Thank you for tuning in to our final post in our renewable energy series. Missed the previous posts? Read our intro post here! Today, we explore the benefits and limitations of bioenergy and geothermal energy.
What is Biomass Energy?
Humans have been using biomass energy since the discovery of fire. Until recently, biomass supplied more renewable electricity than wind and solar power combined, accounting for over 50% of U.S. renewable energy consumption in 2010. Biomass energy is obtained through the burning of biomass (plant and animal material) and holds the potential to help us meet our growing energy needs. The European Union estimates that biomass holds the potential to meet up to one-third of global energy demand.
*Unlike the other renewable resources featured in this series, biomass does produce air pollutants and greenhouse gas emissions. Biomass is only considered a sustainable option if developed properly.
What are the Pros of Biomass?
1. Abundant: Biomass comes in many forms and is easily adaptable to a variety of settings and environmental conditions. The United Nations Environment Programme estimates that the nearly 140 billion metric tons of biomass is generated every year from agriculture can provide renewable energy to 1.6 billion people in developing countries, many of whom lack access to electricity. Unfortunately, not all biomass is created equal. Some energy sources have a large environmental footprint. The Union of Concerned Scientists (UCS) identifies four types of beneficial biomass that do not pose a significant threat to the environment, they are
- energy crops (grasses) that don’t compete with food crops for land
- portions of crop residues (such as wheat straw or corn stover)
- sustainably harvested wood and forest residues, and
- clean municipal and industrial wastes (tree trimmings, paper, food waste).
As with all resources, sustainable management is key maintianing resource abundance. Removal of biomass should not damage the long-term productivity of the resource. To aid in resource preservation, the UCS recommends creating sustainability standards for the production of biomass to ensure soil conservation, habitat protection, and proper resource regrowth.
2. Low carbon: When properly managed, biomass sources produce fewer carbon emissions than coal and natural gas and are considered to be a part or our terrestrial carbon cycle – the cycling of carbon from plants, to the soil, and into the atmosphere. Biomass-fired power plants release the CO2 into the atmosphere, which is quickly taken up by replacement plant growth, resulting in low net carbon emissions. When poorly managed, biomass fired power plants are a significant source of air climate pollution and serve as a threat to public health.
3. May help reduce waste: As population grows and standards of living improve globally, we will observe rapid increase waste. Rotting agricultural waste releases methane and other greenhouse gasses into the atmosphere, contributing to global climate change. Biomass energy may help governments divert their wastes from landfills to power plants while generating revenue from the sale of electricity.
What are the Cons of Biomass?
1. Land footprint: When poorly managed, biomass has a large land footprint. Arable land is a finite resource – only 4% of our planet will grow crops. Designating cropland for biomass production means we will have an even smaller percentage of arable land to feed our growing population, potentially leading to an increase in food prices. Biomass is also harmful to the environment, especially when ecosystems are cleared through deforestation.
2. Water footprint: Biomass power plants require approximately the same amount of water for cooling as coal power plants. Water is also needed to grow biomass and many biomass crops can be very water intensive. Miscanthus, for example, requires 870,000 gallons of water per year to grow one acre of grass.
3. Produces emissions: Biomass may negatively impact air quality. Emissions vary depending on the biomass resource, the type of power plant used, and the pollution controls installed at the plant. Biomass is known to produce harmful emissions. For example, nitrogen oxides (NOx) produced from biomass are lower than those produced from coal, but higher than natural gas. NOx emissions lead to increased levels of ground level ozone (smog), which can cause respiratory diseases. Sulfur oxides (SOx), soot, ash, carbon monoxide (CO), and carbon dioxide (CO2) are also produced in bioenergy generation.
What is Geothermal Energy?
Geothermal energy comes from tapping underground reservoirs of steam and hot water beneath the earth’s surface and is one of the least explored resources of renewable energy. Geothermal energy is captured by using steam captured from hot water to drive electric generators.
What are the Pros of Geothermal Energy?
1. Clean and renewable: Geothermal energy is a renewable resource that produces very little air pollution.
2. Available: Unlike wind, solar, tidal energy, geothermal energy is available at all hours of the day, providing cities and industry a continuous supply of electrical power. While geothermal may not scale as well as other renewable resources, it can be used in combination with intermittent sources (like energy and wind) to supply additional power when demand is high.
3. Low levelized cost: Geothermal energy is becoming increasingly inexpensive to produce. The levelized cost of energy (LCOE) for geothermal power is $0.05/KW-h, much lower than coal and natural gas ($.07-0.10/KW-h).
What are the Cons of Geothermal Energy?
1. Water footprint: Geothermal plants have a large water footprint. Water is used in order to cool down geothermal plants by re-injection. Depending on the cooling technology used, geothermal plants can use between 1,700 and 4,000 gallons of water per megawatt-hour. Geothermal fluid or fresh water can be used for the cooling process.
2. Emissions: One concern with open-loop systems (like Geysers) is that they can emit some air pollutants including hydrogen sulfide (rotten egg smell), ammonia, and trace amounts of arsenic and minerals.
3. Siting: According the U.S. Department of Energy, reliable and comprehensive geothermal data isn’t easy to come by. This makes finding a suitable site for a geothermal plant difficult.
4. Scale: Many question whether geothermal power can help us meet our energy demands at a large scale. In 2012 global geothermal power capacity was 0.0114 Terawatts (TW) – global energy consumption is estimated at 15 TW. The International Energy Agency estimates that geothermal power has the potential to achieve a tenfold increase in global production by the year 2050. Even if geothermal were to achieve a tenfold increase in production, it would only account for less than 1% of our total energy needs.
Renewable Energy Series:
Post 4: What are the Pros and Cons of Biomass and Geothermal Energy?