What Is Demand Charge? Definition & Guide

Key Takeaways

Demand charges are based on the single highest 15-minute interval of electricity consumption (peak kW) during a billing period
They typically account for 30-50% of commercial and industrial electricity bills, sometimes exceeding 70% for low-load-factor facilities
Solar alone rarely reduces demand charges because peak demand often occurs outside solar production hours
Battery storage paired with solar enables peak shaving, directly cutting demand charges by 20-50%
Ratchet clauses can lock in a high demand charge for 6-12 months based on a single peak event
Accurate demand charge modeling requires interval data (15-min or hourly) from the utility, not just monthly kWh totals

What Is a Demand Charge?

A demand charge is a component of a commercial electricity bill that is based on the highest rate of power consumption (measured in kilowatts) recorded during a billing period. Unlike energy charges, which bill for total electricity consumed (kWh), demand charges bill for the maximum instantaneous load — the peak rate at which electricity was drawn from the grid.

Utilities impose demand charges because they must maintain enough generation, transmission, and distribution capacity to serve peak loads. A facility that draws 500 kW for just 15 minutes in a month forces the utility to maintain infrastructure for that peak, even if average consumption is only 100 kW. The demand charge recovers that capacity cost.

Demand charges are the single largest line item on most commercial electricity bills. A single 15-minute spike in consumption can set the demand charge for the entire month, making load management and solar design software critical tools for commercial project economics.

Types of Demand Charges

Understanding the specific type of demand charge on a customer’s rate schedule is essential for accurate financial modeling with any generation and financial tool.

Most Common

Non-Coincident Demand Charge

Based on the facility’s absolute peak demand at any time during the billing period, regardless of when it occurs. The utility measures the highest 15-minute average demand and applies the $/kW rate. This type appears on most small and mid-size commercial rate schedules.

Time-Dependent

Coincident (On-Peak) Demand Charge

Measured only during the utility’s defined on-peak hours (e.g., 2-7 PM weekdays in summer). Peak demand outside these windows does not count. This type rewards load shifting and makes solar+storage peak shaving particularly effective.

Highest Risk

Ratchet Demand Charge

The billed demand is set at a percentage (often 80-100%) of the highest peak recorded over the previous 6-12 months. A single demand spike in summer can inflate winter bills for nearly a year. Ratchet clauses make demand management a year-round priority.

Rate Component

Demand Rate ($/kW)

The per-kW price applied to peak demand. Rates range from $5/kW for small commercial accounts to $25+/kW for large industrial customers. Some utilities apply tiered demand rates where the $/kW increases at higher demand levels.

Demand Charges by Rate Class

Demand charge rates vary by utility, rate class, and region. The table below shows representative values for U.S. commercial accounts:

Rate Class	Demand Charge ($/kW)	Energy Charge ($/kWh)	Demand % of Bill	Battery Value
Small Commercial (under 50 kW)	$5-10/kW	$0.08-0.14	20-30%	Moderate
Medium Commercial (50-500 kW)	$10-18/kW	$0.06-0.12	30-50%	High
Large Commercial (500-2,000 kW)	$15-25/kW	$0.04-0.09	40-60%	Very High
Industrial (2,000+ kW)	$12-22/kW	$0.03-0.07	50-70%	Critical
Agricultural/Irrigation	$6-12/kW	$0.05-0.10	25-40%	Seasonal

Monthly Demand Charge Formula

Monthly Demand Charge = Peak 15-min Demand (kW) × Demand Rate ($/kW)

Example: A warehouse with a peak demand of 200 kW on a rate schedule with a $15/kW demand charge pays $3,000/month in demand charges alone, regardless of total energy consumption. If a battery system reduces that peak to 140 kW, the monthly demand charge drops to $2,100 — saving $900/month ($10,800/year).

Why Solar Alone Does Not Reduce Demand Charges

Peak demand in commercial buildings typically occurs between 5-8 PM in summer, when HVAC systems run at full load and occupants are still active. Solar production drops off sharply after 4 PM. Without battery storage to discharge during evening peaks, solar panels cannot reliably reduce the 15-minute demand peak that sets the charge. Battery storage is the missing piece: it stores midday solar production and discharges during evening peaks, directly shaving demand. This is why commercial solar+storage proposals consistently outperform solar-only systems on demand-charge-heavy rate schedules.

Practical Guidance

Demand charges affect system design, storage sizing, and financial projections. Here is role-specific guidance for solar professionals:

Request 12 months of interval data. Monthly kWh totals are useless for demand charge analysis. You need 15-minute or hourly interval data to identify peak demand timing, duration, and frequency.
Size storage to shave the top 20-30% of peaks. Diminishing returns set in quickly. Shaving the top peaks delivers the best $/kW savings; flattening the entire load profile requires oversized (and uneconomic) battery capacity.
Check for ratchet clauses. If the rate schedule has a ratchet, a single missed peak can negate months of demand savings. Design the control strategy with backup dispatch logic for battery failures.
Model coincident vs. non-coincident charges separately. Some rate schedules include both. Use solar design software that can model each demand component independently for accurate savings projections.

Install CTs on the main service entrance. Real-time current transformers are required for the battery management system to monitor load and dispatch peak shaving commands accurately.
Verify utility metering intervals. Confirm whether the utility meters demand in 15-minute or 30-minute intervals. This affects how aggressively the battery must respond to load spikes.
Commission the peak shaving controller before going live. Test the battery dispatch logic under real load conditions. A misconfigured controller that misses peaks will eliminate the financial benefit.
Coordinate with the utility on demand response programs. Some utilities offer additional incentives for battery dispatch during grid peak events, stacking value on top of demand charge reduction.

Lead with the demand charge line item. Show the customer exactly how much they pay in demand charges each month. Most commercial customers have never isolated this cost, and the number is often surprising.
Present solar+storage as a unified solution. Solar reduces energy charges; storage reduces demand charges. Together they address both sides of the bill. Selling solar without storage on a demand-heavy rate leaves money on the table.
Use before/after load profiles. Visual charts showing the demand peak before and after battery peak shaving are the most effective sales tool for commercial solar+storage proposals.
Quantify the ratchet risk. If the customer’s rate has a ratchet clause, show the 12-month cost impact of a single demand spike. This creates urgency and justifies the storage investment.

Model Demand Charge Savings with Solar+Storage

SurgePV’s generation and financial tool models demand charges, peak shaving, and battery dispatch to show exact commercial savings.

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How to Calculate Demand Charge Savings

Calculating potential demand charge savings from solar+storage requires three data inputs and a straightforward process:

Obtain 12 months of interval data from the utility (Green Button or CSV format). This shows the facility’s load profile at 15-minute resolution.
Identify the monthly peak demand for each billing period. Note the time of day, day of week, and season when peaks occur.
Model battery dispatch against the load profile. The battery charges from solar during midday and discharges during peak demand windows to cap the grid draw below a target threshold.
Apply the demand rate to the reduced peak. The difference between the original peak and the shaved peak, multiplied by the $/kW demand rate, equals the monthly savings.

Demand Charge Savings Formula

Monthly Savings = (Original Peak kW − Shaved Peak kW) × Demand Rate ($/kW)

Sources

Frequently Asked Questions

Can solar panels reduce demand charges?

Solar panels alone rarely reduce demand charges in a meaningful way. Peak demand for most commercial buildings occurs in the late afternoon or early evening when solar production is declining. Without battery storage to discharge during these peaks, the 15-minute demand reading that sets the monthly charge remains largely unchanged. Pairing solar with battery storage enables peak shaving, which directly reduces demand charges by 20-50% depending on the load profile and battery sizing.

What is a demand charge ratchet?

A demand charge ratchet is a billing clause where the utility sets your minimum billed demand at a percentage (typically 80-100%) of the highest peak demand recorded in the previous 6-12 months. For example, if your facility hits 400 kW in July and the ratchet is 80%, you will be billed for at least 320 kW of demand every month for the next year, even if actual demand drops to 200 kW in winter. Ratchets make a single demand spike extremely costly and are a strong argument for battery-based peak shaving.

How much can battery storage reduce demand charges?

Battery storage typically reduces demand charges by 20-50%, depending on the facility’s load profile, peak duration, and battery sizing. Facilities with short, sharp demand spikes (under 1 hour) see the largest reductions because a modestly sized battery can absorb the peak. Facilities with sustained high loads require larger batteries for the same percentage reduction. According to NREL research, the optimal battery size for peak shaving is usually 20-40% of the facility’s peak demand, with diminishing returns beyond that threshold.