Good Energy Blog: The Brightfield movement turns trash dumps into solar farms. Also, we can store our energy underground. 

Brightfields reclaim landfills for solar farms. Also, fracking technology finds a cleaner use 

Let’s start with the obvious thing — the less we send to landfills, the better off we are.
They smell bad. No one wants big mountains of trash down the street from where they live. They’re made up of everything we didn’t use or couldn’t recycle.  Landfills represent our inefficiency.

Although closed landfills are often capped, covered and planted with green grass, they’re still difficult to reclaim for most purposes. The waste that has been dumped there continues to settle for years, often making them too unstable to build on. Inevitably, they off-gas methane as the organic materials that have been dumped there decay. And the capping materials, which are intended to contain hazardous substances, aren’t effective once they’ve been penetrated. That means that any kind of construction work is challenging. Developers refer to them as brownfields, and usually won’t go near them.

Unless, of course, we’re talking about utility-scale solar energy developers. Closed landfills offer many qualities that make them ideal for solar energy farms: cheap land nobody else wants, plenty of wide-open surface, no tree cover and adjacent energy transmission lines.

Brownfields that have been turned into solar farms are known as “brightfields,”(1) and they are a growing opportunity for utility-scale solar. There has been 80% growth in solar projects on landfills over the past five years (2), and the trend looks to continue.

There are unique considerations for brightfields, however.

As landfills age, they tend to shift and settle less, making them better candidates for solar farms. Proper venting and methane capture also play a big part in making a conversion feasible. The gas is sometimes captured and piped to gas-powered generating plants. One of the biggest concerns is construction technology. Once a landfill is capped, maintaining waste containment is the top priority. That means the ground can’t be penetrated. Deploying solar panels on capped dumps requires special construction techniques and equipment.

Mount Olive solar farm is one of the most successful brightfield conversions, and is at the forefront of the movement.

Opened in December 2022, it’s the largest brightfield project in North America. Once known as the Combe Fill North Landfill Superfund site, the solar farm now has a 25.6 megawatt capacity. It operated as a landfill for more than 10 years, closing soon after the federal government enacted stricter regulations for waste disposal in 1976. When the operators went bankrupt in 1981, the property had not been properly capped and closed.

Then the Environmental Protection Agency designated it a Superfund site, allotting money for remediation. Turning the dump into productive land again took over 40 years, but the solar panels housed on it now power more than 4,000 homes. Another bonus is, the property was acquired through a redevelopment and tax lien foreclosure process that put $2.3 billion in the city’s coffers. Along with powering homes, the site adds annual tax revenue of around $50,000 to the city and employs several residents. (3)

There are over 10,000 closed landfill sites in the United States (1). With the Inflation Reduction Act offering such strong incentives to developers, it’s likely we’ll see more projects like Mount Olive in coming years.

One of the biggest challenges in renewable energy is keeping the lights on when the sun goes down. Solar and wind energy are clean and increasingly cheap, but they aren’t always available. We need to store some of the abundant energy produced when conditions are good.

Most often, when we think of energy storage, we picture something like a lithium-ion battery, but lithium-ion batteries are expensive, require minerals that are hard to source and have limits around how long they can store energy. The energy transition is going to need cheap and effective alternatives that are not so resource intensive.

One example is pumped hydro, a tool that has been serving the energy grid for decades. It stores energy in the form of water pumped to the top of a hill. When the water flows down through a generator, it produces electricity. But finding a good location for pumped hydro can be a challenge, and large parts of the country don’t have access to the kind of geography that makes it practical.
But as James Temple reports exclusively at MIT Technology Review (1), scientists might have an answer. Instead of pumping water up, they pump it down.

Houston-based Fervo Energy is testing a new type of geothermal energy storage that might offer a solution that can be deployed a grand scale. They force water into the ground with enough pressure that the subterranean rock flexes, and then they cap it. When energy is needed, they release the water, which passes through a turbine to recover the energy. The company has been testing the method in the Nevada desert with promising results.

Fervo’s engineers used fracking technology that has seen widespread use for petroleum extraction in recent decades. They sunk two shafts deep into the earth and then pumped pressurized water down to 8,000 meters below the surface of the earth, causing fractures between the two shafts, and opening up a channel for water to flow between them. The temperature at that depth is 380°F, and as the cold water is heated, the pressure grows.

They then capped the “generating” well and continued to pump water under pressure into the other shaft, eventually capping that, as well.

When the engineers opened the generating well, water flowed at expected pressure for days, demonstrating that the fractured subterranean rock acted much like a balloon, expanding under pressure and collapsing when there was an outlet for the pressure.

The geology needed for this kind of installation is much more common than pumped hydro. Paired with a clean energy source such as solar or wind, Fervo’s geothermal energy storage may offer a tool to store energy when the sun is shining or the wind is blowing, until it can be sent into the grid when it’s most needed.