The congestion between NP15 and SP15 in the last week has been good news for SP15 batteries. The low midday SP15 real-time prices are reminiscent of this spring when negative pricing during ideal charging hours abounded. For the CAISO fleet in SoCal, this meant lots of cheap charging opportunities in the midday hours while evening prices still reached double digits. We covered more of the market details in our most recent article, ‘Spring/Fall Curtailments’, but in this report, we’ll take a closer look at the CAISO fleet’s arbitrage opportunities and how well they’ve done capturing those opportunities in the past week, as well as in the past two quarters.

The figure below displays the charging and discharging pattern for the CAISO battery fleet, along with the real-time prices for NP15 (brown) and SP15 (black). In five out of the last eight days, SP15 has dipped below the $0/MWh mark in the middle of the day, reaching past -50/MWh at its lowest point on Tuesday, September 17^th. Batteries, however, missed some of the lowest prices, like those on 17^th, which occurred in the later afternoon hours and after the highest levels of charging occurred. NP15 joined in on the negative midday prices in two of the days, but mostly, the congestion, low demand, and high solar generation gave the edge to batteries in SoCal. If you’d like to see this figure in your inbox daily, make sure to add the CAISO Daily Battery Dashboard to your preference page or email [email protected] for more information.

Figure 1 | Price Responsiveness – Battery Operations and RTM Price