Shared BESS for Factory Tenants: Separate Control from Energy Allocation

A shared battery is one physical power system, not a separate battery account for each tenant. Before asking suppliers to price a multi-tenant BESS, agree where it connects, which controller can command it, which electrical constraints remain local, and how any benefit will be allocated. A spreadsheet credit cannot change the path of current or increase a tenant feeder’s capacity.

This guide is for industrial-park asset managers, FDI factory tenants and owner procurement teams evaluating shared storage in Vietnam. It provides architecture choices, a reproducible energy-accounting example and an RFQ evidence schedule. It does not establish permission to resell electricity, a tariff, tax treatment, a fire approval or a construction design.

Prepared for QuangAnhcons · Editorial focus: multi-tenant electrical interfaces and BESS procurement · Sources checked: 16 October 2026.

Three boundaries must agree without pretending they are the same

The electrical boundary identifies the common connection point, transformers, bus sections, protection zones and tenant feeders. The control boundary identifies who measures that point and who can change battery power or operating mode. The commercial boundary identifies the parties receiving a service, the evidence used to calculate it and the agreed treatment of losses and unavailable periods. A proposal that draws only the battery container leaves all three questions open.

Start with the actual supply and tenancy arrangements. One landlord-owned master meter feeding separately metered tenant branches is not equivalent to several legally independent electricity connections. Do not assume that a physical connection between them is allowed, or that one supplier’s agreement covers another tenant. Collect the actual connection documents, asset ownership and operating permissions. Our electrical due-diligence guide for leased factories explains why installed transformer capacity is not proof of available capacity at a tenant’s handover point.

Keep the contract’s service description narrow. It might concern an agreed contribution to reducing import at a common meter, or an agreed accounting allocation of measured storage output. Neither description alone promises backup, a tenant-specific peak reduction, a verified carbon benefit or money saved. Each additional promise needs its own boundary, baseline, measurement method and authority.

Choose an architecture that can deliver the stated service

Common-bus storage behind a common master meter can influence the net active power crossing that common boundary. Tenant meters still measure energy crossing their own feeders. Discharging at the common bus does not make a particular tenant’s downstream meter report less consumption when that tenant continues to draw the same load through it. If the business agreement allocates a share of the common benefit, describe it as an allocation, not as a physical tenant-meter reduction.

Separate storage behind each tenant connection provides a clearer physical attribution at each tenant meter, but requires several equipment packages, local integration and maintenance responsibilities. A central platform may coordinate requests, yet local protection, connection limits and owner permissions remain binding. Shared software is not necessarily shared electrical storage. Compare the added interfaces with the intended service before assuming centralization is cheaper.

A common service serving separately supplied premises needs an architecture and approved commercial arrangement before a dispatch algorithm. Do not propose tying independently supplied buses together merely to move stored energy between accounts. Such a scheme can change fault levels, earthing, operating authority, metering and protection boundaries. Treat it as a separate engineering and authorization question, not an EMS configuration shortcut.

An emergency-supply promise requires further evidence. A grid-following installation does not acquire islanding or black-start capability because several tenants reserve a percentage of its energy. The exact PCS, isolation arrangement, neutral/earthing design, essential-load boundary, protection and operating permissions must support the mode. A tenant outside the approved island cannot receive backup merely through an accounting entitlement.

As a concrete manufacturer-specific warning, the official SMA Sunny Island X manual’s section Sunny Island X as System Manager — System with Utility Grid describes that particular configuration as grid-connected without battery backup. Other configurations are listed separately. This is not a recommendation of an SMA product or a claim that all storage lacks backup; it shows why a generic product-family name is insufficient. Require the offered model, controller arrangement, firmware and applicable manual revision.

A common-meter energy balance does not allocate ownership

The following is a Class E hypothetical accounting exercise. Every power, interval and loss figure is invented. It describes a balanced aggregate active-energy ledger at one common bus with no PV, no other generation, no export and constant average powers within each interval. It is not a measured project, a dispatch recommendation, a PCS rating, a cable calculation or a legally valid settlement method.

Define positive battery power as AC discharge into the common bus. Negative power means charging from it. For each interval, master import equals tenant A load plus tenant B load plus common loads and assumed distribution loss, minus signed battery power. The loss term excludes the BESS conversion path; battery power is already measured at its AC boundary. Do not apply another conversion-efficiency factor to that measured AC quantity.

Each interval is 15/60 = 0.25 hours. Tenant A energy is (120 + 90 + 60) × 0.25 = 67.5 kWh; tenant B energy is (80 + 110 + 70) × 0.25 = 65 kWh. Common load and distribution loss total 30 × 0.25 = 7.5 kWh. AC discharge is (60 + 40) × 0.25 = 25 kWh, while charging is 20 × 0.25 = 5 kWh. Net battery AC contribution is therefore 20 kWh.

Master import totals (150 + 170 + 160) × 0.25 = 120 kWh. Independently, 67.5 + 65 + 7.5 + 5 − 25 = 120 kWh. The unit check is kW multiplied by hours, producing kWh. This verifies the invented interval balance only. It does not prove meter accuracy, battery round-trip efficiency or a beginning-to-ending SOC balance; no DC-energy or SOC data was supplied.

If an illustrative contract allocated gross discharge 60:40, its ledger would credit 15 kWh to A and 10 kWh to B. If it instead allocated net contribution on the same arbitrary ratio, the credits would be 12 and 8 kWh. These are two different conventions, not two answers to one defined contract. Who pays for charging, standby energy, losses and reserve availability still needs to be stated. The 60:40 ratio is invented and not an entitlement or recommended allocation.

Notice that the tenant consumption meters still total 132.5 kWh. Subtracting a credit from a tenant’s commercial statement does not alter that physical reading. Nor can the common-meter reduction establish what each tenant’s maximum demand would have been without storage. A claimed peak benefit needs synchronized interval data and an agreed counterfactual, not a monthly kWh percentage. Record whether demand is measured as active power, apparent power, a particular interval average or another contract-defined quantity.

With real data, calculate a residual at each time-aligned interval and retain its sign: master import plus BESS net discharge minus tenant loads, common loads and explicitly modelled losses. Do not bury missing meters, duplicated channels or clock errors inside a generous loss allowance. Establish uncertainty and investigation rules from the actual instruments and project basis; this example supplies no universal permissible percentage.

One command owner, with local limits that cannot be traded away

A shared service needs a controller-authority matrix before remote dispatch is enabled. Identify the owner of the master-meter target, the BESS operating envelope, tenant requests, reserve policy and maintenance lockout. A commercial optimizer can request power; it must not bypass battery limits, protection, a valid operating restriction or an authorized local isolation. Economic priority and safety authority are different categories.

Two controllers repeatedly writing competing setpoints can produce a system that looks responsive in demonstrations but behaves unpredictably when priorities conflict. The official SMA ennexOS section Control of external devices via Modbus warns that externally written settings can override SMA energy-management settings. That warning applies to the documented interface, not every EMS. Procurement should require each offered interface’s command priority, supported functions and failure behavior, verified against its exact documentation.

Do not put an arbitrary communications timeout or fallback kW value into the RFQ as an engineering truth. Request the OEM’s supported behavior and a project-specific risk assessment. A zero-output fallback may be unsuitable if the installation relies on storage to respect an import restriction; continued output may be unsuitable when the controlling meter is invalid. The solution can include an independently approved limit, load restriction or shutdown sequence, but it must be designed and tested for the actual site.

Tenant data permissions also matter. The asset owner may need aggregate demand while tenants consider production profiles confidential. Define access to raw records, retention, export formats, role permissions and incident response. Keep personal credentials and remote-access details out of a public RFQ appendix. A metering dashboard is not, by itself, an accepted billing system or a cybersecurity assessment.

Ask bidders for a bounded service and an auditable acceptance package

Issue one consistent architecture and assumptions register to all bidders. List the assets and meters included, normal supply state, intended services, excluded backup modes, tenant boundaries, data availability and unresolved approvals. Separate a firm functional requirement from a provisional study item. A bid based on a common master meter cannot be compared directly with a bid silently assuming separate tenant meters and individual storage packages.

Request an annotated SLD, metering schedule, sign convention, time synchronization method, control ownership and operating-state register. Require a model-specific performance envelope at the agreed AC boundary, auxiliary consumption treatment, reserve restrictions, maintenance assumptions and warranty duty conditions. The existing BESS AC-deliverable-energy acceptance guide addresses that performance boundary; it does not decide how tenants share benefits.

Use staged decision gates rather than invented delivery durations. First close the connection and tenancy architecture; then the metering/control design; then the approved commercial mechanism and unresolved permissions; then the integrated test plan. Installation and energization follow the authorized project programme. This is a procurement interface guide, not a complete construction schedule, so no critical path, OEM lead time or utility approval duration is claimed.

The acceptance plan should demonstrate valid meter directions and timestamps; commanded versus actual power; simultaneous tenant requests; rejected requests; reserve restrictions; loss and recovery of communications; maintenance inhibits; and complete data export. Use simulations or controlled tests agreed by competent parties where live testing would create risk. Do not unplug a live CT circuit, bypass protection or force islanding to demonstrate a dashboard function. The site electrical safety procedures, isolation and permit-to-work controls remain governing.

Retain the approved settings baseline, revisions, alarm/event logs, test limitations and unresolved defects. Acceptance of a data export is not acceptance of the power system. Acceptance of PCS operation is not approval of energy resale. The factory electrical interface register provides a structure for assigning these separate decisions to their actual owners.

Standards scope, open decisions and a useful next step

The official catalogue for IEC 62933-3-1:2025, Edition 1.0, published 20 November 2025, covers planning and performance assessment of grid-connected EES, including monitoring and control information. IEC 62933-5-2:2025, Edition 2.0, published 9 December 2025, concerns system-level safety for grid-integrated electrochemical storage across its life cycle. These scopes help define the technical evidence package; neither grants an electricity trading right or specifies the tenant allocation proposed here.

Only public catalogue scopes and the cited official manufacturer manual sections were reviewed for this article. No licensed standard clauses, test thresholds or installation settings are reproduced. The matrices, accounting example and procurement gates are original editorial proposals. The responsible designers must establish the project-selected IEC/TCVN basis, applicable Vietnamese QCVN and current connection, electrical-safety, fire and commercial requirements for the actual topology and service. No generic list is presented as proof of compliance.

Before commissioning a shared-storage feasibility review, assemble the supply agreements, tenancy boundaries, current SLD, synchronized meter records, proposed service definition and any actual supplier manuals. QuangAnhcons can discuss a defined electrical-interface and RFQ review. Leave uncertain permissions and performance promises visible; a useful proposal states what can be established, what still requires investigation and which party must close each decision before commitment.