Mix Master

Determining the power mix for Tucson is not a one-size-fits-all endeavor. Each source has benefits and drawbacks, which means there is no perfect solution. To gain a little perspective on the decisions TEP makes when powering Tucson, click on a source to see how it performs alongside other options in the mix.

Select a Resource
Capital Cost

Capital Cost refers to the initial expense of building and energizing a project. It includes engineering, materials, labor, equipment, and financing costs.

Levelized Cost

Levelized Cost refers to the average cost to produce a unit of energy over the entire life of the resource. It includes the capital cost as well as fuel, operations and maintenance costs annualized over the operating life of the resource. The length of the operating life will vary depending on the resource.


Intermittency is a measure of the amount of time a resource is unavailable for dispatch due to planned and unplanned outages, maintenance, etc. For renewable resources, intermittency also represents times when the wind doesn’t blow or the sun doesn’t shine.

Water Use

Water Use refers to the amount of water consumed to generate a unit of energy. Most water consumed in power generation is used for cooling. Water use represents the difference between the amount withdrawn for cooling and the amount returned to the source afterward.

Land Use

Land Use refers to the area of land needed to construct and operate a resource, including ancillary facilities such as maintenance shops, storage areas and landfills.

Air Emissions

Air Emissions refers to the conventional regulated emissions (nitrogen oxides, sulfur dioxide and particulate matter) produced while generating a unit of energy. Air emissions are a function of the resource itself (e.g. solar panels have zero emissions) as well as any control equipment.

Carbon Emissions

Carbon Emissions refers to the amount of carbon dioxide (CO2) and other greenhouse gases emitted while generating a unit of energy. Carbon emissions are a function of the resource itself and the efficiency of the resource (the energy produced per unit of fuel).

Coal refers to a new, advanced, supercritical, pulverized coal-fired steam electric generating unit (EGU). Coal is crushed into a fine powder (i.e. pulverized) and injected into a large boiler lined with piping through which water flows. The combusted coal heats the water into steam, which is transferred to a steam turbine. Blades in the turbine spin a shaft, and an electrical generator converts that rotational energy to electrical energy.

Nuclear represents new construction within the United States. Nuclear power uses the heat produced through a controlled nuclear fission reaction to heat water into steam, which in turn drives a turbine generator.

Wind refers to utility-scale (typically greater than 1 megawatt each) wind turbines. Wind contact with the blades produces rotation in the turbine, which is connected to an electrical generator.

Utility-scale Solar refers to a large (e.g. 10 megawatt) solar facility developed by the utility or by a third party under a purchase power agreement. These systems use PV panels with inverters, and they may include tracking equipment that allows the panels to “follow” the sun throughout the day.

Natural Gas Combined Cycle (NGCC) refers to one or more natural gas-fired CT generators paired with equipment that uses the exhausted hot air to heat water into steam that drives another turbine generator. The use of exhausted heat significantly improves the efficiency of the plant (e.g. more energy for the same amount of fuel).

Natural Gas Peaking refers to a new natural gas-fired combustion turbine (CT) generator. Natural gas is combusted with compressed air and the exhaust from that combustion drives a turbine. An electrical generator connected to the turbine converts rotational energy to electrical energy.

Rooftop Solar refers to a residential system including photovoltaic (PV) panels and an inverter to convert direct current (DC) to alternating current (AC) power.

Solar Thermal with Storage refers to systems that concentrate solar energy on a heat transfer fluid. The heated fluid is used to produce steam that drives a turbine generator. These systems can be sized to produce excess heat during periods of intense sunlight. That excess heat can be stored for use during cloudy periods or after sundown. Ten to 18 hours of storage is typical.

Battery Storage refers to large banks of batteries capable of supplying power for short durations to compensate for intermittent renewable resources or support high energy demand. The batteries recharge overnight, when energy use is low. They typically have an efficiency of approximately 75% to 85%, meaning that the amount of energy they supply is 15% to 25% less than the amount of energy needed to recharge them.