What a commercial solar PV design includes and what drives its price

27 October 2026 · 4 min read

A solar plant on a factory roof is not “panels and an inverter”. It is a generating installation with a grid connection, fire safety and roof structure – and the design is what turns it into a building that can be permitted, built and connected.

Why commercial PV is different from residential

A family house means a few kilowatts and a simple connection. A commercial plant has tens to hundreds of kilowatts, is connected as a generating plant with its own grid operator conditions, sits on a roof nobody designed for panels, and enters the fire safety solution of the whole building. Each of these things has its place in the design – and when it is missing, the project stops at the grid operator, at the fire brigade or at the building authority.

Design stages

Study and concept – panel layout according to the roof shape and shading, estimate of generation and self-consumption, power variants, indicative payback. It decides how large a plant makes sense.
Connection application – site plan, single-line diagram and technology data for the grid operator. Only its statement says how much power may be exported to the grid; often the result is an export limit or a condition of MV connection. More in grid connection.
Permit documentation – if the installation requires a permit: site plan, technical report, fire safety solution, statements from utility operators and the concerned bodies.
Detailed design – what the installer builds from and what the installation is tendered on.
As-built documentation – after installation, for the inspection, the grid operator and future maintenance.

What the detailed design contains

Our detailed design of a commercial plant contains these parts:

Part	What is in it
Site plan and panel layout	Roof plan with panels, dimensions from edges and penetrations, access strips and clearances from roof hatches and fire walls.
String wiring	Grouping of panels into strings by orientation and shading, assignment to inverter inputs, DC cable lengths.
DC and AC diagrams	Single-line and overview diagram from the panels through the inverters and plant switchboard to the point of connection and metering.
Plant switchboard	Wiring diagram, layout, protection devices, surge protection, main circuit breaker and disconnection point, metering.
Cable routes	Cable runs on the roof and inside the building, penetrations, installation method, cable schedule with types and lengths.
Calculations	Cable and protection sizing, voltage drops, short-circuit conditions, generation calculation, grid impact for larger outputs.
Earthing and lightning protection	Bonding of the mounting structure, surge protection, assessment of the panels' effect on the existing lightning protection system and separation distance.
Fire safety	Inputs for the fire safety solution: roof clearances, emergency shutdown, labelling, cables with the required reaction-to-fire class.
Technical report and bill of quantities	Description of the solution, grid operator conditions, material list for supplier enquiries.

We prepare the design so that several suppliers can price the installation from it – it is not tied to a specific manufacturer of panels or inverters unless the investor explicitly wants that.

The roof: structure and anchoring

Panels and mounting structures add load to the roof and, on flat roofs, wind effects on ballasted systems. Before the design, the roof build-up and its reserve must be known; on older halls a structural assessment decides. The anchoring of the structure is designed according to the manufacturer's installation manual – clamp spacings and positions are not arbitrary, and badly clamped panels are a frequent reason for warranty claims.

Fire safety

Photovoltaics enters the building's fire safety solution: on a flat roof, free strips are left at roof hatches and fire walls, DC cables inside the building are run with the required reaction-to-fire class, a shutdown for firefighters is placed at the building entrance and the plant is labelled. The fire safety solution is prepared by an authorised specialist; the plant design gives them the inputs and incorporates their requirements.

What drives the price of the design

Power and connection level – a plant of hundreds of kW at LV is a different scope from a megawatt plant with its own transformer station.
Design stage – detailed design only, or also the permit and as-built documentation.
Source documents – current drawings of the roof and switchboards shorten the work; without them the existing state has to be surveyed.
Roof or ground – a ground-mounted plant adds foundations, fencing, underground cable routes and usually a permit.
Lightning protection and fire solution – whether an assessment of the existing state is enough, or a new design is needed.
Subsidies – documents for a subsidy application (energy assessment, statements) are separate work.

We set the price of the design as a fixed sum after checking the source documents and scope, with the grid operator's and the authority's comments included in the price. More about the whole service on the solar PV plants page.

Frequently asked questions

Does commercial PV need a building permit?

It depends on the power, the location and whether it is a new installation or a change to an existing one. Smaller rooftop plants can be built without a permit, larger and ground-mounted ones need one. We assess this right at the start under the current Czech Building Act.

Can I order the design only after choosing the installer?

Better the other way round: a design not tied to a manufacturer serves as the tender specification and the offers are then comparable. Specific types are added before installation.

How long does the design take?

The detailed design of a rooftop plant is a matter of weeks; what decides is the quality of the source documents and the speed of the grid operator's statement, which is needed for the connection design.

Planning a similar project?

Send us the site and your intent. We reply within 48 hours.

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