Robert A. García Cooper says voltage limits are already breached on low-solar circuits
The technical drama in Puerto Rico’s fight over rooftop solar rules just got more tangled. Energy Czar Josué Colón told regulators this month that an “uncontrolled surge” in rooftop solar was destabilizing the island’s grid and pushed the Puerto Rico Energy Bureau (PREB) to write stricter interconnection rules. Now a leading expert commenting on that same rulemaking says the data tells a more complicated story.
Parts of the grid are already running dangerously high voltage even on circuits with barely any solar installed, he assures, and the fix regulators are drafting could create a new harm of its own if it is not changed first.
The comments, filed August 27 by electrical engineer and researcher Robert A. García Cooper, are part of the Bureau’s process to create new rules for how solar systems and microgrids connect to the grid. García Cooper told regulators that real-world voltage data from multiple feeders show chronic overvoltage conditions that exceed the safety limits LUMA Energy says it will use to decide whether a customer may export power.
To illustrate the stakes, García Cooper described five “prosumer conditions,” meaning five real-world states a section of the grid can be in that determine what a solar customer can actually do with their system. In the healthiest condition, voltage stays within normal limits and customers can export power freely. In intermediate conditions, voltage spikes force inverters to shut off or reduce output, limiting access to net metering. In the most severe condition, voltage remains so high throughout the day that customers cannot export or even use their own solar energy at all. García Cooper said three of these conditions already exist on Puerto Rico’s grid today, affecting customers regardless of any future smart-inverter mandates.
One of his central warnings is that LUMA’s proposed voltage limit, roughly 1.06 “per unit” – a standard way engineers express voltage as a multiple of the normal service level, so 1.06 per unit works out to about 127 volts on a typical 120-volt home circuit – is already being exceeded on feeders that LUMA itself classifies as unsaturated, meaning they carry relatively little solar.
He cited measurements from Feeder 1421-05 in Fonalledas, which has only 11.78% solar penetration but recorded average voltages of 127.7 to 128.1 volts, above the threshold LUMA considers unsafe. A second feeder, 1903-01 in Juan Domingo, showed similar results, with line-to-neutral voltages, the reading from a single incoming power line, averaging 128.8 volts, and line-to-line voltages, the combined reading across the two power lines that feed a typical Puerto Rico home, exceeding 254 volts for more than 160 hours in one week.
“These values exceed the Class B threshold that LUMA confirmed as its proposed unsafe condition limit,” García Cooper wrote, adding that the overvoltage is “an operational parameter within LUMA’s authority” and not caused by solar saturation.
He also warned that once the Bureau mandates Volt-VAR smart inverter settings, a key feature of the draft regulation, customers will begin losing real power output. Volt-VAR settings direct an inverter to spend part of its capacity stabilizing voltage, technically known as reactive power, rather than delivering all the usable electricity, or real power, the solar panels are generating. That trade-off keeps the grid steadier, García Cooper said, but it also means less energy, and less savings, for the customer. He argued that loss represents a measurable economic harm that must be compensated, and that without a compensation mechanism, the regulation will create a new system-wide injury the moment it takes effect.
García Cooper proposed a simple measurement method using standard utility-grade metering to calculate the amount of real power a customer loses when Volt-VAR is activated. He argued that compensating customers for this service would increase hosting capacity, the amount of solar a given circuit can safely absorb, across the grid, reduce the need for costly upgrades, and align prosumer incentives with grid stability.
Beyond the technical issues, García Cooper raised an equity concern that has become increasingly central to the Bureau’s deliberations. Under current law, new solar customers may be required to pay for grid upgrades triggered by their interconnection, while earlier customers who contributed to the same constraints cannot be charged retroactively. The general ratepayer base cannot be charged either. García Cooper called this a “deadlock” with no legal funding mechanism.
He argued that early adopters were disproportionately higher-income households who could afford solar when prices were far higher, while today’s adopters, often lower-income families, are being asked to pay for upgrades partly caused by earlier installations. “A regulatory framework that assigns upgrade costs exclusively to the later arriving prosumer… does not satisfy the proportionality and benefit received principles of Joint Resolution 5-2026,” he wrote.
García Cooper urged the Bureau to explicitly name this gap in its final order, recommend legislative reform to the cost-allocation rules under Act 114-2007, and require maximum transparency in how upgrade costs are calculated and assigned.
He closed by posing three questions he said must be answered before the regulation is finalized: how the framework satisfies proportionality, how it prevents unfairly charging new customers for problems caused by earlier customers, and what remedy exists for customers on feeders where overvoltage is caused by utility operations rather than by solar saturation.
The filing lands in the middle of an already contentious rulemaking. The Solar and Energy Storage Association of Puerto Rico (SESA) and Solar United Neighbors (SUN) are separately urging PREB to preserve automatic interconnection rights and modernize the rules to support continued market growth, arguing against the tighter restrictions Colón has requested. The Energy Bureau is expected to release the next version of the draft regulation in the coming weeks as the rulemaking process continues.
