How Long Does it Take to Build a Solar System?

Solar photovoltaic (PV) electrical systems can be among the simplest construction projects as long as a few conditions are met:

  • The roof is in good repair and has adequate support or, in the case of a grand-mount, the land is level and well-drained;
  • The municipality where the system is located has an established protocol for granting engineering and/or building permits;
  • The municipality has a policy in place for levying property taxes (or not);
  • The utility is cooperative in supporting interconnection (which in the case of a commercial project may require making upgrades to wires and transformers).

An experienced and knowledgeable contractor can navigate each of these hurdles.

Provided the conditions described above are satisfactory, an installation can take from 1-18 months, depending on the size of the system and the weather.  The actual length of time will depend on a number of factors described below.  In all cases the project can be broken down into three phases.

1. Engineering and permitting

The design of most projects can be completed in as few as 1-4 weeks.

  • A small commercial or residential project can be designed remotely by examining satellite photographs of a roof (and then visiting the roof to confirm the angle of the rooftop, if not flat, and the condition of the roof). Engineering drawings can be drawn easily in 2 days and submitted to a building department for approval if needed.  (Note:  Towns differ on their policies; check with the local public works director or building department.)   Building department approval can take from 1 week to 1 month, depending on the department’s knowledge, experience, and backlog.
  • A larger commercial project will require more detailed drawings after one or more site visits. The roof must not only be in good condition but must be buttressed sufficiently for the weight of panels.  Panels may be attached to the roof or set on buttresses; either way, weights can be considerable and older building rooftops may need to be reinforced which can take additional time.  These drawings – which in some towns must be prepared signed by a licensed structural engineer — may take 2-3 weeks and will generally be required to be reviewed and approved by the building department.

Once drawings are submitted the time required for permitting varies.  Some building inspectors may be empowered to sign off on drawings themselves; others might require a meeting and approval by a local planning and zoning board.  Of course, if a building is located in an historic district additional approvals and review might be required.  This could take up to 3 months, depending on meeting schedules.

2. Construction

Construction will require ordering equipment (panels, inverters, wires, ballusts, etc.) and lining up crews.  Most small projects can be staged within 1 month; contractors will carry sufficient inventory to build soon after approvals are received.  Larger projects may require a month to line up materials and another month before crews are ready.

Provided construction can start and end in mild weather (before December in the Northeast US, for example) it should take no more than 1-2 days for each 10 kW of panels (about 40 panels).  The larger the project the faster the install.  For a 1 mW project expect a two week to 1 month install with a margin for bad weather.   These times apply to both rooftop and ground-mount installations.  Even though the crews may require different knowledge and experience the time lines are similar.

Note, however, that ground mounts may require an additional 2-3 weeks for ground preparation – leveling ground, preparing drainage basins and culverts, pouring concrete piers.

Panel wiring and inverter installation can be performed by a licensed electrician at the same time crews are working on the panel install.

3. Utility Interconnection

All systems must be tied into the utility grid and the utility must send out inspectors before a system is commissioned or turned on.   In the case of a small installation, the inspection should take no more than 2 weeks to 1 month to schedule, no matter how much the backlog.  Unless the electrician has no experience and has ignored local building codes and manufacturer’s specifications, the utility inspector should be able to quickly assess the system and flick the switch.

A large commercial installation, however, may require additional wires to be strung or transformers installed.  These upgrades to the system could take 3-6 months.