The operator spent €904 million on German and Dutch grids between 1 January and 30 June – up 20.5% from the €750 million it invested in the same period last year.
CEO Mel Kroon explained that the company needed to invest in grid infrastructure and software to connect variable sources of electricity.
"The energy transition will create an entirely new situation in which Tennet, market parties and end consumers of electricity will be dealing with large-scale, weather-dependent generation of wind and solar energy.
"This not only requires the construction of new infrastructure – such as grid connections for many offshore wind farms and high-capacity onshore connections – but also the development of innovative hard- and software systems for real-time coordination of the variable supply of green electricity."
In 2015, the operator pledged to invest €22 billion in onshore and offshore electricity infrastructure by 2025 to attempt to relieve grid congestion.
Tennet claimed that it is "making solid progress" on onshore projects to distribute clean energy in the Netherlands.
The Dutch government published a roadmap to add an additional 7GW of offshore wind capacity between 2023 and 2030 in March, increasing its total fleet to 11.5GW.
To connect this extra capacity, Tennet will initially use its standardised 700MW alternating current (AC) system, but as projects come online that are further from the shore, it will deploy direct current (DC) connections.
Tennet aims to complete three further grid connection systems for the German North Sea by the end of 2023, increasing its transmission capacity to 8,032MW
The company is preparing tenders for earth cables for the 700km SuedLink and 580km SuedOstLink DC systems, which will have a combined capacity of 6GW.
The operator expects the cables to transmit power from wind farms in northern Germany to major consumption centres in the country’s south from 2025, it added.
It also expects a third additional system to be in place by 2027, increasing its transmission capacity to nearly 11GW.