16 August 2019

Renewable Energy Versus Fossil Fuels

Welcome back. Although I’ve touched on renewable energy in earlier posts, it’s time I did more to promote its use and the conversion from fossil fuels (oil, coal, gas, nuclear). A recent study provided the incentive. 
U.S. energy consumption by source, 1950-2018
(from www.eia.gov/todayinenergy/detail.php?id=39092).
Renewable Energy
Let’s review a bit. The Environmental Protection Agency lists the most common renewable energy technologies as solar, wind, biogas, geothermal, biomass, low-impact hydroelectricity and emerging technologies, such as wave and tidal power.

Global new investment in renewable energy sources, 2004-2018
(from www.cleanenergywire.org/news/germany-comes-5th-global-renewable-investment-ranking).
The benefits of renewable energy are well-documented by the Union of Concerned Scientists and others. They include no greenhouse gas with less global warming; reduced air pollution and improved public health; inexhaustible energy; jobs and other economic benefits; stable energy prices; and reliability and resilience.

But we can’t ignore the drawbacks, the major ones being higher upfront costs; intermittent availability (sun doesn’t always shine, wind doesn’t always blow, drought happens), which occasions the need for energy storage; and geographic limitations (not all areas are suitable).

Forecast of power generation capacity additions
(gigawatts) through 2030 by source

(from geoharvey.files.wordpress.com/2015/04/4-26-graph.jpg).
Energy Returned on Energy Invested
Renewable energy sources offer significant benefits over fossil fuels, yet a key factor driving the use of fossil fuels is their higher energy returned on energy invested. That refers to the ratio of the energy a resource will deliver to the energy it takes to obtain the resource.

The ratio of fossil fuels is generally calculated to be over 25:1 (e.g., the energy to obtain 1 barrel of oil will yield 25 barrels of energy or more); the ratio of renewable energy sources is typically less than 10:1.

That recent study I mentioned found those ratios should actually be much closer.

Fossil Fuel Energy Investment
The researchers, all affiliated with the UK’s University of Leeds, focused on the energy it takes to obtain fossil fuels.

They note that, as fossil fuels become more difficult to extract, the energy investment will increase and the ratio will fall. (While true, fracking has reduced the investment and interrupted a long decline.)

For a more immediate adjustment, they point out that fossil fuel ratios have been calculated based on the extracted resource. There has been no accounting for the energy required to transform the extracted resource into a finished fuel (e.g., gasoline, electricity). A more direct comparison with renewable energy sources should estimate the measurement of energy invested at the final stage, when energy enters the economy.

(In line with that adjustment, it would be better to describe the energy-return-on-investment ratio based on the energy it takes to deliver that energy than the energy it takes to obtain the resource. That, by the way, is how it’s described in Wikipedia.)

To estimate the magnitude of the difference, the researchers calculated the global time series (1995-2011) ratios for fossil fuels at both the extraction and final stages. The extraction stage ratios were on the order of 30:1; the final stage ratios were about 6:1 and trending downward.

Wrap Up
The researchers conclude that the energy-return-on-investment ratios of fossil fuels and renewables may be much closer than expected. Moreover, the ratio of fossil fuels will decline with a shrinking source.

Although more recent data on fossil fuel ratios would be desirable, the study findings coupled with the benefits of renewable energy suggest there’s no reason to wait to convert from fossil fuels wherever and whenever possible. Thanks for stopping by. 

Rooftop solar panels, Nottingham, UK (from www.solarpowerportal.co.uk/news/e.on_awards_solar_panel_cleaning_services_largest_ever_cleaning_contract).
Review of renewable energy benefits and resources:
Energy returned on energy invested:
Study of energy-returned-on-energy-invested ratio in Nature Energy journal: www.nature.com/articles/s41560-019-0425-z#article-info
Article on study on EurekAlert! website: www.eurekalert.org/pub_releases/2019-07/uol-ffi071019.php

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