Direct Solar Energy
Passive solar and daylighting are conserving energy in buildings at a highly significant rate, but the actual amount is difficult to quantify. Well-designed passive solar systems decrease the need for additional comfort heating requirements by about 15% for existing buildings and about 40% for new buildings.
The generation of electricity using PV panels is also a worldwide phenomenon. Assisted by supportive pricing policies, the compound annual growth rate for PV production from 2003 to 2009 was more than 50%—making it one of the fastest-growing energy technologies in percentage terms. As of the end of 2009, the installed capacity for PV power production was about 22 GW. Estimates for 2010 give a consensus value of about 13 GW of newly added capacity. Most of those installations are roof-mounted and grid-connected. The production of electricity from CSP installations has seen a large increase in planned capacity in the last few years, with several countries beginning to experience significant new installations.
Integration of solar energy into broader energy systems involves both challenges and opportunities. Energy provided by PV panels and solar domestic water heaters can be especially valuable because the energy production often occurs at times of peak loads on the grid, as in cases where there is a large summer daytime load associated with air conditioning. PV and solar domestic water heaters also fit well with the needs of many countries because they are modular, quick to install, and can sometimes delay the need for costly construction or expansion of the transmission grid. At the same time, solar energy typically has a variable production profile with some degree of unpredictability that must be managed, and central-station solar electricity plants may require new transmission infrastructure. Because CSP can be readily coupled with thermal storage, the production profile can be controlled to limit production variability and enable dispatch capability.
Solar technologies offer opportunities for positive social impacts, and their environmental burden is small. Solar technologies have low lifecycle greenhouse gas emissions, and quantification of external costs has yielded favour- able values compared to fossil fuel-based energy. Potential areas of concern include recycling and use of toxic materials in manufacturing for PV, water usage for CSP, and energy payback and land requirements for both. An important social benefit of solar technologies is their potential to improve the health and livelihood opportunities for many of the world’s poorest populations—addressing some of the gap in availability of modern energy services for the roughly 1.4 billion people who do not have access to electricity and the 2.7 billion people who rely on traditional biomass for home cooking and heating needs. On the downside, some solar projects have faced public concerns regarding land requirements for centralized CSP and PV plants, perceptions regarding visual impacts, and for CSP, cooling water requirements. Land use impacts can be minimized by selecting areas with low population density and low environmental sensitivity. Similarly, water usage for CSP could be significantly reduced by using dry cooling approaches. Studies to date suggest that none of these issues presents a barrier against the widespread use of solar technologies.
Over the last 30 years, solar technologies have seen very substantial cost reductions. The current levelized costs of energy (electricity and heat) from solar technologies vary widely depending on the upfront technology cost, available solar irradiation as well as the applied discount rates. The levelized costs for solar thermal energy at a 7% discount rate range between less than USD2005 10 and slightly more than USD2005 20/GJ for solar hot water generation with a high degree of utilization in China to more than USD2005 130/GJ for space heating applications in Organisation for Economic Co-operation and Development (OECD) countries with relative low irradiation levels of 800 kWh/m2/yr. Electricity genera- tion costs for utility-scale PV in regions of high solar irradiance in Europe and the USA are in the range of approximately 15 to 40 US cents2005 /kWh at a 7% discount rate, but may be lower or higher depending on the available resource and on other framework conditions. Current cost data are limited for CSP and are highly dependent on other system factors such as storage. In 2009, the levelized costs of energy for large solar troughs with six hours of thermal storage ranged
from below 20 to approximately 30 US cents2005
/kWh. Technological improvements and cost reductions are expected, but
the learning curves and subsequent cost reductions of solar technologies depend on production volume, research and