Ultracapacitor manufacturers that have commercialized the technology find themselves in a constant competitive environment in which consumers weigh the pros and cons of various technologies to determine which one best suits their applications. Who do these manufacturers compete with for each and every energy storage installation?
Batteries are a main competitor of ultracapacitors. Poor or no low-temperature performance, poor cycling ability, short lifetime, high cost, and safety issues top the list of advanced batteries' weaknesses. The strength of these advanced batteries, of course, is high energy density. By comparison, ultracapacitors have minor safety considerations and in all other respects, do not have the weaknesses of batteries. As a matter of fact, these attributes actually fall into the strengths category for ultracaps. And don't forget, the high power of ultracaps cannot be beat. It is clear that ultracapacitors have a very short list of weaknesses: a single item (the safety concerns), which is subject to debate as a matter of degree. On the other hand, the list of advanced batteries' weaknesses is long and significant.
So what about traditional batteries, such as lead-acid? They have all the same weaknesses of advanced batteries, but without the high price tag. Again, we face a nasty list of weaknesses that consumers have lived with for more than 100 years!
Flywheels are another ultracap competitor. Flywheels' weaknesses include persistent maintenance requirements, high investment costs and safety issues. Flywheels have high energy density compared to ultracapacitors and can generate some power performance, but the list of weaknesses for flywheels is longer and more significant than for ultracaps.
How about asymmetric capacitive devices? These are decent competitors that give up some power and low-temperature performance compared to ultracapacitors. They also retain the maintenance-free, long life time, and low cost structure, which can be lower than that of ultracapacitors. Energy is generally higher than that of an ultracapacitor, but the cost of that energy density boost is the partial loss of performance that you would get in the most capable ultracapacitors.
Finally, there are the large-scale storage strategies like pumped hydro and compressed gas. Most applications cannot make these affordable strategies work. These strategies are geographically challenged, significantly limiting their application space and practicality as a long-term solution to most of today's energy storage challenges.
If not for their energy density, we might never see batteries again in any application. It is true that batteries are improving their weaknesses and costs are coming down. However, there's a long way to go and some weaknesses will never come off the list, unless new laws of physics are realized. The good news is that ultracapacitors make batteries better. Using these technologies together is a natural pairing. Those who take the plunge and do this commercially at scale stand to reap years of rewards and market share unmatched by anything in energy storage. (See Making Batteries Better With Ultracapacitors.)
So I am puzzled. Faced with an energy storage decision today, why would you deal with all of these weaknesses and risks when you don't have to? The obvious choice for energy storage has to be ultracapacitors, which should show up in every application (and have already been proven in many) around the globe. To do something different is to pass over the best solution for the application. I suspect such decisions are driven by factors such as fear, greed, or any other emotional decision-making criteria. And making technical decisions based on emotional criteria is not a recommended strategy for anyone. Ultracapacitors are not new products anymore. Mainstream broad deployments in high-visibility industries, such as hybrid buses and wind farms, are a testimony to their reliability and acceptance in industry. Risks are low and rewards are high for using this robust power delivery technology that pays off quickly and delivers for years.