EDP completes 368MWh Sandrini battery project

EDP Renewables North America has completed the 92MW/368MWh Sandrini Energy Storage project in Kern County, California, adding four hours of dispatchable battery capacity alongside the existing 300MW Sandrini Solar energy site.

EDP Renewables North America developed the battery with Redwood Coast Energy Authority, which has contracted 100% of the storage capacity through an energy storage service agreement. RCEA also purchases 100MW of generation from the neighbouring Sandrini Solar development.

The battery can deliver its rated 92MW output for four hours, corresponding to 368MWh of installed energy capacity. That duration gives the asset a different operating role from the shorter batteries that entered many electricity markets primarily to provide frequency response and other fast ancillary services.

Four-hour storage can still react rapidly to grid conditions, but it also has enough energy behind the inverter capacity to shift meaningful volumes of electricity between different parts of the day. That is particularly useful on solar-heavy systems, where photovoltaic production peaks during daylight while demand can remain elevated after solar output has begun falling.

Sandrini therefore adds a controllable asset beside a much larger variable generator. Co-location does not mean every megawatt-hour entering the battery must originate from the solar plant — EDP’s original project arrangements allow the BESS to charge from either solar production or the grid — but sharing the wider energy site can create advantages around land, operations, electrical infrastructure, and commercial management.

The battery itself requires a substantial power system beyond its cells. Bidirectional inverters, transformers, high-voltage switchgear, protection, metering, communications, thermal management, fire protection, auxiliary supplies, and plant-level control equipment must operate as a single 92MW asset at the grid connection.

Those systems determine how quickly Sandrini can change power, how accurately it follows dispatch instructions, and how it responds during voltage disturbances, frequency events, faults, and other abnormal network conditions. Large batteries are therefore increasingly treated as power stations built around power electronics rather than simply containers filled with cells.

Energy capacity introduces a second layer of operating constraints. Repeatedly moving hundreds of megawatt-hours through lithium-ion cells requires control of temperature, state of charge, depth of discharge, and cycling patterns if the installation is to retain usable capacity across its contracted life.

The operator must consequently weigh the immediate value of a dispatch instruction against its effect on the battery. Charging during a low-price period and discharging later may create an attractive gross spread, but round-trip losses and degradation reduce the value of each cycle.

Contracted storage capacity gives Redwood Coast Energy Authority access to a resource that can complement its renewable procurement without requiring solar output to match demand hour by hour. Stored electricity can be dispatched after the strongest period of photovoltaic production or retained for conditions when system flexibility carries greater value.

The arrangement does not convert solar generation into continuous baseload electricity. Four hours of storage is finite, and the battery can only discharge energy that has previously been charged. It does, however, change the time at which part of the site’s electrical output can be made available.

California has provided a large-scale test bed for that operating model because solar capacity has grown quickly enough to create pronounced changes in net electricity demand through the day. Batteries are increasingly used to absorb energy during periods of abundant supply and return it as solar generation falls, reducing the size of the ramp that has to be covered by other resources.

The engineering implications increase as the storage fleet grows. Grid operators need consistent inverter behaviour, coordinated protection, predictable voltage and reactive-power control, communications with dispatch systems, and confidence that large groups of battery plants will respond correctly during network disturbances.

Sandrini adds 92MW to that controllable fleet while sitting beside a renewable site three times its power rating. Its 368MWh capacity is large enough to alter the dispatch profile of part of the neighbouring generation rather than functioning solely as a rapid-response ancillary-services asset.

The project also extends EDP Renewables’ US storage portfolio. The company has been developing increasingly large batteries alongside its renewable generation business, reflecting a wider shift in which the commercial value of wind and solar is becoming more closely linked to when their electricity reaches the network.

That changes storage from an optional addition into part of the design discussion around large renewable assets. Connection capacity, wholesale price profiles, curtailment, grid-service revenues, battery degradation, and the timing of contracted demand increasingly have to be considered together.

Sandrini has now moved from that modelling exercise into operation. The 300MW solar site still produces when conditions allow, but 92MW/368MWh of that wider location is now dispatchable — a distinction that becomes increasingly valuable as renewable penetration rises.