Will a solar plant provide light in the building during an outage?

Only if the design allows it: you need a hybrid inverter or an inverter with confirmed island mode, and usually batteries. A standard grid-tied plant shuts down together with the grid.

Who decides whether panels can be installed on the building roof?

The roof is common property of the co-owners, so the question goes through a residents' decision in the manner set by law. Confirm the details with the OSBB lawyer.

Does the platform publish plant prices and output?

No. The platform does not give prices or output figures without a confirmed source, and the calculator results are approximate and require engineering verification.

Solar panels for an OSBB: roof, design, resident decisions

Author: Svitlo-Lux editorial team. Published 2026-10-23, updated 2026-10-23. Review (engineering): approved (Project owner).

A solar plant on an apartment building is not just panels. It is a chain of decisions: who owns the roof, which load you want to cover, whether it must work during outages, and who will be responsible for operation. This page walks you through that chain in the right order and helps you prepare a concrete conversation with the designer.

What a solar plant does and does not do

Panels turn light into direct current, and the inverter feeds it into the building network. The key point for an OSBB (condominium association): a standard grid-tied plant runs in parallel with the grid operator and, for safety reasons, shuts down when the grid has no voltage. So solar panels for an OSBB do not make the building autonomous on their own. If the goal is lighting in the stairwell, or pumps or an elevator running during an outage, you need a separate design: a hybrid inverter, or an inverter whose manufacturer confirms island mode, plus batteries.

The second expectation concerns output. It varies by season and depends on orientation, tilt, shading and panel condition. The platform does not publish output figures without a confirmed source of solar irradiation data for a specific address, so any number on this page would be invented. A quantitative estimate comes from the designer, based on a roof survey and your consumption data.

The project goal determines the design
OSBB goal	What it means for the design	Main risk
Reduce purchases of electricity for common needs	Grid-tied plant, sized for daytime consumption of common loads	Generation without consumption at that time gives little benefit; surplus has separate metering and conditions
Keep lights and water running during an outage	Hybrid inverter, batteries, dedicated backup line	Expecting the plant to power the whole building
Both goals at once	Hybrid design with loads split into critical and non-critical	Excess complexity and budget without priorities
Show a contribution to common property	Focus on transparent reporting and maintenance terms	Replacing the technical goal with a symbolic one

The roof: ownership, load capacity, fire safety

The roof of an apartment building belongs to all co-owners, so using its area for equipment requires a decision in the manner set by law and the charter. Specific rules and vote quotas are not given here: confirm them with the OSBB lawyer and prepare questions for the general meeting in advance. It is also worth checking whether part of the roof has been leased to third parties, such as telecom operators, and whether any contracts are in force.

Technical survey

Roof type and condition, time until major repair: installing on a roof that will soon be replaced creates double costs.
Load capacity of the slab and the mounting method: wind and snow load, ballast or anchored mounting. The conclusion comes from the designer or structural engineer.
Free area after setbacks, walkways, roof access points, ventilation shafts, antennas and lightning protection.
Shading from neighboring structures, parapets and rooftop additions at different times of day.
Cable route, location for the inverter and protection cabinet, distance to the electrical room.
Fire safety requirements and approvals that apply to your building: confirm the list with the designer and the relevant authorities.

Grid-tied or hybrid: a comparison for an apartment building

Two typical approaches
Criterion	Grid-tied plant	Hybrid system with batteries
Operation without the grid	Usually shuts down together with the grid	Possible for a dedicated backup line, if confirmed by the manufacturer
Project complexity	Lower	Higher: backup line, communication between inverter and battery
Role of batteries	None	Storing surplus and backup during an outage
What must be agreed	Grid connection, metering, operator conditions	The same, plus load priorities and battery requirements
Typical mistake	Buying it expecting light during a blackout	Underestimating motor inrush (starting) current on the backup line

If backup is what interests you, first calculate the needs of critical consumers, and only then the panel capacity. For this there are the backup power calculator, the battery capacity calculator and the inverter power calculator. The results are approximate, and for elevators and pumps they always carry the label "engineering calculation required".

Check equipment compatibility separately. Panel-inverter pairs depend on the string voltage range, and inverter-battery pairs depend on voltage, chemistry and the communication protocol with the battery management system. By default the platform catalog marks unknown pairs as needing a compatibility check, and the project should do the same.

Selling surplus, metering and tariffs

For the project model it is enough to understand the structure of the questions: whether there is a capacity limit for connection, who is the party to the contract on behalf of the building, how metering of common needs will be arranged, and who benefits from the savings. The answers affect the payback calculation, so find them out before publishing a fundraiser.

How to prepare the decision

State the goal. Write in one sentence what exactly you want: savings on common needs, backup, or both. The design depends on it.
Collect consumption data. You need monthly figures for common loads, the operating schedule of elevators and pumps, and whether metering exists. Without this, an output estimate is meaningless.
Order a roof and electrical room survey. Get a written conclusion on area, loads, shading and the condition of the electrical room.
Get several proposals. Compare the equipment set, warranty terms, service and division of responsibility, not just the total price.
Prepare the residents' decision. Draft a clear brief for the meeting: goal, options, risks, contract requirements. Legal details go through your lawyer.
Only then open a fundraiser. Before launching a fundraiser on the platform, complete organization registration and checks. A fundraiser cannot be considered ready for contributions without them.

What to ask suppliers and designers

Who performs the survey, and is a written roof conclusion included in the cost of work?
Which inverter is planned: grid-tied or hybrid, and does the manufacturer confirm operation without the grid?
How does the project resolve compatibility of the panels with the inverter input range?
What redundancy is provided for critical consumers, and what is deliberately left without power?
What are the warranty terms for panels, inverter and installation, who takes requests, and how quickly do they respond?
How is panel degradation addressed, and does the manufacturer state the expected power loss by year?
What does acceptance include: protocols, diagrams, datasheets, instructions for on-duty staff?
Who cleans the panels and inspects the mounting, and what happens if the roof is repaired?

Checklists before purchase and during acceptance

Before purchase

There is a general meeting decision on using the roof, adopted in the manner required by law.
There is a written conclusion on the roof condition and loads.
The goal and the list of consumers that must work during an outage are defined.
There are at least two comparable commercial proposals with the same scope of work.
Current rules for connection, metering and selling surplus have been confirmed.
It is agreed who is responsible for equipment maintenance and insurance.
The budget covers not only equipment but also design, approvals, metering and service.

During acceptance

Document set: design, diagrams, equipment datasheets, test protocols.
The actual configuration matches the design: type and number of panels, inverter, protective devices.
Grid disconnection test: system behavior is recorded in the acceptance act, if backup is part of the task.
Monitoring works, and data access is handed to the responsible OSBB person.
Instructions for on-duty staff and service contacts are provided.
Warranty dates are recorded in the acceptance act.

Where to go next

Use the solar panel calculator to estimate area and capacity from your own inputs, and the approximate cost calculator with your own prices. The payback article explains which input data you need to collect. If your initiative is ready for a public fundraiser, start with organization registration.

In this section

Solar payback for an OSBB: how to calculate
How to calculate payback of a solar plant for an apartment building: formula, input data, degradation and maintenance adjustments, a worked example.

Frequently asked questions

Will a solar plant provide light in the building during an outage?: Only if the design allows it: you need a hybrid inverter or an inverter with confirmed island mode, and usually batteries. A standard grid-tied plant shuts down together with the grid.
Who decides whether panels can be installed on the building roof?: The roof is common property of the co-owners, so the question goes through a residents' decision in the manner set by law. Confirm the details with the OSBB lawyer.
Does the platform publish plant prices and output?: No. The platform does not give prices or output figures without a confirmed source, and the calculator results are approximate and require engineering verification.

Solar panel calculator Approximate cost from your own prices Register an OSBB

Partner commercial offer

SunEco is a separate commercial supplier and a partner of the platform. It is only one of several possible options, not a recommendation; the platform does not sell equipment.

SunEco catalogue: a link to a specific product is not confirmed, the supplier's home page will open

This material is for general information only and is not a power supply design, legal or financial advice. Calculations are indicative; installation and protection selection must be done by qualified specialists only. The platform does not accept or hold funds.