Introduction

Net Billing Tariffs (NBT) and Net Metering represent two distinct methods for crediting solar customers for the energy they export to the grid.

• NBT applies separate rates for energy imports and exports, often aligned with real-time energy market pricing.
• Net Metering credits customers at a one-to-one rate for exported energy based on retail energy prices.

Both systems influence customer bills, energy usage patterns, and annual reconciliations, such as true-ups.

Historical Background

• Net Metering was designed to incentivize early solar adoption by offering simple credit systems.
• NBT evolved to align solar credits with real-time energy market values, reflecting broader grid economics.

System Implementation

Tariff Modeling

Our system categorizes tariffs using the transaction_type property, which defines how energy imports and exports are managed. This guide explains how to distinguish between Net Metering (NM) and Net Billing Tariffs (NBT), helping you identify them in our system and understand their billing mechanics.

• BUY: Charges only for imported energy
• SELL: Credits only for exported energy
• NET (NM): Charges or credits based on net usage within a chargePeriod
• BUY_IMPORT/SELL_EXPORT (IMPORT/EXPORT): Real-time resolution of imports and exports (instantaneous netting)

These configurations allow accurate modeling for both NBT and Net Metering scenarios.

Key Differences:

Identifying NM and NBT in Our System

1. Net Metering (NM):

• Transaction Types:
  • NET: Energy usage is calculated as imports minus exports over a billing period
  • BUY: Applies when customers import more than they export
• Behavior:
  • Monthly netting determines charges or credits
  • Exports offset imports at retail rates
• Example:
  • PG&E E-1 (Net Metering) uses NET and BUY for monthly netting

2. Net Billing Tariffs (NBT):

• Transaction Types:
  • BUY: Applies to imported energy
  • BUY_IMPORT and SELL_EXPORT: Track imports and exports separately
  • SELL (optional): Determines export credit value, often at lower-than-retail rates
• Behavior:
  • Imports and exports are billed separately
  • Exported energy is credited at a reduced rate (e.g., wholesale or avoided cost)
  • Surplus export energy may be compensated at the SELL rate during annual true-up
• Example:
  • NEM 3 tariffs use BUY, BUY_IMPORT, SELL_EXPORT, and sometimes SELL for net surplus compensation during true-up, reflecting a Net Billing setup

In both cases, interval data is entered as a property input. For net billing, enter two interval data series—one for imports and one for exports—both with the same duration and start time. While using a net billing approach can yield accurate results for net metering tariffs, the reverse is not true.

Calculator Functionality

Net Metering Approach

Uses a single consumption object with a dataSeries containing both positive and negative values:

"propertyInputs": [
    {
        "keyName": "consumption",
        "fromDateTime": "2024-09-01T00:00:00-07:00",
        // Start dateTime of interval list, may vary from calculation start time 
        "dataFactor": 1,
        "dataSeries": [
            // Comma-separated values in this list: 1,2,3,...
        ],
        "duration": 3600000
        // Millisecond value for 60 minutes
    }
]

Net Billing Approach

Uses independent dataSeries and exportDataSeries lists to separate imports and exports:

"propertyInputs": [
    {  
        "keyName": "consumption",  
        "fromDateTime": "2024-08-01T07:00:00.000Z",  
        "unit": "kWh",  
        "duration": 3600000,  
        "dataSeries": [  
            1,  
            2,  
            0,  
            1,  
            2,  
            0,  
            0,  
            0  
        ],  
        "exportDataSeries": [  
            0,  
            0,  
            1.5,  
            0,  
            0,  
            1,  
            3,  
            7  
        ]  
    }
]