Design, installation and performance
Off-grid system
Also known as: off grid, standalone system, islanded system.
Definition
An off-grid system is not connected to the grid and works on panels and batteries alone. It is the option for places with no access to the electricity grid, such as remote farms or non-interconnected areas, where it replaces fuel generators.
With no grid to fall back on, an off-grid system is sized on different criteria: covering average consumption is not enough, supply also has to be guaranteed through the worst run of cloudy days. That margin is expressed in days of autonomy, and it is what determines the size of the battery bank, normally the most expensive line item in the project.
The design forces you to prioritise. Large, long-running loads — air conditioning, electric water heaters, big motors — send the size of the system soaring, so many off-grid projects combine efficiency measures, gas for heating and a backup generator for occasional peaks. Every watt saved in consumption is worth several times its cost in installed capacity.
Its economic comparison is not against the grid tariff, but against the real alternative at the location: a diesel or petrol generator, with its fuel, its transport, its maintenance and its noise. Against that, off-grid solar usually wins comfortably over horizons of several years.
The essentials of Off-grid system
- There is no grid connection: all night-time energy comes from the batteries.
- It is sized by days of autonomy, not just by average consumption.
- The battery bank is usually the most expensive line item.
- It is compared against the cost of a fuel generator, not against the grid tariff.
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Frequently asked questions about Off-grid system
How much does an off-grid system cost?
Considerably more than an on-grid system with the same panel capacity, because it incorporates the battery bank, the charge controller and an inverter capable of working islanded. The cost depends above all on the autonomy required: every extra day of backup multiplies the storage capacity needed.
Can an off-grid system run air conditioning?
It can, but it changes the scale of the project: it is a large, long-running load that demands more panels and many more batteries. On off-grid installations it is worth considering high-efficiency equipment, restricted use to certain hours or alternative solutions before sizing to cover it in full.
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