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Author Topic: Batteries  (Read 8987 times)

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Re: Batteries
« Reply #15 on: May 06, 2015, 10:36:57 pm »
Is Compressed Air Energy Storage (CAES) Scalable? Scalability is actually what makes CAES cost effective. IOW, YES!

Compressed Air Energy Storage
Trishna Das
James D. McCalley
Iowa State University
Ames, Iowa

Agebert NOTE: VERY brief summary of this educational chapter. I did not crunch any numbers. The math is above my skill set.  :(  But I can read graphs and English quite well.  ;D


CAES storage reservoirs for underground storage can be classified into three categories: salt, hard rock, and porous rock. These geologies are found to account for a significant fraction of United States (Fig. 2). Previous studies indicate that over 75% of the U.S. has geologic conditions that are potentially favorable for underground air storage [18]. Fig. 3 (at link) shows different storage mediums throughout US.


Currently the major drawback for CAES is its dependability on fuel source for the power generation. Natural gas prices contribute to the economics of CAES. Like any energy conversion system CAES also has its share of losses, thus working with an efficiency percentage around 60 % to 70 %. Some of these backlogs in CAES technology are currently overcome by enhanced CAES configurations and concepts. These advancements are given in a later section.


The CAES model developed is able to capture the influence of storage reservoir dynamics on performance measures such as demand met and input spillage percentage. From Fig.12, it is seen that irrespective of turbine and compressor sizing, a good enough reservoir volume is required to ensure effective addressing of wind variability issues by CAES for this particular wind farm.


We can notice that as the maximum pressure limit increases, the revenue per year and the operational performance measures too increase. So it corroborates the model‘s ability to account for internal storage dynamics and their direct influence on CAES operational and economic outcome.

Since the model has the ability to simulate CAES operation for longer periods of time within reasonable simulation time while also capturing finer second-second or few minutes variations, it could enable performing very finer sub-hourly, say 5-mins, unit commitment studies. Therefore the model can lend itself well in long term production costing studies to evaluate generation planning strategies.



In IEEE 24-bus Reliability Test System (RTS) wind and CAES were integrated and production costing studies were conducted. The production costing study is an hourly simulation for 48 hours (2 days). The data for load and wind generation is taken from Bonneville Power Administration (BPA) for Nov 2nd and 3rd in the year 2010. This data was chosen as it covered good variation in wind pattern. The program was developed using MATLAB with TOMLAB optimization platform.


The production costing study was done with 25% wind capacity penetration with wind farms at bus 17, 21, and 22, and a CAES at bus 21. The turbine rating is 50 MW, compressor is 50 MW and the storage reservoir is 200 MWh.The system contains various mix of generation facilities such as 7 coal generation plants, 2 nuclear generations, 3 natural gas generations, 2 oil fired plants with variable ramping rates, with CAES being the fastest ramping unit. The total system generation without wind generation and CAES unit is 3400MW.

We can observe from Fig. 12 that during high wind spell of the first day the compressor reduces the wind spillage by charging the CAES reservoir, and thereby contributing to down-regulation and earning revenue from the ancillary service market. CAES also participates actively in providing spinning reserves and up regulation, as seen from the plot for turbine.

From the above figures (in addition to figure 12 there are others at the link) it confirms that with increase in wind penetration CAES gains greater benefits from the grid operations.

On the other hand, it is important to quantify how the grid benefits by the installation of CAES unit.

Some of the metrics to quantify the grid benefits are

system production cost,

wind spillage percentage,

quality of regulation,


transmission congestion relief,

system stability improvement and so on.

CAES sizing is a key issue that influences the grid benefits as observed from Fig. 15 (at link). In Fig. 15 as the CAES sizing is increased the wind spillage is reduced. At 10% wind capacity penetration it is observed that the grid without CAES had 4% of wind spillage and with increased CAES size the spillage was reduced to nearly 0.5%. The blue curve in Fig. 15 shows wind energy penetration for corresponding wind capacity penetration in the system. It would be interesting to investigate the correlation between the CAES sizing, and wind energy penetration.


In this chapter, a state space model for compressed air storage technology was developed, which monitors the storage dynamics at any instant of time in terms of the reservoir pressure and mass of compressed air stored.

The model was validated using the operational curves from Huntorf CAES. The CAES model developed is simulated as a collocated facility to address the wind variability issue of a particular wind farm. The model facilitates capturing storage dynamics‘ influence on CAES‘s operational performance and economic indices. Eventually some standard CAES configurations consisting of variations in turbine, compressor and reservoir ratings are simulated and a wide range of performance indices are computed for assessing the worth of each configuration for that particular geography.

From the results we understand that such a venture would require huge investments with very long payback periods. Thus CAES acting as an auxiliary support for individual wind farms may not be as wise as investing in a system level CAES with higher capacity.

Economic assessment of the storage benefits was studied with the CAES model developed and incorporated into the production costing program. The assessment platform with the unit commitment and economic dispatch program modules dispatched the CAES unit under increasing wind penetration levels.

From the results we  observe that CAES plays a vital role in the ancillary and reserve markets with increasing wind penetration, thereby benefitting grid as well as earning revenue to cover its huge investment costs.

The profits earned by the CAES indicate that this venture would be lucrative with the changing grid scenarios involving increasing integration of variable generations. The study points to an interesting direction that the CAES compressor providing down regulation service is especially effective in absorbing the high wind spells, and thus reducing wind spillage and providing economic and quick ramping regulation service to the grid.

Storage‘s participation in ancillary services is attractive because the new generation portfolio not only requires more regulation services, but also higher ramping capabilities and more operating reserves to counter the costs associated with deeper and more frequent cycling of fossil units.

Rob not the poor, because he is poor: neither oppress the afflicted in the gate:
For the Lord will plead their cause, and spoil the soul of those that spoiled them. Pr. 22:22-23


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