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The Five Dimensions of Microgrids

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A few weeks ago I posted a two part series on PG&E’s likely reorganization details. One of these details is how they intend to mitigate the Public Safety Power Shutoffs (PSPS) used to reduce the chances of sparking additional wildfires. Although there were multiple actions to do this, the primary strategy for remote parts of their service territory was a series of 20 microgrids. These will allow long stretches of transmission line to be de-energized while keeping the remote consumers powered.

The details on these microgrids are pretty fluid at this point (as the phase-one project funding for these is initially being processed by the CPUC), as any good microgrid engineer would understand.

One of the most powerful abilities of microgrids is to scale over a wide range of applications. Since PG&E is involving the communities using these in design decisions, the specifics for each microgrid will not be firm until the individuals serviced by each of these and other stake-holders have had a chance to make their inputs.

This post is on the five dimensions of flexibility, not the details of microgrid design and integration which were covered by earlier posts. It is also specific to microgrid applications similar to the PG&E Microgrids. The five dimensions are:

  • Facility / grid-segment size supported by the microgrid
  • Level of service provided to each consumer with the microgrid
  • Sustainability of the energy sources used by the consumers
  • Evolution-stage as the microgrid is implemented
  • Realization of different functions that benefit different consumers

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John Benson's picture

Thank John for the Post!

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Bob Meinetz's picture
Bob Meinetz on May 5, 2020 4:18 pm GMT

John, has CPUC or any other entity performed a peer-reviewed analysis of the economic and environmental impacts of dividing the PG&E grid into separate "microgrids"?

From an engineering standpoint it's next to impossible separate microgrids, each powered independently by propane or diesel generators, can do the job more efficiently by avoiding the economies of scale available from PG&E's centrally-powered grid. Proponents point to avoidance of AC transmission losses, ignoring the fact DC transmission at low voltage is far less efficient even over short distances. Add to that the carbon cost of fuel transportation (assuming propane / diesel are delivered by truck); the economic costs of added maintenance and integration; the inability to inspect and upgrade all generation sources en masse; the possibility added wiring and maintenance might actually increase the risk of fires - and we have what looks like a windfall for fossil fuel interests and a potential disaster for the environment and ratepayers.

Seems like an independent cost/benefit analysis of these factors should be the first step, should it not?

Matt Chester's picture
Matt Chester on May 5, 2020 4:25 pm GMT

In your research, have you seen microgrids being more tied to specific regions or geographies than others? Would an area like California that is prone to wildfires and PSPS be more likely to adopt, and are there other areas that have characteristics that make them most suitable/likely to adopt?

Ahmed Badruzzaman's picture
Ahmed Badruzzaman on May 21, 2020 5:54 pm GMT

Great discussion-thanks. The topic is of great interest to me. I co-teach a UC Berkeley Big Ideas course, Energy and Civilization, where we examine enerhy transition, past, present, and future in the context of both the developed and developing worlds.  This takes me to the transition happening in my native Bangladesh, a rural country, with hundreds of rivers making running transmission lines a challenge and microgrids look attractive. But there is more to it as I note next.

The government undertook an ambitios grid-based rural electrification plan using the US coperatives model, in the late 1970's, but it was fraught with problems. Grid reliability was bad.  Then came NGO's in the early 2000's with ideas of off-grid solar home electrification that  managed to bring electricity to areas that had never seen electricity; over 12% of the population.   It changed lives in ways it is hard to imagine sitting here in Californi. Over USD500 million was invested in the effort. Related to this effort, I helped do a pilot project on small energy systems, including solar home systems, in two villages, using CSR funding from my former employer, a large international energy company operating in the country.  Initially it was a big deal for the villagers; their lives changed in many ways.

But as government's grid-based electrification reached the area, the enthusiasm for the off-grid solar including the one we set up, dropped.  Then the government program moved into roof-top solar and began selling their solar electricity to their grid using netmetering. This obviously put the NGO-implelement solar projects at a huge disadvantage, with stranded electricity.  Ours was a short-term pilot project and we learned many things. So all was not lost. However, the NGO-based donor-funded program is sitting on top of an infrastructure that is made obsolete by the government-run program.  The positive I now hear is that some folks have retained their roof-top solar paneIs to tide them over when the grid fails. Yes, they do add resilience.   I have suggested to the NGO folks that they make a deal with the government rural electrification board and integrate their system with the government coperatives.   

BTW, Bangaldesh is not alone in this dilemma. Many developing countries have this issue on what to do with off-grid or micro-grid systems initially set up to fill a need in the absence of the main grid, but then the main grid arrives, making it redunadnt.  Something to think about here in California too? 

Bob Meinetz's picture
Bob Meinetz on May 22, 2020 5:01 pm GMT

Ahmed, the situation in Bangladesh is analogous to California in many ways.

Both the NGO-implemented solar projects and home solar arrays generate electricity at the same time. When the sun is shining there is lots of electricity - too much, in fact, for either system to be a good investment.

When there is no sunshine here (cloudy weather/nighttime), there's no solar electricity at all, just like in Bangladesh. In California, we have a relatively stable grid with nuclear and gas generation to fill in. Though some Bangladeshis may be able to afford diesel generators, it's much more efficient, cost- and fuel-wise, to provide electricity from a central source.

So we're back to the importance of a well-maintained, robust power grid. Though it's a significant investment, it's capable of bringing electricity to everyone - with benefits for everyone, too.

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