One of the limitations in using renewable resources for power generation at scale is the fact that nearly all renewable generation sources have some achilles heel in harvesting the natural resource. For instance:

• Solar (PV, thermal, etc) only generates when the Sun is shining. Average capacity factor, 24%.
• Wind only generates when wind velocity is above x threshold of m/sec. Average capacity factor, 30%
• Hydro (gravity, wave, tidal) only generates when there is sufficient resource, drought, calm seas, and shifting currents impact production. Average capacity factor, 70%.
• Waste gas generates at small scale and only when there is sufficient gas as dictated by the decomposition or production process. Average capacity factor, less than 50%.
• Geothermal generates only as long as there is heat and some material to carry the heat’s energy. As heat and resource are mined and released (old plants) the overall production of the resource decreases. Average capacity factor, 90%.

Each of these renewable electric generation means has their charm and some have more favorable characteristics than others, but they all could benefit from some sort of energy storage mechanism at utility scale to compensate for times when the renewable resource is not producing. This has long been a challenge for wind producers as wind production frequently is mismatched to consumption patterns for the power.

Peak consumption time tends to be during the day where renewables like solar produce at their peak. Wind is unpredictable by definition so the need to store the energy for future use becomes a vital part of the equation to make the projects viable and reliable. After all, I think everyone expects the light to power up when the switch is flipped.

There seem to be 3 major approaches to the storage challenge:

• Compressed gases (as reported yesterday in Renewable Energy Access)
• Pumped water – using surplus electricity to pump water uphill back into a reservoir for instance
• Battery storage schemes where electricity is kept until needed

It seems to me a fourth approach (which may be happening, but I haven’t seen anything about it) would be to use the surplus electricity to process other fuels with better storage characteristics. An example would be to use the renewable electricity surplus to process hydrogen gas that can then be used in the future for other purposes (including potentially transportation as well as electric generation.

This is clearly a barrier to economic viability as well as large scale renewable adoption. Until this challenge is met, there will be a natural governor on the velocity of progress on renewable electricity generation.