Controlling Energy Hub Pannenweg
One of the first operational energy hubs in the Netherlands, and the first Group Transport Agreement (GTO) with grid operator Enexis.
What is an energy hub, and what is a GTO?
An energy hub is a collection of electricity grid connections that share a single contract with a grid operator — instead of each connection having its own individual contract. This bundling makes better use of the available technical capacity. In return, the connections need to coordinate (communicate) with each other, to prevent the shared limits from being exceeded.
There are two common contract types for energy hubs:
- GTO (Group Transport Agreement) — with static limits for consumption and feed-in.
- CCBC (Collective Capacity-Limiting Contract) — with static limits, combined with flexible limits via GOPACS.
The challenge
Business park Pannenweg II was running up against the limits of the electricity grid. Individual companies could no longer expand, electrify, or add solar panels, because their grid connection capacity had been reached. Some companies were even facing daily fines for exceeding their limit.
Reinforcing the grid was not a viable short-term option, since laying new cables and transformers takes several years. At the same time, it became clear that not every company was continuously using its full connection capacity.
The solution
Led by Wim Schilders, manager of the Energy Trading Platform Pannenweg (EHP-P), work began in 2022 on an energy hub, initially allowing participating companies to exchange locally generated solar power among themselves. From April 2024, the first 20 companies started distributing electricity among each other.
A next major step followed in November 2025: 14 companies, bundled under EHP-P, signed a Group Transport Agreement (GTO) with Enexis — the first this grid operator has ever entered into. With a GTO, participants combine their individual transport rights into a single shared capacity limit, which they then divide among themselves based on who needs room at any given moment.
ACC's role
To keep the hub within the agreed GTO limit, real-time control is needed at group level. We delivered the cloud-based intelligence that makes this possible: hub software that continuously calculates how much capacity is available for the group, and determines what action is needed to stay under that limit — for example charging or discharging a battery, or temporarily curtailing solar panels.
This cloud layer works together with Withthegrid's Teleport Gateway, which collects real-time metering data at every participating location, forwards it to our system, and executes the received control commands locally — even when the cloud connection is temporarily unavailable. Energy Hub Pannenweg uses 17 Teleports to monitor the connections and control the assets.
“ACC is a reliable partner for Withthegrid and a great party to work with. They can move fast, are flexible, and are happy to think along with us. This contributed to the successful go-live of our joint project to unlock participation in the aFRR balancing market for our customers.”
The energy management system (EMS) developed by ACC monitors what each company consumes and generates every 10 seconds. Surplus generated power is stored locally in a battery, so it can be used at a later moment. This minimizes curtailment of solar generation, and makes sure as much generated power as possible is put to use. The software calculates the available capacity for the group and determines which assets need to be controlled, such as charging/discharging a battery or limiting PV output, to keep the hub within the agreed collective GTO limits.
The energy trading platform enables trading between participants, both on the day-ahead market and on imbalance, which companies are automatically exposed to. This happens fully transparently and is recorded between producer and consumer.
The GTO structure requires precise, real-time monitoring: ACC's hub software, combined with the Teleports, lets companies steer supply and demand in real time; generated energy can be stored or distributed within the group without putting extra strain on the grid, and the shared grid capacity is continuously monitored to comply with the agreed Enexis limits.
Results
Technical deep dive
For those who want to look deeper: below we explain two parts of our approach at a more technical level.
Sub-hubs
Within an energy hub, capacity can be subdivided into nested hubs, or sub-hubs: smaller groups of connections within the hub, each with its own feed-in and off-take limit. A connection always belongs to exactly one sub-hub; a sub-hub can contain multiple connections. The number of sub-hubs within a hub is not limited, with the sole constraint that this number can never exceed the number of connections itself. Energy Hub Pannenweg has four sub-hubs, each with its own feed-in and off-take limits.
The main hub and (nested) sub-hubs each have separate feed-in and off-take limits.
Control runs in two steps. First, each sub-hub is kept within its own limit. Next, the system determines how much flexibility — controllable capacity — remains per sub-hub. That remaining flexibility is used to keep the energy hub, the main hub, in balance: the sub-hub then effectively acts as a flexible asset within the larger whole.
Concretely, the system runs through the following cycle every 10 seconds:
- 1Retrieve realized data for all connections.
- 2Check per sub-hub whether the limit has been reached.
- 3If the limit has been reached → calculate the required correction, retrieve the available flexible capacity within the sub-hub, and send a control signal to the flexible asset with the largest capacity.
- 4If the limit has not been reached → calculate the available capacity, check which assets are already applying a correction at that moment, and compose a new control signal with the extra available room. The remaining capacity of the sub-hub is recorded.
The loop of checks and control actions the hub software runs every 10s.
Once all sub-hubs have been processed, the process repeats at the level of the entire hub — with each sub-hub treated as a flexible asset with the available capacity just calculated. The new control signal is sent to all involved assets.
Battery optimization
A separate control layer applies to battery systems within an energy hub. Instead of the optimization system controlling a battery directly, it first sends its signals to the hub software. The hub software checks each signal against the technical room available at that moment, before it reaches the battery.
Battery control is based on two factors:
State of Charge (SoC)
the battery's current energy level, expressed as a percentage of usable capacity. SoC determines whether there is still room to charge (at a low SoC) or discharge (at a high SoC), and ensures the battery keeps operating within its technical limits.
Market signals
external price or imbalance signals from the electricity market that indicate when it is financially attractive to charge or discharge. These signals typically form the basis for battery trading and imbalance optimization.
Based on the combination of market signal and current SoC, the optimization algorithm generates a control signal indicating whether and how much the battery should charge or discharge. That signal goes to the hub software — the intermediate layer between the optimization algorithm and the physical battery.
The role of the local EMS
Energy Hub Pannenweg uses Withthegrid Teleports as the local EMS on all connections within the hub. These monitor whether sufficient capacity room is available and whether the action stays within SoC limits. If so, the Teleport passes the signal through and the battery executes the action. If that room is missing — for example due to an SoC limit or another constraint within the hub — the Teleport blocks the signal. This prevents the battery from carrying out an action that is technically infeasible or unsafe.
Project timeline
2022
Start of local exchange of solar power between companies at Pannenweg via an independent energy network.
May 2023
First major press attention — business park Pannenweg II is presented as the first business park in the Netherlands to solve grid congestion itself by combining network control with an energy trading platform, with Enzo Diependaal (Rethink Zero) as technical project lead and Om | Nieuwe Energie as energy supplier. The first 20 companies were connected on June 1.
Read more on Solar & Storage MagazineApril 2024
Official go-live of the energy hub — 20 companies have since distributed electricity among each other without putting extra strain on the grid. From that point on, thanks to agreements with Enexis, the companies are allowed to distribute electricity among themselves — normally only the grid operator is permitted to do so.
Read more on Rabobank.nl2025
Simultaneity based on solar power alone turned out to be limited to around 35%. Because of this, battery systems were installed in 2025 to buffer energy, and work began with Enexis on sharing grid capacity via a GTO.
November 26, 2025
Signing of Enexis's first Group Transport Agreement (GTO), with 14 selected companies within EHP-P. At that point, more than 45 companies at the park were already trading electricity among themselves via the energy hub.
Read more on the Enexis websiteJanuary 2026
Start date of the GTO and go-live of the software, built by ACC, that controls the hub.
March 2026
Addition of imbalance-based battery steering to generate extra revenue at times the battery is not needed to operate the energy hub within its bandwidth.
Other articles about Energy Hub Pannenweg
Further developments
2026 and beyond
- August 2026: Extension of the hub software to support multiple batteries, including within sub-hubs.
- Investigating the possibility of using the flexibility of EV charging hubs to help keep the energy hub within its bandwidth.
Running up against the limits of your own grid connection?
We're happy to think along with you about how an energy hub, GTO, or CCBC could help your business park too.