How a mirror field runs past sunset
Solana is a concentrating solar power plant, or CSP (a design that uses mirrors to focus sunlight into heat rather than turning light straight into electricity the way a rooftop panel does). Long curved mirrors, called parabolic troughs, track the sun across the sky and focus it onto a pipe running down their center. Inside that pipe runs a heat-transfer fluid that reaches temperatures on the order of 700 degrees Fahrenheit, per the developer's public descriptions.
That heat boils water into steam, and the steam spins an ordinary turbine, the same basic machine a gas or coal plant uses. The part that sets Solana apart is a set of large tanks holding molten salt (a hot liquid mineral mix that stores heat well). During the day the plant can send some of its heat into the salt instead of the turbine, then draw it back out after sunset, giving roughly six hours of generation after dark at last public report.
What it cost, and who signed the check
None of this was cheap. Solana came online in 2013 at a cost reported on the order of $2 billion, financed in large part by a federal loan guarantee of roughly $1.45 billion from the U.S. Department of Energy. That guarantee let the developer, then the Spanish company Abengoa, borrow at terms a first-of-its-kind desert plant could not have gotten on its own.
Arizona Public Service agreed to buy the output under a long-term power purchase agreement (a fixed deal to take the plant's electricity for decades). At roughly 280 megawatts of gross capacity, Solana was among the largest plants of its kind in the world when it opened. Whether ratepayers got a bargain depends on what you compare it to, and that comparison changed fast.
Why almost nobody built another one
In the years right after Solana switched on, the price of plain photovoltaic panels fell hard, and then the price of lithium-ion batteries followed. A developer who wanted power after sunset no longer needed mirrors and hot salt. They could build a field of ordinary panels and park a battery next to it, usually for less money and with fewer moving parts.
The plant now reads less like a template than a survivor. Arizona has kept building solar, but the new projects across APS and Salt River Project territory are overwhelmingly panels paired with batteries, not concentrating plants. The heat-storage idea was not wrong. It was overtaken, and the desert now runs on a cheaper version of the same promise.
Worth watching this month
1. Watch the Arizona Corporation Commission's open meeting agendas, where APS and SRP resource and rate matters surface, though most items are routine.
2. Check the U.S. Energy Information Administration's monthly plant-level data for Solana's recent generation, which tells you whether the plant is still running near normal.
3. Follow APS resource planning filings for any mention of new storage procurement, the modern stand-in for what Solana was built to do.
4. Watch monsoon-season dust and cloud reports from the National Weather Service Phoenix office, since heavy dust cuts a mirror plant's output more than it cuts flat panels.
5. Keep an eye on Atlantica Sustainable Infrastructure updates, the current owner, for any operational notes on the plant.