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Control algorithms

Peak shaving reserve

Reserve part of the battery to keep grid import under its limit, shave load peaks that would otherwise exceed the connection or transformer capacity.

The peak shaving reserve protects a part of the battery so it is always available to keep the grid import below its limit. When site load would push the import over the configured limit, the battery discharges just enough to hold the grid at that limit, regardless of what causes the peak.

This is useful when the hard constraint is power, not price: a transformer or grid connection that must never be exceeded, or a battery that must keep headroom to support DC fast charging.

How it works

The reserve is a lower bound for the battery's state of charge (SoC), as a percentage of the battery. It changes the behaviour of the active control algorithm (cost optimization or self-supply) in three ways:

  • Peak shaving discharge (always allowed). When the load minus PV threatens to exceed the grid import limit, the battery discharges exactly the overage. The grid then stays at the limit and never drops below it, so nothing is exported to shave a peak. This holds regardless of the energy price, because the import limit is a physical constraint on the connection. The full load counts, including EV fast charging. This discharge may draw the battery all the way down to its minimum SoC.
  • Reserve floor (protects the reserve). As long as the SoC is above the reserve, the battery is used freely by the normal strategy. Once it drops to or below the reserve, discharging for other purposes (self-supply balancing to zero, price arbitrage) is blocked, and that energy is kept for shaving the next peak. Only the peak shaving discharge above may still use it.
  • Priority refill. When the SoC is below the reserve, replenishing it takes priority over other charging strategies. The battery charges from PV surplus and, if needed, from the grid regardless of price, staying a small margin below the import limit so the refill itself never causes a peak.
Available for discharge above the reserve Peak shaving reserve bottom part, protected 0% 100%
The battery with the peak shaving reserve at the bottom (orange). The hatched part is protected: it is only used for peak shaving, and the dashed line marks the lower bound of the reserve.
Situation What the battery does
Load minus PV stays below the import limit Charges from PV surplus or stays idle, depending on the chosen strategy
Load minus PV threatens to exceed the import limit Discharges exactly the overage; the grid stays at the limit (always allowed)
SoC above the reserve, no peak The normal strategy uses the battery freely
SoC at or below the reserve, no peak Discharging for other purposes is blocked; the reserve is refilled with priority

Choosing a value

Set the reserve high enough that the reserved energy covers the expected daily peak-shaving need, so the battery is charged in time for the recurring peaks (for example a morning and an evening peak when PV is low). A site that does not optimize for cost and only wants to protect its connection can set the reserve high, keeping the battery close to full and only tapping it during peaks. The midday PV surplus and the price-independent overnight refill top it back up.

A reserve of 0 (or empty) disables the behaviour: the algorithm then runs without a protected reserve.

Configure the value under project settings. Consult your installer for the appropriate value for your specific installation.

See also