Osmose, when technology “stabilises” renewable sources

The energy transition raises two important issues. The first is numerical: there are many small-scale renewable plants across the country, which makes management more difficult than before. The second is the discontinuity of sources, since wind and sunlight are not always available. So how will we reach the goal of 100% green energy by 2050?

In order to help solve this dilemma, Europe has launched the Osmose project, created as part of the Horizon 2020 programme. At the forefront for Italy is Terna, the electricity transmission system operator, which is conducting a series of tests between the Puglia and Basilicata regions. The programme began in early 2018 and the study phase recently ended: we are now entering the phase of tests in the field, which will continue until October-November. The project is expected to conclude between late 2021 and early 2022.

«Our goal is to study methods and tools so that production from renewables can effectively be used on the grid. In order to integrate renewables it is necessary to increase the flexibility of the grid and the electricity system as a whole», that is to say its capacity to adapt supply to changes in demand, explains Luca Orrù, project manager for Terna. After all, the acronym Osmose stands for “Optimal System-Mix Of flexibility Solutions for European electricity”.

In practice, Terna’s research focuses on four of these possible “flexibility solutions”. Let’s see what they are.

1. Flexibility of demand. The first branch of the project deals with the flexibility of energy demand. «Demand has always been understood to be static: the user needs 100 megawatts, so I provide 100 megawatts», continues Orrù. «But one of the ways to guarantee greater flexibility for the system is for the user to change their own energy demand. The same could also be said for small domestic users, but at Osmose we are focused on a series of large industrial plants. In particular, we have studied whether these plants could reduce their consumption when necessary for the grid. Obviously they would do this upon request and with economic remuneration. In the past the focus was very much on demand side responseas a flexibility resource: today we are more realistic and Osmose will show that on this front we could achieve less than we’d hoped».

2. Synthetic inertia. The second application is linked to production plants. «We took two large-scale wind farms, one from Enel and one from Edison», explains the Terna engineer, «and we are studying the possibility that these plants could provide what we call synthetic inertia». Let’s explain. Electricity grids are managed with alternating current, which is produced by alternators, i.e. rotating machines connected to the turbines which produce energy. For example, in a thermoelectric power station the steam produced by the boiler is directed to a turbine which turns, producing mechanical energy, which will then be converted into AC electricity by the alternator. This system has an enormous advantage: it responds naturally to changes in demand. This is very important because consumption changes notably not just with the seasons, but even over the course of a single day.

For technical reasons, this advantage does not apply to plants connected to renewable sources. As a result, a system based only on renewables – the objective that we are committed to achieving within the next 30 years – would have serious stability problems and a very high risk of blackouts. «For this reason we are also studying how wind farms and photovoltaic plants, connected to the gird by electronic devices, could respond better to rapid changes in demand, thus increasing the stability of the grid», notes Orrù.

3. Avoid overheating. The third area investigated looks at the dynamic limit concept associated with each power line, known as the «dynamic thermal rating». Essentially, if it is established that a given line can carry 1,000 megawatts, this limit is always valid or changes at most based on the summer/winter season. The main reason is safety: the electricity heats up the pylon cables, which then expand and sag. So the energy released onto each line must be controlled to prevent the cables from getting too close to the ground. This is why we need static limits, which are established in advance.

«Some time ago we realised that these thresholds could be changed based on atmospheric conditions», continues Orrù. «For example, if it’s very windy or cold, the static limits we are used to working with can be greatly exceeded without posing any safety risks. Our activity therefore consists not only in testing new sensors on the power lines to measure the environmental conditions and therefore indirectly the physical conditions of the power line, but to predict them several hours in advance and thus understand what our margins are to increase their transmission capacity. With these systems, in some cases, we can even double the static limit value». The problem we seek to solve with this method is congestion, which often means we have to cut production from renewable sources because there is not enough transmission capacity on the grid.

4. Energy Management System. Lastly, the Energy Management System is a new algorithm that optimises the entire process. It successfully predicts energy demand and production levels, while taking account of the flexibility of the demand and the grid. This way, the system helps control room operators to foresee or resolve any congestion.