Solar Step-Up Substation Specification Checklist: What to Prepare Before Quotation

A clear RFQ helps the buyer and supplier establish the project requirements before quotation. This checklist brings together the project, inverter, grid and site information that a solar EPC or owner can share when enquiring about a step-up substation. It can help reduce avoidable clarification and identify details that still need review.

Everything below is a set of inputs to provide or confirm — not fixed values, and not a selection decision. If some items are not available yet, the project can still be reviewed on a preliminary basis. In that case, simply state the current project stage and share whatever documents you already have.

Before you send your RFQ, have these ready:

• Country and project location, and the current project stage
• Any single-line diagram (SLD) you already have
• PV inverter data (model, AC output, quantity)
• Interconnection voltage level and the applicable grid-connection documents
• Site environment and layout constraints
• The scope split (what your side supplies versus what the supplier supplies)
• Acceptance document requirements
• The delivery plan (quantities, destination, target dates)

Project and Site Information

Start with where the project is and what stage it has reached.

• Country and site of the project, and whether it is inland, coastal or high-altitude.
• Project stage (early development, tender, or construction) — this tells the supplier how much can be treated as preliminary.
• Site altitude, and the ambient temperature range the equipment must operate in.
• Pollution or corrosion severity at the site, and whether indoor or outdoor installation is planned.
• Any seismic or wind-loading requirements set by the project’s civil or structural documents.
• Where a value depends on a standard or a site study, provide it together with the document it comes from. If the basis is not fixed yet, list the item as to be confirmed rather than assuming a number.

We do not fill in site values on your behalf. If your project has no specified altitude, temperature range or pollution level yet, say so — it becomes a review point, not a blocker.

PV Inverter and AC Output Data

The inverter side frames the low-voltage side of the substation, so the more you can share here, the fewer later clarifications you need.

• Inverter make and model, and whether the inverters are central or string type.
• Rated AC output voltage of the inverter or inverters.
• Number of inverters and their individual ratings, plus the total AC capacity of the plant section feeding the substation.
• Number of AC collection or combining points that will connect to the substation.
• Whether an SLD or the inverter datasheets are available.

Give the data you have. If the AC side design is still open, note which parts are provisional.

Grid Connection Documents

Interconnection requirements are set per project and per utility, so this section asks you to provide the documents that apply to your site.

• Interconnection voltage level, and the connection arrangement at the point of connection.
• The applicable grid-connection documents for the project — provide those issued by the utility or the owner.
• The point of connection, and the power-factor or reactive-power requirements stated in those documents.
• System frequency.
• Short-circuit capacity at the connection point, if it is available.
• Whether communication or telecontrol interface documents are required by the utility.

This checklist does not assume any country’s limits. Provide the documents that apply to your project, and where a requirement is not yet issued, mark it as pending instead of substituting a default.

Transformer and Substation Scope

This is the equipment itself and the boundary around it.

• Transformer rating (kVA) and voltage ratio, if already fixed.
• Vector group, if already fixed.
• Cooling method required, and whether an oil-immersed or a dry-type unit is intended.
• Whether a box-type or prefabricated substation or enclosure is part of the scope.
• Number of incoming and outgoing feeders, and any layout limits (footprint, clearances, access).
• Transport and installation limits (weights, dimensions, lifting, site access).
• The scope split: which items your side supplies and which the supplier is to include.

Explore our solar step-up transformer substations and share the available project requirements. The equipment configuration and supply scope are reviewed for each project.

Protection, Metering and Communication Interfaces

This section is about interface documents, not protection settings. Its purpose is to let interface coordination begin.

• CT and PT ratios and accuracy class required for protection and for metering.
• The location of the metering point.
• A list of the trip and interlock signals the substation must exchange with the rest of the plant.
• The communication protocol required — for example IEC 61850, if the owner requires it — together with the monitoring or telemetry point list.
• Any interface documents issued by the utility or the owner.

Protection settings, selectivity coordination and acceptance-test scope depend on the project’s protection philosophy and are agreed during project review. This checklist only asks you to provide the interface data those later steps will build on.

Delivery, Documentation and Next Steps

Documents and requirements to share

• Available grid-connection documents and project specifications.
• A preferred general arrangement or outline drawing, if one has been prepared.
• The project requirements for certifications, approvals, factory tests and acceptance documents.

Documents to request from the supplier

State which drawings, test reports or certification documents you need the supplier to submit for review, and when they are required. The supplier should confirm the documents available for the proposed equipment and the agreed supply scope.

Commercial and logistics inputs:

• Quantities, and any phased delivery requirements.
• Incoterm and destination port.
• Packing and transport restrictions.

RFQ package summary

A complete first enquiry shortens clarification, but it does not by itself produce a final quotation — the final price and delivery depend on project review, configuration confirmation and commercial terms. If some inputs are still open, send what you have and mark the rest as pending.

Share your available project documents with Unita for a preliminary review. If some details are not yet available, tell us your project stage and the information you have — contact us.