Value of lost load

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Value of Lost Load (VoLL) explained simply

VoLL is the estimated amount customers would be willing to pay to avoid a power outage. It is represented by a customer damage function (CDF), which shows the loss per kilowatt (kW) of interrupted electricity as a function of outage duration, season, time of day, and notice.

Key idea
- The CDF relates how much a customer loses per kW of load during an outage. Different customer groups experience different losses, so there are separate curves for each group. In large areas, these can be averaged into a composite VoLL.

Three customer groups
- Residential
- Small and medium commercial/industrial (SMCI)
- Large commercial/industrial (LCI)

What the curves mean
- All three curves have a similar shape, but the losses (the height of the curves) are much higher for larger customers. Short outages cost less per kW than longer outages, and the exact numbers depend on the customer group and duration.

Examples of VoLL numbers (loss per interrupted kW)
- EGAT study (2000):
- Residential: about 11.45 Baht per kW in the first hour
- Large commercial/industrial: about 29.55 Baht per kW in the first hour
- Small to medium commercial/industrial: about 89.50 Baht per kW in the first hour

- EPRI study (more recent):
- Residential: about US$1.50 per kW in the first hour, dropping to about US$0.46 per kW in subsequent hours
- Large commercial/industrial: about US$10 per kW in the first hour, dropping to about US$4 per kW later
- Small/medium commercial/industrial: about US$38 per kW in the first hour, dropping to about US$9 per kW later

Why VoLL matters
- VoLL helps utilities estimate the total cost of outages and decide how much to invest in keeping power available (reliability improvements).
- Because losses vary by customer type, analysts often use separate CDFs for residential, SMCI, and LCI, or a composite average for the whole area.