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Monday, December 19, 2016

The Story of the Semi-off-grid Apartment Building

Picture an apartment building in a city that gets almost all of its electricity from nuclear power stations. It has solar panels and a gas powered generator.

The power lines from the utility are only connected to the ventilation fan that runs continuously at the same power level. A gas powered generator heats and cools the building via a heat pump in addition to powering lights and appliances. The constant current flow from the nuclear power station to the ventilation fan is the building's baseload electrical energy need.

On sunny periods of sunny days, the generator output decreases because the panels are providing electricity. The panels are acting as fuel (and emissions) reduction devices for the generator.

The owner is very concerned about climate change and wants to minimize emissions. One day, a stranger knocks at the apartment owner's door and tells her she should disconnect from the nuclear power and add more solar panels because, ah, sunshine is free. So she does but soon finds that the gas bill and attendant emissions are higher than they used to be.

Why is that? Because the solar energy was often produced when not needed (nobody was home) and was wasted. Adding more solar panels didn't change when they produced power, it only increased how much was wasted when they did produce power. The extra panels displaced what nuclear had been providing but only when they were producing power for part of sunny days, which is why they were never able to reduce gas flows to the level seen when the ventilation fan was being continuously powered with nuclear 24 hours a day, every day.

The stranger returns yet again and tells her to add batteries to store the wasted solar. Alas, this city is located where there is very little sun for months at a time and the cost of having enough batteries to store months worth of energy (called seasonal storage) is twice the value of their entire apartment complex (this is actually the case with my home).

Because the addition of more solar panels did not lower the emissions to the level seen when there was a ventilation fan running on nuclear power, the owner reconnected it to the grid and sold the extra panels on Craigslist.

The apartment owner eventually learned that the stranger who she had assumed was a power systems engineer, was actually the pizza delivery guy, who having been imprinted at an impressionable age with antinuclear dogma, had been parroting things he had read on the internet but didn't really understand.

The End

This story is an analogy to explain how a real power grid works and why emissions rise when nuclear is removed from it. It also demonstrates that a grid is composed of many players and they all have different costs. Assuming that the solar panels were the cheapest to install and operate, you still could not eliminate the other, more expensive players because intermittent sources like wind and solar can't do the job alone. To minimize emissions a grid must minimize fossil fuel use. Using wind and solar as fuel reduction devices to minimize the use of natural gas in load following and peaking power stations and using nuclear for baseload instead of coal could rapidly decarbonize our grid.

The story  is also a warning that we shouldn't be taking advice from the fry cooks, journalism, and philosophy majors out there writing articles about a complex topic like power engineering.

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