What the Distribution Impact Study is checking

A Distribution Impact Study is Meralco’s engineering assessment of what happens on the distribution circuit when your solar system starts exporting power back to it. Meralco’s grid was designed for one-way flow — from Meralco’s substation, down the primary line, through the distribution transformer, into homes. A rooftop solar system reverses that flow during sunlight hours, and if enough systems on the same circuit all export simultaneously, the local circuit can experience voltage rise, protection coordination issues, or reverse-power problems at the transformer.

The DIS answers three questions specific to your address: how much export capacity does the local circuit already carry from previously approved solar? Does adding your system push the circuit past a threshold where an upgrade or protection change is needed? And if so, what needs to happen before your system can safely interconnect?

Most residential systems under 10 kWp on established residential feeders do not trigger any circuit-level issue, and the DIS is essentially a formality. Larger systems and systems on already-solar-heavy circuits are where the study starts to have real technical teeth.

When Meralco requires a DIS

Under the current Meralco Net-Metering Program flow, a DIS is triggered based on system capacity and cumulative circuit loading:

• Systems ≤5 kWp: usually cleared through a simplified process without a full circuit study
• Systems 5–10 kWp: a standard DIS is required but typically resolves without technical issues on residential feeders
• Systems 10–100 kWp: a full DIS with detailed circuit modeling — this is where delays and required upgrades start to appear
• Systems above 100 kW: fall outside the net-metering framework and go through the larger distribution utility grid impact study process

Meralco also requires a DIS re-run if there is any material change between the initial application and the actual installation — different inverter model, larger array, changed export capacity. Getting the DIS numbers right on the first submission saves weeks of back-and-forth.

Documents you (or your installer) will submit

The DIS technical submission is the installer’s job, not yours. But knowing what is in the file helps you evaluate whether your installer knows what they are doing. A typical submission includes:

• Meralco account number and service address (for circuit identification)
• Manufacturer specification sheets for the inverter — with certified anti-islanding and grid-support functions per the Philippine Distribution Code
• Single-line diagram of your PV system through to the point of common coupling
• System export capacity (usually equal to inverter nameplate AC rating)
• Panel specification sheet (for verification of DC side sizing)
• The building permit or a copy of the OBO application receipt
• Signed Net-Metering Application form and Interconnection Agreement

The inverter specification is the most technically loaded document. Meralco checks for compliance with the Philippine Grid Code and Distribution Code — specifically anti-islanding (IEEE 1547 / UL 1741 equivalent), voltage and frequency ride-through, and reactive power capability. Not every imported inverter has the certifications Meralco recognizes, which is one reason installers stick with a short list of proven brands (Sungrow, Solis, Huawei, Growatt, Deye for residential in the PH market).

How long the DIS takes

Meralco’s published turnaround under the Ease of Doing Business framework is 20 working days for the DIS itself, though in practice the elapsed time from submission to certificate of interconnection is longer because the process has multiple stages:

• Submission and completeness check: 1–2 weeks
• Technical review and circuit modeling: 3–5 weeks
• Issuance of DIS results / conditions: 1 week
• If conditions require equipment changes on Meralco’s side (protection settings, tap changer on the transformer, feeder upgrade): additional 4–12 weeks depending on scope

For a typical 5–8 kWp residential job with no circuit-level issues, the whole DIS-to-interconnection sequence takes 8–12 weeks from complete submission. For a 20+ kWp commercial job on an older feeder, it can stretch to 4–6 months if Meralco needs to upgrade equipment at the transformer or set new protection coordination.

What can trigger a re-study or require upgrades

A few situations reliably cause DIS delays or additional work orders. Your installer should flag them before you sign a contract:

• Cumulative circuit loading already high: if several nearby homes already have solar on the same feeder, the reserve capacity may be exhausted. Meralco may cap the size of new systems or require a feeder upgrade paid partly by the customer.
• Small/old distribution transformer: older residential transformers rated 25–37 kVA can hit thermal limits when back-fed. Larger systems may need a transformer replacement before interconnection.
• Rural or edge-of-service-area feeders: voltage-rise sensitivity is higher on long, lightly loaded feeders. Meralco may set stricter export limits or require volt-var settings on the inverter.
• Anti-islanding non-compliance: if the specified inverter does not carry a Meralco-recognized certification, the DIS will reject the design until an approved model is substituted.

None of these are common failure modes for a standard residential 5–8 kWp system on a QC subdivision feeder. They come up mostly in commercial rooftops and in areas where dozens of homes are already grid-tied.

How installers manage timing

A competent installer runs three tracks in parallel rather than in series. While your OBO permit is being processed, they simultaneously submit the Meralco Net-Metering Application and start the DIS, and simultaneously order the equipment. This is why one installer can quote 3–4 months from contract to switch-on while another quotes 6–8 months — the difference is not physical construction time (that is 3–5 days on the roof) but how well they parallelize the paperwork tracks.

You can check this: ask your prospective installer to walk you through their timeline. If they describe permit-then-DIS-then-install as sequential steps, they are adding 6–8 unnecessary weeks. If they describe it as parallel tracks with clear owners on each side, they know what they are doing.

A well-run DIS is invisible to the homeowner — you find out it existed only when the installer says the Certificate of Interconnection has been issued and the bi-directional meter installation has been scheduled. That is the goal.

Related guides

• Meralco Net-Metering Program: complete step-by-step guide
• Getting a solar building permit from QC OBO
• RA 9513: what the Renewable Energy Act means for homeowners