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The alternative energy possibilities that were explored for this project are:

Lead Acid Batteries- Vented or flooded lead acid batteries are typically used as the primary storage source in most substations. This alternative looks to be the most reliable and economical solution. The biggest drawback of lead acid batteries is the maintenance requirements. However, since lead acid batteries have seen extensive field-testing and are capable of handling both the momentary and continuous loads at a very reasonable price, this alternative is still the best solution for a redundant system.
Ultracapacitors- Ultracapacitors are better suited for handling momentary load requirements than batteries. However, supplying the continuous load for eight hours becomes very expensive and far from reasonable. Ultracapacitors are best utilized in combination with another storage source where the ultracapacitors would be sized to handle a short duration load, such as the momentary requirements of the trip coils. The other source in combination with the ultracapacitors would be responsible for continuous loads. Another advantage of ultracapacitors over batteries is that they require very little, if any, maintenance.
Fuel Cells- The fuel cell technology analyzed was the Proton Exchange Membrane (PEM). One of the major issues faced by fuel cells is that fuel cell units needs to start and ramp up before it is fully capable of supplying the dc load. There would have to be some other dc supply operating the station equipment until the fuel cell can take over the load. Also, fuel cells are relatively expensive, especially in comparison to lead acid batteries. The major advantages of fuel cells over batteries are the minimal maintenance requirements and the environmental adaptability of the units. Fuel cells can be operated in a much larger temperature range than batteries and can even be implemented outdoors.
Flywheel- A single flywheel could not meet both the continuous and momentary load requirements. Load requirements could be met if units were placed in parallel, but costs would increase to the point where the system cost is unreasonable.
DC Generator Set- This alternative would be able to handle both the continuous and momentary loads but wouldn't add very much reliability to the system. Generators are far less reliable than traditional flooded lead acid batteries. Also, generators have high maintenance costs. Idaho Power would like to stay away from maintenance intensive alternatives.
Dual Chargers- Although dual chargers were thought to be a very economical alternative to improve reliability, adding a redundant charger does not make the system much more reliable. The charger is already one of the most reliable elements in the system so adding another charger results in little change in reliability. Also, since chargers are supplied by the station power, adding a redundant charger would not be of any use to the dc system when a station power outage occurs.

Hybrid System- A hybrid system is a combination of any two of the discussed alternatives. Hybrid systems were considered because some alternatives may complement one another. For example, one alternative may be better suited to supply momentary loads, while another alternative may be better suited to supply a continuous load. An example of such a hybrid system is a battery system sized to only supply a continuous load and an ultracapacitor system sized to only supply a momentary load.

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