Solar and wind power are becoming increasingly popular sources of energy, but for obvious reasons these sources aren't able to produce consistently -- solar power generation is impossible at night and wind farms don't do much on a calm day. Companies are now scrambling to find a way to harness these alternative methods and use their power as needed instead of as produced. And until this issue is resolved, alternative fuels are unlikely to truly catch on and surpass fossil-based counterparts. As this issue becomes a bigger bottleneck for the industry, investment and production of energy storage systems are expected to rise dramatically over the coming years. According to a recent report from Pike Research, worldwide installed system revenues will grow at a strong pace this decade, increasing from $1.5 billion in 2010 to $35.3 billion annually by 2020. With the tremendous potential for energy storage applications, it appears as if it is just a matter of time until this sector explodes. Should the industry take off as some are expecting it to, some ETFs focusing on critical components of this sector could get a major boost. Here, we profile three funds that seem poised to benefit from this coming boom.