Dynamic Line Rating — Pushing The Grid To Its Max In Denmark
It’s getting windy in the small country of Denmark. Or rather, massive amounts of electricity from wind will come from the shallow waters around the country and hit the shores for the country to use, and to sell to the rest of Europe.
The Danish government has agreed on a framework for tenders of offshore wind to the tune of 9 GW of power! It was previously agreed that the build-out of this magnitude should happen, but now we are getting really close to the wind farms actually being built.
It could potentially be up to 14 GW if the companies that buy into the task utilize the full capacity. And this is on top of the 2.4 GW already in service. So we are looking at a nameplate capacity of +16 GW in a country that consumes 6 GW at peak load. Denmark has 2.8 million households, and this new capacity could provide enough energy for +16 million households total.
Apart from sending surplus electricity abroad, this vast supply of energy is also to be used for Denmark’s big bet on power-to-x with gigantic hubs of liquid synth-fuel facilities on selected harbors on the more than 8,000 km (5,000 miles) coastline of the country.
The agreed upon 9 GW is to be completed and in operation by 2030. This is a big deal, but this is not what I wanted to tell you about, because, well, the renewable build-out is happening all over the world right now. Renewable energy capacity is racing up the S-curve.
What I stumbled on when learning about this expansion in offshore wind was a suggested solution to, in part, solve the capacity bottleneck of the grid. It’s called Dynamic Line Rating, and it’s one of those things almost nobody has heard about, but it’s of the utmost importance considering the super abundant renewable energy flow of the future.
Dynamic Line Rating
It’s worth repeating the name of this concept a few times, because it’s actually very clever. I had never heard of it, but reading about Dynamic Line Rating on the Danish Ministry of Climate and Energy website was an eye-opener. Let me try to convey the idea here, starting with the main point: “Sensors and a smart algorithms can get up to 30% more sun and wind through the grid.” Yes, that’s 30% more transmission capacity throughput on the same wires!
We are talking about high capacity overhead lines up to 400 kV. The ones with heavy cables that visually vary in how “loose” they seem to hang, depending on their temperature. The wires’ temperature depends on the ambient temperature, the cooling of flowing wind, and the amount of electricity being pushed through them.
This is the core problem: On a warm and windless day with burning sun above the cables, the transfer capability decreases, as the heat dissipation conditions are so poor that the cable quickly reaches its maximum permissible conductor temperature.
Until now, there has been a fixed upper limit on how much power can be sent through the overhead lines determined by worst case weather conditions on a hot summer day in order to ensure that the overhead line is always operated properly so that it is not overloaded and damaged or hangs too close to the ground.
The Energinet project named “Dynamic Line Rating” will change all that. Project manager Thomas Strømdahl Nygaard explains:
“Instead of a fixed safety margin and a very conservative limit for how much current we can allow to be sent through the overhead lines, it is now possible to move the limit up and down, depending on what the weather conditions are like at that particular hour. Thereby, we can make better use of the existing electricity grid — we can go closer to the limit, because we can calculate exactly where the limit is in real time.”
If the wind cools the overhead lines, the improved heat dissipation condition thus allow more power to be transported. Dynamic line rating makes it possible for areas with high concentration of wind turbines to transport 30% more power away on a windy day — power that had otherwise been lost due to insufficient transfer capability. It’s simple, really. But how is this monitored? Sensors and very accurate weather forecasts.
The Danish electricity system has undergone enormous change in recent years. For example, the fluctuations in production from wind turbines are extreme — from a share of 0% of the total electricity consumption to well over 100%, sometimes just within a few hours.
It has been necessary to develop a completely new advanced system with a new algorithm and, for a period, obtain measurement data on selected overhead lines for verification of the algorithm to enable Dynamic Line Rating. The real innovation, however, is that the concept is meant to be solely based on weather forecasts and a mathematical representation of cooling conditions for a given overhead line.
“Concretely, Dynamic Line Rating is realized with the help of a very detailed real-time weather forecast and a newly developed algorithm, which calculates a precise forecast for transmission capacity in the overhead lines,” explains Jacob Michael Jørgensen, senior engineer in Security of Supply, who elaborates:
“How much more can be allowed to be sent through the overhead lines depends on wind and weather. It is not always 30% more — but we estimate that we can increase the transmission capacity in the lines for 90% of the hours of the year. In general, it’s a good way to push the maximum out of the electricity grid we already have.”
The Dynamic Line Rating solution has by now been implemented on about 20 of the country’s total of 90 overhead lines, and is expected to be fully implemented at the beginning of 2024. Initial calculations show that there is an economic gain of approximately DKK 400 million ($60 million) by 2030, based on the ability to transport electricity in regions more efficiently.
Dynamic Line Rating cannot replace the future need to expand the electricity grid massively, but it goes without saying that a 30% efficiency gain of both current and future transmission lines is a really big deal in terms of savings on actual infrastructure build out and materials.
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The traditional fossil electricity system with few fluctuations in production, and therefore very uniform transport of energy, has had no need to optimize with dynamic limits, but things are changing — fast. With the before mentioned 9 to 14 GW wind power expansion and solar photovoltaic capacity growing exponentially alongside it, the concept of Dynamic Line Rating is a great way to get the most out of the grid as possible.
Obviously the imminent growth in battery storage capacity will be of vital importance. Big utility batteries will support the grid backbone, and home batteries will also help level out the peaks of the intermittent nature of our renewable energy future. It all has to work together in the smart grid that will be so very different from what we are used to. Put together, these are huge investments, but prices are plummeting, and this will all provide flexibility and resilience to consumers. We are for sure heading into a future with low and stable energy costs overall, and sooner than we expect.
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