Day-ahead TB4 spread by grid node across ERCOT, CAISO, MISO, PJM, NYISO, SPP, and ISO-NE, the BESS siting signal. Mean of the four highest hourly prices minus the mean of the four lowest, per priced node.

Data window 2025-06-24 to 2026-06-23

As of the 2025-06-24 to 2026-06-23 window, the median priced node across the 7 ISOs mapped (ERCOT, CAISO, MISO, PJM, NYISO, SPP, and ISO-NE) showed a $33/MWh day-ahead TB4 arbitrage spread, with the top 10% of nodes at or above $42/MWh.

• Animated hex map of the TB4 storage arbitrage spread for ERCOT, CAISO, MISO, PJM, NYISO, SPP, and ISO-NE, 12,938 priced nodes
• TB4 is the four-hour storage signal: the mean of the four highest hourly day-ahead prices minus the mean of the four lowest, per node per day

Blog: read why the TB4 spread varies by node and grid, and how it shapes day-ahead arbitrage revenue →

Hex fill is the TB4 spread, darker is higher. Each ISO is shaded to its own range. A column is an operating battery, taller is more MW. Hover any hex or battery.

Weekly view: median TB4 per week, drag the slider to scrub. Switch to the 12-month median for the stable siting baseline, barely moved by one storm week.

Every priced node's 12-month median TB4, one overlaid distribution per grid, the thin tails of low-price and congestion nodes trimmed so the body reads. Each ISO carries its own color, click a legend entry to isolate it.

A long right tail means a market holds more high-spread siting hotspots above its typical node; a tight cluster means the arbitrage opportunity is even across the grid.

TB4 is a gross day-ahead energy spread for a 4-hour battery before efficiency losses, operating constraints, and bid execution: the mean of the four highest hourly prices minus the mean of the four lowest, at that node.

• TB2, TB6 and TB8 follow the same rule for 2, 6 and 8 hour durations, the emailed screening list carries all four
• Computed per priced node from public ISO day-ahead disclosures, then taken as the per-node median over the window
• A pure energy-arbitrage signal: it excludes ancillary services, capacity and real-time, so it is one component of storage value, not total revenue

Worked example, one real node. Step 1: for a single day, rank the 24 hourly day-ahead prices and take the top four minus the bottom four, that day's TB4.

Step 2: repeat for every day in the window. The node's median across those days is the single value the map shows for that node. Winter-storm days can spike high, but a median is barely moved by a few extreme days, unlike an average.

Every priced node gets one median this way. The cards at the top read off all 12,938 of them: the median of the medians, the 90th-percentile bar, and the count above it.

Want every battery ranked by actual revenue, not just spread? See the ERCOT and CAISO BESS revenue leaderboards →

Enter any US place and your work email. We email the nearest 20 priced nodes with their TB2, TB4, TB6 and TB8 spreads and distance, a screening list drawn from the same public day-ahead data as the map. Nearest by distance can cross a constraint or congestion zone, so treat it as a starting screen, not a full siting study.

Email nearest nodes