Risk and uncertainty in renewable sources of electric power

*By Manuel Matos

Even though it is unquestionable that generating electricity from renewable sources brings great benefits, especially in a country that does not have fossil fuel reserves (and more generally in a planet where those reserves are limited), some have argued that the intermittent features, especially of wind power, are risk factors that would prevent their use (I will focus specifically on wind power, but most of what will be said applies to other renewable sources).

Truthfully, managing a power system always required strategies to cover the risks associated to a possible lack of power generation.

This risk was essentially the result of malfunctions in the generating groups (turbines+generators) and also of possible failures in the hydro resources (in dry periods). As a consequence, all power systems are capable of generating additional power to cover that risk. And there are also evaluation methodologies that make it possible to quantify that risk, providing indications on the needs to strengthen the system.

It is interesting to highlight that, with regard to the risk components associated to malfunctions in the generating groups, wind power generation presents some advantages as this is characterised by a high number of short-range wind turbines (comparatively to the traditional groups). Therefore, losing a thermal unit will lead to an immediate deficiency in the generation of power of typically 400 MW (1600 MW in the nuclear case). In the case of wind turbines, a couple of turbines may stop working, consequently reducing power generation slightly, but there will never be a significant loss overall.

However, it is clear that the importance of the risk component associated to uncertainty and variability of primary resources, in the case of wind power generation, cannot be ignored and it has been closely studied in recent years. As far as the uncertainty of future generation is concerned, there are now forecasting methodologies for time horizons which go up to 72 hours, presenting acceptable margins of error, and allowing the system operators to efficiently manage risk. Therefore, we are still far away from that thought that we have no idea of what is going to happen. In any way, risk management requires a larger availability and use of reserve capacity, with the associated costs, but only relatively to the remaining uncertainty.

Variability requires the existence of groups in the system that will follow up consumption evolutions, always maintaining the necessary balance between the groups and the generation.

Yet again, this function has always existed in power systems due to the variability of consumptions. However, in this case it is necessary to deal with variations in consumptions and wind power generation, which makes it all the more demanding. In the meantime, the existence of wind power forecasts makes it possible to use the necessary groups beforehand.

In summary, it is true that the development of renewable energy sources poses some challenges when it comes to managing the systems. However, these challenges are not insurmountable, and there are enough means to face them adequately. It is true that everything becomes a little bit more complex, but hasn’t that always been the case? Otherwise, we would still be heating by the fire.

*Full Professor at FEUP and Researcher at INESC TEC

Jornal i, 7 August 2012