Last year, the buzz was all about the digital technologies of the intelligent grid. Everything picked up the title of smart. We had smart switches, smart relays, smart meters, and on the list went. The Smart Grid would correct the aging infrastructure, overcome the mass exodus of engineers and technicians to retirement, and prevail over the increasing demand for power.

This year the focus is energy independence and economic recovery through green power. Accordingly, green power (predominantly wind and solar) will deliver high-paying green jobs, provide an unlimited supply of green electrical power and save the environment by eliminating the carbon footprint of generating electricity.

This implies that if Smart Grid technology and green power were harnessed together, all of our problems would be solved. It seems logical, but on closer look, these solutions, if taken alone, would lead us to a new set of problems.

Let's Look First At Wind Generation

Wind is getting the lion's share of the renewable-energy attention. Regulators, politicians and environmentalist are pushing it as the solution, but they tend to overlook one critical issue: wind is a highly intermittent power source and electricity is only produced when it is blowing. The typical capacity factor for wind-generation farms ranges from 15% to 30%, which means that too often wind is not dispatchable.

The electricity wind turbines produce should not be considered base-load generation as it cannot be reserved for peak time use either. In other words, it is a use it or loose it scenario. During the research and writing of the “Connecting Renewables to the Grid” supplement (T&D World, March 2009), it became apparent there was a critical element missing: energy storage.

Recently, I met up with Rick Bush in Colorado. He had just returned from Europe, where he toured wind and solar facilities, and talked with utility industry leaders about coupling renewables with storage technologies. Our visit gave us a chance to catch up and compare notes.

As more renewable energy is deployed, there is more interaction with base-load plants. Rick found in his travels that many countries already have more wind generation than they can presently handle, which is leading to curtailments of wind generation. There is too little wind in times of peak demand and too much wind in times of low demand. The judicious use of energy storage would help us solve this problem; abundant off-peak wind-generated electricity would be very welcomed during peak demand periods.

The fundamental concept of energy storage is simple: generate electricity when wind and solar are plentiful and store it for later use when demand is up and supplies are short.

Thermal-energy storage also can be used to shave the peak by making ice in off-peak times and provide cooling during peak without operating VAR-sucking and watt-consuming compressor motors. After all, cooling counts for about 40% of our summer peak. It's really not that complicated.

The confusion factor begins with the task of selecting the technology. The user has to understand what the technology offers and what it costs to provide that service. There is such a variety of energy-storage devices coming out of the universities and laboratories, but are there real choices? Just because it is technically possible to build a technology, is it economically reasonable?

What About Bulk Energy Storage?

Commercially, there are several mature energy-storage technologies. How do we evaluate these technologies and integrate them into the grid? It might appear to be complicated, but it is just getting back to the basics. We need to understand what issue we are trying to address with the specific technology. If the problem is thermal (air conditioning during peak), there is ice storage or maybe chilled water. If we need a fast response, but not a long duration (power quality), we have flywheels, SMES and supercapacitors. If we need large amounts of megawatts for many hours, there is pumped-hydro storage, compressed-air storage and sodium-sulfur batteries in vogue in Japan.

We have to determine the value position of the battery technology: What is the discharge duration? What is the power rating? How much capacity is needed? And what is the required response time?

Now you can see why I said that our green solutions are likely to bring about a whole new set of problems if we don't do our homework. What we do not need is to cobble together energy solutions. We need to understand what will give us an effective renewable energy source with the enabling technology of energy storage, combined with renewable sources that rival that of our base fossil and nuclear stations.