1. Modelling of Grid Connected Solar Integrated Pumped Hydro Storage
Facility
-Karthik Ayeratharasu Rajasekharan, Candidate for Masters in Energy Systems
Northeastern University, Boston MA
Project Description
This project is an attempt to study the impact of various purchase and sale strategies on the
profitability of operating a Solar Integrated Coastal Pumped Hydro Storage facility in various
modes, using systemic dynamics approach. The facility described in this project purchases
electricity from utility when spot-market prices are low to store sea water at higher elevation, and
generate electricity from water and sells it back to the grid when the prices are high. The
arbitrage between the purchase and selling determines the economic feasibility of the system.
Furthermore, an on-site solar generating unit is installed to the existing facility to understand its
influence on the operating profit. The facility is optimized by determining the operating
constraints by conducting a sensitivity study for various purchase and sale strategies.
Modelling Questions:
1. What are the primary characteristics that determine the profitability and financial
performance of a PHS facility?
2. What is the optimal size of reservoir for such a facility?
3. What is the effect of integrating solar energy on the operating profit of running this
facility?
4. Does the integration has any effect in reducing the energy purchased?
5. What is best operating mode to make the best use of solar integration?
6. What are the optimal pricing strategies for such a facility to use?
Conclusions& Insights
Operating modes advantage:
For same operational conditions, it is found that the Mode B of operation improves the operating
profit. Although it might look insignificant, this increase in profit margin is attributed by the
revenue from on-site generation. It is visible that the mode B operation increases the revenues
from the on-site generation. This can be seen as the reduction in the energy purchased from the
grid. Mode B operation definitely has a significant impact in up-stream energy savings. This
further would benefit in curtailing the emissions of GHG. Furthermore, the results suggest the
Mode A operation is profitable for system with low on-site generation capacity.
Purchasing and Sale Strategy:
The model is designed to accept three decisions about the facilities fiscal behavior: a purchasing
limit, which is the intended discount below the trailing average market price that the facility will

2. accept when buying power from the grid, a selling limit, which is the intended premium above
the trailing average market price that the facility will accept when selling power to the grid, and
the user controllable 'fullness' strategy which modifies both strategies based upon how full the
facility's reservoir is; the more full, the less willing to buy and the more willing to sell the facility
becomes.
All other variables in the model held constant, the facility performs well under basically any
configuration, but seems to perform best when the facility is eager to purchase, even at
counterintuitively high prices. We attribute this performance to the dramatic spike in electricity
prices that results from Peak Hours. This windfall profit, even though it only spans a few hours
of the day, is substantial enough to drown out most of the other price signals. This would
suggest that if smaller pumping systems were more efficient, the facility could save operating
costs by using a slower input than its output.
Facility Characteristics:
Various characteristics are configurable by the user to describe the facility's size and siting. The
deliverable power is an obvious determinant for financial performance: a 500MW facility earns
roughly 10 times the revenue of a 50MW facility. Reservoir size and altitude, however, which
combine to determine the amount of energy stored in the system at any given time, vary rapidly
cease to have any meaning to facility performance. A massively oversized reservoir generates
the same operating revenues as a much smaller facility - until the reservoir is unable to store
sufficient energy to deliver throughout the full peak.
This suggests, quite strongly, that reservoir sizing is of the utmost importance to a facility as
excess reservoir capacity is, essentially, money wasted. If a facility finds itself with easy access
to more reservoir capacity, it should be prepared to install more generating power so that it can
exhaust its supply. The reservoir levels always operate within a certain distance of the upper
limit, any margin below the lower limit is water that sits and does nothing useful
The solar PV integration has very less impact on the capacity of the facility. This is because
energy generated by solar power is in kWh scale, whereas the capacity of the facility is rated in
MW range. One of the findings reveals that this facility would be even more profitable when it
is operated in tandem with wind energy generation. On that case, this facility will also be
addressing the intermittency problem in wind generation.