Technology Comparisons
Technology Description
Each technology has some inherent limitations or disadvantages that make it practical or economical for only a limited range of applications. The capability of each technology for high power and high energy applications are indicated by the following symbols:
Ratings
Large -scale stationary applications of electric energy storage can be divided in three major functional categories:
- Power Quality. Stored energy, in these applications, is only applied for seconds or less, as needed, to assure continuity of quality power.
- Bridging Power. Stored energy, in these applications, is used for seconds to minutes to assure continuity of service when switching from one source of energy generation to another.
- Energy Management. Storage media, in these applications, is used to decouple the timing of generation and consumption of electric energy. A typical application is load leveling, which involves the charging of storage when energy cost is low and utilization as needed. This would also enable consumers to be grid-independent for many hours.
Although some storage technologies can function in all application ranges, most options would not be economical to be applied in all three functional categories.
Size & Weight
Size and weight of storage devices are important factors for certain applications. Metal-air batteries have the highest energy density in this chart. However, the electrically rechargeable types, such as zinc-air batteries, have a relatively small cycle life and are still in the development stage.
The energy density ranges reflect the differences among manufacturers, product models and the impact of packaging.
Capital Costs
While capital cost is an important economic parameter, it should be realized that the total ownership cost (including the impact of equipment life an
d O&M costs) is a much more meaningful index for a complete economic analysis. For example, while the capital cost of lead-acid batteries is relatively low, they may not necessarily be the least expensive option for energy management (load leveling) due to their relatively short life for this type of application.
The battery costs in this chart have been adjusted to exclude the cost of power conversion electronics. The cost per unit energy has also been divided by the storage efficiency to obtain the cost per output (useful) energy.
Installation cost also varies with the type and size of the storage. The information in the chart and table here should only be used as a guide not as detailed data.
Notes:
- The costs of storage technologies are changing as they evolve. The cost ranges in this chart include approximate values in 2002 and the expected mature values in a few years.
- The Metal-Air batteries may appear to be the best choice based on their high energy density and low cost, but the rechargeable types have a very limited life cycle and are still under development.
Life Efficiency
Efficiency and cycle life are two important parameters to consider along with other parameters before selecting a storage technology. Both of these parameters affect the overall storage cost. Low efficiency increases the effective energy cost as only a fraction of the stored energy could be utilized. Low cycle life also increases the total cost as the storage device needs to be replaced more often. The present values of these expenses need to be considered along with the capital cost and operating expenses to obtain a better picture of the total ownership cost for a storage technology.
Per-cycle Cost
Per-cycle cost can be the best way to evaluate the cost of storing energy in a frequent charge/discharge application, such as load leveling.
This chart shows the capital component of this cost, taking into account the impact of cycle life and efficiency. For a more complete per-cycle cost, one needs to also consider O&M, disposal, replacement and other ownership expenses, which may not be known for the emerging technologies.
It should be noted that per-cycle cost is not an appropriate criterion for peak shaving or energy arbitrage where the application is less frequent or the energy cost differential is large and volatile.