2.6 Sustainable Energy Systems – Renewable Energy

After considering seriously reducing energy usage, and implementing as efficient appliances and technology as possible, we can think about using energy resources that are not finite in their resource. Such resources are known collectively as “Renewable Resources” and technology that harness these resources are called “Renewable Energy Technologies”.

Almost all end uses of energy, such as lighting, electrical outfitting, refrigeration, telecommunications, water pumping and purification, food processing, grain milling and other energy applications can be supplied by technologies that use renewable sources. Furthermore, in many cases renewable energy technologies are technically and financially flexible; their operating costs are also lower and, once set up, they are not subject to fuel price fluctuations. The extensive use of renewable energy not only enables local production with secondary benefits of opportunities for job creation, but it also provides environmental benefits.

Figure 2.6.1 A list of the 4 types of energy we are aware of with their theoretical resource in the world.

(Source The Game Plan, [see reference 1])

Figure 2.2.4 sourced from Slideshare.net (Author: Skeen) under a Creative Commons Attribution- 3.0 license
http://www.slideshare.net/skeen/game-plan-v10-1

 

• We get most of our energy from the sun – as well as being the source for fossil fuels, it also creates wind power (through atmospheric heating), wave power (via the wind), direct (or new) solar energy, hydro power (through the water cycle) and biomass energy (energy from burning plants and trees).

• Solar radiation that falls upon the Earth's land surfaces, approximately 220x106TWh, is 2,000 times greater than the world's annual primary energy demand, approximately 9410 million Tons of Petroleum Equivalent for 2002 (109,000TWh). Source: Aguilera et al [see reference 3]

• Gravitational energy from the moon creates the tides and can be harvested as tidal energy

• Heat in this sense was created when the earth was formed, is stored beneath the crust of the earth and can be harnessed in a form known as geothermal energy

 

Benefits of Renewable Energy

Renewable energy resources (sun, wind, water flow, geo-thermals) are distributed, in various quantities, as energy demand is decentralised so lower transmission losses can occur.

No implications of finite resources running out, a constant flow of energy from the sun provides an ongoing source of energy.

Renewable resources are pollution free. Although the technology itself will create waste and use energy during its construction and maintenance phases, there is no burning of fossil fuels during operation so no pollution.

Carbon payback is a term referring to the time taken for the carbon used in the manufacture of the renewable energy technology to be saved by the carbon free energy it produces. This can be a short period of time for renewable energy technologies. For a wind turbine for example, the carbon payback can be as short as 6 months.

 

Drawbacks to Renewable Energy

The renewable resource is inherently intermittent: the sun does not always shine, the wind will not always blow, and water flows are seasonal. These factors need to be taken into account when designing renewable energy systems.

There is a low energy density of renewable resources compared to fossil fuels, for a fully renewable energy system a considerable reduction in consumption is therefore required.

There can be high initial capital costs with large scale renewable energy such as wind or hydro power. However this can be offset by the fact that there are comparably lower ongoing costs as there isn't a constant need to purchase fuel (with the exception of biomass systems).

Some renewable technologies such as hydro can have significant environmental consequences such as flooding of natural habitats destroying ecosystems and displacing populations (2 million people were displaced by the flooding of the Yangtze in China for a hydro dam).

Below is a table that outlines most of the major renewable energies available and a description of the technologies that implement them

Energy Source	Technology	Description
Solar - direct	Solar Photovoltaic (PV)	Solar panels convert the radiation energy from the sun into electricity through silicone cells
Solar - direct	Solar Thermal	Heat from the sun is used to heat water for domestic use in houses
Solar - direct	Concentrated Solar Power (CSP)	Large scale solar farms focus the sun’s energy to produce high temperatures that run a steam engine to produce electricity
Wind	Wind Turbine	Wind power is converted to rotational energy by aerodynamic blades which turn an alternator to produce electricity
Biomass	Biomass Space Heating	Wood is burned efficiently to heat buildings
Biomass	Biofuels for transport	Energy crops are grown and processed to produce fuel to run vehicles
Biomass	Biomass Electrical Power production	Wood is burned to produce steam to run a generator to produce electricity in a similar way that large scale coal-fired power plants operate.
Biomass	Anerobic Digestion	Organic matter decomposes under water to produce methane which is burned to produce electricity
Tidal	Tidal Power Plants	As the tide comes in the water is held and released through a turbine to produce electricity
Waves	Wave power	The motion of the waves are used to turn generators to produce electricity
Rivers/Streams	Hydro Power	The flow of water down a hill is sent through a penstock to an impellor which turns a generator to produce electricity
Heat from Earth's core	Geothermal Power	In place where the Earth's crust is thin, heat from the Earth’s core is used to produce steam which turns a generator to produce electricity
Burning Waste	Landfill gas	Decomposing waste produces methane which is burned to produce electricity