Sinking carbon on solar farms: a new kind of PV + storage 

At Bighorn Solar in Pueblo, Colorado, the Lightsource bp team is taking steps beyond clean energy generation with an innovative Environmental Management Plan. In addition to providing emissions-free energy for EVRAZ Rocky Mountain Steel, the site will serve as a biodiversity haven and carbon “sink,” pumping CO2 from the air into the soil and vegetation on-site.  

Enhancing biodiversity with short-grass prairie conservation 

The utility-scale solar farm is in the southwestern tablelands, a semi-arid ecoregion at the western edge of the central great plains. The project lies within a short grass prairie ecosystem, once home to free-ranging bison and grizzly bears, and today dominated by grazing livestock.  

As part of Lightsource bp’s commitment to increase net biodiversity on its project sites, the 300 MW solar farm has been designed to serve a dual purpose: delivering renewable energy to lower carbon emissions from electricity generation while sharing the land with conserved shortgrass prairie habitat.  In all, 3,051 acres of shortgrass prairie will grow on and surrounding the Bighorn Solar site. 

Before construction began, Lightsource bp and partners designed a site-specific seed mix, suited to the local climate, ecosystem and soil. The mix contains staple short grasses like western wheatgrass, buffalograss and little bluestem, as well as a low concentration of purple prairie clover to provide nectar for pollinating insects.  

During construction, the team minimized disturbance of existing ground layer as much as possible. They reestablished high-quality habitat on disturbed areas and enhanced existing vegetation with the native seed mix.  These species will quickly stabilize the soil and minimize erosion as their root systems develop. 

 Without this conservation intervention, invasive plant species would likely take over existing shortgrass prairie on the land. Cheatgrass (aka Downy Brome) is of primary concern. This noxious weed spreads rapidly, increasing wildfire potential and injuring people and animals with spiky seeds. 

This conserved prairie habitat will additionally provide a safe home for invertebrates like native bees, small mammals and prairie songbirds.   

Enhancing decarbonization with carbon sequestration 

During photosynthesis, plants convert carbon dioxide from the atmosphere into sugars and carbohydrates, stored within the plant matter. In a prairie ecosystem, the bulk of carbon-storing plant matter lives underground in the deep roots of grasses and other species. When these root systems die, they decompose and become carbon-rich soil, which can remain underground for hundreds to thousands of years. In this way, prairie habitat acts as a “carbon sink,” pulling C02 underground to reduce its concentration in the atmosphere. 

 The Bighorn project will remain undisturbed for decades, allowing for many generations of shortgrass prairie plants to live and die on-site.  Research data indicates that over the first 25 years Bighorn’s 40-year lifespan, the on-site prairie habitat will remove and store the equivalent of 36,000 tons of CO2. 

Soil samples have been collected to establish baseline soil carbon. Future sampling will determine the total amount of soil carbon increase over time, due to reestablishment of shortgrass prairie habitat. We predict that carbon storage in the site’s soil will increase about 17% over the project’s life.  

In addition to mitigating climate change, the addition of extra carbon will further fertilize deep layers of soil to provide a strong foundation for the entire ecosystem of plants, animals and microbes.