In the context of energy development, Load Calculation and Energy Yield Analysis represent the two sides of the “energy equation.” To design a system that works, you must balance how much energy is needed (Load) against how much the site can realistically produce (Yield).
1. Load Calculation: “The Demand”
Load calculation determines the total electrical or thermal power required by a building, facility, or community.1 It isn’t just a single number; it’s a profile of how energy is used over time.2
Key Calculation Methods:
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Electrical Load: Summing the wattage of all connected devices (3$P = V \times I \times PF$).4 Engineers use a Diversity Factor to account for the fact that not every light and motor is on at the same time.
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Thermal Load (HVAC): Determining the energy needed to heat or cool a space.5 This uses the Manual J protocol, considering square footage, insulation (R-values), and “internal gains” (heat from people and electronics).6
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Load Profile (The Curve): A 24-hour graph showing “Peak Load” (highest demand) vs. “Base Load” (minimum continuous demand).7
2. Energy Yield Analysis (EYA): “The Supply”
While a load calculation tells you what you need, the Energy Yield Analysis tells you what the environment can give. This is most common in Solar (PV) and Wind projects.
The Analysis Process:
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Resource Assessment: Collecting historical weather data (Solar Irradiance or Wind Speed) for the specific GPS coordinates.
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System Modeling: Inputting hardware specs (panel efficiency, inverter ratings, or turbine power curves) into simulation software like PVsyst or OpenWind.8
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Loss Accounting: Subtracting “real-world” losses, such as:
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Soiling: Dust or snow on panels.9
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Shading: Nearby trees or buildings.10
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Transmission: Energy lost in wires and transformers.
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Probability (P-Values): Financial models use $P_{50}$ (50% chance of reaching this yield) or $P_{90}$ (conservative estimate for bank loans).
3. The Relationship: Why They Must Match
If your Load Calculation is higher than your Energy Yield, the system will fail or require expensive grid/generator backup.
| Feature | Load Calculation | Energy Yield Analysis |
| Focus | Internal (Appliances, People, HVAC) | External (Sun, Wind, Climate) |
| Key Metric | Peak kW / Annual kWh Demand | Annual kWh Generation / Performance Ratio |
| Risk | System overload or blackouts | Financial loss or under-performance |
| Tool Example | ETAP, AutoCAD MEP | PVsyst, Helioscope, RETScreen |
4. How to Conduct These Studies
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Step 1: Audit the site to create an inventory of all loads.
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Step 2: Use sub-hourly weather data (15-minute intervals) for the yield analysis to capture “clipping losses” where production exceeds inverter capacity.11
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Step 3: Compare the Load Profile to the Yield Curve. For solar, this often reveals the “Duck Curve” where production peaks at noon, but demand peaks at 6:00 PM—indicating a need for battery storage.
Would you like me to help you calculate a sample load for a specific building, or would you prefer a list of the specific losses to include in a solar yield report?