PV + Storage Dispatching
The dispatching strategy for co-located PV and storage systems in Re-Twin is based on market schedules, similar to the approach for a standalone Battery Energy Storage System (BESS). The key difference is the presence of an on-site generation source, which introduces the decision to sell, store, or curtail (not send to the grid) the generated power.
Important: The PV and storage components are dispatched together as a single, unified portfolio to maximize overall profitability. The model does not simulate an internal "buy/sell" transaction between the two assets. Instead, it makes decisions based on the opportunity cost presented by external market prices. For the PV-generated power, the model chooses the most profitable action: sell it to the market, charge the battery for later dispatch, or curtail it during negative price periods.
Below, we explain how different co-location configurations are dispatched.
Dispatching Scenarios
PV Only
In a PV-only configuration, the model's objective is to maximize profitability by deciding whether to sell the generated power or curtail it. Curtailment is the default action during negative price periods, as we assume no EEG subsidy is available under these conditions. The dispatch model chooses between the Day-Ahead and Intraday Continuous spot markets based on the price forecast for each.
Note: Intraday Auctions are not currently modeled.
Behind the Meter (BTM)
In a Behind the Meter setup, the storage is located "behind" the grid connection point and can only be charged by the co-located PV system. It cannot import power from the grid.
The dispatch logic is an extension of the PV-only case. The model optimizes the use of PV generation by choosing one of three actions:
- Sell the power directly to the market.
- Store the power in the battery for later dispatch.
- Curtail the PV generation.
This decision is based on an imperfect forecast of the Day-Ahead and Intraday market prices. Since the storage is charged by a controlled generation source, it is eligible to participate in the positive aFRR market. The optimization model factors in this potential revenue stream when making dispatch decisions.
Front of the Meter (FTM)
In a Front of the Meter configuration, the PV system and the storage are modeled as two independent but co-located assets, each with its own connection to the grid.
The primary distinction from the BTM case is the storage's ability to charge from both the co-located PV system and the grid itself. This flexibility unlocks significant advantages:
- Enhanced Arbitrage: The storage can buy cheap power from the grid during periods of low market prices or when PV generation is unavailable (e.g., at night).
- Full Ancillary Service Participation: The ability to import from the grid allows the storage to participate in the full spectrum of ancillary service markets, including both FCR and positive and negative aFRR.
This dual-charging capability enables more complex and potentially more lucrative revenue stacking, as the optimization model can leverage a wider range of market opportunities for both the PV and the storage unit.
Revenue Estimation
The model estimates revenue from three primary sources:
1. Revenue from Ancillary Services (Capacity)
This is the income earned for making capacity available to the grid operator, regardless of whether it is activated. For each service (FCR, aFRR, mFRR), the revenue is calculated as:
Revenue = Power Committed (MW) * Capacity Price (€/MW)
2. Revenue/Cost from Ancillary Services (Energy)
This is the income earned or cost incurred when the reserved capacity is activated to deliver or absorb energy.
- Positive Activation (e.g., aFRR positive): Energy delivered is multiplied by the energy price, generating revenue.
- Negative Activation (e.g., aFRR negative): Energy absorbed is multiplied by its price. This is typically a revenue stream (being paid to take energy) but is treated as a negative cost.
3. Revenue/Cost from Wholesale Markets (Arbitrage)
This represents the core profit from buying low and selling high in the spot markets. For both the Day-Ahead (DA) and Intraday Continuous (IDC) markets, the net revenue is calculated for each time interval:
Net Revenue = (Energy Sold - Energy Bought) * Market Price