Can Iowa Pork Offset Its Way to Carbon Neutral?

 Written by Jacob Willsea

Iowa is home to the largest swine industry in the USA, housing 23 million pigs at any time. Between feeding, processing, and manure handling/storage, the Iowa swine industry emits 0.5 metric tons (MT) of CO_2e per pig space annually, totaling 11.5 million MT CO_2e/year. Reduction of the carbon footprint for the pork industry has been a topic of interest for years, resulting in improved energy efficiency in animal housing and meat processing and greenhouse gas (GHG) reductions in manure management. Some farms are implementing onsite renewable energy systems to reduce their carbon footprint, including installing wind turbines, solar panels, and anaerobic digesters. This begs the question: Can installing renewable energy on farms make Iowa pork production carbon-neutral?

Let's start by looking at the current Iowa electricity sector:

Figure 1. Iowa electricity generation source.

Despite renewable energy sources supplying 57% of Iowa's energy, the energy industry still emits 0.38 MT CO_2e per megawatt-hour (MWh) of electricity produced. Therefore, to offset the 11.5 million MT CO_2e produced by the pork industry, an additional 30 million MWh of renewable energy would need to be supplied to the grid. One option for providing this energy to the grid could be the installation of wind turbines on farms.

Thirty-seven million MWh of Iowa's energy is currently supplied by the 12,500 MW of wind turbines installed across the state. To make up the required 30 million MWh to offset the swine industry, another 10,100 MW of wind turbines would have to be installed. About 10 MW of wind turbines can be placed on one section of land (1 mi²), so installing 10,100 MW would occupy about 650,000 acres. Although wind turbines can be farmed around, they still eliminate about 0.75 ac of farmable land/MW installed due to required access roads, concrete footings, and power substations. This loss equals $0.43/pig space from reduced corn sales (200 bu/ac and $6.50/bu). The wind turbines would produce about 1,310 kWh/pig space-year. On average, a swine farm uses only 26 kWh/pig space-year, so the farmer can return 1,284 kWh/pig space to the grid. The energy company's electricity buyback rate of $0.06/kWh would yield $77/pig space per year for the farmer. Wind turbines cost about $1,000,000/MW installed, so installing 10,100 MW of wind turbines would cost about $440/pig space. Assuming a project life of 10-years, a time value of money of 8%,  and that maintenance on the windturbines is $24,000 per MWh per year, then after selling the electricity back to the grid and accounting for crop loss the project would have a net present cost of $0/pig space.

An alternative renewable electricity source could be solar power. Solar panel efficiency is continuously improving. Could we offset the swine GHG emissions with solar power?

Technological developments have improved the efficiency of solar panels to about 20%. Full sunlight supplies about 0.93 kWh/ft², so with Iowa's 4 hours of full sun each day, a solar panel could absorb 0.37 kWh/ft²/day and output 27.13 kWh/ft²/year. To produce the required 30 million MWh of electricity, about 25,500 acres of solar panels, or 48 ft²/pig space, would have to be installed across Iowa.

Like wind turbines, solar panels would make $77/pig space from selling electricity to the grid. Assuming the solar panels are installed on farmable land, the farms would take a loss from reduced crop production. If a farmer installs 48 ft² of solar panels per pig space instead of planting corn, the farmer will lose about $1.44/pig space/year from reduced productivity. The capital cost for the solar panel installation is about $450,000/acre, which equates to $500/pig space. After selling electricity back to the grid, the total cost for this project would be $328/pig space over a ten year project life.

Recall that 30 million MWh of fossil fuel-based electricity must be replaced with renewable electricity to offset the swine industry fully. Let's revisit the overview of the Iowa electricity sector, this time with the electricity output in MWh:

Figure 2. MWhs of electrical generation form renewable and non-renewable sources annually in Iowa.

Fossil fuels only produce 28.7 million MWh/year of electricity in Iowa. Therefore, even if all non-renewable fuel sources were replaced with renewable electricity today, 30 million MWh cannot be offset. Furthermore, the value of 30 million MWh is estimated using the electricity sector's carbon intensity (CI) score. The CI score measures GHG emissions per unit of energy output. The CI score is the baseline for estimating the amount of renewable electricity it would take to offset fossil fuel emissions. With every improvement in the electricity sector, lower levels of GHGs are emitted for every unit of electricity produced, meaning a lower CI score. As the grid becomes greener, it will continually take more renewable electricity to offset the same amount of CO_2e. The graph below illustrates how the solar panel area required to offset one MT CO_2e changes as the electrical grid shifts toward renewable energy.

Figure 3. Installation of solar panels required to achieve different levels of carbon reduction as a function of a cleaner electrical generation grid resulting from clean energy installation.

                The calculations so far have all assumed a constant electricity demand in the coming years. Electricity demand will increase proportionally with the increase in electric vehicles (EVs) on Iowa roads. Today, EVs comprise only 0.2% of Iowa's 2.5 million registered vehicles. Every EV requires 3.9 MWh/year, so if Iowa had 100% EVs on the roads, the electric grid would need to supply an additional 9.4 million MWh annually. Although this increase in electricity demand would make the transition from fossil fuels for electricity production take longer, the full transition to a renewable electric grid is inevitable.

Here is the key takeaway: while adopting renewable electricity systems on farms will support our progression toward a fully-renewable grid and energy independence, it can be a good way to consider your swine farm "green" or "carbon neutral," that title will only be temporary. A future increase in electricity demand will allow farms to consider themselves carbon neutral for a longer period, but once the grid does become fully renewable, emitting no GHGs, your solar panels and wind turbines will no longer be offsetting any emissions, and your swine farm will be a net emitter of GHGs again. This highlights the unfortunate fact that farms will not be able to credit their way to net zero emissions, underscoring the importance of other on-farm strategies that must be implemented for emission reduction.

Manure management is one of the direct methods to reduce your carbon emissions. Upgrades to your storage systems, including covered lagoons and anaerobic digesters, can capture and utilize the methane emissions from your storage. Manure application timing can also make significant impacts on your carbon emissions. Spring and split applications of manure throughout the growing season can limit the length and amount of manure in storage, once again reducing the overall emissions from your farm.