Page 72 - North American Clean Energy March April 2016

Image 1. Connection diagram of a power plant combining PV and storage inverters
energy storage
figure 1. Power delivered by a PV plant on a sunny day
figure 2. Power output regulation thanks to an ESS at a PV plant on a day with scattered clouds
by Carlos Lezana
ALMOST EVERY REGION IN THE WORLD has deployed renewable energy generation. In the United States, for example, most states have a renewables portfolio standard which requires
a speci c portion of all generation to be produced from renewable energy. In part, this has propelled the US to become one of the biggest markets in the world for solar energy and for energy storage projects.
Although energy storage is just now gaining signi cant momentum, some studies predict that this market will surpass $50 billion by 20201. During this time, numerous storage technologies will be ghting for their predominant position in the market. What is clear is that batteries will play a key role inside the storage sector as the main electrical energy storage technology. Additionally, US policy is now leading the way with some important Federal decisions. For instance, the US Department of Energy declared that energy storage will play a key role for the country’s search of energy security and independence. Also, the Department of Defense has invested more than $800 million in energy storage programs since 20092. California and Puerto Rico are paving the way and more states are shortly behind, like Texas, New York, and those connected to PJM transmission.
Energy storage projects are being deployed with photovoltaic (PV) systems anywhere from smaller residential systems to the largest utility-scale projects. And although
all sectors are increasing, utility-scale grid-tied photovoltaic systems have experienced a considerable increase in market share worldwide. With a global installed capacity close to 200 GW3, photovoltaics have risen to occupy a prominent position within the power generation technologies. It is
also important to note, that in order to achieve a higher penetration rate, it is imperative to integrate photovoltaics into the grid seamlessly, and this can be done using Energy Storage Systems (ESS).
Conventional electricity generating plants (thermal, nuclear, etc) implement a number of regulation mechanisms to ensure energy production is equal to consumption at all times. is is done to guarantee grid stability. However, this regulation requires speci c response times. e integration of renewable energies (solar and wind power) may compromise this stability, due to the fact that the variability of this energy resource is far higher than that of conventional plants.
Figures 1 and 2 show two actual cases in which PV energy is produced at a 1MW power plant on a sunny day and on a day with scattered clouds, in addition to the output power when ESS are included in the plant.
In this way, for example, conventional power plants have an output power variability of 3-10%/min, but PV plants can reach values of up to 80%/min, depending on their size. is fact takes particular importance in weak grids such as those in islands or small grids based on diesel generators, where high penetration levels could endanger the stability of the system.
figure 3. Example of storage inverters performance
72 MARCH/APRIL 2016 nacleanenergy.com
Energy Storage Systems for Utility-Scale PV Plants
figure 4. Connection diagram of a power plant combining PV and storage inverters