Solar Energy Storage: Page 10 of 14

Emerging Technologies, Markets and Applications

First, intermittency that is associated with variable resources, such as clouds over solar arrays: This type of intermittency can introduce dramatic swings in solar power delivery in which anything from 1% to 90% of the resource can suddenly drop off or come back on line.

Second, intermittency that is associated with variable load and demand spikes: Solar and renewables are designed to deliver energy, or kWh, but they do not do a good job of delivering power, or kW. In some cases, load is coincident with renewable generation, such as air conditioning loads, which generally peak when solar plants are producing the most. However, many loads are not coincident with solar. Demand peaks due to manufacturing or EV charging occur throughout the day or night, not necessarily when solar is delivering at maximum.

Third, ramp-ups and ramp-downs that occur during shoulder periods: ISOs in states with high renewable portfolio standards are very concerned with how to spin up and spin down reserve power plants in proportion to the fast increases or decreases in delivered renewable power, as large numbers of solar power plants either come on line in the morning or go off-line in the evening.

All three types of intermittency are growing problems for grid management as more solar comes on line. The use of conventional gas peaker plants to mitigate the intermittency is not a scalable solution for utilities and would require constructing new peaker plants in proportion to the growth of solar power plants, reducing the positive climate impacts of solar. The deployment of an ES system along with each solar power plant can address intermittency.

The second important driver is lowering the cost of delivered power. This takes two forms—the declining costs of both PV and ES systems, and the low capacity factors of solar systems.

As the market has demonstrated over the last 5 years, declining PV costs drive an ever-expanding market, creating economies of scale that lead to even further cost reductions. This same transformation is occurring for ES systems, although the market is still in its early stages. We believe battery and ES system prices will continue to decline over the next decade as the market continues to grow and drive down costs further.

A second, more subtle form of cost reduction is the possibility of increasing the energy capacity available through combined PV plus ES systems. Solar power plants are notoriously underutilized. Given the daily and seasonal bell curves of solar production, solar systems are designed for close to their maximum potential energy generation annually. For example, a 100 MW solar power plant is typically designed for no more than 120%–130% of that figure at its dc inputs, and it will operate at the full 100 MW only a relatively few hours out of a year. Throughout a typical year—including nighttime hours—a typical solar plant may produce no more than 15%–20% of its theoretical maximum energy yield, or its capacity factor. Contrast that with a large coal or nuclear power plant, which may operate at a capacity factor of 50%–80%. However, if you were to augment that PV plant with an ES system, it gives you the opportunity to increase its capacity factor—to operate the plant for more hours of the year—in effect reducing its cost per kWh. This idea is still relatively new, but shows promise for further innovation.

New battery and storage technologies are moving out of the lab into the real world, and these will improve performance and drive down costs simultaneously. In addition, new approaches for delivery of the combined energy from PV and ES systems with algorithms and applications that manage the energy delivery of both in an integral fashion are being developed.

For example, with a combined PV and ES system, it’s possible to square off the shoulder periods of a typical solar day from the traditional Gaussian bell-shaped curve to one that looks more like a square wave. With such a production curve, it is much simpler for ISOs and utilities to manage ramp-up and ramp-down periods in the mornings and evenings. If they can predictably and reliably determine when the PV system will come on line or go off-line, utilities can turn off or dispatch their peaker plants accordingly. There is less chance of a sudden load demand creating a brownout, because the transition from peaker power to solar power can happen within a few minutes rather than over an hour or two.

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