Distributed solar photovoltaic power systems are becoming increasingly popular across the world. Their integration into power grids designed for large conventional power plants, however, are struggling to absorb and adapt to them.
I’ll first discuss the issues today’s transmission grids face vis-a-vis renewable energy projects. I will try to keep it simple without the technical jargon such as phase angles etc. Then, I’ll brief upon how synchrophasors may address these issues.
Grid security is a paramount concern for developed and developing countries. Transmission networks in use today are designed to take electricity generated from large conventional power plants based on coal, natural gas, and potential energy of water (in case of hydro power projects). All these fuel sources have one thing in common — their availability and supply can be controlled and, thus, the power generated from such power plants can be easily predicted and modified to maintain grid stability.
The same does not apply for most renewable energy sources like solar and wind energy. Local wind speeds and solar radiation are difficult to predict on a hourly basis, which, in turn, makes it hard to predict how much electricity these power plants would inject into the grid.
As a result, it becomes difficult to forecast how the grid would behave with the injection of unpredictable amounts of electricity. Changes in critical parameters of the grid, like frequency, beyond a certain limit can lead to blackouts. These parameters change when the grid’s limits are stretched through over-supply or over-drawl of electricity.
Issue of over-supply from solar and wind energy projects has become an issue in developed markets like Germany where consumers are sometimes paid to consume excess electricity in the system. Germany and California, both of which have seen a tremendous boom in the rooftop solar power systems, are now encouraging people to install solar panels facing west instead of the usual south. According to recent research, west-facing solar panels give a smoother power curve (less peaks and troughs in generation) when the solar radiation increases towards the middle of the day.
Now, how can the grid be protected or insulated from such fluctuations, especially when the rooftop solar power systems are becoming increasingly popular? Synchrophasors. A synchrophasor measures and monitors various parameters of the grid. It monitors the parameters in real-time so as to enable the grid operators to take quick corrective measures to bring the parameters to their optimum levels.
Real-time monitoring and quick response is essential, as failure of any one branch of the grid could knock out an entire region’s transmission network, referred to as the cascading effect. Half of India’s transmission network was knocked out twice in less than 48 hours in 2012 due to cascading failure that started from over-drawl of electricity and led to the shut down of several thermal and hydro power projects in the north and northeast parts of the country. The 2003 blackout in the US and Canada was also a result of a cascading failure.
So synchrophasors can help grid operators to manage the power from intermittent sources like rooftop solar power systems (utility-scale projects are large entities and are better equipped to control their generation; they can be asked to forecast their generation with some level of accuracy). But what if it is too late to correct the parameters of the grid and it is set to fail or has already failed?
Conventional power plants use turbines that are equipped with sensors that cut themselves off from the grid when they sense a significant change in the parameters, as the grid needs to be in an optimum state to take up electricity. A city, serviced with a branch of the larger grid that can operate in isolation, can tension functional during a blackout without affecting the transmission network as a whole. This is called the islanding effect.
India’s capital Delhi was able to partially achieve islanding during the 2012 blackouts by taking power from Bhutan’s hydro power projects. Following the blackouts, though, the Indian government started working on a comprehensive islanding plan for major cities.
Now, all power plants outside the island need to shut generation in order to protect the regional grid. Rooftop solar power systems may mistake power from neighboring solar power systems as grid power and continue feeding electricity. This is called the anti-islanding effect.
Now, we can talk about the microsynchrophasors being funded by the US Department of Energy. These devices have an even shorter measurement interval, meaning they measure and report more data about the grid parameters. These are also equipped with GPS and 4G LTE to enable the grid operators topoint out the precise location of a system that may be affecting the grid.
Microsynchrophasors can thus prove vital for maintaining the stability of a transmission network by enabling operators to access real-time information about the status of various critical parameters of the grid.