Why are microgrids so important to our planet’s sustainable future? The answer is straightforward science. As more clean energy (such as solar and wind) is needed, we must accommodate more intermittency in the flow of electrons since the sun doesn’t always shine and the wind doesn’t always blow. Transmission networks, the backbone of our electricity grid and a major component of every economy’s critical infrastructure, should be ready for this. But they are not.  

If the big electricity grids now in place can’t handle the extra clean power which is ready to flow in from solar and wind projects, then microgrids can pick up the slack while new investments in grid modernisation take hold.

Transmission networks typically operate at very high voltages (69 kV to 765 kV), allowing for much more significant power flow than would be possible at distribution class voltages (typically 5 kV to 25 kV), as power flow capacity increases with the square of the voltage.

If the big electric grids now in place can’t handle the extra clean power which is ready to flow in from solar and wind projects, then microgrids can pick up the slack.

Most US transmission lines are above ground. However, increasingly, transmission lines are being buried underground and, with the advent of offshore wind generation, subsea. There are about 400,000 miles of transmission lines across the US. These lines connect larger generating units to bulk substations, where the voltage is stepped down to lower distribution-class voltages through large power transformers.

Big infrastructure investment  
US President Joe Biden’s signature on the Bipartisan Infrastructure Law meant that $65bn could begin to flow into projects that would help ensure the grid is more reliable, more resilient and more ready for the future. The new law will pave the way for significant expansion and modernisation over the coming decades.

There are many forces at play in the evolution of the grid. These include ageing grid infrastructure, reliability and resilience improvement, and lower-carbon energy transition.

The transition to lower-carbon energy has major implications for the design, build-out and operation of the transmission system. Upgrade and expansion will provide benefits to grid reliability and resilience. The transition also has two related components, with electrification of additional loads like electric transportation and home heating, and the integration of major distributed energy resources (DERs) such as wind, solar and battery storage.

Electrification will impact the medium voltage (5–25 kV) distribution grid, as well as the low voltage secondaries. Utilities will likely have to add additional distribution circuits and upgrade substation transformers.  

Don Kane, Senior Engineer in the Environment and Energy group at Parsons Corporation, explains: ‘Ultimately, additional load will impact the transmission grid, especially in those locations already experiencing congestion during times of peak load. For example, EV [electric vehicle] charging can be encouraged to avoid the times of traditional system peak loads and be incentivised to leverage local renewable generation when available. Vehicle battery storage will also be able to support the grid during non-travel times, using emerging vehicle-to-grid (V2G) technologies. This has the potential to not only minimise the load impacts of vehicle charging but can also support local renewable generation integration.’

Projected demand  
The projected electricity demand increase from EV charging is daunting. A 2018 study by researchers at University of Texas, Austin, provided a state-by-state estimate of the increased energy for vehicle charging. Increased energy usage for each state varied from 10% to over 50% beyond current energy use, with total additional energy increase of several thousand GW hours per day.

How and when that charging occurs plays a critical role in the actual hourly electricity demand increase in any particular area. Also critical will be the rate of EV adoption in the near future, and whether appropriate rate policy is adopted to incentivise better charging practices. It is likely that localised transmission and substation capacity increases will be needed, especially where grid congestion issues exist.

In many parts of the US, there are significant backlogs of grid interconnection requests from renewable energy developers, as utilities struggle to complete the usually complex interconnection studies. Although submitting a request is fairly easy, a significant – not necessarily trivial – number of requests have minimal likelihood of ever getting built.

The US Federal Energy Regulatory Commission (FERC) has recently begun to intervene, issuing a notice of proposed rules to streamline the interconnection process, adding requirements and penalties for transmission providers to complete studies on time, along with more stringent requirements for developers to prove they can actually build what is proposed. Some US states and regions are taking this challenge aggressively, attempting to not only react rapidly to proposed generator interconnections, but to also come up with a more proactive, holistic and inclusive plan for transmission grid expansion and upgrades to enable and encourage renewable generation in optimal locations.  

The State of New York, for example, conducted an expansive power grid study in 2020, in coordination with state regulatory and other agencies, and six major electric utilities. The report identified 52 near-term projects with a cost of $4.2bn. However, this does not include several other planned multi-billion-dollar transmission projects like the 339-mile Champlain Hudson Power Express and the 175-mile line in the Clean Path NY project. In addition, plans are underway to upgrade facilities in Long Island to access approximately 9,000 MW of offshore wind, slated for installation over the next 5–15 years.

There are also more general studies and proposals on the national scale, which would allow for more flexible and efficient balancing of generation and load on a grid with significant intermittent renewables.  

In this way, areas of the US that have a natural abundance of hydro, solar and/or wind resources can produce far more energy without having to be curtailed as often. There are a variety of ideas for a national HVDC (high voltage direct current) network, like those from the National Renewable Energy Lab (NREL) and the Energy Systems Integration Group (ESIG), which would create high-capacity ties between the Eastern, Western, ERCOT (Electric Reliability Council of Texas) and Quebec interconnections.  

These new and innovative proposals would also leverage expanded offshore wind generation on both coasts and include significant expansion of the existing AC transmission networks within each interconnection. A ‘macro-grid’ like this would cost trillions of dollars over a few decades. This is a daunting prospect that will require new ways of justifying and distributing costs across larger portions of the country, as well as changes to the traditional energy markets and regional operations of the grid. Requiring much more coordination between the regional transmission organisations (RTOs) and independent system operators (ISOs) and across the separate interconnections.

The US has six RTOs or ISOs – Pennsylvania New Jersey Maryland Interconnection, Midcontinent ISO, ERCOT, California ISO, New York ISO and Southwest Power Pool.

There are plenty of other headwinds for grand initiatives like this, not least of which is the difficulty we have today with getting new transmission lines sited and built, especially when the proposed lines cross through regions that do not observe any direct benefit to the lines. 

Recent project cancellations like Northern Pass in New Hampshire and project delays like New England Clean Energy Connect in Maine highlight the massive risk involved for companies that pursue ambitious investments. Both projects would have delivered 24/7 dispatchable, renewable hydro power from Quebec into the New England grid, helping the states in the region achieve their own renewable energy targets. Local opposition to portions of the proposed lines were enough to prevent or delay the projects from proceeding, causing expensive write-offs of a few hundred million dollars for the companies involved.

Nevertheless. according to Parson Group’s Kane: ‘There are massive opportunities for industries that are poised to support this effort, as well as exciting, well-paying jobs for new scientists, engineers, construction workers and high voltage line workers.’

Microgrids clearly will play a role in enhancing resilience for critical facilities and communities.