TITLE:
Pumped Storage Power Generation System. FIELD OF THE INVENTION:
The present disclosure relates to power generation systems for optimized hydropower generation, more particularly to an enhanced pumped storage power generation system, which uses a two storage system and a plurality of pumped turbine generators, wherein pumping time approximates generating time of operation.
BACKGROUND OF THE INVENTION:
Pumped Storage Systems (PSS) is a type of hydroelectric power generation system used by power plants for load balancing. Energy is stored in the form of water, pumped from a lower elevation reservoir to a higher elevation reservoir.
Low-cost off-peak electric power is used to run the pumps to pump up water to the elevated reservoir. During periods of high electrical demand, the stored water is released through penstock lines to the turbines to produce electric power. The system though theoretically a net consumer of power, increases profitability by selling more electricity during periods of peak demand, when electricity prices are highest.

PSS designed in prior arts have conversion efficiency of 70 to 80 percent, this results in actual power generation time being less. Therefore there is always a daily deficit between power generated and power required. To account for this daily deficit, large amounts of water have to be pumped on lower traffic days like Sunday, when the time duration of cheap power availability is more. This however necessitates a much larger elevated reservoir making the whole system expensive and rendering it unprofitable due to its in-built theoretical inefficiency and underutilization of various components.
In prior art systems the powerhouse that encloses the pump-turbines are located underground (below the lower reservoir level) to avoid cavitation. Higher flow (specific speed of pumping operation) results in higher cavitation coefficient and requires more submergence of the pump-turbine machines. This requires the powerhouse to be placed at a higher depth, increasing the degree of excavation and the time needed to construct the powerhouse.
The Head of a pumped storage system is the difference of height between the upper and lower reservoirs of a storage system. In prior known systems the head variation range during the pumping and generation operation varies at a higher range and affects the efficiency of the pump-turbine generators.

Thus there is a need for developing an enhanced pumped power storage system for load balancing of power plants that addresses the present problems of inefficiency, utilization and cost of power generation.
OBJECTS OF THE INVENTION:
1. It is the primary objective of the present disclosure to provide an enhanced pumped storage power generation system.
2. It is another objective of the present disclosure to provide low cost power storage.
3. It is another objective of the present disclosure to maximize the available low cost power (off-peak time) to pump water to elevated storage tank.
4. It is another objective of the present disclosure to intelligently control the pumping time and the generating time by using an arrangement of penstock and generators capacities.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 shows the schematic of the pumped power generation system.
Figure 2 shows the schematic of arrangement of pump-turbine machines of the pumped power generating system.

SUMMARY OF THE INVENTION
The present disclosure discloses a system by which pumping time is approximated to the generating time of operation of a pumped storage power generating system. The disclosure discloses a system having a lower storage tank at a location lower than the upper storage tank, wherein said upper storage tank is at an higher elevation from the position of lower storage tank; a power house being placed in the flow path of the downward flow of water through an arrangement of penstock to generate electricity by having a plurality of pump-turbine machines so selected so that the cumulative generating capacity is at least 10 to 30 percent more than the required generating capacity.
DETAILED DESCRIPTION OF THE INVENTION:
The present disclosure proposes an enhanced pumped power generation system and the same is explained below with reference to the accompanying drawings in accordance with an embodiment of the present invention.
Figure 1 shows the schematic of the enhanced pumped power generation system, which comprises two storage tanks connected through a penstock arrangement (3) to pump up water to the elevated storage tank (1) and for downward flow of the water to the lower storage tank (2). The two storage tanks are placed at different levels of elevation to capture the potential energy of water for enabling the generation of power. A Power house (5) comprising a plurality of pump-turbine

machines are placed in the download ward flow path of the water. During peak demand time kinetic energy of the flowing water is converted into electric energy by the turbines, and during off peak times, water collected in the lower tank (2) is pumped back to the elevated storage tank (1) using cheap available power.
The disclosed system uses a plurality of pump-turbine machines. The additional capacity allows the system to suck in more power daily within the available window of cheap power so as to ensure enough daily generation of peak power to meet peak demand. In pumping mode, all pump-turbine machines run at full capacity but in generation mode, they run at a lower capacity. Figure 2, depicts an example schematic of three automated pump-turbine machines (7, 8 and 9) being installed in the Power house (5), to pump water and generate electricity. These pump-turbine machines have a generating capacity of 45 MW each, adding up to a total generation capacity of 135 MW. An example of a 100 MW PSS with a 200 meters head and 7 hours of generation capacity is illustrated in Table B below to highlight the dam-reservoir specification comparison of the disclosed system and prior known PSS systems.
The generating capacities of the pump-turbine machines have been selected so as to approximate the pumping time to the generation time. The additional capacity allows the disclosed system to pump in more water daily within the available window of cheap power so as to ensure enough daily generation of peak power to meet peak demand.

In pumping mode all the pump-turbine machines run at full capacity and in generation mode they run at about 75% capacity (equivalent to generation capacity of the prior art system design). The approximation of the pumping time to generation time with present disclosed system eliminates the daily power deficit as found in prior art systems. This results in a much smaller, optimized elevated storage tank with a capacity to hold enough water for daily peak electricity generation time.
Equalizing pumping and generation time eliminates the need for extra pumping on off peak power days like Sunday to compensate for the daily deficit of generation. This in fact, reduces the required size of the elevated storage tank (1) to less than half as required by prior art pumped storage systems for the same amount of energy generation. Also in case of lower storage tank (2) as the pumping time is approximately equivalent to the generation time, there is no daily backlog, so the lower storage tank can be of smaller capacity (just enough to hold the daily requirement of water plus some additional capacity for the evaporation losses). This translates into big savings in terms of total system cost and also the time required to build the system is reduced significantly as well. Importantly, the utilization of the elevated storage tank (1) and lower storage tank (2) is nearly 100% every day in the disclosed system.

Larger storage tanks (elevated and lower) lead to bigger dams, thereby resulting in more area of water submergence and more land required. This translates into more time for construction, more cost, and more environmental damages.
Equalizing pumping and generation time is an ideal scenario for the most optimized PSS system; though other configurations (e.g. generating time is equal to 90% of the pumping time, etc.) are feasible, depending upon the power landscape, i.e. the availability of cheap power, peak power requirements, etc.
The system in an embodiment uses dedicated pumping machines, instead of pump turbine machines, to enhance the pumping capacity.
In the present disclosed system, the adding of more pump-turbine machines with less capacity results in less flow per pump-turbine machines; less flow leads to less cavitation coefficient, and hence less submergence requirement. This allows the powerhouse (5) to be placed at a higher elevation, reducing the degree of excavation and the time needed to construct the powerhouse.
High Availability: Due to over provisioning of pump-turbine machines to approximate pumping time to generation time, there is some underutilized capacity in generation mode of operation. This unused capacity can be used in case of failure of other pump-turbine machines in the generation mode adding redundancy to the system, thus effectively reducing the downtime and increasing

the availability. The example below (Table A) compares 100 MW PSS for traditional and alternate configuration. Table A:

Traditional Configuration Alternate Configuration
Number of pump-turbine machines 2 3
Capacity of each pump-turbine machines 50 MW 45 MW
Capacity used during generation 100 MW 100 MW
Unused capacity 0MW 35 MW
Generation capacity available in case of one pump-turbine machines failure 50 MW 90 MW
Head Variation: In the disclosed system design, due to smaller size of dams and 100% volume utilization of elevated & lower storage tanks, the daily head variation is constant for 7 days a week/365 days a year, leading to a more efficient system design.

Utilization comparison: To compare the utilizations of two storage tanks an example is discussed below, with efficiency of 75%, peak power generation requirement of 7 hours and availability of cheap night power is 7 hours. For a prior art PSS the daily window of cheap power (for pumping) is only 7 hours; this results in actual power generation time being less than 5.25 hours (due to the practicality of 75% efficiency). Though the requirement of peak power is 7 hours daily, so there is daily deficit of 1.75 hours. To overcome this daily deficiency additional volumes of water have to be pumped on cheap power availability days like Sundays (when the window of cheap power is bigger). This operating model necessitates that the elevated storage tank be targe enough to hold sufficient volumes of water to support generation for about 17-18 hours (1.75 hours daily back log for 6 days + generation capacity of one day i.e., [1.75 x 6] + 7 = 17.5 hours). The daily utilization of elevated storage tank capacity is limited to water needed for 7 hours of generation, but to support a sustained daily generation operation, the capacity of the elevated storage tank needs to be large enough to hold water for 17.5 hours. This result in 40%utilization (on daily basis; except Sunday) of the total capacity of the elevated storage tank designed for 17.5 hours.
In the disclosed system due to the additional pumping capacity, pumping time is approximated to the generating time, resulting in elimination of daily deficit of 1.75 hours and 100% utilization of both the storage tanks. Moreover, resultant size of the storage tanks is much smaller.
Table B.The table below depicts an example comparing dam-reservoir

specifications of prior art system design (17.5 hours of storage capacity) to enhanced system (7 hours of storage capacity) of operations for the 100 MW PSS with a 200 meters head and 7 hours of generation.

Dam Specification Prior art 17.5 hours Present Disclosed 7 hours
Height of Dam above ground
(meters) 18 7
Depth of dam below ground
[30% to that of the height
above
ground] (meters) 5.25 2.1
Total height of dam
(meters) 18 + 5.25 = 23.25 7 + 2.1 = 9.1
Volume of concrete for
dam
construction (cubic
meters) 407,947 83,654
Width of dam at the base
(meters) 20.97 9.36
Volume of the Storage tanks
(cubic meters) 3.59 1.4

As the height of the dam increases, so does the width. This results in an exponential increase in dam size and cost, i.e. double the height of the dam results in quadrupling the cost. On the other hand, the cost of electro-mechanical components (e.g. pump-turbines, etc.) is a linear factor of its capacity. Thus, in the disclosed present design, the emphasis is on reducing the exponential costs (dam height) by over-provisioning linear costs (electro-mechanical components).
Those skilled in the art to which the invention relates will appreciate that the many variations of the described example implementations and other implementations exist within the scope of the claimed invention.