The consensus used to be that renewable energy was too expensive and too scarce to be a viable source of energy to run our proud, electrified societies. Since then, solar panel prices have fallen, becoming more efficient along the way, and homeowners are installing them on crowded roofs.
When it was once thought that we would never have enough solar energy, in some cities this happens too much. In South Australia, where solar power can be huge on a sunny day, electricity authorities face problems with network stability, and take measures to limit solar energy to the grid.
Isn’t it usually better?
The problem facing South Australian utilities is one way to properly manage an electricity grid with many thousands of distributed energy sources. Typically, in conventional modern power grids, voltage and frequency are controlled within certain limits by carefully matching supply from large power plants with consumer demand. Rapid-reaction plants can be delivered online to meet shortcomings, and be turned off when demand drops and everything buzzes pleasantly.
Unfortunately, solar energy is not so easy to regulate, much less when it comes from thousands of individual households, each with its own roof installation and mains inverter. This has led to authorities considering measures such as charging homeowners to export energy to the grid during peak periods in an attempt to slow down the huge absorption of home solar systems. Export limits are also offered for the suburbs with the highest concentration of domestic solar energyas substations in certain residential areas struggle to cope with the huge influx of energy.
With 280,000 homes in South Australia equipped with solar energy on the roof, or 35% of the state’s housing stock, this essentially creates a huge power plant that the authorities have almost no control over. In some situations, South Australia’s energy needs are met 100% by solar energy alone, with gas, wind and other generating resources, after which they export their energy to interstate markets. However, things can quickly become dangerous in situations where there is nowhere to take the excess energy. In a recent incident, interstate connections were cut off for routine maintenance on a day of particularly high solar supply. The electricity regulator has decided to shut down 12,000 domestic solar systems through newly released energy to keep the demand in the network above 400 MW, a level high enough for large gas power plants to remain online.
This was achieved by relatively harsh means, but if not checked, the voltages would rise high enough that domestic solar inverters would suddenly deviate en masse, leading to a sudden drop in supply and a wide drop-out. The same can happen in the case of short-term voltage drops. If a main generator goes offline and the mains voltage falls below the set levels, thousands of home inverters can suddenly disconnect in response, exacerbating the problem and causing interruptions.
A major eclipse, in which large chunks of the web go offline at once, is difficult to return; black starts are stressful and expensive and is avoided at all costs. The authorities are therefore taking steps to limit the chances of these problems in the future. The new installations are authorized to have inverters that are supplied with surge protection, which allows them to continue to operate through voltage disturbances to avoid sudden shocks to the network. Furthermore, inverters that can be controlled remotely by the electrical body are needed, controlled via the Internet or via 4G data connections. Substations are also upgraded with improved voltage management hardware, to allow suburbs with high solar penetrations to better export their energy to the wider network.
Other measures can also help. Grid storage batteries such as Hornsdale energy reserve can help by storing excess energy when it is available for later use, when the demand for solar energy is lower. Home batteries could be a great solution in these cases as well, allowing homeowners to make the most of the outlet of solar panels, even when the grid is sufficient. At present, these measures are not cheap, and the penetration of the battery into the home is a small part of that of solar energy, but government subsidies are available to stimulate absorption.
Home storage is best implemented in accordance with network control measures, but instead of stand-alone, otherwise thousands of home battery systems that go offline at the same time may pose the same risk as home solar energy at the moment. Besides, this is not a panacea in itself – a long, bright week in the summer can saturate the resources of home batteries.
Such measures were not necessary when domestic solar energy first came on the market. The small number of hardware homeowners did not have enough generation capacity to shake the network in one way or another. However, as the number of home generators has taken off, it is necessary to implement a way to command this huge resource. By applying control to home solar generators, it allows the electric power to make the most of the generating capacity without exposing the network to the risk of interruptions due to overvoltage or undervoltage. The availability of huge amounts of solar energy is a great victory for renewable energy in the fight against climate change. However, investment will be needed to keep the electricity grid going if this new technology is used to its full potential. If home solar generators provide Australia with electricity, they will have to work together.