Introduction

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

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

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, offering simple credit systems.
• NBT evolved to align solar credits with real-time energy market values, reflecting broader grid economics.

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System Implementation

Tariff Modeling

Our system categorizes tariffs using the transaction_type property, defining how energy imports and exports are managed. This guide explains how to distinguish between Net Metering (NM) and Net Billing Tariffs (NBT), with a focus on 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:

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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 the annual true-up.
   • Example:
     • NEM 3 tariffs use BUY, BUY_IMPORT, SELL_EXPORT, and sometimes SELL for net surplus compensations during true-up, reflecting a Net Billing setup.

In both cases, interval data will be 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:

using 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 start time of calculation 
        "dataFactor": 1,
        "dataSeries": [
            //comma-separated values in this list 1,2,3,...
        ],
        "duration": 3600000
        // ^ millisecond value for 60 minutes
    }
]

Net Billing Approach:

using 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  
    ]  
}