Heatwave, weak wind push battery revenues higher in June

Tight supply and a soaring heat once again squeezed German power markets in June. After the marked shift in market dynamics observed in May, June largely confirmed that this was no temporary phenomenon. 

High temperatures and persistently weak wind generation once again shaped the market environment and created favorable conditions for battery trading. 

The prolonged heatwave during the second half of the month reinforced this trend. As periods of renewable oversupply became less frequent, market value increasingly shifted towards scarcity conditions, steeper evening ramps and wider intraday price spreads. 

To quantify these developments, we evaluated simulated earnings for a representative 10 MW/20 MWh standalone battery in Germany. As in previous months, individual market strategies were benchmarked against a forecast-based cross-market optimization approach. 

Among wholesale markets, continuous intraday trading once again delivered the strongest standalone performance, increasing from €15,400 ($17,560)/MW/month in May to €17,700/MW/month. Both day-ahead and intraday auctions also improved, reaching €12,500/MW/month, while a stacked wholesale strategy combining auctions with continuous intraday trading rose from €19,000/MW/month to €20,300/MW/month.

Ancillary service markets presented a more mixed picture. FCR remained a strong standalone option, rising modestly to €14,900/MW/month, up 6% from May. Within the automatic Frequency Restoration Reserve (aFRR) markets, however, revenues reflected changing system conditions. Positive aFRR increased markedly from €7,000/MW/month to €11,000/MW/month, while negative aFRR declined from €17,100/MW/month to €13,000/MW/month. The stacked aFRR strategy remained broadly stable at €12,000/MW/month, whereas revenues from aFRR energy decreased from €2,600/MW/month to €1,400/MW/month.

The strongest overall performance came, as usually, from combining markets. Suena Energy’s forecast-based cross-market optimization generated €25.0k per MW/month, outperforming the combined wholesale strategy by around 23% and exceeding all other market strategies by between 41% and more than 1,600%. 

Shifting scarcity 

June largely continued the market regime established in May, but the underlying drivers became even more pronounced. A prolonged heatwave across large parts of Europe coincided with persistently weak wind generation, tightening the supply-demand balance and pushing the average day-ahead spot price to €109.5/MWh — around €12/MWh higher than in May and roughly 70% above June 2025.

Solar generation also remained a defining market feature. Strong photovoltaic output continued to depress prices around midday, creating attractive charging opportunities for battery storage. However, compared with May, these periods became less extreme. The number of negative-price hours fell from 77 to 52, making negative prices unusually rare for a summer month.  

Instead, as temperatures intensified towards the end of the month – with Germany recording new national temperature records on three consecutive days – and price volatility increasingly shifted towards the evening hours, when photovoltaic generation declined and cooling demand remained elevated. 

As a result, the market increasingly relied on more expensive gas-fired generation to meet demand. On several occasions, 15-minute prices exceeded €700/MWh during the evening ramp, creating pronounced intraday spreads and attractive discharge opportunities for battery storage.   

These changing market conditions were also reflected in ancillary service markets. With fewer periods of renewable oversupply, the need for downward flexibility declined, contributing to weaker revenues in negative aFRR. At the same time, tighter supply conditions and steeper evening ramps increased the value of upward flexibility, supporting stronger revenues in positive aFRR. 

Summer outlook

June demonstrated once again how quickly battery value can shift as power system conditions change. While early summer opportunities continued to be driven by strong solar generation, tightening supply conditions increasingly rewarded flexibility during the evening ramp. 

Looking ahead, these dynamics are likely to become even more pronounced. If strong solar generation continues through the summer, Germany could experience greater intraday price divergence, with a higher likelihood of deep midday negative prices followed by steep evening price spikes as photovoltaic generation declines and conventional generation sets the marginal price. 

At the same time, June underlined that strong battery revenues do not depend on frequent negative prices. Although the number of negative-price hours declined even further from the already reduced levels seen in May, overall revenues remained robust as scarcity-driven price spreads continued to create attractive trading windows. In an increasingly renewable-based power system, success will therefore depend less on capturing a single market opportunity and more on dynamically optimising across wholesale and ancillary service market.