Solar and Wind Energy Solar and wind energy are two forms of renewable energy that are already implemented at a substantial scale. In order to further expand the capacity for wind and solar energy, however, there are still issues that need to be considered. On top of the remaining needs to drive down costs and improve efficiency, connection with the grid also needs to be substantially improved through development of better power conversion and energy storage technologies, as the generation capacity for renewable energies rapidly expands. Solar Power The solar energy reaching the ground is estimated to be approximately 170 W/m 2 (21 trillion kw in total). Since global energy demand is about 0.16 trillion kw i, it is possible to satisfy the global energy demand with less than 1% of the solar energy reaching the ground. There are two kinds of methods for harnessing solar energy as electric power: solar thermal power generation and photovoltaic (PV) power generation. For respective methods, 3GW (2014) and 135GW (2013) were installed and they are expanding. Where we are heading IEA estimated the output of solar thermal power generation to be about 5,000 TW/y, in the csp roadmap ii. In the Solar Photovoltaic Energy roadmap iii, it was assumed that the output of PV would be about 4,000 TW/y (10% of total output) in 2050 in the case of the 2 C scenario, and the output is estimated to exceed 6,200 TW/y (16% of total output) in the hi-ren scenario. (See the following figure.) Forecast of PV distribution in each region OECD/IEA2014,Technology Roadmap Solar Photovoltaic Energy 2014 edition,iea Publishing Where we are Solar thermal power generation: The capacity of solar thermal power generation introduced in 2014 was 3GW iv. The trough type is dominant while tower type is still playing a minor role in the market. The maximum efficiency of commercially available solar thermal power generators can go as high as the double of PV, while they remain considerably more expensive. Photovoltaic power generation: The installed capacity of PV as of 2013 was 135GW 6.
There are mainly two types of technologies deployed today; silicon crystals and compound semiconductors As for production amounts, the crystal type accounts for nearly 90% although silicon crystal production remains costly, requiring cost reduction for further expansion. As for the thin-film and compound types, low efficiency remains as the problem. Our challenges and way forward Technological challenges Regarding solar thermal power, we are currently striving to improve the efficiency of a solar energy collector. In order to meet the demand for grids, we are developing the technology to coping with load fluctuations combined with the heat storage technology. For PV, the race for higher efficiency continues. The following figure shows the latest research. Variation in the efficiency of solar cells (research and trial production phases) Source: NREL (http://www.nrel.gov) Social challenges By manufacturing products for solar thermal power and maintain power generation systems in emerging economy, we can promote employment and disseminate of solar thermal power generation at the same time creating synergy. As for photovoltaic power generation systems, the prices of solar panels (cells) dropped due to the effect of mass production, but they are installed at various places, and so it is necessary to reduce the cost for installation. Directly, we need to decrease the prices by standardizing installation methods, etc. Game changers Multi-junction solar cells: Ordinary solar cells convert only a portion of all wavelengths of solar radiation into electric energy. By combining multiple solar cells with different wavelength ranges for photoelectric conversion to produce a single cell, we can expect
multiplying the efficiency of power generation. Global standardization of technologies: For solar thermal power generation, plant-level engineering is essential therefore design and construction are carried out for individual plants. By standardizing the structures and materials that do not sacrifice performance, we can produce power generation systems in various regions and reduce cost significantly. In addition to the cost of panel, same can be said about installation process. By standardizing installation methods and jig structures taking into account installation conditions, we can reduce total cost. Wind Power Wind power has already been installed widely and still has vast potential for further potential across the globe. Figure 1 shows the wind conditions around the world. Figure 1 Wind conditions and the installation of wind power generation systems OECD/IEA2013, Technology Roadmap Wind energy2013edition IEA Publishing. For example, European Environment Agency (EEA) predicts that we can introduce 30,400 TWh in 2030, even under the most stringent conditions considering economic performance, and this will be 7 times of the total electricity demand of Europe 1. At present, win turbines with diameter of 100m are mainstream, and their cost in windy places comes close tho that of fossil energy. In the technological aspect, we need to reduce cost and increase output and take measures for issues such as low-frequency noise, thunderbolts and bird-strike. In the social aspect, a key challenge for wind power 1 Europe s Onshore and Offshore Wind Energy Potential, EEA 2009
is to coexist with surrounding nature and private residence without disturbing them. Where we are heading IEA estimated, in the wind energy roadmap 2, that the output of wind power generation will be about 6,000 TWh/y (15% of total output) in the 2 C scenario, and will exceed 7,000 TWh/y (18% of total output) in the hi-ren scenario in 2050. (See Figure 2) Figure 2 Estimate of diffusion of wind power generation in each region OECD/IEA2013, Technology Roadmap Wind energy2013edition IEA Publishing Where we are By 2012, the equipment of 282 GW was introduced, and global output reached 527 TWh. At present, the land-based 2MW class is dominant typically produced by heavy electric manufacturers in the US, Europe, and Japan. Recently, many Chinese manufacturers have also entered the market. Our challenges and way forward Technological challenges As availability of onshore site is decreasing, it is indispensable to develop offshore technologies including floating type. This requires underwater cables, larger wind turbines and surrounding equipment, all of which need to reduce cost significantly. The manufacturers in Europe, the U.S., Japan, and China are at demonstration stage of systems as big as 6 to 15 MW. On land, there are windy site but not all of them have sufficient space for large equipment, which makes it an imperative to develop smaller and more efficient systems. Social challenges For further cost reduction, it is important to create competitive market of wind power technology. Standardization of technology is also crucial to bring down the costs. 2 OECD/IEA2013, Technology Roadmap Wind energy2013edition IEA Publishing.
Onshore sites must compete with other purpose of land use as the availability of sites is finite. This requires well-designed system not only for the performance but also coexisting with surrounding scenery and avoid disturbance on nature and residential environment. Game changers Airborne type: There is the airborne type wind power generation technology using lightweight wind turbines and airships. In general, the wind is stronger in higher altitude therefore we can expect more output. In addition, it may be possible to simplify installation work, because the equipment produced at a factory can be transported by an airship to the installation site. This might open up opportunities for even lower-cost wind power generation system. Diffuser type: Inspired by the aerodynamic design of jet engines, diffuser-type wind turbines have been developed. A small windmill with a diameter of about 10 meters can achieve the efficiency of the current large windmill with a diameter of about 100m. Such compact wind turbines can be installed where there is only a handful of spaces. i ii Calculated from the fact that global energy consumption was 12.27 billion tons (2011). IEA2010,Technology Roadmap Concentrating Solar Power,IEA Publishing. iii IEA2014,Technology Roadmap Solar Photovoltaic Energy 2014 edition,iea Publishing. iv Survey by ESTELA (European Solar Thermal Electricity Association)