A permanent home and a weekend property can have very different electricity needs despite identical floor areas. Off-grid sizing begins with appliances, schedules and the loads that must keep operating during low generation, not the number of square metres.
Divide demand into three groups
| Group | Examples | Design decision |
|---|---|---|
| Continuous critical loads | Refrigerator, communications, basic lighting | Priority and reserve |
| Flexible loads | Washing, water pumping | Schedule during generation |
| Large thermal loads | Space heating, hot water, cooking | Separate energy and power assessment |
Measure actual consumption where possible. A low-power appliance running continuously can use more daily energy than a powerful device used briefly. Nameplate power alone is insufficient for an energy budget.
Daily energy and simultaneous power
In a hypothetical example, a 2 kW appliance operating for half an hour consumes 1 kWh. Three such appliances running together demand 6 kW even if their total daily energy is modest. The inverter and battery must satisfy both requirements.
Build a realistic schedule and test difficult combinations. Continuous supply should not depend entirely on every household member remembering an informal rule about switching appliances off. Where appropriate, controls can prioritise or limit loads automatically.
Winter and seasonal occupancy
Heating demand may increase as solar generation declines. A summer holiday property has a different critical month from a permanent residence. Long unoccupied periods also require appropriate battery storage conditions, monitoring and restart instructions.
Distinguish ordinary daily autonomy from emergency operation. A household may accept postponing laundry during poor weather but require refrigeration and communications to remain available. Write these priorities into the design brief.
Information to prepare
- Occupancy schedule and appliance list, with measured energy where available.
- Photographs and dimensions of the installation surface.
- Critical loads and acceptable periods of restricted operation.
- Planned new appliances and a suitable protected equipment location.
A published reference and its limits
The Zaros off-grid project records 10 kW solar and 25 kWh storage. We do not infer a number of autonomous days because that requires the actual demand profile and operating records.
Explore off-grid systems and energy storage. For a grid-connected home seeking only outage protection, a targeted backup system may be assessed alongside a fully autonomous alternative.
Two homes, different designs
A holiday home used mainly in summer has a different profile from a year-round home with winter heating. The same annual consumption can conceal very different runs of high-demand days. Record demand by season and distinguish refrigeration, lighting and communications from loads that can be deferred.
Before choosing equipment, decide how many low-generation days the home must withstand and which comfort requirements are non-negotiable. These choices shape the architecture more than a generic recommendation to “add a bigger battery”.
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