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On-grid, off-grid and hybrid solar systems differ in how they use the electrical grid and energy storage. Before choosing, assess daytime and nighttime consumption, critical loads and the required backup duration. The system type alone does not establish what a particular installation can do.
🔹 On-grid (grid-tied)
A grid-tied solar system operates in synchronization with the external grid. Solar generation supplies current consumption, while the grid covers any shortfall. Exporting surplus energy depends on the connection design and agreed connection terms.
When the external grid fails, a conventional grid-tied inverter stops supplying it. This protection prevents power from being fed into a disconnected grid. Backup requires a separate solution included in the project design.
- Advantages: using solar generation during daytime consumption, with less equipment in a basic configuration without a battery.
- Suitable for: homes and businesses with grid access where the main purpose of solar is self-consumption. Payback requires an individual assessment.
🔹 Off-grid (stand-alone)
An off-grid system is designed to operate without the external electrical grid. Solar panels, the inverter and batteries are selected together for the loads and seasonal generation. A compatible generator can be included where needed for periods with insufficient solar energy.
- Advantages: supplying remote sites without a connection to the external grid.
- Limits: stored energy is finite. Usable battery capacity, equipment power, weather and consumption management must be considered.
🔹 Hybrid
A hybrid solar system combines solar generation, the external grid and the option to store energy in a compatible battery. In an agreed configuration, a backup circuit can supply selected loads during an outage. This requires checking the inverter capabilities, grid isolation design and settings.
- What to assess: backup duration depends on the load, battery charge, usable capacity and available generation. Power, starting currents and transfer time require separate checks. Hybrid operation alone does not guarantee uninterrupted power for the entire site.
How a generator and battery storage work together
For a business, a long outage involves several different tasks. Controls and communications may need continuous power, motors have brief starting demands, and some production steps can be postponed. Compare a generator and a battery against the same list of loads and operating schedule. Comparing their nameplate power alone does not show which processes will remain available.
A generator converts fuel into electricity. A battery delivers previously stored energy and needs a source to replenish it. In an agreed configuration, storage can supply selected circuits between generator runs, while the generator serves loads and charges the battery. Each operating mode needs confirmation in the design and the documentation for the selected equipment. A terminal labelled GEN is not sufficient evidence of compatibility.
This arrangement can form part of an off-grid or hybrid solar system. However, a generator does not turn a conventional grid-tied inverter into an off-grid device. The design must identify which equipment establishes local voltage and frequency, how the utility grid is isolated, and whether the solar inverter can operate in that environment. These are engineering questions for qualified specialists, rather than instructions for connecting equipment outputs yourself.
An illustrative scenario for a small production site
Consider a site that must keep controls, safety lighting and some ventilation running during an outage, while a large process heater can wait. This is a teaching scenario, not a completed project. The owner and process specialist first agree which operations must continue. An engineer can then define the backup circuit and check demand at different stages of operation.
- The grid is available. Solar covers part of consumption and the battery follows its agreed schedule. Daily optimisation does not use up the entire emergency reserve.
- An outage begins. The designed backup arrangement supplies selected loads. The acceptable interruption must be checked separately for controls and other sensitive equipment.
- Stored energy falls. Compatible controls request a generator start when an agreed condition is met. Starting, stabilisation and the manufacturer's warm-up requirements are considered before accepting its power.
- The generator takes the load. Only its available capacity is used for battery charging. When site demand rises, controls must limit charging or take another action defined in the design.
- Conditions change. Generator shutdown, return of the grid and replenishment of the reserve follow an agreed sequence. Failed starting and lost communications also need a defined response.
The value of this scenario is not measured solely by hours without generator noise. The owner needs to know which processes are supported, the assumed starting battery charge, available fuel and the response to a subsequent outage. These conditions make competing equipment proposals comparable.
Input data for comparing backup options
Prepare a consumption profile and a critical-load list. For each load, record operating power, phase requirements, starting behaviour, operating duration and the acceptable interruption. Identify equipment that can be disconnected or started in sequence. Average daily demand does not reveal a compressor's brief starting requirement, while the sum of equipment ratings does not describe actual simultaneous use.
Distinguish battery power from usable energy capacity. Power determines which loads can operate together; energy capacity limits the available supply. The calculation needs initial charge, the agreed reserve, losses and system auxiliary consumption. Energy measured at the battery terminals should not automatically be treated as energy delivered to the loads.
For an existing generator, provide the exact model, fuel type, continuous rating, electrical characteristics, control interface and service history. Request the manufacturer's fuel consumption data at relevant loads. Advertised maximum output may differ from sustainable operation, and a single litres-per-hour figure does not describe the full operating schedule.
Record fuel availability, delivery arrangements and installation and maintenance constraints. For solar, use seasonal generation measurements or a suitable forecast. A prolonged winter outage should not be assessed using summer output. The guide to solar with storage for self-consumption explains the daily energy balance in more detail.
Include the current single-line diagram and an inventory of installed equipment. Distinguish components that must remain from those that may be replaced. If a proposal relies on an existing generator, ask it to state which checks will establish suitability. Unknown equipment condition should remain an explicit assessment item. For a new configuration, define the supply boundary: switching, controls, external connections and configuration work need to be included alongside the battery and inverter.
Compatibility, control and scenario validation
The inverter must accept the generator's supply quality within agreed operating limits. Voltage and frequency may vary as loads change. If charging fails to start or the connection repeatedly drops, the cause needs diagnosis. Widening acceptance limits or disabling protection without assessment can create another problem for the connected equipment. Settings should follow the documentation, measurements and requirements of the complete circuit.
A start command is different from confirmation that the generator is actually delivering acceptable power. Control must also account for battery condition, charging limits, stop conditions and any required cool-down period. Thresholds and delays are not universal. Specify who approves and changes them, and who receives failure alerts. The guide to battery and energy-flow control explains the different control roles.
Before acceptance, agree checks for transfers between sources, starting critical loads, low battery charge and a failed generator start. Trained personnel should carry out testing under a safe programme. The record should identify actual loads, starting conditions, events and limitations, rather than merely confirm that the equipment switched on.
Compare costs without assuming guaranteed savings
Assess a generator alone, battery backup and a combined arrangement using the same outage schedule and critical loads. Include equipment, integration, fuel, servicing, purchased charging electricity, losses and battery resource use. If one option supports fewer processes, a lower price does not establish a better outcome.
Shorter generator running time can change fuel consumption, but it does not automatically produce the same percentage saving. Charging requires energy, and engine operating conditions will change. Assess several outage durations and periods of weak solar generation. The final choice depends on the required continuity of the process and the full cost of providing it.
💡 How to Choose a Solar System
- On-grid is considered for using solar generation alongside an available grid.
- Off-grid is considered for sites without the external grid, with generation, storage and a backup source assessed together.
- Hybrid is considered for combining self-consumption and backup under defined load requirements.
For an assessment, prepare a consumption profile, a list of critical equipment, the required backup duration and roof or site information. Explore our grid-tied solar systems, off-grid solutions and hybrid systems.
For a practical discussion, prepare these inputs and identify the processes that must keep running. This helps define the system and backup limits before equipment is selected.