addition, certain of our PPAs allow the offtake purchaser to terminate the PPA if we do not meet certain prescribed operating thresholds or performance measures or otherwise by the payment of an early termination fee, which would require us to remove the renewable energy facility from the offtake purchaser’s site. These operating thresholds and performance measures are readily achievable in the normal operation of the renewable energy facilities.
Concentrated solar power
Concentrated solar power plants use mirrors to concentrate the energy from the sun to generate heat which will be either temporarily stored or used to drive traditional steam turbines or engines that create electricity. Our concentrated solar projects consist of parabolic troughs that concentrate reflected light onto a receiver tube. The tube is filled with a working fluid, typically molten salt, which is then heated by the concentrated sunlight and used to heat water for a standard steam power generation system. The energy produced by the CSP facilities is produced in AC.
Utility-scale wind and solar facilities
Our utility-scale solar and wind generation facilities are larger scale power plants for which the purchaser of the electricity is an electric utility, governmental entity or other third party or where the power is delivered directly to the grid. Our utility scale solar facilities are typically ground mounted solar photovoltaic or PV systems. The systems use either thin film, monocrystalline or polycrystalline PV modules that are attached to either fixed tilt racking or mounted on single axis (one direction) trackers, which allow the modules to track the sun as it moves throughout the day. The modules absorb direct and reflected sunlight to create electrical energy. Electrical energy is generated in direct current or DC and then converted to alternating current or AC using an inverter. The inverters are connected to a medium voltage power collection system that feeds into a substation, which increases the voltage further for interconnection with the existing electrical transmission system.
Our utility scale wind facilities consist of groupings of wind turbine generators spaced over a contiguous area. The wind turbine generators have three main sections, the rotor, nacelle, and tower. The rotor has three blades affixed to the hub at 120 degrees from each other. The nacelle houses the generator and gearbox and is attached to the hub through the main shaft at the front of the nacelle and the tower through the yaw drive at the bedplate of the nacelle. As wind turns the rotor, the main shaft turns the gearbox to increase the speed and turn the generator. The generator creates AC electrical energy. These turbines are connected via a medium voltage power collection system that feeds into one or more substations that are used to increase the voltage before transmitting the energy generated to the high voltage transmission system.
Item 3. Legal Proceedings.
See Note 18. Commitments and Contingencies to our consolidated financial statements included in this Annual Report on Form 10-K for disclosures concerning our legal proceedings, which disclosures are incorporated herein by reference.
Item 4. Mine Safety Disclosures.
Item 5. Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.
Class A Common Stock
TerraForm Power's Class A common stock began trading on the Nasdaq Global Select Market under the symbol “TERP” on July 18, 2014. Prior to that, there was no public market for our Class A common stock.
Upon the consummation of the Merger, our certificate of incorporation was amended and restated. TerraForm Power's authorized shares of preferred stock and Class A common stock were increased to 100,000,000 shares and 1,200,000,000 shares, respectively. There are no other authorized classes of shares, and we do not have any issued shares of preferred stock.
As of February 28, 2019, there were 13 holders of record of TerraForm Power’s Class A common stock and the closing sale price per share of our Class A common stock on the Nasdaq Global Select Market was $12.51. Affiliates of Brookfield held approximately 65% of TerraForm Power's Class A common stock as of that date.