Reference Document
Methodology
How WattMarkets processes and presents grid data. This document is intended to be auditable and comprehensive.
1. Data Collection
WattMarkets collects price data from seven U.S. Independent System Operators (ISOs): ERCOT, PJM, MISO, SPP, CAISO, NYISO, and ISO-NE. Data is sourced from official ISO publications and APIs.
| Data Type | Update Frequency | Source |
|---|---|---|
| Day-Ahead (DA) | Daily after market clearing | ISO publications |
| Real-Time (RT) | 5-minute intervals | ISO feeds |
All prices are stored in $/MWh (dollars per megawatt-hour).
2. Timezone Handling
All timestamps are stored internally in UTC. When displaying data, we convert to the relevant ISO's local timezone:
| ISO | Local Timezone |
|---|---|
| ERCOT, MISO, SPP | Central Time (CT) |
| PJM, NYISO, ISO-NE | Eastern Time (ET) |
| CAISO | Pacific Time (PT) |
API responses include timestamps in ISO 8601 format with timezone offset.
3. Price Aggregation
WattMarkets aggregates prices at two levels: individual settlement points and ISO-wide averages.
3.1 Settlement Point Prices
Each settlement point (load zone or hub) reports real-time prices from the ISO. These are the actual market clearing prices used for settlement. We track both Day-Ahead (DA) and Real-Time (RT) prices where available.
3.2 ISO Averages
For each ISO, we calculate a simple average across all tracked settlement points. This provides a quick indicator of overall price levels in that market. ISO averages include high, low, and mean prices.
3.3 Price Thresholds
We use the following thresholds to categorize price levels for display:
| Range | Category | Description |
|---|---|---|
| $0–$40 | Low | Below typical baseload prices |
| $40–$75 | Normal | Typical market conditions |
| $75–$150 | Elevated | Higher than typical prices |
| $150+ | High | Significant price event |
4. Material Change Detection
The "What Changed" feed surfaces significant price movements. We detect three types of material changes:
| Change Type | Threshold | Description |
|---|---|---|
| Price Spike | >50% increase | Average price increased vs. previous interval |
| Price Collapse | >40% decrease | Average price decreased vs. previous interval |
| Percentile Jump | >30 points | Price percentile changed significantly |
Only the most recent 7 material changes are displayed to avoid noise. If no material changes are detected, the feed shows "No material changes."
5. Data Classifications
WattMarkets distinguishes between two types of data:
Authoritative (Settlement)
Historical prices from official ISO publications. These are final, settled values that will not change. Available via the Settlement Reference.
Indicative (Real-Time)
Current and recent prices displayed on the homepage. These are preliminary values that may be revised by the ISO. Use for situational awareness, not for settlement or verification.
6. Limitations
- —Price data is not a forecast. It reflects current and historical conditions only.
- —Real-time data has inherent latency (typically 1-5 minutes).
- —Coverage varies by ISO. Not all settlement points are tracked.
- —This is not investment advice. Do not use for trading decisions without independent verification.
This methodology document is provided for transparency. If you have questions or require clarification, contact us via the contact page.