Page 277 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

264 Fundamentals of Ocean Renewable Energy

wind power, there are relatively high frequencies of zero and maximum power,
but these two extremes are much less frequent in the 100% wave scenario,
indicating that the wave resource is less extreme, but more likely to be present
(i.e. more reliable) than the wind resource. A more even distribution across
all capacity factors results from all of the combined wind/wave scenarios.
However, very specific optimization would be required to determine which of
these scenarios is advantageous from both generation and demand perspectives.
Further, colocation of wind and wave farms can lead to more complexity in the
structural design of the devices due to loading and fluid-structure interactions.

9.5 OPTIMIZATION TOOLS
9.5.1 HOMER

Whilst a number of tools are available to optimize distributed and hybrid
renewable energy systems, we selected Hybrid Optimization Model for Electric
Renewable (HOMER; www.homerenergy.com) as an example to describe some
of the capabilities of these tools. HOMER is an example of a computer-based
optimization tool developed by National Renewable Energy Laboratory of the
US for hybrid renewable energy systems. The main components of this model
are simulation, optimization, and sensitivity analysis.

Simulation
Assume that you have designed a configuration for a hybrid renewable energy
system. This system has several components such as one or several wind
turbines, a storage system (e.g. batteries, hydrogen tank), and diesel generators
(for hybrid systems). HOMER simulates the performance of the system every
hour for the duration of a year. It calculates the energy produced and compares
it with electricity demand. The hourly time series of demand should be
provided as an input to the model. HOMER calculates the surplus or deficit
at each time step, and tries to address these differences by storing energy
during surplus periods, and using stored energy, diesel generators, or grid
imports, in times of deficit. Several criteria can be imposed by the user as
constraints to determine whether the performance of a system/configuration
is acceptable; for example, minimum percent of the time that energy demand
should be met, the share of the power supplied by renewable energy (in a
hybrid system), and a limit on the emissions can be imposed. In the simulation
phase, HOMER also calculates total net present cost of the system (i.e. all
future costs are discounted to the present by a discount/interest rate). The
costs include initial capital cost, the O&M cost during the lifetime of the
project, fuel, and power purchased from the grid. The revenue from selling
the power is then subtracted from the total cost to compute the net present
cost. LCOE can also be computed given total cost and energy produced
during a year.