Federal and state governments in the U.S. have strongly supported renewable electric power supply for decades. The renewable power industry has received tens of billions in financial support over the years. In addition, many states require utilities to provide increasing renewable power levels each year. The results are interesting after 25 years of regulations and programs intended to development and grow U.S. renewable power, according to The Energy Collective.

Hydroelectric power — Hydropower was the original U.S. renewable power source beginning the late 19^th century and continues to be the largest renewable power source today. Total hydroelectric net power generation has varied over the years due to the annual rainfall, maintenance and operation restrictions imposed by regulatory agencies to possibly improve downstream ecosystems. The hydroelectric power generation average trend has been fairly constant over the past 25 years. Maintaining existing hydroelectric power capacity continues to face environmental concerns, as does possible expansion of future power generation capacity.

Geothermal power — Geothermal became a significant power source beginning in the 1950’s.  Geothermal power grew and peaked during the 1990’s and has been relatively constant ever since. The development barriers to further expansion are costs and limited access to geological formations that are suitable for new efficient geothermal power plants. 

Wood and bio-waste power — The use of wood and bio-waste fuels for power generation began to grow in the late 1980’s. Wood fuels make up about 2/3’s of the total power generated from this class of renewable. Bio-waste fuels include biogas captured from capped municipal waste dumps and solid fuels.  Wood/bio-waste provided the second largest source of U.S. renewable power until 2008. Wood/bio-waste power generation has been relatively constant since the early 1990’s. The development barriers for wood/bio-waste power generation are largely costs. The future expansion of bio-waste power generation could be supported by the possible development of cellulosic biofuels. Cellulosic biofuels byproducts or bio-waste will likely be required to fuel new power plants in order to comply with the Energy Independence and Security Act (2007) greenhouse gas reduction targets.

Solar PV/thermal power — Solar photovoltaic power was developed over 50 years ago and became commercially successful for smaller, distributed (off-the-grid) niche market applications. Larger solar PV power plants, which connect into local power grids, generally developed after state and federal governments started supporting this renewable power source’s development in the 1980’s. Large solar thermal power plants also began to grow in the 1980’s. Both solar PV/thermal have grown relatively slowly compared to other commercial power generation sources. Although solar PV has experienced significant technology improvements and cost reductions over the past 25 years, this technology is still costlier than other renewable power sources. Solar thermal plants are higher cost than many state-of-art PV plants, but can have the advantage of energy storage capability. This storage technology allows generating power effectively round-the-clock. Although growth in solar PV/thermal power has recently increased very significantly, this industry’s largest barrier to future expansion continues to be relatively high costs.

Wind power — Wind power began its initial commercial development during the 1980’s and has grown at rates much greater than all other renewable power sources. Wind power began expanding very rapidly beginning the early 2000’s due to state and federal government support and technology developments. A contributing factor to wind power’s recent success comes from the economy of size. Earlier 50-350kW class wind turbines were generally uneconomic without perpetual government subsidies. State-of-art 1.0-6.0mW wind turbine technology reportedly should be sustainable without excessive subsidies. If the recent rate of growth is sustainable, wind power could possibly equal hydroelectric power within the next 20 years. Wind power expansion continues to have significant development barriers. Wind farms face ongoing environmental concerns relative to protected birds and bats, and offshore projects have been subject to huge local public opposition similar to what fossil fuel plants have historically experienced.  Offshore projects, such as the Massachusetts Cape Wind project, have taken a decade to acquire needed permits.   

Renewable power performance — A major weaknesses for wind and solar PV power generation are relatively low capacity factors. Wind and solar PV can only produce power when the wind blows and sun shines. The normal variations in wind/sunshine lead to wind power having average capacity factors of about 30 percent and solar PV capacity factors closer to 20 percent. This means that wind turbines/solar PV are only capable for delivering 30 percent to 20 percent of maximum design power capacity on average during a given the year.

Wood/bio-waste, geothermal, solar thermal with energy storage capability, nuclear and all fossil fuel power plants have capacity factors of 80-90 percent. These technologies can supply reliable power around-the-clock, which is required for power grid base-load capacity. The hydroelectric capacity factor is about 50% and is constrained by reservoir management. Hydroelectric can be scheduled to supply reliable around-the-clock, base-load power for limited periods of time depending on stored water availability and government agency operating constraints.

Developmental renewable power — Other possible renewable power technologies include hydrokinetic power from tidal/wave energy, ocean thermal and river/stream hydropower, small hydroelectric facilities, and additional types of biomass/waste fuels. All of these renewable power sources may someday become commercial, but today face very large efficiency and cost challenges compared to existing commercially successful technologies.

Read more about solar power for homes and geothermal heating and cooling.