> For the complete documentation index, see [llms.txt](https://docs.voltmasters.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.voltmasters.io/control-algorithms/peak-shaving-reserve.md).

# Peak shaving reserve

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 (for example a site whose cooling load peaks above its connection capacity when the sun is low), or a battery that must keep headroom to support DC fast charging.

## How it works

The reserve is a percentage of the battery's state of charge (SoC). It changes the behaviour of the active control algorithm ([cost optimization](/control-algorithms/cost-optimization.md) or [self-supply](/control-algorithms/self-supply.md)) in three ways:

* **Peak shaving discharge (always allowed).** Whenever the load minus PV would exceed the grid import limit, the battery discharges exactly the overage so the grid stays **at** the limit — never below it, so it never exports to shave. This holds regardless of the energy price, because the import limit is a physical constraint on the connection. Any load counts: general site consumption, and EV fast charging as one particular case. 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 — 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.

{% hint style="info" %}
The peak shaving discharge only ever pulls the grid **down to** the import limit, never past it, so a site that is not allowed to export is never pushed into export by peak shaving.
{% endhint %}

## 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 cost-agnostic site that 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](/voltmasters-platform/10.-project-settings/10.5-project-settings.md). Consult your installer for the appropriate value for your specific installation.


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