When wholesale electricity prices drop below zero during periods of excess renewable generation, as they did over the recent holiday weekend in Europe, flexibility becomes a revenue source.

From pv magazine Deutschland

When electricity prices fall deeply into negative territory, as they did over the recent holiday weekend, flexibility becomes a revenue stream. In other European markets, households with battery storage and electric vehicles are already actively earning money. Jan Hicl, chief product officer at Delta Green, explains how the business model works.

Politically, Germany is increasingly expected to make smaller PV systems more market-oriented – from the removal of feed-in tariffs during negative wholesale price periods to discussions about mandatory direct marketing. The direction of travel is clear. But why stop there? Residential batteries, flexible loads, and wallboxes can do significantly more if they are controlled intelligently and systematically.

This is exactly where Delta Green comes in. The Czech company aggregates distributed assets, mainly in single-family homes, into a virtual power plant and is already active in several European markets. For utilities, the system reduces price and balancing risks while creating additional revenue opportunities for customers.

At Delta Green, where Hicl became a shareholder in 2024, he drives the development of flexibility solutions enabling smarter electricity use in households, communities, and small businesses. Before entering the energy sector in 2022, Hicl led product teams at Socialbakers and co-founded the software studio S9Y, where he worked on the launch of InstaCover, an AI-driven startup now used by major insurance companies. His career has consistently focused on the intersection of technology, innovation, and product leadership.

pv magazine: Last weekend, day-ahead prices in the Germany-Luxembourg bidding zone fell to minus €0.50 ($0.58)/kWh. Can you quantify how much a typical household with a Delta Green-managed battery earned?

Jan Hicl: May 1 was a perfect setup – a Europe-wide holiday, clear skies, and strong renewable generation met a grid with minimal demand. For individual German households with batteries we manage, revenues of €30 to €40 in a single day were not unusual. That is not a monthly figure – that is the revenue for one day. More important, however, is the portfolio-level picture. Large utilities selling electricity under fixed-price contracts bear the full cost of negative wholesale prices. Their customers have no incentive to respond, because the price signal never reaches them. The loss per customer can easily reach several tens of euros on a day like May 1. Multiplied by 100,000 households, a holiday becomes a financial nightmare.

pv magazine: What exactly happens in your system on a day like this?

Hicl: The advantage of negative day-ahead prices is that we know about them 24 hours in advance. That leaves plenty of time to prepare. Our platform forecasts wholesale prices over a rolling 72-hour horizon and coordinates all flexible household assets – battery, wallbox, and inverter. On a morning like May 1, we start withholding battery capacity: we prevent the battery from charging from solar generation so it is as empty as possible when the negative price window begins. Electric vehicles are treated the same way. Charging is paused and then triggered precisely during the cheapest hours.

This logic turns conventional home energy management on its head. Instead of maximizing self-consumption, we maximize grid consumption at the moment the grid pays you to consume electricity.

For this to work for everyone, the customer must also benefit – and they do. Even under a fixed-price contract, the household receives a direct payment for every kilowatt-hour consumed during the negative price window. On May 1, that amounted to around €0.10/kWh after taxes and grid fees during negative pricing hours. It may sound modest, but it is money received without doing anything other than letting the battery and EV charge. The customer is paid, the utility limits its losses. That is the deal, and it must be transparent to work.

pv magazine: In a white paper, you cited average revenues of €40 per month for a German household. What assumptions is that based on?

Hicl: A typical German household with a PV system, home battery, and EV can generate around €40 per month in flexibility value based on historical data – and that is from just two markets: day-ahead price optimization and imbalance management. No exotic instruments, no industrial-scale infrastructure required.

Day-ahead optimization alone delivers €22 per month. This captures both ends of the wholesale price curve – extremely negative hours on sunny holidays when renewables flood the grid, and high evening peaks in summer when solar output drops and expensive gas plants set the price. Imbalance management adds another €18 per month.

Every supplier must balance its deliveries against forecasts. When it is wrong, it pays imbalance prices. On days when the entire market is wrong simultaneously, these prices can rise to €10 to €15 per kilowatt-hour, which is 20 to 30 times the normal wholesale price. Our AI models monitor the portfolio and grid signals in near real time to reduce imbalance risk before penalties occur. In a large portfolio, this is where the real financial exposure sits.

pv magazine: How much control does the customer retain over their system?

Hicl: Households can set a minimum state of charge, reserve capacity for backup power, exclude their EV from optimization, or limit charging cycles. Customer comfort is non-negotiable – the system never exceeds defined boundaries. To receive a bonus, around 90% of activation requests must be fulfilled, but customers can opt out at any time in any month without justification.

pv magazine: How do you avoid conflicts with self-consumption optimization?

Hicl: These are real but short-lived. Charging a battery from the grid while the sun is shining can seem counterintuitive. But when the wholesale price is minus €0.50/kWh and the household effectively receives around €0.20/kWh after taxes for consumption, it becomes worthwhile. Customers understand this quickly once the numbers are shown.

pv magazine: Your estimates for Austria are €71 per month, for the Czech Republic €52 per month, and for Poland €45 per month. Why are revenues so different?

Hicl: Counterintuitively, the maturity of the German market reduces overall upside. Germany has the most developed flexibility markets in Europe – there are more mechanisms to absorb renewable fluctuations before prices spike. In Austria, the Czech Republic, or Poland, there are fewer buffers, so prices react more strongly and remain elevated for longer when renewables surge.

pv magazine: Is Delta Green therefore always a balancing-responsible aggregator?

Hicl: We describe our model as “flexibility-as-a-service” and operate our own customer portfolio of around 10,000 customers – but this is purely for testing technology and refining our product offering. We do not aim to become a large European utility.

In each market we enter, we work with established utilities that already have customer relationships, regulatory licenses, and trading infrastructure. This readiness layer is typically the hardest part of any market launch – and this is where we invest heavily. The result is a partner that can go from zero to thousands of registered households within months instead of years. E.ON is a reference we can point to in several European markets.

pv magazine: How are customers paid for providing flexibility?

Hicl: The basic model is a platform fee per household – a simple software-as-a-service approach. We also receive a revenue share when we manage market activations on behalf of the utility. Utilities that want full control can run activations themselves; we remain the technology layer. For end-customer bonuses, the utility defines the model. The most common approach is a fixed monthly payment tied to two simple metrics: connection quality (how reliably devices are online) and activation success rate. We monitor and report both automatically, giving utilities a clear, auditable basis for payouts. Per-activation payments are technically the fairest model but harder to explain on a consumer bill, so most utilities prefer fixed monthly bonuses.

pv magazine: In Germany, there is discussion about mandatory direct marketing for small PV systems. What does that mean for Delta Green’s market entry?

Hicl: It helps, but we do not need it. Most European utility portfolios – including all our E.ON partnerships – are based on fixed-price contracts. We already operate fully in that model. When end customers are shielded from wholesale prices, the value of flexibility flows into the utility’s P&L rather than the household bill. It is a different distribution, but the same underlying mechanism. However, market price linkage does make customer conversations easier. When a household sees its bill reacting to the market, it understands why flexibility matters and engages more actively. For Delta Green, the policy debate in Germany is a tailwind, not a prerequisite. We are prepared for both scenarios, and our track record across regulatory environments proves it.

via pv magazine International https://ift.tt/m654A9W