IN a statement earlier last week, the National Grid Corp. of the Philippines (NGCP) cautioned against relying too heavily on solar and other variable sources of renewable energy (RE), pointing out that without careful planning and management, these could cause instability in the grid, which, in turn, would hurt the reliability of electricity supply across the country. The statement was evidently inspired by a recent incident in Central Luzon, where some relatively brief cloud cover over the San Marcelino solar plant in Zambales caused a sudden voltage fluctuation. The NGCP was able to act immediately to compensate for it and prevent a blackout, but the occurrence illustrated the potentially bigger problems that could arise as the country’s energy system incorporates more RE, primarily solar and some wind power.
To be clear, it is not the case that the NGCP is resistant to the expansion of RE, and it said as much in its statement. “Any new power source introduced into the system will help keep supply stable,” it said. “However, not all renewable energy technologies are equal. Some technologies [such as wind or solar] are, by nature, variable or supply intermittently, and therefore need to be handled more carefully.” The San Marcelino plant, owned by AC Energy, has a capacity of about 384 megawatts (MW), with another 200 MW being added, so compensating for it experiencing a sudden drop in output can be done. But if the same situation was encountered by the Terra Solar plant straddling Bulacan and Nueva Ecija, for example, which is almost eight times as large as San Marcelino, or by several solar plants at once, the problem might become unmanageable.
One nightmarish scenario played out in Spain and Portugal last April, in which almost the entire Iberian Peninsula experienced a blackout lasting from 10 hours to more than an entire day in some places. About 60 percent of the generating capacity for the two countries comes from solar power. One large solar farm in southwestern Spain malfunctioned and went offline, causing a severe voltage fluctuation in the grid. That, in turn, triggered an automatic disconnection from the grid in neighboring France, where most of the backup power to stabilize the Iberian grid would have otherwise come from. In addition, the grid instability also caused several other solar plants in Spain to automatically disconnect, meaning that, for a time, the grid not only had voltage and frequency fluctuations, but also insufficient supply.
For a transmission grid to work properly, the electricity it carries has to be at the correct voltage and frequency. Voltage is determined by the capacity of the transmission lines. For example, if a trunk line has a capacity of 230 kilovolts (kV), then the grid operator has to ensure there are 230,000 volts on that line. If there is a drop in supply from generating plants, then the operator does not have enough power coming into the system to ramp it up (through transformers) to the full 230 kV, and thus there will be a deficit in energy being delivered to the distribution end. Frequency is on-off cycle of alternating current; here in the Philippines, that is 60 hertz. In a thermal or hydropower-generating plant, that frequency is maintained by the speed of the spinning generators. Wind-power generators can work the same way, but their rotational speed varies a great deal, so most rely on electric inverters that convert their variable alternating current (AC) to direct current (DC) and then back to stable frequency AC for transmission. Solar power also requires inverters, but these are simpler than those for wind, since the electricity they generate is DC.
In order to maintain grid stability, i.e., proper voltage and frequency, the NGCP needs to have access to reserve sources of power. An entire discussion of how reserves work would take up too much space, but these are just generating sources that can add power to the system when needed: these are the “ancillary services” that we occasionally read about in the news. Before RE, the only real handicap to having sufficient reserves was having enough generating capacity. With RE, because it is variable (except for sources such as hydropower), the paradox is the more capacity, the more reserves are needed.
This is where the notion of RE capacity targets runs into the brick wall of reality, and it is an especially annoying situation because the RE targets — 35 percent of the energy mix by 2030 and 50 percent by 2040 — are completely arbitrary, not based at all on what the overall energy system can or can be expected to accommodate, but rather virtue-signaling. And because the RE targets are completely arbitrary and unrealistic, much of the onus of preparing the country’s energy infrastructure to run reliably on a large amount of RE capacity has been placed on the NGCP, the implication being that if the targets are missed, it will not be because the capacity is not or could not be available, but because the grid operator is insufficiently prepared to integrate it.
The reality is, however, that the NGCP — or anyone who would be operating the national grid — is as prepared as can be for RE integration, provided enough reliable reserves are secured. In fact, the NGCP has in recent months advertised how much additional capacity, RE or otherwise, it can accommodate right now, and it is a figure that significantly exceeds the country’s projected demand for at least the next decade. Nothing about the grid needs to change, except for increasing the amount of reserves (which, unfortunately, will drive up electricity costs for consumers) because all of the regulating technology, such as the inverters, is on the generation side.
The good news is that the Department of Energy does seem to be coming around to the realization that RE generation and adequate reserve capacity have to go hand in hand. It now strongly prefers solar projects that have integrated battery energy storage systems, such as the Terra Power project, since batteries can be a reliable reserve. That, however, is not a firm mandate, and it should be.
ben.kritz@manilatimes.net
Bluesky: @benkritz.bsky.social