The series of earthquakes that struck parts of Puerto Rico in early January focused a spotlight on vulnerabilities still facing the island's electric power grid.

Incomplete reports suggest that most solar-plus-battery distributed generating systems rode out the quakes. Many of those systems were installed following hurricanes Irene and Maria in 2017. The storms combined to wreck much of the island's electric power infrastructure.

Two people with Rocky Mountain Institute inspect a rooftop solar array in Barranquitas, Puerto Rico. Source: The Freeing Energy ProjectThe earthquakes represent a "first-order indicator that Puerto Rico is subject to disasters and that its grid is at risk," said Roy Torbert, Islands Energy Program principal with the Rocky Mountain Institute (RMI).

An earthquake measuring 6.4 on the Richter scale struck southwest Puerto Rico on January 9. It damaged the 990 megawatt, oil-fired Costa Sur power plant, which generates around 40% of the island's electricity. Officials said that repairs could take up to a year to complete. A turbine reportedly was damaged, as was the plant's foundation.

Last autumn, Puerto Rico's energy authority released a plan calling for an investment of more than $20 billion over 10 years to modernize the island's electric power grid. The plan includes adopting a more decentralized approach to electric power generation and distribution, including up to eight microgrids, natural gas-fired power plant and cybersecurity and emergency preparedness enhancements.

The U.S. Energy Department defines microgrids as localized grids that are able to disconnect from the traditional grid to operate autonomously. Because they are able to operate while the larger grid is down, microgrids are seen as one tool to help strengthen grid resilience and mitigate grid disturbances. They also may function as a grid resource for faster system response and recovery.

In May 2018, Puerto Rico's energy regulators adopted groundbreaking rules to help encourage microgrid deployment across the island. It identified three main types of microgrids.

• Personal microgrids that are intended to provide power to one or two consumers. These systems may, with regulatory permission, provide excess energy and grid services to neighboring customers.
• Cooperative microgrids that are intended to serve three or more cooperative members. These systems are organized under two subcategories: small co-op microgrids of less than 250 kW or large co-op microgrids of more than 250 kW. Co-op microgrids may sell excess energy and services to others.
• Third-party microgrids that are intended to have owners or operators who sell energy services to customers under rates approved by regulators and set on a project-by-project basis. Owners may earn a rate of return for the first three years of operation.

Enabling legislation

Speaking last August at a microgrid symposium, Alison Mason of SunJuice Solar said that Puerto Rico now has some of the most "ambitious and progressive legislation" regarding privatization, solar energy, microgrids and electric cooperatives. "The only things missing are cash, credit and a sufficiently large trained solar workforce," she said.

In the year after the microgrid rules were adopted, Mason said that one system had been qualified by the Energy Bureau. It was commissioned last June for Esperanza Village in Juncos and consists of 18 kW of solar photovoltaics, 32 kWh of battery storage, four Schneider 600 A MPPT80 charge controllers and three Schneider XW 6048 inverters. The system serves nine homes for senior citizens and is sub-metered with Leviton revenue-grade meters.

Rooftop solar for schools

Although most of the recovery plans remain on paper, roughly 100 megawatt-hours of battery energy storage capacity has been installed since Hurricane Maria, said Torbert.

Rooftop solar panels offer an opportunity to teach children about renewable energy. Panels were installed on 10 school buildings last fall with the help of RMI, Save the Children and Kinesis Foundation. The buildings are in mountainous regions of the island, and some of the schools were without power for months after the 2017 hurricanes. Credit: Rocky Mountain InstituteIncluded in that amount is around 240 kW DC of solar and 290 kWh of lithium ion battery storage. That capacity was installed on 10 school buildings last fall with the help of RMI, Save the Children and Kinesis Foundation. The buildings are in mountainous regions of the island, and some of the schools were without power for months after the 2017 hurricanes.

(In early March, the CBS News program 60 Minutes reported on solar energy systems being installed in Puerto Rico as well as in the Bahamas. Click here to see that video report.)

The solar-plus-storage arrays are designed to produce enough electricity to operate critical pieces of equipment at each school, Torbert said. That includes a water pump, a refrigerator and communications equipment in the principal's office. Following a disaster, the schools can serve as gathering points for the local community and offer electronic device battery charging and refrigeration for medicine.

During the earthquake the systems operated as intended, Torbert said. Days after the January earthquakes, roughly 95% of the installed systems were reported to be functional.

Torbert said the costs ranged from $100,000 to $200,000 per school. The cost included structural improvements, energy efficiency upgrades, system controls and a decade's worth of operations and maintenance service.

Structural integrity

A building's structural integrity is no small issue. One school that was close to the quake's epicenter collapsed. The collapsed building did not host a solar-plus-storage array, Torbert said, but the incident points to the importance of structural integrity. All totaled, Torbert said that roughly 2,500 structures on the island suffered damage or collapsed as a result of the quake.

In 2018, Rocky Mountain Institute published a report Solar Under Storm: Designing Hurricane-Resilient PV Systems. Its recommendations included:

• Using high-load PV modules (5,400 Pa)
• Requiring a structural engineering review and wind-tunnel report review
• Specifying a bolt hardware locking solution and bolt quality control process
• Specifying through bolting of modules as opposed to top-down or T clamps
• Requiring structural engineer review of lateral loads
• Not using self-tapping screws
• Specifying dual post pier foundations.

Its collaboration recommendations included collaborating with module suppliers, racking suppliers and other equipment suppliers to implement the correct tests and ensure that equipment is consistent with assumptions used in engineering calculations.