Alan Croes is Head of Energy System Planning (ESP) at TenneT, the department dedicated to energy transition perspectives and designing the grid of the future
Alan: 'For Target Grid, we have drawn up basic rules, design principles. With these, all parties that participate have the same framework of solutions in mind. We outline a foundation of possible solutions needed for future developments. But I like to stress: this should not deter others or make them sit back. Target Grid is a collaboration between TenneT and society, and we are actually going to talk to many stakeholders and include their insights in our plan. We are really open to that. Target Grid should deliver a widely supported vision of the future.'
'One basic rule is that Target Grid is working to expand a direct current (DC, direct current) high-voltage grid. Innovative and therefore interesting to zoom in on. After all, with the many large-scale wind farms, the North Sea is becoming a huge power hub. And if solar and wind become so dominant in the system, then a DC grid alongside the AC grid really is the next step in grid design. The AC grid gives security of supply to users, is redundant, top-notch reliable. A DC network is built for the bulk transmission of electricity over long distances. So it is not redundant; it is less annoying if a failure occurs somewhere in that network'.
Same kilowatt hour, different value
'That deserves explanation: delivering electricity to customers is more important than collecting electricity from producers. If a producer cannot transmit power due to a delay in the DC grid, the value of kilowatt hours is lost. But no more than that. When supplying customers, residential, industrial and everything in between, it is a completely different story. The value of that electricity is much higher because the customer adds value to it. Cooking, heat, lighting, transport, production of materials. A kilowatt hour is then worth just ten or twenty times more. So it is much more important that the AC grid is reliable and of high quality. That is why that is redundant and why a DC transmission grid does not have to be.'
Can we have offshore electricity with taking DC bulk transport far into the country?
Direct current on land too
'We are taking this technology and philosophy from offshore to onshore. Can we bring offshore electricity DC bulk transport far into the country? Land in Geertruidenberg and deliver in Germany, a few hundred kilometres away? The logic of this can be seen in the Target Grid Map. That shows reinforcements of the AC grid and a new DC grid. Without those DC connections, you would have to make many more and costly reinforcements in the AC grid. So we build the AC grid to satisfy customers, and the DC grid allows producers to bring their electricity directly to customers.
Besides direct current, interconnection is also the next step in grid design. Power highways that combine transport of energy from offshore wind with transport between countries. This international cooperation is really needed. Preferably with countries that have contrasting profiles, so that electricity production is complementary. So in our offshore grid, you see connections between Denmark, Norway, England and Belgium and between the Netherlands and Germany, of course. Interconnection capacity is one of the cheapest forms of flexibility.'
Quantity and quality
'With interconnection and direct current, we are working on the grid capacity needed in a system with more wind and solar. That also brings volatility - highly variable generation. Step two is stability. It is not going to be easy to keep the grid frequency stable hour by hour, minute by minute and second by second. That's the next challenge for Target Grid.'