Example: a behind-the-meter building with solar and storage

This example builds on the API onboarding flow. Follow that guide first to authenticate, create your meters, and create the asset — this page only covers the methodology-specific parts layered on top. The snippets below reuse the same authenticated client and your account_id.

What this methodology is for

The building_btm_sensored methodology measures building-level impact from multiple behind-the-meter interventions at once. A single building often hosts several distributed energy resources — rooftop solar, a battery, maybe more — sitting behind one utility meter. This methodology reads the directly sensored interval meters for each resource and disaggregates the building into counterfactual scenarios, so you can answer “what would this building have drawn from the grid with no solar and no battery?” from measured data rather than a modeled baseline.

The meters and the sign convention

The methodology relies on an energy balance across up to four electricity meters, in WattCarbon’s sign convention (grid import and building consumption are positive; onsite generation is negative):

Role	Symbol	Sign	Meaning
Utility / net	U	import positive	The revenue meter at the grid interconnection. Required.
Solar	S	generation negative	Onsite PV generation.
Storage	B	charging positive, discharging negative	Battery charge/discharge.
Building load	L	consumption positive	The building’s own load, if separately metered. Optional.

These satisfy U = L + S + B: what the grid sees is the building’s load plus whatever solar and storage add or remove. The building-load meter is optional — when present it’s used to reconcile the other three and catch a flipped sign or unmetered load.

Set up the meters and asset

Create the meters and the asset using the onboarding guide; this example only adds the methodology on top.

1. Create one electricity meter per role — follow Step 1 — Create a meter for a utility/net meter, a solar meter, a storage meter, and optionally a building-load meter. Keep each meter’s id.
2. Upload each meter’s interval data — follow Step 2 — Upload meter timeseries. Mind the sign convention above: solar generation is negative, battery charging positive and discharging negative, the utility/net meter import-positive.
3. Create the building asset — follow Step 3 — Create an asset, attaching all of the meters you created via meterIds. The asset’s location drives the weather data used for M&V.

The methodology snippet below assumes you captured those IDs as utility_meter_id, solar_meter_id, storage_meter_id, building_load_meter_id, and the asset as asset_id. Add this methodology instead of the generic Step 4.

Add the methodology

The methodology takes the meters by role rather than as a flat meterIds list — don’t set meterIds yourself, it’s derived from the role fields. projectInstall is a nested date period; its reporting window (the day after completionDate) bounds the measured impact, so meter history from before the system was installed is excluded.

client.post(
    f"/accounts/{account_id}/assets/{asset_id}/methodologies",
    json={
        "kind": "building_btm_sensored",
        "utilityMeterId": utility_meter_id,
        "solarMeterId": solar_meter_id,
        "storageMeterId": storage_meter_id,
        "buildingLoadMeterId": building_load_meter_id,  # optional
        "projectInstall": {
            "startDate": "2024-03-01",
            "completionDate": "2024-03-01",
        },
    },
).raise_for_status()

This produces three disaggregated scenarios over the reporting period:

• Observed — the metered net load U, the building as it actually ran.
• Solar only — U − B, the net load with the battery removed but solar retained.
• No intervention — U − S − B, the building’s native load with neither solar nor storage.

The gap between observed and no intervention is the combined impact of everything behind the meter; the gap between solar only and no intervention isolates the solar.

What you get

The asset’s primary methodology is now building_btm_sensored, producing the whole-building disaggregation and its observed / solar-only / no-intervention scenarios. WattCarbon runs M&V on it and computes hourly savings. Results land on the asset detail page in the web app, and EACs are minted from the primary methodology on the usual cadence.