Selling surplus rooftop solar electricity is not simply a matter of selling whatever electricity a facility does not use.
Whether surplus electricity can be sold in practice depends on the applicable regulatory case, the grid connection arrangement, the network’s ability to receive additional power, the metering configuration and the operating architecture of the system.
Vietnam’s Decree No. 243/2026/ND-CP was issued and took effect on June 26, 2026. It amends provisions of Decree No. 57/2025/ND-CP and Decree No. 58/2025/ND-CP, including provisions relating to the sale of surplus electricity from self-generated, self-consumed rooftop solar systems.
For an industrial facility, the key question is therefore not only:
“How much surplus electricity can we sell?”
A more useful set of questions is:
Does the rooftop solar source fall within an eligible case? When does surplus generation occur? What grid, metering and control requirements need to be addressed before surplus-electricity revenue is included in the investment case?
For a broader regulatory overview, see Decree 243/2026: Key Updates on DPPA & Rooftop Solar.
Surplus generation does not automatically mean the electricity can be sold
A rooftop solar system may generate more electricity than the facility is using at certain times, but this does not automatically mean all of that surplus is eligible for sale.
Decree 243 defines the categories of self-generated, self-consumed rooftop solar sources that may sell surplus electricity, subject to the applicable conditions for each case. EVN also summarizes these amended provisions in its overview of Decree 243/2026/ND-CP.
For an industrial business, this distinction matters:
Surplus generation and eligible surplus electricity are not the same thing.
A facility may export electricity during weekends, production breaks or other low-load periods. Before that electricity is included in a financial model, however, the business should first confirm the applicable regulatory case, the actual connection arrangement and the relevant implementation requirements.
A practical sequence is:
Surplus generation → applicable conditions → ability to sell → revenue assumption.
Selling Surplus Rooftop Solar Electricity: How Should Businesses Interpret the 50% Limit?
Under the amended provisions, surplus electricity may be sold by agreement between the seller and buyer, generally up to 50% of the electricity generated at the output of the rooftop solar source based on solar irradiance.
Surplus electricity is determined at the output of the inverter.
This should not be interpreted as:
- 50% of the installed system capacity; or
- simply 50% of whatever electricity the facility does not consume.
In actual operation, the amount of surplus electricity depends on how closely rooftop solar generation aligns with the facility’s electricity demand over time.
Two factories with similar total electricity consumption can have very different surplus profiles if their production schedules, operating shifts or weekend loads are different.
This is why surplus-electricity assessment should begin with the facility’s load profile, rather than monthly electricity consumption alone.
For more context, see Industrial Load Profile Analysis: What Data to Review?.
When Can the Parties Agree to Sell More Than 50%?
From the effective date of Decree 243 through December 31, 2030, the parties may agree to purchase and sell surplus electricity above the 50% level where the grid at the connection area has sufficient receiving capacity and the transaction meets the applicable requirements for safe grid and power-system operation.
For a business, this should be treated as a conditional mechanism, not an automatic entitlement.
A financial model should therefore not use a surplus-sale ratio above 50% as its base case unless the relevant grid conditions and purchasing arrangement have been clarified.
The practical implication is important: a regulatory mechanism that allows a higher surplus-sale ratio does not by itself establish how much electricity a specific industrial project will be able to sell.
How Does BESS Affect Surplus Electricity?
Decree 243 provides that surplus electricity eligible for purchase may include electricity discharged from an energy storage system, provided that the stored electricity was charged from the rooftop solar source.
This is particularly relevant for projects combining rooftop Solar PV with a battery energy storage system (BESS).
It should not be assumed that all electricity discharged from a BESS automatically qualifies as surplus rooftop solar electricity.
Where the BESS can charge from multiple sources, the operating strategy, controls and metering architecture should be defined during the design stage so that the source of stored energy can be appropriately identified for the intended operating and commercial arrangement.
From an engineering perspective, BESS should follow a clear sequence:
Load analysis → application definition → power and energy sizing → control strategy → integration → EMS → operation.
Battery capacity should not be selected first and justified later.
For further context on storage applications and system design, see BESS Solutions for Industrial Facilities.
For projects combining generation, storage and industrial loads, see Solar and BESS Integration for Industrial Facilities.
Why Should kW and kWp Not Be Used Interchangeably?
During implementation guidance in Ho Chi Minh City, the Electricity Authority clarified that rooftop solar development capacity and the parameters used to determine surplus electricity are different.
Development capacity is determined based on inverter capacity, expressed in kW, while the irradiance-based generation calculation refers to the nominal capacity of the installed PV modules, expressed in kWp.
Further implementation discussion is available in EVN’s article on rooftop solar implementation issues in Ho Chi Minh City.
This means kW and kWp should not be used interchangeably when describing project capacity or regulatory application.
It also does not mean the regulation establishes a fixed DC/AC design ratio.
The actual system configuration still needs to be determined from site conditions, roof constraints, irradiance, equipment characteristics, load profile and the operating objectives of the facility.
Metering Should Be Considered During Design, Not After Installation
Where surplus electricity is expected to be sold, metering should be treated as part of the system architecture rather than as an administrative item to be addressed after construction.
The project team should clarify:
- the actual source connection point;
- connection voltage;
- delivery point;
- metering arrangement;
- relevant data requirements; and
- responsibilities of the parties under the applicable case.
Where BESS is included, metering may also need to support the operating logic used to distinguish the source of energy charging the storage system.
Public implementation guidance in Ho Chi Minh City has also addressed surplus-electricity sales, connection levels, grid-loading considerations and implementation requirements. See EVNHCMC and Ho Chi Minh City Department of Industry and Trade guidance on Decree 243.
For industrial facilities, metering, connection and controls should therefore be considered early enough to influence the technical architecture before equipment configuration is finalized.
Does Zero-Export Apply the Same Way to Every Rooftop Solar System?
No single Zero-Export configuration should be assumed to apply to every project.
One implementation point clarified by the Electricity Authority is that the voltage at which a customer purchases electricity is not necessarily the same as the actual connection voltage of the rooftop solar source.
For example, a facility may purchase electricity at a higher voltage while the rooftop solar source is connected at a lower-voltage point within the facility’s electrical system.
The applicable connection level therefore needs to be determined from the actual electrical arrangement of the source rather than assumed from the customer’s electricity-purchase voltage.
Before defining a Zero-Export or reverse-power-control scheme, the business should clarify:
- the actual connection point;
- the source connection voltage; and
- whether the project is intended to sell surplus electricity.
The detailed technical requirements should then be reviewed against the project configuration and the regulations applicable at the time of implementation.
Zero-Export should therefore be treated as a project-specific control requirement, not as a standard configuration to be applied identically across all rooftop solar systems.
Does the Ability to Sell More Surplus Mean the System Should Be Larger?
Not necessarily.
The appropriate rooftop solar capacity still depends on the facility’s time-based load profile, roof conditions, self-consumption potential, existing electrical system, connection arrangement, grid hosting conditions and expected operating changes.
A change in the surplus-electricity mechanism does not, by itself, justify oversizing the rooftop solar system.
The same principle applies to BESS.
The presence of surplus electricity at certain times does not, by itself, establish a case for energy storage. BESS should only be configured after the application, load data and operating strategy are sufficiently defined.
For this reason, the design question should not be:
“How much rooftop solar can fit on the roof?”
It should be:
“What system configuration best matches the facility’s load, operating requirements, connection conditions and investment objectives?”
What Should a Business Check Before Selling Surplus Electricity?
Before finalizing the system configuration or including surplus-electricity revenue in the financial model, the business should clarify five areas:
- Eligibility: Does the rooftop solar source fall within a case where surplus electricity may be sold?
- Load profile: When does surplus generation occur, how significant is it, and how does it vary with the facility’s operating schedule?
- Grid connection: Where is the source actually connected, at what voltage level, and what grid constraints need to be confirmed?
- Metering and controls: Are the metering arrangement, BESS configuration and export-control requirements aligned with the actual project architecture?
- Commercial assumptions: Is the expected surplus-sale ratio based on confirmed conditions, or is it still an assumption?
The logic can be summarized simply:
Surplus generation ≠ automatic eligibility for sale ≠ a reason to design the project around maximizing surplus electricity.
For an industrial facility, the first priority remains a system configuration that matches the site’s load, operating requirements, safety conditions and investment objectives.
Surplus-Electricity Sales Should Be a Design Input, Not a Default Assumption
The surplus-electricity mechanism should be considered early in the design process, but it should not become the commercial assumption that determines the entire project configuration.
Surplus ratio, grid hosting capacity, connection point, metering, BESS and the control architecture can all affect both the technical design and the financial model.
365Energy approaches Solar PV, BESS and EMS as modules within an integrated energy system for industrial facilities, subject to the actual project scope, site conditions and operating requirements.
For businesses evaluating rooftop Solar PV with surplus-electricity sales, a practical next step before finalizing capacity is to:
review the load profile, assess the connection arrangement, define the metering requirements and confirm the regulatory conditions applicable to the project.
Note: This article reflects publicly available regulations and implementation guidance reviewed as of October 2, 2026. It is intended for general information only and does not replace project-specific legal advice, authorized engineering design or a determination by the relevant authority or electricity utility.
References
Government of Vietnam — Decree No. 243/2026/ND-CP
View the official Decree on the Government Portal
EVN — Overview of Decree 243/2026/ND-CP
View the EVN regulatory summary
EVN — Rooftop Solar Implementation Issues in Ho Chi Minh City
View the EVN implementation article
EVN — Ho Chi Minh City Guidance on Decree 243/2026/ND-CP
View the EVN guidance article