48 Chapter 4 Table 1: Power to energy ratios From this table it is clear that the hybrid type applications have a much higher power need than the energy applications do. This also validates the comment that is frequently heard that with a large energy storage systems that power is much less of a concern because it is already there. Of course, that does not mean that we should not take care in our cell selection when sizing a large battery. As has been stated previously we may find that we can reduce the overall capacity of the battery if we can get a high enough power cell thereby reducing the customer cost and optimizing the system to meet the customers actual performance needs.
Large Stationary and Grid Systems These same calculations, formulas, and processes that I have included above can be used in evaluating and sizing a battery-based energy storage system for a large grid or stationary system. The challenge for most battery manufacturers is that the amount and level of detail of the requirements from these types of applications are typically much less than would be expected from one of the large automakers. Examples of this may be seen in some of the recent request for proposals (RFPs) for energy storage systems for grid and renewable integration applications.
The author has seen many RFPs which require energy storage of “60 MW for 30 min” as the entire battery specification. From this the only real sizing that we can do is to convert it to energy: If they need 60 MW of power for 30 min, then we can convert it to energy that would be 120 MWh (60 MW Ч 2). More than that we need to refer back to the section on converting customer requirements and we need to meet with the power electronics equipment suppliers to determine what voltages their inverters and systems need to run at and what other requirements they may have.
In general, the less detailed the requirement documents are, the more work and time is needed to be spent with the customer in order to gain a full and deep understanding of what they are trying to achieve with the system. Quick Formula Summary Just like in your basic algebra class in high school, as long as you have two variables you can calculate the third. Below is a list of the calculations that were included in this chapter. With these formulas you should be able to make most of the basic calculations necessary to get a beginning understanding of your energy storage system’s performance.
12 V S/S 48 V HEV PHEV-20 PHEV-40 EV-100 15:1 to 20:1 25:1 to 40:1 30:1 to 35:1 6:1 to 7:1 3:1 to 4:1 2:1