market in a 24-month period preceding the new regulatory period, plus a premium based on the financial condition of the Spanish electricity system and prevailing economic conditions. The amount of the return is recalculated at the end of each six-year regulatory period. The first regulatory period began on July 14, 2013, and will end on December 31, 2019. The next regulatory period will begin on January 1, 2020.
The costs we incur to operate, maintain and manage our renewable energy facilities also affect our results of operations. Equipment performance represents the primary factor affecting our operating results because equipment downtime impacts the volume of the electricity that we are able to generate from our renewable energy facilities. The volume of electricity generated and sold by our facilities will also be negatively impacted if any facilities experience higher than normal downtime as a result of equipment failures, electrical grid disruption or curtailment, weather disruptions, or other events beyond our control.
Seasonality and resource variability
The amount of electricity produced and revenues generated by our solar generation facilities is dependent in part on the amount of sunlight, or irradiation, where the assets are located. Shorter daylight hours in winter months result in less irradiation and the generation produced by these facilities will vary depending on the season. Irradiation can also be variable at a particular location from period to period due to weather or other meteorological patterns, which can affect operating results. As the great majority of our solar power plants are located in the Northern Hemisphere, we expect our current solar portfolio’s power generation to be at its lowest during the first and fourth quarters of each year. Therefore, we expect our first and fourth quarter solar revenues to be lower than in other quarters.
Similarly, the electricity produced and revenues generated by our wind power plants depend heavily on wind conditions, which are variable and difficult to predict. Operating results for renewable energy facilities vary significantly from period to period depending on the wind conditions during the periods in question. As our wind power plants are located in geographies with different profiles, there is some flattening of the seasonal variability associated with each individual wind power plant’s generation, and we expect that as the fleet expands the effect of such wind resource variability may be favorably impacted, although we cannot guarantee that we will purchase wind power plants that will achieve such results in part or at all. Historically, our wind production has been greater in the first and fourth quarters, which can partially offset any lower solar revenues in those quarters.
We do not expect seasonality to have a material effect on our ability to pay a regular dividend. We intend to mitigate the effects of any seasonality that we experience by reserving a portion of our cash available for distribution and otherwise maintain sufficient liquidity, including cash on hand in order to, among other things, facilitate the payment of dividends to our stockholders.
Cash distribution restrictions
In certain cases, we obtain project-level or other limited or non-recourse financing for our renewable energy facilities which may limit our ability to distribute funds to the Company. These limitations typically require that the project-level cash is used to meet debt obligations and fund operating reserves of the project company. These financing arrangements also generally limit our ability to distribute funds to the Company if defaults have occurred or would occur with the giving of notice or the lapse of time, or both. Over the course of 2016 and 2017, our ability to distribute funds from our renewable energy facilities was limited for substantially all of its renewable energy facilities with non-recourse financing due to project-level defaults related to the SunEdison Bankruptcy and the failure to timely deliver audited financial statements. Substantially all of those defaults have now been cured or waived. However, if we fail to timely deliver financial statements in the future, or other defaults occur and continue on our non-recourse financing arrangements, we could again be limited in our ability to distribute funds to TerraForm Power in order to pay corporate-level expenses and debt service obligations, as well as to pay dividends to the holders of our Class A common stock, and in our ability to comply with corporate-level debt covenants. See Item 1A. Risk Factors. Risks Inherent to an Investment in TerraForm Power, Inc.