Solar Power and Grid Stability: Scenarios and solutions

hawaii.gridx299Renewable energy is often intermittent, and that variability presents a variety of challenges to power grids. The nature and magnitude of the challenges depends on the time frame — from fractions of a second to seasonal or even multiyear variations — as well as the nature of the grid itself. The latter is evident in two of my articles from last week looking at how seconds-to-minutes fluctuations in solar power complicate grid controllers’ efforts to maintain alternating current at the 60 hertz frequency and the roughly 110 volt power levels required by North American devices.

Fluctuating AC frequency stars in my Technology Review dispatch from the paradise of Kauai, where the island utility is riding an electrical roller coaster as it pushes solar towards 80 percent of peak power flows. Clouds form around the Hawaiian islands’ mile-high peaks and wreak havoc as they float over solar farms, eliminating three-quarters of their generation in less than a minute. On Kauai’s tiny island grid the resulting power supply dips are deep enough to slow down Kauai’s handful of diesel-fuelled generators, causing the AC frequency to crash below 60 hertz.

My story tracks the Kauai Island Electric Cooperative’s hitherto troubled experience with using batteries to smooth out the solar power flows. Discharging a first set of batteries to fill the solar power gaps burned out the battery cells.

Larger continental grids experience solar power quite differently, as I described last week in IEEE Spectrum. Fluctuating output from even the biggest solar farms has little impact on a big grid’s AC frequency, which is maintained by the collective momentum of literally hundreds of conventional power plants spinning in sync. However, fluctuating output from lots of small rooftop solar systems can cause gyrating voltage on a big grid’s local distribution lines.

My piece for Spectrum shows how California is empowering solar systems to solve the voltage problem. The inverters that turn each system’s DC output into AC power for the grid are being deputized to serve as miniature grid regulators that monitor and dynamically adjust the voltage levels on the local lines.

California’s ‘smart inverters’ mark an about-face in how grid operators think about distributed power generation, and are definitely a good-news story. As reader @etlipman commented: “You know exciting changes are afoot when regulators and utilities that have in the past perceived something as a nuisance are starting to see it as asset!”

Amid Blackouts, India’s New Leader Vows 24-7 Power for All

Blackouts this week in New Delhi and surrounding states are providing a dramatic backdrop for a bold promise by India’s new prime minister, Narendra Modi, whose Hindu nationalist party swept to power in a landslide election last month. As a scorching heatwave drove power consumption beyond the grid’s capacity, Modi’s government vowed to deliver “round-the-clock power for all by 2022,” reports the Wall Street Journal.

That will be an awesome task. Nearly one-quarter of India’s 1.26 billion citizens lack grid access. And India’s utilities have struggled to keep up with demand from those who are connected. Power cuts are frequent. Continue reading

Blackouts Ahead on Our Unruly Power Grids

ImageTen years after the Northeast Blackout that shut off power in seven U.S. states and Ontario cascading power grid failures remain a fact of life. And, as I argue today on Spectrum’s Energywise blog, engineers are little closer to predicting and preventing them.

The good news is that engineers are beginning to accept that they have a complex system problem on their hands — an insight that could help them find solutions.

Such understanding was in short supply one year after the Northeast blackout, as I discovered with the publication of my August 2004 cover story for IEEE Spectrum commemorating its one-year anniversary profiling the apparent mathematical inevitability of cascading power-system failures. That message raised a firestorm of protest from engineers who saw their can-do creed under attack.

Today, however, the black sheep who spotted the tell-tale signs of a chaotic self-organizing system in blackout databases have come in from the cold. The University of Wisconsin’s Ian Dobson, for example, says he is having success attracting grants — no mean feat for interdisciplinary research targeting the uber-unsexy field of power transmission. And the IEEE set up a task force on cascading failures (with Dobson at the table).

One obvious cause for rising consciousness is the fact that blackouts just keep happening Continue reading

German Parliament OKs Bold HVDC Grid Upgrade

Germany’s bold transmission plan is a go. The Bundesrat, Germany’s senate, has accepted the plan’s enabling legislation forwarded to it by the Bundestag (Germany’s parliament), according to the authoritative German Energy Blog. There is every reason to expect that the plan’s core element — four high-voltage direct current or HVDC transmission lines profiled by Spectrum last month — will get built.

That is good news for Germany’s grid and those of its neighbors. All are straining to manage powerful and variable flows from the wind turbines and solar panels that provided 12 percent of Germany’s power generation last year.

Elements of both the HVDC system design and the legislation should ease construction of the HVDC systems. On the design side, Germany’s transmission system operators have specified advanced converters whose ability to arrest and clear DC line faults will reduce the risk of running overhead lines. This means the HVDC lines can use existing rights-of-way used by AC lines. In fact, they can be hung from the same towers. Read the May 2013 story for extensive discussion of the advanced modular multilevel converters.

The enabling legislation, meanwhile, will simplify line permitting by making a federal court in Leipzig the only forum for legal disputes concerning the projects. Separate legislation passed by the Bundesrat and Bundestag makes  Germany’s federal networks regulator, the Bundesnetzagentur or BNetzA, the sole permitting authority for power lines that cross Germany’s state or national borders. These measures — for better or worse — cut out state-level officials that face greater pressure from local project opponents and may be more sympathetic to their concerns.

Add it all up and Germany is en route to become the first country with HVDC lines playing a critical role at the core of their power grid. It is arguably the first real challenge to AC’s century-plus reign as the top dog in power transmission since DC-advocate Thomas Edison lost the War of Currents. Tesla and Westinghouse may just be rolling over.

This post was created for Energywise, IEEE Spectrum’s blog on green power, cars and climate

Supergrid Technology Beats Expectations

HVDC breaker Source AlstomAn industrial research consortium that is a who’s-who of the European power industry says development of technologies to produce high-voltage DC (HVDC) supergrids accelerated in 2012 — “surpassing expectations.” The assessment comes in the supergrids technology roadmap updated earlier this month by Friends of the Supergrid, whose members include power equipment suppliers such as Siemens, ABB and Alstom, as well as transmission system operators and renewable energy developers.

Summarizing the conclusions of an expert group within the International Council on Large Electric Systems — better known as CIGRE, its French acroynm — the Friends of the Supergrid says there is now no doubt as to the feasibility of HVDC networks ferrying renewable energy resources from wherever they are in surplus to wherever they are needed: “CIGRE Working Group B4–52 considered this question, specifically whether it was technically and economically feasible to build a DC Grid, and the answer was yes.” Continue reading

Electrical Upgrade Prescribed for Japan’s Crimped Grid

An advisory body for Japan’s powerful Ministry of Economy, Trade and Industry (METI) has endorsed a tripling of the capacity to pass power between Japan’s otherwise estranged AC power grids: the 50-hertz AC grid that serves Tokyo and northeastern Japan, and the 60-hertz grid that serves western Japan. This frequency divide hascomplicated efforts to keep Japan powered since the March 2011 earthquake and tsunami — a task that keeps getting harder with the inexorable decline in nuclear power generation (at present just one of Japan’s 54 reactors is operating). Continue reading

Beacon Power Hits a Speed-bump, but it’s No Solyndra

Flywheel energy storage developer Beacon Power filed for bankruptcy last weekend, prompting immediate comparisons to infamously failed solar manufacturer Solyndra. But while both firms used millions of dollars in federal loan guarantees to expand their businesses, Beacon Power — which Spectrum profiled this summer – has working assets and a good shot at restructuring and carrying on. Continue reading