Renewable energy has an intrinsic value that has been recognized for centuries by populations that have tapped energy embedded in wind, water and sunlight to meet their daily needs.
That value lies in the fact that these sources of energy can be harvested to generate more energy in their lifetime than that used during their fabrication, operation and decommissioning. This energy yield is known as the energy payback ratio (EPR), which is the energy output divided by the energy input. For example, over their 20-year lifespan, wind turbines can produce 40 times the energy used in their manufacturing. Solar photovoltaic (PV) arrays, which generate electricity from sunlight, have an EPR of approximately 20.
Low impact or run of river hydro, for which there is minimal impoundment of water behind a dam, has an EPR of 100. Biomass energy with an EPR of 30 uses wood waste as the fuel source to generate heat and power. Biogas, which results from the decomposition of organic matter found in agricultural manure, municipal sewage sludge, and landfill gas, contains methane and is used in thousands of jurisdictions worldwide to supplement energy supplies. Geothermal heat, which can be found at depths of 5 kilometers, is used to transform water or fluids with low boiling points into steam or vapours that spin turbines to generate electricity.
The ‘fuels’ of wind, water and sunlight that run these renewable energy technologies are not only inexhaustible, but non-polluting. On the other hand, coal plants emit air pollutants such as mercury, sulphur dioxide, nitric oxides and particulates, and the greenhouse gas carbon dioxide. Renewables do not have the complexity of a technology such as nuclear power. Wind turbines and solar PV arrays can be fabricated and installed by skilled trades people, as opposed to the highly trained personnel needed to design, construct and operate nuclear facilities.
Renewables, especially solar, are highly scalable. Photovoltaics can be installed on virtually millions of empty residential and commercial rooftops and marginal land. Hence, renewables have exponential growth potential in the marketplace from manufacturing, distribution, sales and installation. This growth translates into job potential and diversification for students seeking new vistas. The energy resources for renewables are widespread and diverse. While some regions may benefit from high solar irradiance, other regions may exhibit excellent wind regimes, tidal forces and hydro resources.
A major challenge for renewables such as wind and solar is their intermittency. Solar energy is absent during night and is reduced during overcast days. Wind power can be extremely variable due to weather patterns. Therefore, reliable regional wind forecasting is needed to balance the electrical grid. Coincidentally, solar power during daylight hours helps to balance wind power, which usually produces most power overnight. In order for wind and solar electricity to be available on demand, pumped hydro storage, batteries, compressed air, ultracapacitors and super flywheels have entered the market. These systems store electricity for immediate dispatch during peak demand. In the future, plug-in electric vehicles may act as storage devices to support a smart grid.
A second challenge for renewables is the misunderstanding that they cannot match the power density of hydrocarbons like coal, oil and natural gas. Power density can be thought of as the amount of power generated by a device over a given area, expressed as watts per square meter (W/m2).
For example, a 670 MW coal power plant may have a power density of approximately 300 W/m2; however, its supporting coal extraction area can encompass 30 square kilometers of land resulting in an overall power density of 20 W/m2. In comparison, a single wind turbine may have a power density of 8,500 W/m2. But because of wind shadow effects, wind farms must space scores of turbines over large areas resulting in a power density of 10 W/m2. The world’s largest wind farm, the 845 MW Shepherd’s Flat in Oregon, is spread over 78 square kilometers giving a power density of 11 Watts/m2.
Solar power has a leg up on power density if one considers that millions of empty residential, commercial and industrial rooftops are available for photovoltaics. Current rooftop PV arrays offer power densities of 150 W/m2. Solar farms such as the 58 MW Copper Mountain PV system in the Nevada desert have power densities greater than 30 W/m2.
A third challenge for renewables is the presumption that they have a high capital cost. While this thought may have had merit a decade ago, there has been a significant drop in the cost of renewables, especially solar. Solar PV can now be installed for $3,000 per kilowatt — a 10-fold reduction since 2000. Wind farms can be developed for $2,300 per kilowatt. In comparison, a new pulverized coal plant with carbon capture and sequestration controls will cost $7,000 per kilowatt. A nuclear plant, if it can receive approval following a protracted planning and construction period, will cost $8,000 per kilowatt.
In the near future, hydrocarbon energy integrated with renewable energy and energy storage will provide reliable dispatchable power. Economies of scale will continue to lessen prices of renewables as millions of people purchase small, decentralized energy systems for their homes and businesses. Diversified jobs in this new energy sector will escalate exponentially during this transformative period.
As announced on June 26, 2013 by the International Energy Agency: “renewable power is expected to increase by 40 per cent in the next five years. Renewables are now the fastest-growing power generation sector and will make up almost a quarter of the global power mix by 2018.”
This is good news for the construction industry.