As grid-scale battery energy storage systems (BESS) become central to making renewable energy projects more financially sustainable, more developers are choosing to integrate them on new projects. Likewise, existing asset owners are retrofitting BESS to enhance dispatch flexibility and improve, project returns. In both cases, project teams need to decide whether to manage the integration under a single full-wrap contract or under a split contracting structure.
Under the Full Wrap model, the principal entity contracts with the Engineering, Procurement and Construction (EPC) contractor, who is responsible for delivering the construction work, equipment and integration services under a single EPC contract. The EPC contractor then subcontract specific scopes to third party suppliers and contractors, such as the BESS supplier, construction work contractor and integrator.
A Split Contract sees the principal entity contracting separately with the construction work contractor, equipment supplier and integrator. Each contractor is responsible for their respective scope of works and the principal (either itself or through a consultant) is responsible for the management and coordination of delivery.
The full wrap model is generally preferred by principals seeking simplicity. There is a single point of accountability, reducing interface risk and limiting the need to resolve disputes (including recovery of costs) between multiple parties. This structure also aligns more comfortably with project financing, as lenders tend to favour a unified contract structure backed by familiar security instruments.
In contrast, the split model offers more flexibility and potential cost savings (though removing the EPC contract margin), particularly in a tight EPC market. Risks, however, abound and emphasis is often placed on coordination, a clearly defined responsibility matrix and expert in-house or external support.
Key split contracting considerations
- Principal contractor role – Depending on how the works are scoped, a decision needs to be made if one principal contractor will be responsible for WHS compliance for the entire site, or if separate principal contractors will be appointed for specific portions of the site.
- Development approvals – In many cases, planning approvals and lease terms would not have been drafted with future BESS expansion in mind. Changes to site use or new environmental assessments or approvals may be required, depending on the jurisdiction and project history.
- Offtake considerations – Where offtake or support agreements are in place, the integration of a BESS may have implications for those arrangements. Project owners should consider whether any amendments, notifications or consents may be required depending on how the BESS will interact with the existing energy output or market participation strategy.
- Technology – The BESS must be integrated and compatible with the technology used by the existing renewable energy project, including Supervisory Control and Data Acquisition (and the energy management system. This especially comes to the fore when integrating a new BESS onto a comparatively older project. Accordingly, the relevant BESS integrator must possess sufficient expertise to reconcile any technological differences and ensure the smooth operation of the assets.
- End-of-life strategy – When integrating a BESS, project developers and owners should ensure an end-of-life strategy which plans for the disposal, recycling or replacement of the BESS in compliance with local environmental laws.
- Project finance – In a third-party project finance context, contract structure can significantly influence lender appetite. Full-wrap arrangements commonly have a consent deed linking the lenders, EPC contractor, and project company to provide direct rights and enforceability. In contrast, split models often require additional due diligence and enhanced security to address integration risks. Lenders may seek conditional deeds of novation between the project company, EPC contractor and BESS integrator (and separately, with the Operations and Maintenance () contractor and BESS O&M provider) to ensure step-in rights and continuity. Additional security, such as parent company guarantees or bank guarantees from both the BESS integrator and BESS O&M provider, may also be required to mitigate risks of low performance, availability issues, or latent defects over the asset life.
Hybrid integration in solar: unlocking operational and commercial value
BESS integration into solar PV projects is rapidly becoming a core strategy for enhancing both grid reliability and commercial performance. Among the various integration methods, DC-coupling, where solar and storage assets share a single inverter and connection point, is typically preferred. This configuration streamlines grid interaction, reduces balance-of-plant costs, and eliminates the need for separate metering or dual-connection infrastructure. It also improves system efficiency by enabling direct charging from the solar array without intermediate AC conversion.
Beyond technical advantages, DC-coupled hybrid systems present a strong commercial case. By storing excess energy generated during periods of low demand or negative pricing, and discharging it during peak pricing intervals, these systems enable participation in energy arbitrage, frequency control ancillary services (FCAS), and other grid support mechanisms. This revenue stacking potential is particularly valuable in a volatile market. While hybrid development is increasingly being adopted at the greenfield stage, the economic impact of curtailment, particularly in high-penetration renewable zones, has prompted many asset owners across the National Electricity Market to explore retrofitting BESS onto existing solar PV assets.
Retrofitting BESS into existing projects introduces additional layers of technical and regulatory complexity. Initial feasibility assessments should consider whether amendments are needed to land tenure agreements, planning approvals, or other project authorisations. Upgrades to inverters and hybrid controllers may be required, depending on the existing site design and age of the PV plant. Compliance testing, including AEMO’s Dynamic Model Acceptance Testing, may also be triggered, adding further cost and time to integration. Grid constraints can limit the feasible capacity or discharge profile of the battery, directly influencing system design and commercial returns. Despite these hurdles, a well-executed retrofit can significantly improve project economics and operational flexibility, particularly when supported by clear integration strategies.
For solar projects integrating BESS, whether through greenfield development or as a retrofit, the choice of contracting model remains a key commercial consideration. While full-wrap EPC arrangements continue to appeal to investors and lenders seeking a streamlined, lower-risk structure, BESS integration often demands deeper involvement from the asset owner due to its technical and regulatory complexity.
There is no one-size-fits-all model when it comes to BESS integration with renewable energy projects. What is clear is that as storage becomes a central pillar of renewable energy projects, integration will remain a critical area of legal and commercial focus.
The Hamilton Locke team advises across the energy project life cycle – from project development, grid connection, financing, and construction, including the buying and selling of development and operating projects. For more information, please contact Matt Baumgurtel.
