This is the total cost of producing energy using a renewable device and is measured in cents per kilowatt-hour. It includes the build cost, installation cost, the running costs and any other costs related to the device. The price also considers performance fluctuations due to bad weather and downtime due to maintenance. An example of an energy price is ¢8 per kWh, the rough cost of producing energy using photovoltaics.
This is the length of time a renewable device can be used before it needs to be replaced. For example, a typical offshore wind turbine will last around 25 years. In contrast, a hydroelectric dam can last for 200 years or more.
Energy per Square Kilometre
This is the amount of energy a renewable device can generate each year per square kilometre of land or water. For example, a typical photovoltaic array can generate some 300 GWh per square kilometre of land. That’s enough energy to power over 20,000 homes. In contrast, offshore wind turbines can generate just 26 GWh per square kilometre of water. That’s less than 10% of the amount that photovoltaics can produce within the same area.
This is the time period required to offset the total cost of a device using the revenue generated from energy sales. As an example, it would take around 13 years to offset the cost of a typical onshore turbine and around 21 years to offset the cost of a tidal stream. The economic offset period is based on a standard electricity price of ¢10.5 per kWh and an energy inflation rate of 5.4%. The electricity price reflects the current average electricity price in the USA and the inflation rate reflects the average energy inflation rate over the last ten years within the USA.
Carbon Offest Period
This is the time required for a device to generate enough clean energy to offset the carbon dioxide equivalent emitted from its manufacture and use. For example, a tidal lagoon would need to operate for around four years to offset the carbon emissions that occur due to its manufacture and use. In contrast, a hydroelectric dam would most likely never offset the carbon emissions that result due to its manufacture and use.
This is the amount of energy the renewable device could produce in a single year through the utilisation of all prime locations. For example, if photovoltaics were installed in all viable prime locations on the planet, an estimated 470 million GWh of energy would be generated. That’s more than four times the world’s current energy demand. In contrast, if offshore wind turbines were installed in all viable locations, just 6 million GWh would be generated. That’s less than one-tenth of the world’s energy demand. Because of the huge numbers involved, the global potential will be measured using petawatt-hours (PWh), with each petawatt-hour equal to one million gigawatt-hours.
The Renewable Solution
Now we know the key metrics used to assess which renewable device is best, let’s take a look at our first device – onshore turbines.
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All figures presented in this section are estimates based on best available data, assume optimum locations, and, wherever possible, are based on comparable studies. That said, many of the studies assume different economic conditions, climatic conditions, time frames and locations. Furthermore, the technologies discussed in this section are in a constant state of development. As a result, the figures presented within this section provide a rough guide only and should not be viewed as a definitive performance level.
For the total world energy demand, a figure of 104.4 million GWh has been used. The figure is based on 2012 data and sourced from International Energy Agency – 'World Balances for 2012' – www.iea.org.
All UK to USA currency conversions have been set at $1.656 USD for each £1 GBP. The figure is based on the conversion rate as of the 1st January 2014 and sourced from XE – 'XECurrency Table: USD - U.S. Dollar' – www.xe.com.