Portsmouth Water stabilises energy costs with Wattstor’s Price Protect tariff

Portsmouth Water has partnered with Wattstor to deliver a 3MW solar project at its Highwood reservoir, doubling its renewable capacity to 6MW in its largest clean energy project to date.

Read the full press release here

The long-term, 25-year agreement is underpinned by Wattstor’s Price Protect tariff, which caps electricity costs over the full term while still allowing Portsmouth Water to benefit if wholesale prices fall. This gives the utility long-term cost certainty for one of its largest operational expenses, while continuing to invest in renewable generation.

Serving around 324,000 homes and businesses across South East Hampshire and West Sussex, Portsmouth Water is using the project to support both its net zero ambitions and cost management strategy.

Bob Taylor, CEO at Portsmouth Water, said:

 “We have committed to being net zero by 2040 and we’ve already nearly halved our gross carbon emissions since 2016. Buying renewable energy generated on our own sites is a crucial part of our plan. Additionally, as energy is one of our biggest costs, protection from price shocks is also very important. Wattstor’s Price Protect tariff has capped our electricity costs at a flat, competitive rate and gave us the certainty to go ahead with this project. That certainty now helps us keep bills fair while continuing to deploy renewables at scale.”

Water companies are under increasing pressure to manage costs while continuing to invest in infrastructure and sustainability. By stabilising energy spend, Portsmouth Water is taking a practical step that supports both affordability for customers and long-term investment in clean energy.

This is the first time a UK water company has deployed this model at scale, but it is designed to be repeatable. By combining a capped-price tariff with solar-plus-storage, Wattstor enables utilities to reduce exposure to volatile energy markets while unlocking projects that might otherwise be delayed, reduced in scope, or not viable.

Kevin Ball, Chief Commercial Officer at Wattstor, said:

“This project depended on tackling the engineering and the commercial model side by side. With a DC-coupled solar-plus-storage system, deployed through a Price Protect tariff, Portsmouth Water can now make full use of the reservoir roof area, leading to over 85% of the annual electricity demand being renewably generated onsite.”

The system uses DC-coupled solar and battery storage, allowing energy to be captured and stored before conversion to AC power. This approach avoids grid export constraints and ensures more of the generated energy is used on site. It also enables larger solar deployments on constrained grid connections, increasing overall carbon savings compared to standard configurations.

The Highwood site required careful environmental management. The reservoir is fully roofed to prevent algae growth and sits alongside a country park and protected habitats. The project has been designed to minimise disruption, with all cabling installed underground using directional drilling rather than open trenching. This preserves public access, protects biodiversity, and avoids impact on the surrounding landscape.

The result is a large-scale renewable energy scheme that delivers both operational resilience and environmental sensitivity—setting a model for future water industry projects.