Energy Storage is Too Expensive! Or is it?
By Charles Toca
I'm sometimes told that energy storage is too expensive - clarification, I'm told that advanced energy storage systems (AES), like the VRB or ZBB flow battery, the Beacon flywheel, or the NGK molten sodium-sulfur battery, are too expensive. I always have to chuckle and respond, compared to what?
* Solar PV?
* Pumped Hydro?
* Fuel Cells?
* Transmission lines?
* Nuclear power?
* Black-outs?
"It's the application, stupid!" - to copy a line from Bill Clinton's presidential campaign. Energy storage is a tool. One should use the best tool for the job. And that includes the cost consideration.
Of course, I'll concede that the actual cost of these advanced systems can be difficult to determine. Some systems are quoted without including all the hardware needed to make them useful, like the inverters and power conditioning systems or thermal boosters. Other systems, like flow batteries, need to be quoted based on their capacity and energy storage. A one megawatt system with one hour of storage - 1 MWhr - will cost a lot less than a one megawatt system with 10 hours of storage - 10 MWhr. However, if you chose to measure a system based on the cost per megawatt hour, then the 10 hour system will be the best value - if you need 10 hours of storage. Conversely, a flywheel with 15 minutes of storage may price at an astronomical cost per MWhr, which is totally irrelevant if your only need is capacity. So the first step in doing a cost comparison is to determine what kind and size of system is best for your application - then the quote is valid.
The second step is to realize that an AES is not a generator. That seems obvious, but I'm surprised how many times I'm asked about the heat rate, or the cost per kW. Most power planners are conditioned to ask for this information because power generators are their frame of reference. So, any quote that is more than $1,500 per kW is immediately determined to be too high. These planners must be gently reminded that most AES systems require very little ongoing operations and maintenance and very little "fuel" cost, factors that greatly increase the cost of a generator. ("Fuel cost" would be power consumed due to the efficiency of the system in storing and delivering energy).
For one cost comparison example, consider a small grid system in the mountains of California, with limited local generation and connection to the transmission system. This is the case for several communities, but one specific system comes to mind with a maximum 5 MW demand and a singlepower connection, on a long distribution line, to an investor owned utility.
This community suffers from chronic outages whenever bad weather or cold affects their single power line. One way to solve this problem would be to build additional connections to the grid and to install local generation. In fact, they decided to build another power line, over the mountains, to a different grid.
An alternative would be to install an AES large enough to match their capacity. Not only would the AES provide back-up power, but it could also power shift by storing power at night for delivery during the day, increasing their capacity. In addition, the price arbitrage would pay for the system eventually - unlike a new power line. And installing an AES avoids the right-of-way issues that add cost and delay to a project.
Such a system would improve power quality, voltage support and provide emergency power - but what if there is an extended outage? This community has already decided to install wind turbines to generate their own power and for export. Of course, we know about the unreliability of wind and the stress it can place on a small distribution grid due to its intermittent generation of power. If an AES is installed, then the wind output can be smoothed to avoid stress on the grid. If an outage occurs, the AES can be recharged from the turbines. The power planner now has two options for evaluation, the old standby of building more wires, or a clean energy plant that pays for itself. If it is so expensive that it takes 20 years to pay for itself (not likely), it is still a much better deal than wires - which will also incur continuing costs for maintenance.
I'll share some application comparisons with power generators in the next post.
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