> 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/voltmasters-platform/10.-project-settings/10.3-curtailment.md).
# Curtailment
### What is curtailment?
Curtailment is the deliberate reduction of the output power of one or more PV inverters. The Voltmasters EMS applies curtailment when injecting surplus solar energy into the grid would result in a financial loss, for example during periods of negative energy prices on the EPEX spot market.
### How the curtailment algorithm works
Every hour, the EMS evaluates whether PV production should be limited, based on the EPEX spot price and your configured energy contract (consumption cost and injection price).
Three situations typically occur:
1. **Injection price is positive**: production can run at full capacity; injecting into the grid is financially beneficial.
2. **Injection price is negative, consumption price is still positive**: production is reduced to cover only local consumption. This prevents injecting energy at a negative price while still avoiding unnecessary grid import.
3. **Both injection and consumption prices are negative**: PV inverters are turned off where possible. The system attempts to import energy from the grid at a favourable price and charge the battery.
When imbalance trading is active, the orders from the trading party take priority. Curtailment is applied on top of those orders where necessary.
### How to enable curtailment for a PV inverter
A PV inverter must be set to **controllable** before the EMS can apply curtailment to it.
1. Navigate to **Devices** and open the settings for the relevant PV inverter.
2. Under the device settings, set the inverter to **Controllable**.
Once set to controllable, the EMS will automatically curtail that inverter when market conditions require it.
### Green power certificates
If your installation generates green power certificates, enter the certificate value under each PV inverter's settings in the field **Green power certificate price per MWh**. The EMS takes this value into account when deciding whether to curtail: if the combined value of the certificate and injection compensation is lower than the relevant threshold, the inverter may be curtailed sooner.
The algorithm uses this value as long as the field is filled in on the inverter's settings.
### Curtailment settings overview
The curtailment settings page shows:
* **Contract parameters**: a summary of your configured consumption and injection scaling factors and costs.
* **Strategy explanation**: a description of how the EMS decides between full production and curtailment for each price scenario.
* **Logging**: a 15-minute table showing the EPEX spot price and the resulting injection and consumption prices for each time slot, allowing you to review past curtailment decisions in detail.
Voltmasters EMS: curtailment dashboard
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