Puerto Rico's massive debt restructuring, which includes its electric utility the Puerto Rico Electric Power Authority, has put the spotlight on the United States territory. But amid the financial turmoil, PREPA is refocusing efforts on another front: energy storage. 

The U.S. territory has a Renewable Portfolio Standard that aims to obtain 20% of its electricity from renewable energy by 2035, and in 2013, required renewable energy developers to incorporate energy storage into installations, and meet technical requirements. Now a couple of storage-plus-renewable projects are in the works. 

One such storage project in Puerto Rico aims to demonstrate the load-shifting ability of hybrid batteries.

Sonnedix is developing a project in Salinas that involves building a 250-kWp solar array that will be used to charge a 1.25-MWh aqueous hybrid ion battery array from Aquion Energy.

The project is designed as a pilot to test Aquion’s battery chemistry, said Sean O’Day, director of future solutions at Sonnedix. The Miami-based company’s longer term interest is to be able shift the load of solar plants beyond daylight hours in order to develop what O’Day calls “baseload solar” projects.

The Aquion storage project will provide overnight energy needs of the 16-MW Horizon Energy solar plant in Salinas that was developed by Horizon Energy LLC, a subsidiary of Sonnedix Group, in partnership with Yarotek, a local developer. The $40-million solar farm began commercial operation in August 2015.

If successful, the storage project would reduce about 50 kW to 70 kW of constant parasitic load that would otherwise be supplied by fossil fuel generation from the local utility grid and would make the Horizon solar farm almost grid independent.

Aquion said its batteries are designed to provide long duration charge and discharge cycles that can enable a solar farm to operate as a baseload plant to be dispatched on demand.

There are at least two benefits of the solar plant being self-sufficient. As electricity prices continue to rise, it helps the economics of the solar plant. Secondly, there is an environmental benefit because it enables PREPA to burn less petroleum, which fuels much of the island’s electrical output.

In Sonnedix’ case, the Salinas storage project is paying for itself, O’Day said. Without overnight storage, the larger solar project would have to buy power from the utility at retail rates, which fluctuate with the price of oil but average about $275/MWh. “That justifies the financial case for load shifting,” O’Day said.

Puerto Rico's potential for energy storage

Puerto Rico could be ripe territory for projects that combine energy solar power and energy storage. In December 2013, Puerto Rico set up minimum technical requirements that require all new wind and solar projects to include minimum energy storage capabilities aimed at helping to stabilize the island’s grid.

Each project must have enough energy storage to provide 45% of the plant’s maximum generation capacity over the course of one minute, for use in smoothing out the ramp rate of power coming on and off with changes in sunlight or wind speeds.

Each new project also must have enough storage to meet 30% of its rated capacity for about 10 minutes so it can be called on for frequency regulation.

For some projects, the storage mandate has added as much as 20% to capital costs. PREPA’s financial problems have also affected developers who now have to bear a $0.04/kWh debt surcharge.

The Aquion storage project in Salinas was not done in response to those PREPA requirements, O’Day said. He said the 16-MW solar project has its own storage capacity that can provide frequency regulation service and ramp down the project from 100% to zero in 10 minutes.

O’Day said Salinas is a flagship project for Sonnedix and that the company is pursuing further partnerships with developers of combined solar and bulk energy storage projects around the world.

O’Day declined to give details of the projects Sonnedix is pursuing, but in general, he said places where power is generated by high priced fuel are attractive, especially if peak demand does not coincide with peak solar output. Many island grid meet those requirements, but he also said he is looking at mines and at markets where islanded microgrids are feasible.

“Simple solar power is a heavily commoditized,” he said. The better opportunity is to sell a “utility-like power product.”