Inverter for an apartment building: parameters and compatibility

Types of inverters and how they differ

Three classes of devices matter for an OSBB (condominium association). A backup (standalone) inverter powers a dedicated line from batteries and from the grid through a charger. A hybrid inverter combines connection to solar panels, the grid and batteries. A grid-tied solar inverter feeds energy into the grid and shuts down when there is no voltage in it. The difference between them is the main cause of misunderstandings: by buying a grid-tied device, the building gets savings but not light during a blackout.

Read more about hybrid and three-phase solutions on a separate page of this section. Here we focus on the parameters that must be checked for any device.

Power: continuous, peak, not just the number in the name

Continuous power shows how much load the inverter holds constantly. Peak power, which the device can deliver for a short time, is needed to start motors. Both values come from the datasheet, and you must check under what conditions they are stated: temperature, mode, peak duration.

The platform calculates power with the formulas of the calculation module: continuous power equals the sum of load powers with a simultaneity factor, and peak power is taken from the "one motor starts, the rest run" scenario with a starting margin. These are engineering assumptions with configurable values, not a guarantee. For elevators and pumps, inrush currents depend on the drive, see the datasheet. The inverter power calculator shows the steps and missing data.

Phases and load balance

Many building consumers are three-phase, while lighting and low-current systems are single-phase. The phase distribution scheme is set by the designer: it affects the choice between one three-phase device and several single-phase ones, the permitted imbalance and behavior when one phase is overloaded. Do not assume a single-phase inverter will suit a three-phase motor.

• Make a list of backup line consumers with the number of phases marked.
• Ask the supplier to state in writing the permitted load imbalance.
• Clarify whether the scheme has a neutral and what happens to one phase if it is disconnected.
• Check whether the platform picked mixed phases: in that case the calculation engine adds a warning that an engineer is needed.

Compatibility with batteries

The inverter and battery must match in chemistry, voltage range and communication protocol with the battery management system (BMS). The DC voltage of the battery pack must fall within the inverter's input voltage window, taking discharge and charge into account. Without confirmed communication, the inverter does not know the real state of the cells, and the system works in a limited mode or does not start.

The platform catalog works on a fail-closed principle: a pair is considered compatible only based on confirmed characteristics of both sides, complete data and an expert rule with a source. In other cases the status is "compatibility check needed". We recommend applying the same approach in the contract: require written confirmation of compatibility from the manufacturers from the supplier.

Operation without the grid and switchover

For each device ask three things: whether it supports standalone operation, what the switchover time is, and whether there is a separate backup output with its own power limit. For specific loads, such as a server or security system, it matters whether the switchover happens without a break. For motors it is usually more important that the start after switchover is confirmed by the manufacturer.

A separate question: whether a grid-tied inverter already on the roof can take part in a backup scheme. This depends on the model and the connection scheme, and the answer must be given by the manufacturer or designer in writing.

Questions for the supplier and the acceptance checklist

• Continuous and peak power: under what conditions are they stated and how long is the peak?
• Supported battery types and voltage ranges, and the list of communication protocols confirmed by the manufacturer?
• Is there an off-grid mode, what is the switchover time and what are the limits of the backup output?
• Phases, permitted imbalance, behavior on overload?
• Monitoring: who has access, is an event log kept, how is data transmitted?
• Warranty, service, response time, is there a manufacturer representative in Ukraine?
• Which certificates and documents will the supplier hand over with the equipment?

Typical mistakes when choosing an inverter

It helps if each of these questions has a written answer in the document package for the meeting. Then residents see that the decision is based on verified requirements, not on a seller's general promises.

Who decides what in an OSBB

Technical parameters are set by the designer, but the goal and the budget limits are set by the community. In practice this is a division of roles: the board prepares the inputs and collects proposals, the engineer gives a conclusion, the lawyer checks the contract, the meeting makes the decision. Platform pages help formulate questions and do not replace any of these roles.

• Board: list of loads, access to the electrical room, collecting documents for elevator and pump equipment.
• Engineer: calculation of power, phases, modes and compatibility, list of room requirements.
• Lawyer: contract, warranty terms, responsibility for installation and service.
• Residents' meeting: goal, budget limits, reporting procedure for funds spent.

Monitoring, service and operation

An inverter without monitoring turns into a black box: a fault is discovered only during an outage. Agree which parameters are shown to the responsible OSBB person, how the event log is stored and who receives notifications. Separately define who may change settings: factory charge limits and priorities are best changed only with written approval from the board and the service organization.

For the meeting it is handy to sum this up on one sheet: what was bought, who maintains it, what happens during an outage and whom to call. Such a sheet is also useful for new board members.

Next steps

Collect the list of loads, estimate power in the calculator, and then check the inputs against the proposals. If you plan a solar part, read the sections on solar panels for an OSBB and on batteries. When the team has settled on needs and budget, complete the organization registration.

In this section

• Hybrid and three-phase inverters for an OSBB

  When an OSBB needs a hybrid inverter, how three-phase schemes differ from single-phase ones, and what to check about phase balance, switchover and compatibility.

Frequently asked questions

Is it enough to choose an inverter by the total power of the loads?

No. You must also check the peak power for motor starting, phases, compatibility with batteries and the operating mode during an outage.

Do all solar inverters support operation without the grid?

No. Standard grid-tied inverters shut down when there is no grid. Standalone operation must be confirmed in writing by the manufacturer of the specific model.

Which peak power value should be used for calculations?

The value from the datasheet, with the stated conditions and peak duration. The marketing name of the model should not be used as a source.

Next steps

Inverter power calculatorBackup power calculatorRegister an OSBB