How much would a 10% solar standard reduce Minnesota’s greenhouse gas emissions?

Presenting Curt Tosh's farm-based solar project - Solar Works in Central Minnesota!

This week a bill was introduced to the Minnesota legislature to establish a 10 percent solar energy standard by 2030.  This would be on top of the existing requirements for utility renewable energy, bringing the total amount of energy coming from renewables in the state to at least 35 percent in 2030.

This bill is being promoted for it’s job creation aspects, but clearly a key benefit is the reduction in greenhouse gas emissions from the electricity generation sector (which currently produces 32% of the state’s greenhouse gas emissions).  So, by how much would a 10% solar standard reduce Minnesota’s emissions?  Would it allow us to meet our greenhouse gas reduction goals?

The first (and easier) part of trying to put some numbers to this is estimating how much electricity Minnesota will use in 2030.  EIA summaries tell us that Minnesota consumed a little under 68 million megawatt hours in 2010.  Power projections produced for the Annual Energy Outlook tell us that in MRO West (our electricity grid region), the annual growth in electricity consumption will be very modest through 2030, typically under 1% annually.  If you assume these growth rates apply to Minnesota, we may consume over 73 million MWh in 2030, or 8 percent growth over 20 years.


10 percent of that is 7.3 million MWhs in 2030.  Figuring out exactly how much greenhouse gas this would save is trickier.  In 2010, electricity generation accounted for 32% of the total 155.6 million metric tons of CO2 equivalent emissions.  Rough math using EIA consumption figures provides a greenhouse gas coefficient for Minnesota electricity of 0.73 metric tons of CO2e per MWh.  However, this figure will surely go down over the next 20 years as utilities work to meet the existing renewable energy mandates already on the books.  Xcel Energy, which has to meet a more aggressive renewable energy standard then the rest of the state, already has a coefficient closer to 0.5 mt/MWh, which will be declining (see slide 17) to something like 0.42 mt/MWh by 2025.

So, assume the state’s net greenhouse gas coefficient for electricity is somewhere around 0.5 mt/MWh in 2030 (assuming other utilities and imported electricity are both dirtier than Xcel).  If 10% of our electricity demand is met by solar energy, this would be a savings of 3.6 million metric tons of CO2e.  3.6 m metric tons is about 2.3% of our 2010 emissions total, or about 7% of emissions from the electricity sector in 2010.

Using an net coefficient average emissions factor for calculation may be too simplistic, but it’s the best I’ve got right now.  Those more in the know say that renewable energy like solar will most frequently replace natural gas production, rather than coal or nuclear, as gas is easier to cycle on and off.  I’m not sure whether this would increase or decrease the benefit of this level of installed solar (but I’m working on it).

Update: I was pointed to this journal article by Carbon Counter, which attempts to calculate “marginal emissions factors”, rather than average factors. It turns out, since the Midwest is coal-heavy, usually an “intervention” (adding solar, for example) would displace coal power first, rather than gas.  The marginal emissions factor they calculate for the Midwest is about 13% higher than the 0.73 mt/MWh I mention above.  The Midwest is somewhat unique in this regard, as most regions show gas as the most common “marginal fuel source”.  It also has the highest marginal emissions factor of all the regional electricity generators looked at in the study.  A 12% increase over 3.6 million mt is 4.03 million mt.

At something near 3 or 4 million metric tons of emissions saved, would a 10% solar standard help us meet our state emissions reduction goals?  Nowhere near on its own, but it would be a significant step in the right direction, especially when combined with strong action in other sectors like transportation and agriculture.  Think of it as part of the Minnesota version of the wedge game.

Thinking about backup power

The New York Times reports that post-Sandy “a chimpanzee could sell generators by the truckload.” From their story on the disaster-preparedness economy:

Ms. Giangeruso, who notes that last year, after the “Snowtober storm” on Halloween, her house was powerless for six days. “If we are talking in the neighborhood of $6,000, it is worth every dollar. If I could get it right now, I’d write a check,” she says. “The wives in this area don’t want jewelry for Christmas. They want generators.”

I was curious why this article didn’t mention renewables as a backup at all. Unlike generators, they can be used in non-emergency times to offset some of your utility costs. They also don’t require you to have a large tank (or pipe) of fossil fuel on-site at all times in case of power outage.

On Amazon, you can know purchase a 255 watt solar panel for $334. A 75 ah heavy duty battery will cost you $200. If I’m doing my math correctly, two of these batteries could run an efficient refrigerator for almost two days. You’d never have to worry about your mobile phone (a modern lifeline) running dry.

Given my household’s usage, just four solar panels would offset 30% of our annual electricity usage. A very rough ballpark estimate puts the installed cost, with batteries, at $4,000. Using current electricity prices, that system would have a 23 year payback without rebates, and 8 years with Xcel and federal rebates. Peace of mind during extended outages (however rare) should also add some value.

Depending on your willingness to accept risk, $4,000 or so for such a system might make sense. Does it make sense for a utility? Many mobile data/phone providers are starting to back up their towers with batteries specifically in response to emergency outages. New Jersey also apparently has 200,000 solar panels installed on utility poles throughout the state. Certainly large installations like this could have a climate benefit, but do they make a dent when it comes to emergency power? It seems liked they would have to be paired with distributed battery storage and some way to curtail per-unit usage in an affected area (no plasma screens during emergencies).