by Planning Engineer and Rud Istvan

Microgrids and “clean” energy are intertwined in the minds of many. There is a common belief that microgrids will facilitate “clean” energy and that “clean” energy will better support microgrids.

Some express hopes that improvements in technology will allow “clean resources” and microgrids to jointly make the existing grid structure obsolete.

This posting makes the case that it is more appropriate to perceive “clean” energy technology and the advancement of microgrids as competitors. They both have their individual greatest widespread chance of success when coupled with the bulk grid, versus working in tandem. While there may be some cases where there is synergy between the advancement of “clean energy” and microgrids, the more common occurrence is that their conflicting goals will be at odds with each other.

What exactly is a Microgrid?

The definition and expectations for microgrids can vary. Basically a microgrid is an electric system that can operate independently (for a limited or extended time period) in isolation from the bulk grid. Examples can vary from single off-grid residences to campuses/cities/regions which are tied to the grid but capable of disconnecting and being self-sustaining as well.

The Lesson of Sandy

In 2012 “Hurricane” Sandy resulted in extensive and extended power outages in the Northeast. Standing out during that period were systems which had the ability to disconnect from the outaged grid and provide energy from their local resources. These microgrids proved to be of great value in many cases. Princeton’s microgrid provided service for the day and half it took to restore the grid. Their microgrid was enabled by a large gas turbine cogeneration plant supplemented by a solar panel field which provides around 5.5% of their need.

In general power outages result from local distribution outages not losses to the bulk grid. Large storms do take out large swathes of local distribution resulting in wide area outage. Such storms also take out some transmission, but usually much less as these are typically larger more resilient facilities. In addition the bulk system usually has sufficient redundancy so that the loss of these facilities does not automatically translate into user outages. In storms where portions of the bulk grid are lost, they generally are ready for service in advance of the distribution subsystems they serve.

Microgrids are not immune from distribution outages. Undoubtedly, some areas with microgrid capability were not able to operate post Sandy due to local problems. A region served by independent microgrid system built upon wind turbines and solar panels would likely have many areas out for significant periods following Sandy type winds. Achieving very high levels of reliability following storms will require extreme costs or both bulk interconnections in addition to microgrid capability. Although some media reports post-Sandy have suggested that, do not think that complete grid independence can generally work to enhance reliability and resiliency. If you want the best bang for your buck providing microgrids to enhance storm recovery efforts, you will connect to the grid and use cheap fossil fuel back-up generators.

An analogy to help understand some of the fuzzy thinking

Comparing the functionality between microgrids and larger bulk systems can be seen as similar to comparing cars and trucks. While cars and trucks both do many of the same things and can have similar features, they have different specialties. Trucks are generally better at hauling heavier weights and towing and may have better off road capabilities. Cars are primarily for carrying passengers and typically offer more comfort and better fuel economy. Now you might have an old car that could be replaced by a new truck which has better fuel mileage, more nimble handling and greater passenger space. Similarly some cars may have higher towing capacity and be more rugged than some trucks. In the end you can make a truck behave like a car in multiple ways but it will cost a lot more and/or it will behave less like a truck. You can’t make a truck that is green, affordable, comfortable, roomy, nimble, fuel efficient, easily braked, crashworthy and carry’s a high payload with plenty of torque. But as you give up on some of the other characteristics and focus on what’s important in a particular application, a truck can have any one (and maybe more) of those special characteristics.

Hypothetical expensive microgrids can outperform existing bulk grids for any specified purpose (ignoring cost). Promoting the potential value of microgrids based on such comparisons is irresponsible. This post will use well warranted generalities at times in discussing microgrids and bulk power systems, despite that in most all cases with improved technology and significant costs any of these individual limiting generalities could be surmounted and prove an exception.

Microgrids do not have super powers above what is available to the bulk grid despite what some media sources might imply. Natural gas does not become a cleaner fuel just because it powers a microgrid. Economics and improvement that do not work for the bulk grid will likely not work for microgrids either. Technology that can be paired with microgrids can generally be paired with bulk grids. Microgrids can do many things, but a microgrid that is affordable, clean, reliable, grid independent, secure and allows the integration of renewables is a pipe dream at this time.

Independent microgrids

The supposed advantages of grid independence are largely illusory. The grid provides low cost back up and provides for economy exchanges. By covering greater areas and including more resources the bulk grid allows for economies of scale, diversity of resource mix, greater load stability as well as enjoys the benefits that come from the diversity within the broader region of demand. Bulk systems provide essential reliability services and needed operating characteristics at lower costs.

In terms of “clean” generation very few areas have a sufficient diversity of resources with which to provide area loads. There may be a few idyllic areas where the local power supply can be complemented by hydro, wind and solar but most cities with their large load centers are for too dense to rely only upon the meager local resources available and construction options there may be limited for conventional technology as well.

The business cases for microgrids

Microgrids can be justified where the cost and consequences of outages are extreme. In such cases the microgrid operates in synch with the grid and independently during emergency conditions to provide a high level of reliability. Hospital campuses and universities are often microgrids for this reason, as Princeton was justified pre-Sandy.

Some areas have strong security concerns coupled with reliability concerns. A specially designed microgrid can provide insulation from cyber and other service attacks, as it is easier to protect a smaller more controlled system. Note-this is not compatible with an open system providing vast information sharing between loads and resources.

Microgrids can be justified for remote areas where grid service is not available (or unreliable, as in remote northern Canada villages). The value of the microgrid is that it “pools” loads and resources reducing the needed resources and allowing more efficient operation.

A well designed microgrid can shield or insulate a system from power quality disturbances to protect sensitive loads (most wafer fabrication facilities are served from microgrids for this reason).

Lastly enabling renewable energy is often listed as a reason for developing microgrids. The next section will look into that assertion further.

The business case for pairing microgrids and renewables

We frequently see assertions that microgrids are more flexible and will help support renewable energy. The DOE in describing the potential benefit of microgrids states lists this benefit: “Enhances integration of distributed and renewable energy resources” but we could find no elaboration in the source as to how. The traditional grids and microgrids can integrate distributed and renewable resources, as well as incorporate new technology associated with renewables. Despite seeming assertions it not clear how or why microgrids might have a leg up on the traditional grid.

Looking for special abilities that microgrids might have to support renewables we turned to a white paper by SIEMANS titled The business case for microgrids. They identify various values that microgrids might support including “Sustainability” noting that, “A growing number of organizations place a higher value on renewable energy generation and are committing to long-term targets, regardless of expected time to recoup the investment.” In terms of what might drive consumers to consider a microgrid solution they note “Altruism” and state:

Organizations with a strong commitment to green energy and a vision of a sustainable future are likely to invest in renewable power generation and microgrid solutions. These groups may harbor concerns that the main grid faces reliability risks or are concerned about the environmental impact of fossil fuel generation. They will choose to reduce their own consumption and dependence on the main grid at almost any cost.

Although such pairings greatly serve SIEMENS business interests, “Altruism” does not technically make a “business case”. Renewables and microgrids present all sorts of problems for SEIMENS to help solve. The different drivers for microgrids don’t necessarily support the same types of microgrid systems.

When a grid is not available and “clean” energy sources are, obviously microgrids present a huge opportunity. If microgrids are paired with efforts at greater efficiency, diversity and having load near generation that may provide significant benefits, but these benefits could likely accrue with conventional grids as well. We welcome comments below describing any unique special synergies which might exist between microgrids and “clean” resources that we have missed. The best description of the business case might be that renewables may be advanced by microgrids because some who are making large investments in a microgrid for various other reasons might also value green energy and may also want to install renewables as well as purchase a lot expensive technology that will make it easier for renewables to work with that system. But for now it appears that when microgrids and renewables are jointly touted it is because of parroting, pandering, puffery and/or promotion of particular selfish interests.

Conclusion

Children will ask “can we do this?” PE used to annoy his children with the answer “We can do almost anything we want, but we can’t do everything.” They came to learn that response meant that something “unthinkable” would likely have to be given up to indulge the extravagance. There is no bargain to be found by pushing jointly for both more microgrids and the greater integration of “clean” resources. Having both will require huge sacrifices. If society’s utmost desire is a “clean”, highly reliable grid, resilient, secure grid – we likely can build that at some enormous cost. However, if cost is a factor impacting electric supply then tradeoffs will have to be made from among competing goals and technologies. For example, do you want high level protection and limited access to prevent cyber-attacks, or do you want everyone connected to share real time system information and control functions for load shaping? There are many tradeoffs: level of reliability, resiliency, CO 2 emission levels, protection from magnetic pulses and solar flares, aesthetics, autonomy, economy, flexibility, risk…

If your over-arching goal is for the wide penetration of “clean” renewable technologies then generically advancing micro grids will not serve to advance that goal. In most cases the bulk grid will provide for the most economic and reliable integration of large amounts of renewables. The best way to provide the reliability of microgrids is to use low fixed cost, high variable cost fossil fuel gensets. Placing a premium on the integration of intermittent resources as a part of efforts to develop microgrids is a pairing that generally will not work and will likely only serve to retard the advance and acceptance of both technologies.

JC note: As with all guest posts, keep your comments relevant and civil.