Everything you always wanted to know about power systems but were too afraid to ask
Part 1 of Malcolm Metcalfe's Power System Primer
There are two distinctly different methods used to balance supply and demand. These are:
- Balancing supply/demand in an isolated system (one that is not interconnected with the larger grid. Examples are local systems to power a remote location).
- Balancing supply/demand in an interconnected system, where a utility is a part of a major interconnection of many utilities.
energy supply/demand balance
Peak demand is the highest rate of electricity use. Fortunately, it only occurs a few times a year – usually on the hottest days of the year or on the very coldest days of the year, depending on your geography. Our power systems are prepared for these peaks (otherwise we risk potential blackouts), but as urban populations increase, and we add more variable renewable energy resources to our grid, we see more need to accommodate increases in peak demand. Traditionally, utilities would forecast demand in their service territories and resort to upgrading or building new peaking power plants to supply the anticipated increase in electricity demand. This solution tends to be land-intensive and has resulted in significant increases in greenhouse gas emissions.
Peak Demand Management,
For more than 100 years utilities have supplied electrical power to customers and have done so with good reliability. The principle is simple. Loads may do as they wish. They may be random or intermittent and generally are not individually monitored by the utility. Generation, on the other hand, MUST be both dispatchable and monitorable, and electric system operators must be able to manage the real and reactive power from a generator.
Historically, utilities have become very adept at managing generation capacity to maintain a continuous balance between supply and demand. But today, the world is faced with a need to reduce or even eliminate carbon emissions, which complicates the supply-demand balance. Most electricity in the US, for example, is generated by burning fossil fuel. This needs to change, along with change to the electricity supply system and the direct customer use of fossil fuel. We are looking to remove the steady performers, and to replace them with supplies that are intermittent and perhaps random, all the time maintaining a balance between supply and demand.
IN CASE YOU MISSED IT:
Virtual power plants or VPPs are one of the hottest topics in the energy industry today. In fact, investments in VPPs are expected to total over $68.6 billion by 2025 -- this according to Navigant Research, who has published a new white paper on the topic.
Software advancements are enabling greatly expanded capabilities in the distributed energy resources (DERs) that can be aggregated into VPPs, which are now capable of responding to the needs of the power grid at the sub-second speeds required for instantaneous grid balancing.
Titled Stacking Values with Virtual Power Plants in Today's Digital Power Grid: Moving Distributed Networked Energy Into the Mainstream, the paper was authored by Navigant's Peter Asmus and covers:
- The expansion and convergence of VPP market segments
- New distributed energy resource architectures
- Physical VPP grid and market interaction values
- ROIs on VPPs
distributed energy resources,
virtual power plant,
Researchers at DNV-GL did a fine report for the New York Independent System Operator a few years ago. Titled A Review of Distributed Energy Resources, it offered this definition of the various distributed energy resources (DERs) examined in the report:
“… DER technologies are defined as ‘behind-the-meter’ power generation and storage resources typically located on an end-use customer’s premises and operated for the purpose of supplying all or a portion of the customer’s electric load. Such resources may also be capable of injecting power into the transmission and/or distribution system or into a non-utility local network in parallel with the utility grid. These DERs include such technologies as solar photovoltaic (PV), combined heat and power (CHP) or cogeneration systems, microgrids, wind turbines, micro turbines, back-up generators and energy storage.”
Granted, the research team did acknowledge that some sources – including the New York Public Service Commission – included customer load in its list of DERs, but load wasn’t one of the DERs covered in the report. That’s too bad because load can hold its own against other DERs for a variety of grid-supportive purposes.
distributed energy resources,
This past March, Chinese energy regulators put the brakes on further deployment of wind-energy projects in Mongolia during 2016. Why? Call it too much of a good thing. China, now the world leader in solar and wind installations, doesn’t have the transmission infrastructure necessary to transport electricity from the windswept Mongolian steppes to the power-hungry cities that need it.
During 2015, China installed some 33 gigawatts of wind turbines, which was more than half of new wind installations worldwide. But, in the same year, government statistics show “33.9 billion kilowatt-hours of wind-powered electricity was wasted … equivalent to the electricity consumed by 3 million American households a year,” according to an article published by InsideClimate News. ”That was about 15 percent of China's total wind power generation, up from 8 percent a year earlier.”
Do you remember that outage that left some 50 million people in the dark on August 14, 2003? It took down 61,900 megawatts of load in eight eastern U.S. states and the Canadian Province of Ontario. The financial impact was as high as $10 billion in the U.S. and $2.3 billion up north. When government researchers from the U.S. and Canada examined the event, they reported that insufficient reactive power was one of the factors leading to it.
So, here’s the big question: When rooftop solar installations start causing localized voltage headaches for utilities, will there be enough local reactive power to bump that voltage up? There will if we get smart inverters along with new solar deployments.