Pexapark forward curves show Spain’s solar capture factor, the ratio of the solar capture price to the baseload price, at 0.45 in 2027 and stuck at 0.45-0.47 through 2040, against 0.60-0.62 in Germany (1). With the Spanish baseload curve falling from 131 EUR/MWh in 2027 to 50 EUR/MWh by 2035, the solar capture price drops from 63 EUR/MWh to 25 EUR/MWh over the same period. Spring is weakest, with the April capture factor averaging 0.19 across the curve.
Adding a 4-hour BESS that charges only from the co-located plant, a “green BESS”, lifts Spain’s 2027 capture factor from 0.45 to 0.82, an 82% uplift worth 45 EUR/MWh. Allowing the BESS to also charge from the grid, a “gray BESS”, takes the capture factor to 0.93, only 13% above the green case. Green co-location therefore delivers around three-quarters of the total uplift, as Spain’s lowest prices fall in the middle of the day, when the plant’s own output is already available to charge the BESS. The effect is strongest in spring, when green co-location lifts the April capture factor from 0.19 to 0.80.
The uplift peaks at 0.94 for green co-location in 2029-2031, roughly double the solar-only level, before easing to 0.84 by 2036. As more BESS connects, it competes for the same low midday prices and high evening prices, narrowing the day-ahead spreads co-located assets rely on, while falling baseload prices reduce the value of each MWh shifted. In absolute terms, the green uplift falls from 45 EUR/MWh in 2027 to 17 EUR/MWh in 2036, and the gray uplift from 60 EUR/MWh to 23 EUR/MWh.
Germany shows a contrasting pattern. Green co-location lifts the 2027 capture factor from 0.62 to 0.92, worth 46 EUR/MWh, while a gray BESS reaches 1.29, worth 112 EUR/MWh, meaning green co-location captures less than half of the total uplift. Germany’s midday solar dip is shallower, and much of the BESS value comes in winter, when solar output is low and evening peaks are high, so German co-located projects depend far more on grid charging to make full use of the BESS.
For Spanish developers, this limits the additional value from grid charging, which is also becoming harder to secure. From around March 2027, new distribution-connected BESS will need to accept flexible grid access to charge from the grid, including fixed charging windows or curtailment by the distribution grid operator. With most of the co-location value available without the grid , green BESS offers Spanish solar owners a simpler route to the uplift, while the expected erosion after 2031 points to locking in contracted value, such as a PPA uplift for BESS co-located with solar, while spreads remain wide.
Notes: 1) Pexapark forward capture factors (September 2026) for solar co-located with a 4-hour BESS at a 50% storage power ratio, including day-ahead revenues only and up to two cycles per day. Annual figures are averages of monthly values.
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