IHS predicts a market of $30 billion for PV systems and combined storage systems, of which $10 billion would be for the storage hardware alone.