Why a Single Point of Interconnection Changes the Economics
A solar farm that produces most of its energy around midday, while electricity prices peak in the early evening, leaves value on the table. Pairing battery storage with the same site allows developers to shift a portion of that midday output into higher-priced hours. The resulting hybrid project shares land, permitting, grid connection, and operational management in ways that change how the project is financed.
Co-location in this context means a solar array and a battery storage system sharing the same physical site and, typically, the same grid connection point. The solar and storage may remain electrically separate, each with its own inverters, or they may share some power conversion equipment. Either way, the combined facility is planned as one integrated project rather than two independent developments.
Project pipelines in several large markets have shifted toward hybrid configurations, as captured in the International Energy Agency’s World Energy Outlook 2025. The developer’s decision to co-locate has as much to do with interconnection arithmetic as with equipment costs. A battery that shares a connection with solar can avoid the cost and delay of a separate network study. It can also draw on the interconnection rights already held by the solar project: the export capability granted at the point of connection usually exceeds the array’s instantaneous output, and the difference between the two — the available export headroom — is capacity the battery can use, subject to the terms of the existing interconnection agreement. The economics of using that headroom rather than contracting for a new one are tied to the same revenue questions covered in the day-to-day economics of battery storage.
Shared Infrastructure Reduces Fixed-Cost Burden
A co-located project spreads certain fixed costs across two revenue-producing assets. The grid connection, site preparation, access roads, security, monitoring, and some balance-of-plant equipment are built once. A standalone storage project must recover those costs entirely from battery revenue alone. With co-location, the solar asset bears a portion, lowering the battery’s cost threshold even before any operational benefit.
Shared infrastructure also changes how the battery is operated. The storage system can charge during periods of high solar output, reducing the need to export all generation at once. It can then discharge later. This shifts the combined project’s net output profile without requiring the battery to purchase energy from the grid at times when prices may be high.
One Point of Interconnection, Two Assets
A new point of interconnection can involve years of study, network upgrades, and metering equipment. Standalone storage developers often face the same queue delays as solar and wind. A battery co-located with solar can connect behind the same point, using capacity that the solar plant does not consistently need. This reduces duplication of network studies, metering, and relay equipment.
The regulatory framework in the United States has moved to support this sharing. FERC Order No. 2023 sets out how co-located resources may share a single interconnection request and use surplus service when the solar plant is not exporting at full capability. This means the battery can operate within the interconnection capacity already granted to the solar facility, rather than waiting for a separate approval. Similar arrangements exist in other markets, though the details vary.
Charging Source Determines Much of the Treatment
The financial treatment of co-located storage depends heavily on how the battery is allowed to charge. In many jurisdictions, storage that primarily charges from the co-located solar array may be considered part of the same renewable energy facility for capital incentive purposes. If the same battery also charges from the grid, it may be treated as a separate asset, with different incentive eligibility, dispatch obligations, or metering requirements.
In the United States, investment tax credit rules now permit standalone storage to qualify, reducing the historical pressure to pair storage with solar solely to capture the solar credit. Co-location still matters for shared grid access and operational synergy, but the tax distinction between solar-charged and grid-charged storage is less absolute than it once was. Developers still need to confirm how their specific configuration is classified.
This distinction influences which revenue streams are available. A storage asset that can charge from the grid during low-price or negative-price hours can capture more value than one restricted to solar charging. The full range of market products is discussed in how grid-scale batteries make money, but co-location sometimes narrows that range depending on the project’s regulatory status.
The Shared Capacity Trade-Off
A single point of interconnection creates a shared export limit. The battery can absorb solar output that would otherwise be curtailed, but it cannot export at the same time as the solar array beyond the capacity of the connection. During a high-irradiance day with a full battery, the operator must choose between charging, exporting, or curtailing. This shared limit is often underestimated when comparing a hybrid plant with two standalone projects that each have their own connection capacity.
How the site handles this depends partly on whether the system is AC-coupled or DC-coupled. AC-coupled installations keep separate inverters and can be retrofitted more easily. DC-coupled systems share some power conversion equipment and reduce conversion losses when charging directly from solar, but they introduce different fault and control considerations. The choice affects how shared capacity is used at different times of day.
For sites that need discharge over longer periods than a few hours, co-located lithium-ion batteries may not be the best use of the connection. Some developers instead compare the case for longer-duration options such as flow batteries, iron-air, or hydrogen, covered separately in long-duration storage technologies. Beyond shared infrastructure, the duration of flexibility being added affects the value of the co-location decision.
Where the Model Breaks Down
Co-location does not automatically improve project returns. It works best in markets with strong evening price peaks, high solar penetration, and clear rules for hybrid resource participation. In markets where grid charging restrictions apply, storage may be limited to solar-charged operation, reducing its ability to stack market revenues. A battery that cannot charge from the grid has less access to the services that otherwise support storage economics.
In deregulated markets, the co-located battery is still a merchant asset. It faces the same market and contractual risks as other storage resources. Those risks, including how capacity and energy payments interact, affect even established storage technologies like pumped hydro, as discussed in pumped storage hydropower economics.
What Developers Should Watch
The economics of solar and storage co-location continue to shift as interconnection rules evolve and market designs adapt. The main variables to monitor include the rules governing surplus interconnection service, the treatment of grid charging, the classification of hybrid resources in market software, and the cost trajectory of solar and battery equipment. Each of these can affect project returns more than a modest equipment cost reduction.
References
- FERC — Order No. 2023 interconnection queue reforms, including co-located resource and surplus interconnection service provisions.
- IEA — World Energy Outlook 2025, analysis of solar and battery storage project economics and hybrid deployment trends.
