With social responsibility one of the overarching corporate values of a water treatment and purification plant in northern Germany, a project was set up in early 2019 which aimed to increase its on-site production of renewable energy for the plant’s own use. ENGIE Laborelec was hired to investigate.

To develop a long-term roadmap, we started by analyzing the plant’s energy consumption profile, the local grid topology and on-site assets, including a CHP unit that had been operational for seven years. The unit digests sludge from the treatment process to create biogas, which already produces about 60% of the electricity consumed at the site. Its load can be shifted in time only within the limits of the available biogas buffer.

Other assets were selected as candidates for flexible energy use, including a compressor used for aerating the wastewater and the centrifuges used for sludge dewatering, always within certain limits.

Three scenarios

We then defined and calculated a series of scenarios with the aim of installing as much PV as possible (wind turbines were not an option) which would avoid both the need to upgrade the grid connection and injection of excess energy into the grid.

The following scenarios are currently under discussion:

  • Basic scenario—Installing PV without implementing flexible energy use. A maximum of 1400 kWp could be installed without the need for a grid connection upgrade. Almost all PV energy produced would be consumed locally.
  • Scenario 2—Installing PV and implementing flexible energy use to optimize auto-consumption using available assets. This would allow the site to increase the PV installation to 2000 kWp with almost complete auto-consumption.
  • Scenario 3—Installing PV, implementing flexible energy use, and adding storage capacity for maximum return. This would allow the site to further increase its PV production, but at a significant additional cost for the battery installation.

Once the managers make their decision, we can start on an implementation plan. ENGIE Laborelec will also be supporting the customer during implementation, and will operate, monitor and maintain the grid.

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