March 2, 2024
The Partly Cloudy State

Photo: FPL

Equal in size to 30 football fields, FPL's Manatee Energy Storage Center battery storage system in Parrish is one of the largest in the world.


The Partly Cloudy State

Mike Vogel | 9/26/2023


The Sunshine State nickname is more buzzword than actuality — at least if your business is power generation. Central Florida has 277 days a year — 76% of the calendar — that are cloudy or partly cloudy, notes Linda Ferrone, chief consumer and marketing officer for power provider Orlando Utilities Commission. “It’s the partly cloudy state,” Ferrone says. Among large solar-power producing states, “it’s very unique to Florida. California and Arizona don’t have these challenges.”

Solar power, Florida’s investor-owned utilities say, for the present is the most cost-efficient method of adding new power generation. But it has a different cost: Added complexity to the power grid. California and Texas have seen their power grids struggle as their shares of renewable power have grown. Florida operates differently than those states and state policy prioritizes reliability. Nevertheless, solar presents intermittency problems.

The standard utility-scale solar plant in Florida is sized just under 75 megawatts per hour. Utilities like to make that relatable to consumers, as Duke Energy did in a press release this year: “At peak output, each site will generate enough carbon-free electricity to power what would be equivalent to around 23,000 homes.” A key qualifier is “at peak output.” That new plant powers zero homes at night.

Unlike nuclear or natural-gas plants, solar plants produce near their maximum output only during part of sunny afternoons. Heat and humidity affect output. Then there are clouds. Their shadows can knock a solar plant’s production down by 70% in a couple minutes. The fluctuations happen faster than utilities are accustomed to dealing with from traditional power plants. And Florida gets both the daily variety of clouds passing over and multi-day weather events, which can knock down production for extended periods.

OUC and the University of Central Florida have been working on a camera-based technology to forecast cloud arrival and impact to help the utility plan to plug generation gaps with other power sources. Florida solar plants month-in and month-out produce in the 20-30% range of their stated capacity, according to utility filings with the state Public Service Commission.

The intermittency and volatility present challenges for running the power grid. Lakeland Electric plans to add 74.5 megawatts of solar by 2025. To address solar’s high variability, it’s adding six internal combustion engines capable of pumping out 120 megawatts of power in less than five minutes, according to its 10-year site plan filed with the state PSC.

Solar plants generally don’t produce during Florida’s peak demand period during winter mornings, when businesses begin drawing power and people start their day. Solar output falls off during summer’s peak demand periods in the late afternoon/early evening when businesses are active power users and people return home to crank up the air conditioner and household appliances. “Those are both times when the sun is not shining and solar is not producing,” Ferrone says. “On a day-to-day basis, solar doesn’t cut it. You’ve got to have some battery or energy storage.”

Utilities and researchers across Florida and around the world are working to improve energy storage. That emerging technology also will consume land, although not as much as solar arrays. An industry rule of thumb is 5 megawatts of storage to the acre.

FPL has one of the world’s largest solar batteries at 409 megawatts in Manatee County, which it can use during peak times, nights or cloudy days. For two hours, it can power the equivalent of 329,000 homes, or more than 50,000 homes for a 12-hour period. The utility is aiming to add 50,000 megawatts of storage in future years. When a solar plant isn’t producing power, FPL relies on natural gas, nuclear and battery storage, says spokesperson Jack Eble.

The goal is for customers to be able to take for granted that when they flick a switch, a light comes on. “Solar is a huge opportunity for us, but it comes with a lot of complexities we have to solve,” says Justin Kramer, OUC’s manager of emerging technologies. “We want it to be in such a way our customers don’t have to think about electricity.”

Peaks and Troughs

As of Dec. 31, the state’s three largest utilities had total solar maximum output of 5,519 megawatts per hour. During the summer peak hour their output fell to 2,888 megawatts and the winter peak is just 54 megawatts — less than the maximum capacity of a single utility-scale plant, according to the Florida Reliability Coordinating Council.

Tags: Energy & Utilities, Feature, Solar

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