Ethan BrooksBy Ethan Brooks

Updated November 2026

The largest thermal solar plant is generally considered to be the Ivanpah Solar Electric Generating System in the Mojave Desert of California, though the title is contested because capacity figures depend on how a plant is measured. Several large concentrating solar power sites in Morocco, Spain and China are close competitors. Most of them use mirrors to heat a fluid that drives a steam turbine.

Why the Ranking Is Hard to Pin Down

Thermal solar plants are usually ranked by nameplate capacity in megawatts, but that number can mean different things. Some operators report gross output, others report net output delivered to the grid, and a few count only the solar portion of a hybrid site that also burns natural gas. A plant with large thermal storage may also be credited with more capacity than its instantaneous output suggests, because it can dispatch power after sunset.

Shopping for one? See our guide: 7 Best Solar Thermal Energy Power Plant Books for Engineers and Students.

Because of these differences, you should check the reporting basis before comparing two sites. The official figures published by plant owners and national energy agencies are the most reliable starting point.

Factors That Set the Largest Plants Apart

Several design choices determine how large a thermal solar plant can grow and how much it delivers:

  • Collector type. Power towers focus sunlight onto a central receiver, while parabolic trough systems use long curved mirrors that track the sun along one axis. Towers reach higher temperatures, which helps with storage.
  • Thermal storage. Molten salt tanks let a plant keep generating for several hours after dusk. Storage capacity often matters more to a plant’s usefulness than raw mirror area.
  • Site irradiance. Direct normal irradiance is the key measure. Deserts with clear skies, such as the Mojave and parts of Morocco, offer the strongest resource.
  • Land and water. Large mirror fields need flat, open land. Many plants use dry cooling to reduce water use, which lowers efficiency somewhat in hot weather.

What to Do If You Are Researching or Planning a Site

If you are comparing large plants for a study, a report or a project, work through the details in a consistent order:

  1. Confirm whether the figure is gross or net, and whether storage is included.
  2. Check the collector technology, since tower and trough plants have different land and water needs.
  3. Look up the direct normal irradiance for the location from a recognized solar resource database.
  4. Compare the grid connection and offtake agreement, because a plant’s output only matters if it can be sold.
  5. Review the operator’s public performance reports rather than relying on design targets alone.

For background on how these systems convert sunlight into electricity, see How Do Solar Thermal Power Plants Work: A Step-by-Step Guide and Concentrating Solar Thermal Power Basics: How CSP Plants Make Electricity. For a look at one of the most ambitious tower designs, Cerro Dominador Solar Thermal Plant: How It Works and What Makes It Unique is a useful case study.

FAQ

Is Ivanpah really the largest thermal solar plant?

It has been among the largest by gross capacity, but rankings change as new projects open and as operators update their reporting. Check current figures from the plant owner or a national energy agency.

What is the difference between a thermal solar plant and a solar panel farm?

A thermal plant uses mirrors to heat a fluid that drives a turbine, while a photovoltaic farm converts sunlight directly into electricity in panels. Thermal plants can store heat for later use.

Can a thermal solar plant work on cloudy days?

Output drops substantially under clouds because concentrating systems depend on direct sunlight. Storage can carry the plant through short interruptions, but long overcast periods will reduce generation.

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Ethan Brooks

About Ethan Brooks

Ethan Brooks is part of our editorial team and reviews and edits our solar water heaters guides, checking product details against manufacturer specifications and owner feedback.