Solar Peak Shaving Calculator: How it Works
The Solar Peak Shaving Calculator is an automated tool designed for commercial and industrial energy users to estimate savings by reducing “Demand Charges.” By integrating solar power and battery storage, the calculator identifies how much of your building’s highest 15-minute power spike ($kW$) can be “shaved” off, preventing expensive utility fees and lowering your monthly billing peak.
- Solar Peak Contribution (Coincidence Factor)0 kW
- Firm Battery Shaving Capacity0 kW
- New Billing Demand0 kW
How to Use the Peak Shaving Calculator
To get an accurate savings estimate, you will need a recent utility bill (such as from PG&E, SCE, or ConEd) that lists your demand charges.
1. Input Your Utility Demand Profile
First, enter your Monthly Peak Demand, which is the highest amount of power in kilowatts ($kW$) your facility drew from the grid at any single point last month.
Next, enter the Demand Charge Rate. This is the dollar amount your utility charges per $kW$. In many US states, this can range from $15 to over $40/kW, often making up 50% of a commercial energy bill.
2. Configure Your Solar Array
Enter your Solar Array Size in $kW$-DC. The calculator applies a “Coincidence Factor” ($40\%$) to this value.
This accounts for the fact that solar production doesn’t always perfectly align with your building’s peak usage due to cloud cover or the sun’s position. It provides a realistic “firm” contribution to your peak reduction.
3. Define Battery Storage Capacity
Enter the Battery Power (Inverter size) and Battery Energy (kWh).
- The Inverter determines how much power can be discharged at once.
- The Energy (kWh) determines how long that discharge can last.
The calculator requires a minimum 2-hour duration to consider the shaving “firm.” If your battery is too small to last through a typical peak window, the tool automatically adjusts the shaving potential downward to keep the estimate conservative.
Understanding Your Results
Once your data is entered, the Savings Dashboard provides three key metrics:
- Demand Reduction: The total number of kilowatts removed from your utility bill.
- Monthly/Annual Savings: The direct financial impact based on your specific utility rates.
- Load Profile Viz: A 24-hour simulation showing your “Original” load versus the “Shaved” load. The orange bars indicate where the battery and solar are working together to keep your demand below the new billing threshold.
Frequently Asked Questions
Q: What exactly are “Demand Charges” on my utility bill?
A: While standard energy charges ($kWh$) bill you for the total volume of electricity used, Demand Charges ($kW$) bill you for the “size of the pipe” required to serve your facility. It is based on your single highest point of usage in a month. Even one 15-minute spike can result in thousands of dollars in fees.
Q: Why doesn’t the calculator use 100% of my solar capacity?
A: Solar is intermittent. If a cloud passes over your facility exactly when your machinery kicks on, your peak would still hit the grid. By using a $40\%$ coincidence factor, this tool ensures you don’t over-promise savings that might disappear on a cloudy day.
Q: How does the battery know when to discharge?
A: Modern “Peak Shaving” systems use smart controllers that monitor your building’s main breaker in real-time. When the system sees the load approaching a pre-set limit, it instantly discharges the battery to “cover” the excess, keeping the grid-draw flat.
Q: Is there a limit to how much I can shave?
A: Yes. For safety and realism, this calculator caps total reduction at $70\%$ of your peak. Most facilities have a “baseload” (lights, servers, security) that is impossible to shave entirely without going completely off-grid.