Quick Facts
What a load curve is
An electrical load curve is a graph showing electricity demand (in kW or MW) plotted over time. Load curves are fundamental tools for understanding electricity consumption patterns and planning generation, distribution, and storage.
Common load curve types:
Daily load curve: 24-hour demand profile. Reveals peak hours, off-peak periods, and the shape of typical days.
Weekly load curve: 7-day pattern. Reveals weekend versus weekday differences.
Annual load curve: 365-day pattern. Reveals seasonal variations.
Load duration curve: Demand sorted from highest to lowest over a period. Reveals how many hours are at each demand level.
For utilities, the load curve drives planning decisions. For consumers, the load curve reveals operational patterns and opportunities for optimisation.
Typical load curves
Residential daily load curve:
Overnight (1 to 5 AM): Low demand. Refrigerator, water heater on standby, security lighting.
Morning (6 to 9 AM): Peak demand. Cooking, lighting, hot water, geyser.
Mid-day (10 AM to 3 PM): Reduced demand. Workers away. Air conditioning during summer can keep demand elevated.
Evening (6 to 10 PM): Largest peak. Cooking, lighting, air conditioning, TV, all simultaneous.
Late night (10 to 12 PM): Decline as activities settle.
The evening peak is typically the largest. For Indian residential, the 6 to 10 PM peak drives much of the country’s grid sizing.
Commercial building load curve:
Overnight: Low demand. Lighting and security only.
Morning rise (8 to 10 AM): Building opens. Office equipment, lighting, HVAC.
Peak (10 AM to 4 PM): Full occupancy. Air conditioning at maximum.
Decline (5 to 8 PM): Building closes.
Weekend differs significantly: much lower demand throughout.
Industrial load curve:
Continuous (3-shift) operations: Relatively flat load curve. Slight reductions during shift changes.
Single-shift operations: Sharp morning rise, evening decline. Similar to commercial.
Process-driven loads: Specific patterns based on batch processing or production schedules.
For load curve analysis, the most useful metric is the ratio of peak to off-peak demand. This affects ToD tariff economics and storage decisions.
The duck curve
The “duck curve” describes how grid load patterns change with significant solar penetration:
Without solar: Grid demand rises through the day, peaking in afternoon or evening.
With solar: Midday solar generation offsets demand. Grid sees reduced midday demand.
Result: A “belly” in midday and a steep “neck” rising sharply when solar stops.
The shape resembles a duck’s silhouette: head and tail at evening peaks, belly in midday.
Implications:
Conventional plants must ramp up rapidly when solar stops in evening.
The rapid ramp is technically challenging and economically expensive.
Storage (BESS) becomes critical to smooth the ramp.
Energy management systems with predictive ramping coordinate the transition.
For grid operators in solar-heavy regions (Karnataka, Gujarat, Rajasthan), the duck curve is operationally challenging. BESS deployment is partly motivated by the need to manage the evening ramp.
Load curve and solar integration
Solar generation has a characteristic shape that overlays the load curve:
Solar generation is zero overnight.
Rises in morning as the sun rises.
Peaks at solar noon.
Declines in afternoon.
Drops to zero at sunset.
For residential and commercial consumers:
Midday solar reduces grid import to zero or even reverses to export.
Evening peak (after solar stops) requires full grid import.
Annual energy is offset, but peak grid demand remains.
For solar storage:
Battery charges during midday solar surplus.
Battery discharges during evening peak.
Combined solar plus storage flattens grid demand to near-constant low level.
For utility-scale solar plants:
The plant’s output curve is the inverse of customer consumption curves.
Output peaks at midday; consumption peaks in evening.
The mismatch creates the duck curve problem at grid scale.
Load curve and BESS sizing
For BESS sizing decisions, the load curve provides essential information:
Peak demand and duration: How much power needs to be shaved and for how long.
Off-peak periods: When the battery can charge.
Daily energy: Total energy storage required.
ToD prices: Economic incentive for arbitrage.
Example for a commercial customer:
Peak demand: 200 kW.
Off-peak demand: 80 kW.
Peak duration: 4 hours (6 to 10 PM).
Storage size to flatten peak to off-peak level: 120 kW × 4 hours = 480 kWh.
Battery: 500 kWh LFP BESS.
Economics: Peak shaving plus solar plus ToD arbitrage.
The load curve drives this analysis. Without understanding the curve, BESS sizing is guesswork.
Load curve in ToD tariff design
ToD tariffs are designed around the typical load curve:
Peak hours (high tariff): Coincide with evening peak demand.
Off-peak hours (low tariff): Overnight when demand is low.
Normal hours: Daytime between peak and off-peak.
Tariff designers analyse aggregated load curves to set the time blocks and tariff differentials. The objective: incentivise load shifting from peak to off-peak.
For consumers, understanding the load curve helps optimise:
Shift discretionary loads (water heating, EV charging) to off-peak.
Reduce peak-hour consumption through behavior or storage.
Capture ToD tariff savings.
Load curve and EV adoption
Electric vehicle adoption changes the load curve:
If EVs charge at home in the evening (after work): adds load to the existing evening peak, worsening the duck curve.
If EVs charge at work during the day: adds midday load, helping fill the duck’s belly.
If EVs charge overnight (off-peak): adds load to base period, improving load factor.
Smart EV charging strategies aim to shift charging to off-peak or solar hours, supporting grid stability.
For India, EV adoption is accelerating with the FAME scheme. Future load curves will increasingly reflect EV charging patterns.
Common load curve mistakes
Designing without analysing the load curve. Generic assumptions miss site-specific patterns.
Ignoring seasonal variation. Summer and winter curves differ significantly in northern India.
Treating annual average as representative. Daily and seasonal peaks drive design.
Mismatching solar sizing to load curve. Solar offsets midday but not evening peak.
Skipping load curve analysis for BESS sizing. The curve determines storage requirements.
Best practices
For solar plant design, analyse the customer’s load curve to size for self-consumption.
For BESS planning, model the peak duration and depth from the load curve.
For ToD tariff exposure, identify peak hours and load that can be shifted.
For commercial customers, request 15-minute interval data from the DISCOM to construct the actual load curve.
For multi-site operations, aggregate load curves across sites to identify portfolio-level patterns.
Standards and references
Load curve analysis methodology is documented in IEEE 1547, CIGRE guides, and utility-specific procedures. SCADA-based load monitoring is standard for utilities. Smart meter data enables consumer-side load curve analysis.
Related glossary terms
- Load Factor
- Time of Day Tariff
- Contract Demand
- Maximum Demand Penalty
- Battery Energy Storage System
- Must-Run Status
- SCADA in Solar
Key takeaways
An electrical load curve is a graph showing electricity demand over time. Daily, weekly, annual, and load duration curves reveal patterns useful for planning and operation. Residential load curves show evening peaks; commercial show midday peaks. Solar integration creates the “duck curve” with midday belly and evening ramp. BESS sizing, ToD tariff design, and demand management all depend on load curve analysis. For Indian grids with growing solar penetration and emerging EV adoption, understanding and managing the load curve is increasingly important.