Is Renewable Energy 100% Carbon Free?

Renewable energy sources refer to sources of energy that are replenished naturally within a short period of time. The most common renewable energy sources are solar, wind, hydroelectric, geothermal and biomass.

Solar energy is harnessed from the sun’s radiation using technologies like photovoltaic panels and concentrated solar power. Wind energy utilizes wind turbines to generate electricity from kinetic power created by wind. Hydroelectric power converts the energy from flowing water in rivers and streams into electricity via turbines. Geothermal energy taps into the Earth’s internal heat by using steam or heated water sources underground to run generators. Biomass energy utilizes organic materials like plants, agricultural waste and garbage to produce electricity, fuel and heat.

These renewable sources differ from fossil fuels like oil, coal and natural gas which take millions of years to form naturally. Unlike fossil fuels, most renewables like solar and wind energy produce little to no carbon emissions responsible for climate change. However, not all renewable energy sources are completely carbon-free.

Carbon Emissions from Renewables

Many people assume that renewable energy sources like solar, wind, and hydropower have zero carbon emissions because they do not burn fossil fuels directly. However, renewable energy technologies do produce some carbon emissions during their lifecycle – from manufacturing, construction, operation, and decommissioning. For example, producing solar panels requires energy and raw materials that generate emissions.

According to a report by Western Grid, “the lifecycle carbon emissions of renewable energy sources are not zero, they are much lower than fossil fuels” (Western Grid, 2011). The emissions vary based on the specific technology. One analysis found solar PV has lifecycle emissions of 30-50 g CO2/kWh, wind power has 7-34 g CO2/kWh, while coal power has 820-910 g CO2/kWh (Pehl et al., 2017). So while not completely carbon-free, renewable sources generate far fewer emissions than fossil fuel alternatives.

Indirect Emissions

While renewable energy sources like bioenergy, hydropower, and geothermal do not burn fossil fuels directly, they can still lead to indirect greenhouse gas emissions. One source of indirect emissions from renewables is reservoirs created for hydropower. According to the International Hydropower Association, hydropower reservoirs emit greenhouse gases like methane and carbon dioxide, primarily from the decomposition of flooded vegetation and carbon inflows from the catchment area [1]. The U.S. Department of Energy notes that human-made reservoirs alter natural emissions and can increase methane emissions from anaerobic decomposition [2]. However, emission rates are site-specific and depend on the climate, area flooded, and reservoir management. The IPCC estimates the median emissions from hydropower at 24 gCO2e/kWh [3].

Bioenergy from sources like wood pellets and ethanol can also lead to greenhouse gas emissions through biomass harvesting, processing, and combustion. The net emissions depend on the feedstock source and life cycle emissions. While bioenergy is often considered carbon neutral, there is debate about this classification since it does not account for changes in carbon stocks from harvesting biomass.

Transmission and Storage

While wind turbines and solar panels themselves do not produce any direct emissions, transmitting the electricity they generate can result in some carbon emissions. Grid integration and transmission capacity are key factors. A study found that failing to expand transmission capacity could cut possible emission reductions from renewables in half by 2035.

Batteries and energy storage are important solutions for smoothing out the variable supply from renewables. However, most grid-scale batteries today use lithium-ion technology, which has a carbon footprint from raw material mining and manufacturing. According to one analysis, a 100 MW/100 MWh lithium-ion storage system has lifecycle emissions equivalent to around 1,000 metric tons of CO2. While not a huge amount compared to fossil fuel plants, it’s not zero either. New battery chemistries with lower embedded emissions show promise for the future.

Land Use Change

One concern with renewable energy like solar and wind farms is that they require large amounts of land area. According to a 2021 study published in Nature Scientific Reports, transitioning to 100% renewable energy globally would require using 0.17-1.2% of total land area for energy production, with solar photovoltaics requiring the most land area [1]. Land must be cleared and habitats disrupted to build these new energy facilities. The land use change leads to carbon emissions, especially when forests are cut down.

In the United States, utility-scale solar and wind projects are often built on agricultural or desert lands. While this avoids deforestation emissions, there can still be impacts on natural habitats and ecosystems. Proper siting, mitigation, and restoration efforts can help reduce the land use impacts. Overall though, the lifecycle emissions from land use change of renewables is small compared to the emissions they displace from fossil fuels [2].

Offsets Fossil Fuels

One of the main benefits of renewable energy is that it can offset or displace the use of fossil fuels like coal and natural gas for electricity generation. When renewable energy sources like wind, solar, or hydro generate electricity, that directly reduces the need to burn coal or natural gas at conventional power plants (1). According to a case study in Florida, the use of cow manure biogas at a dairy farm to generate electricity resulted in “renewable energy offsetting fossil fuels, so it’s reducing the greenhouse gases going up to the atmosphere” (2). Essentially, every unit of electricity from renewable sources substitutes for a unit from a fossil fuel, lowering carbon dioxide emissions.

(1) https://www.wuft.org/news/2015/12/10/florida-dairy-farm-recycles-cow-dung-to-conserve-energy/

(2) https://www.wuft.org/news/author/tayloranderson/feed/

Renewables vs Nuclear

When compared to nuclear power, renewable energy sources like solar and wind have some key differences in carbon emissions. According to the World Nuclear Association, nuclear energy results in very low lifecycle greenhouse gas emissions, producing about the same amount of CO2-equivalent emissions per unit of electricity as wind power, and about one-third that of solar power (Carbon Dioxide Emissions From Electricity).

This is because while the electricity generation process itself is emissions-free for renewables and nuclear, there are indirect emissions from construction, mining, and manufacturing needed to build the facilities and infrastructure. Nuclear has very high upfront carbon costs but then extremely low emissions for power generation during its lifetime. Solar and wind have lower upfront carbon costs but still require carbon-emitting processes during their operating life cycle.

Overall, analysis shows that nuclear, wind and solar all have carbon footprints many times lower than fossil fuels like coal or natural gas (Solar, wind and nuclear have ‘amazingly low carbon footprints’). When considering the goal of deep decarbonization, renewables and nuclear can both play important roles in displacing higher-emission energy sources.

Developing Countries

Renewable energy projects present unique challenges and benefits for developing countries. According to RTI International, developing countries built more renewable energy than fossil fuel plants in 2019, showing the rapid growth of clean energy. However, developing nations face difficulties in scaling up renewables due to lack of infrastructure, financing, and technical expertise.

The Wikipedia article notes the intermittent nature of renewables like solar and wind requires developing countries to also build dispatchable power plants or storage. Geographic dispersion of renewable resources may also require substantial transmission investments. Plus, developing countries struggle to find low-cost financing for capital-intensive renewables.

Per research, political factors like weak policy frameworks hinder renewable growth in developing nations. Corruption and instability may discourage investments. But renewables provide developing countries energy access and security without expensive fossil fuel imports.

Political Factors

Government policies and subsidies have a major impact on renewable energy adoption and carbon emissions. Many countries provide incentives like tax credits, grants, and preferential rates to spur renewable energy investment. For example, the United States offers the federal production tax credit, which gives wind energy producers a tax credit per kilowatt-hour generated. According to a report by the Nevada Governor’s Office of Energy, subsidies like these are important policy tools to drive the transition to renewable energy and reduce carbon emissions.

Some governments have also implemented carbon pricing schemes like carbon taxes and cap-and-trade systems. A 2009 study found that China could reduce emissions through an aggressive carbon tax without hurting economic growth. The European Union’s Emissions Trading System is the world’s largest carbon market aimed at reducing greenhouse gas emissions cost-effectively. Political factors like these can accelerate renewable energy deployment, but policy uncertainty and fossil fuel subsidies in some countries hamper progress.

Conclusion

In summary, while renewable energy from sources like wind, solar, and hydropower emits little to no direct greenhouse gases, there can still be carbon emissions associated with their development, transmission, storage, and land use changes. Renewables avoid substantial fossil fuel emissions, but likely cannot be considered 100% carbon free based on current technologies and implementation challenges, especially in developing countries. Nuclear power emits minimal lifecycle emissions, but also faces waste, safety, and cost concerns. There are still debates around the exact carbon footprints of different energy sources based on methodology and assumptions. However, it is clear that continued development and adoption of renewables and other low-carbon technologies will be critical for reducing worldwide emissions and mitigating climate change.