How to use solar surplus: 9 options compared

1. Set priorities by value rather than device

Surplus is the power left after current building demand has been covered. It changes from second to second and is far more common in summer than winter. A controller must distinguish power, energy, minimum run time and season.

Assess every option with five questions: is there a genuine need, what are the losses and cost, how flexible is timing, what power can it absorb, and what alternative does it replace?

2. Direct use, battery and hot water

1. Direct consumption: existing household or business loads are supplied without extra conversion. 2. Battery storage: energy is shifted to later hours. 3. Hot water: a cylinder or thermal store absorbs energy; a heat pump can often do this more efficiently than a resistive element.

• Make direct consumption visible first.
• Size the battery to typical surplus rather than exceptional days.
• Observe hygiene and temperature limits for hot water.

3. Heat pump, electric vehicle and business processes

4. Heat pump: heating or cooling can be moved within comfort and building-inertia limits. 5. Electric vehicle: a charger can follow surplus, while vehicle availability and departure energy remain constraints. 6. Cooling, pumps or processes: commercial loads can use solar production windows where their operation is genuinely shiftable.

• Respect minimum run times and switching limits.
• Use a total power cap to prevent simultaneous peaks.
• Always secure the energy that is required by a fixed deadline.

4. Shared use, export and specialist flexible loads

7. Shared local use: depending on ownership and metering, solar electricity may be allocated to several consumers; current legal and metering requirements must be checked. 8. Export: the straightforward default for energy that cannot be used internally. 9. Specialist loads: computing or mining can be considered only where it is controllable and its heat has a genuine use.

A robust strategy combines several options and always retains a safe fallback.

5. Build a robust control strategy

Priorities should not be identical all year. Heat may dominate in winter; EV charging, storage or export may be more relevant in summer. Dynamic prices can change the decision in individual hours.

The controller therefore needs states and limits: minimum battery charge, maximum connection power, hot-water temperature, vehicle target, forecast and minimum run time.

• Use real data before adding hardware.
• Account for efficiency at every conversion.
• Document the rules and review them seasonally.