Technologies
Co-located battery storage puts a battery on the same grid connection as a solar or wind farm, as a retrofit or on a greenfield site. Gridcog models the shared connection, the battery's charging rules and any power purchase agreement (PPA) or subsidy on the renewable asset. It then autosizes the battery against the site's prices and costs.
Curtailment cut a standalone 100 MW solar plant's wholesale revenue in southern Germany by up to 35% in a Gridcog model. With a co-located battery, the loss was 6% at most.
The 130 MW Glenrowan solar farm in Victoria earned an estimated A$14m in the 12 months to July 2025. In a perfect-foresight Gridcog model, a 50 MW, 2-hour battery would have roughly doubled that.
For the 110 MW Wemen Solar Farm in Victoria, Gridcog's autosizing recommended about 163 MW of 4-hour battery.
A co-located battery shares a grid connection point with a solar or wind farm. It can store output the connection can't export, or that would sell at negative prices, and discharge it later. Some co-located batteries charge only from the renewable asset; others can also import from the grid, depending on the market's rules and the renewable asset's contracts.
Developers build co-located projects in two ways.
| Retrofit | Greenfield | |
|---|---|---|
| What it is | A battery added to an operating solar or wind farm | A new site with generation and storage planned together |
| Why developers do it | To use the existing grid connection and cut exposure to negatively priced hours | To design the connection, generation and storage from a blank slate |
| Contracts to work around | The existing PPA or subsidy, which may give the renewable asset first right of way over the grid connection | None: choose between revenue floors, tolling agreements, baseload or peakload PPAs and full merchant co-optimisation |
| Example modelled in Gridcog | 110 MW Wemen Solar Farm, Victoria: about 163 MW of 4-hour storage recommended | meteocontrol: 53 MWp of solar and a 120 MWh battery in Saxony-Anhalt, modelled across two construction phases |
As one site behind one grid connection, interval by interval. The solar or wind farm, the battery, the connection limits and the offtake contracts sit in one simulation, and Gridcog co-optimises when the battery charges, discharges and trades.
Set the site's export and import limits at the point of connection, or a schedule for flexible and dynamic connections such as flexible connection agreements in Germany. Gridcog limits the combined export of generation and storage, and shows how much output the battery absorbs that would otherwise be curtailed.
Battery Charging Options set what the battery can charge from: the grid, all on-site renewable generation, generation in negative-price intervals only, or excess generation above the export limit. That covers green batteries that charge only from the co-located asset and grey batteries that also import from the grid.
Attach a PPA, a contract for difference (CfD) or a subsidy such as Germany's market premium under the Renewable Energy Sources Act (EEG) to the renewable output. Gridcog's Negative Price Adjustment models knock-out clauses, including how many negative intervals it takes to trigger them.
Gridcog's autosizing finds the battery size, and the solar or wind size if you want it to, that gives the highest net cashflow. It weighs capex and opex, the project's length, grid constraints and every price signal the site is exposed to.
Give the battery its own inverter, or let it share the solar inverter in a DC-coupled design. With Gridcog's solar modelling, DC clipping and efficiency losses are calculated automatically and used to charge the DC-coupled battery, within the system's power limits.
Model wholesale, ancillary, balancing and capacity revenues for the battery, and let the solar or wind farm turn down when prices go negative. Results show cashflows, internal rate of return (IRR) and net present value (NPV) for each stakeholder, with interval-level energy flows between the assets.
Modelled in Gridcog
In a Gridcog model of a 10 MW, 2-hour battery co-located with 12 MWp of solar, MiSpeL earned about €2.33m a year. Running fully merchant earned €2.25m, and green-only €1.70m. MiSpeL (Market Integration of Storage and Charging Points) lets a co-located battery import from the grid. It keeps the EEG market premium on the share of exports that came from the solar plant.
Gridcog Senior Energy Analyst Daria Ekimova compared three ways to run the same battery.
| Scenario | Wholesale (€m) | Ancillary (€m) | EEG (€m) | Total (€m a year) |
|---|---|---|---|---|
| Green | 1.37 | 0.19 | 0.14 | 1.70 |
| Merchant | 1.71 | 0.54 | None | 2.25 |
| MiSpeL | 1.69 | 0.51 | 0.13 | 2.33 |
MiSpeL earned the most and worked the battery harder, with more cycling through the low-yield winter months. The post also sets out the practical limits, including metering requirements and grid connection limits.
Daria Ekimova
Senior Energy Analyst
Read the full MiSpeL analysis for large-scale co-located batteries
10 MW, 2-hour battery with 12 MWp of solar, Germany
Adding a battery to a solar or wind farm?
Model your co-located project in Gridcog
Laura Hoffmann-Ostenhof
Central Europe Industry Lead
It depends on risk appetite, access to grid capacity and demand for corporate offtake. Gridcog Central Europe Industry Lead Laura Hoffmann-Ostenhof compared four revenue models for co-located solar and storage in Germany (November 2025).
| Revenue model | How it works | Trade-off |
|---|---|---|
| Subsidy-backed innovation tenders | Fixed subsidies for 20 years, with premiums often around 6 to 9 euro cents per kWh | Bankable and lower risk, but the battery can't import from the grid |
| Shared infrastructure and cable pooling | Generation and storage oversized on one grid connection to use its spare capacity | Lower connection costs and better utilisation, but returns stay capped by the renewable output profile |
| Fully merchant co-optimisation | The connection is optimised across day-ahead and intraday wholesale markets and ancillary services such as frequency containment reserve (FCR) and automatic frequency restoration reserve (aFRR) | The highest revenue potential in Gridcog's model of a 50 MW, 1-hour battery with 75 MW of solar, but volatile and harder to finance |
| Partially merchant with a hybrid PPA | Part of the output is sold under a corporate or long-term PPA; the battery trades when it isn't serving the contract | PPA stability, with room for market upside |
EPC contractors, developers and technical advisors in Germany. Two have published how.
Models standalone batteries and batteries co-located with solar or wind, including 55 MWh of green battery capacity added to an operating solar plant in Germany.
‘No matter how complex a project is, we've always found a way to model it in Gridcog.’
Runs battery energy storage system (BESS) revenue assessments for standalone and co-located projects, green and grey. For a 53 MWp solar and 120 MWh battery project in Saxony-Anhalt, the team compared storage sizes against the planned solar capacity across two construction phases.
‘Storage has become a mandatory component for any project that wants a credible route to market.’
Short explainers from Gridcog's energy analysts on battery retrofits, co-location and offtake.
Scott Bosman, Senior Energy Analyst, on curtailment at a 110 MW solar farm in Victoria and how big a battery should be. Read Scott's Wemen Solar Farm analysis.
Four revenue models for co-locating solar and batteries in Germany, from subsidy-backed innovation tenders to fully merchant co-optimisation. Read the German co-location breakdown.
How existing PPAs, subsidies and negative-price clauses change a battery retrofit, and how to test offtake options for a greenfield site. Read the offtake contracts guide.
Renewable developers and IPPs, investors, energy majors and the consultants who advise them.
Request a live demo
Request a demo and we'll show you how Gridcog sizes a battery for your solar or wind farm.
The team behind Gridcog
Fabian Le Gay Brereton
Chief Executive Officer & Co-Founder
Previously co-founded Greensense, acquired by ERM Power (now Shell Energy).
Pete Tickler
Chief Product Officer & Co-Founder
Co-founded Greensense and led digital innovation at ERM Power (now Shell Energy).
Genna Boyle
Chief Commercial Officer & Head of EMEA
More than 10 years in energy strategy, trading and renewables, with senior roles at Battery Optimiser and Limejump.
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