Direct Solar Energy
however, the awareness of the building sector is not always available. The economics are understood, but they depend on local solar resources and local support and building regulations. Low-temperature solar ther- mal is also a well-established technology, with economics that depend on the solar resource, the applications, and the cost of competing tech- nologies—some regions may need support programs to create markets and enable growth, whereas in other regions solar thermal is already competitive.
PV is already an established technology, but substantial further tech- nological advances are possible with the prospect for continued cost reduction. To this point, however, the deployment of PV technology has strongly depended on local support programs in most markets. Similarly, CSP technology has substantial room for additional improvement, but CSP costs have to this point exceeded market energy prices.
Continued cost reductions are therefore likely to be needed if solar energy is to meet the higher global scenario results presented earlier. Support programs to encourage solar deployment and R&D may both play an important role in seeking to achieve the necessary reductions.
Integration and transmission. Integration and transmission are not a central concern for passive solar applications. Integration issues in low-temperature solar, on the other hand, are especially important for larger systems where integration into local district heating systems is needed, and where the temporal variability of solar output needs to be matched with other supply sources to meet customer demands (see Chapter 8). Due to the availability of the resource only during the day and the short-time-period variability associated with passing clouds, proactive technical and institutional solutions to operational integration concerns will need to be implemented to enable large-scale PV pen- etration; CSP, if implemented with thermal storage, would not impose similar requirements. Moreover, high-penetration PV and CSP scenarios that involve larger-scale developments are likely to require additional transmission infrastructure in order to access the highest-quality solar sites. Section 8.2.1 identifies a variety of the technical and institutional challenges associated with increased deployment of variable generation sources, and also highlights the variety of solutions for managing those challenges. Though Chapter 8 finds no insurmountable technical barri- ers to increased variable renewable energy supply, as solar deployment increases, transmission expansion and operational integration costs are also expected to rise, potentially constraining growth on economic terms. Proactively managing these challenges is likely to be central to achieving the high-penetration solar energy scenarios described earlier.
Social and environmental concerns. Direct solar energy appears to have relatively few social and environmental concerns. Rather, the main benefit of passive solar is in reducing the energy demand of buildings. Similarly, low-temperature solar thermal applications are compara- tively benign from an environmental perspective. One concern for some PV technologies is that the PV industry uses some toxic materials and
corrosive liquids in its production lines.The presence and amount of those materials depend strongly on the cell type, however, and rigorous control methods are used to minimize the risk of accidental releases. Recycling of PV materials may also become more common as deployment continues. Water availability and consumption is the main environmental concern for CSP, though dry cooling technology can substantially reduce water usage. Finally, especially for central-station PV and CSP installations, the ecological, social and visual impacts associated with plant infrastructure may be of concern. Efforts to better understand the nature and magni- tude of these impacts, together with efforts to minimize and mitigate them, may need to be pursued in concert with increasing solar energy deployment.
Conclusions regarding deployment
Potential deployment scenarios range widely—from a marginal role of direct solar energy in 2050 to one of the major sources of energy supply. Although direct solar energy provides only a very small fraction of global energy supply in 2011, it has the largest technical potential of all energy sources and, in concert with technical improvements and resulting cost reductions, could see dramatically expanded use in the decades to come.
Achieving continued cost reductions is the central challenge that will influence the future deployment of solar energy. Reducing cost, mean- while, can only be achieved if the solar technologies decrease their costs along their learning curves, which depends in part on the level of solar energy deployment. In addition, continuous R&D efforts are required to ensure that the slopes of the learning curves do not flatten before solar is widely cost competitive with other energy sources.
The true costs of and potential for deploying solar energy are still unknown because the main deployment scenarios that exist today often consider only a single solar technology: PV. In addition, scenarios often do not account for the co-benefits of a renewable/sustainable energy supply (but see Section 9.4 for some research in this area). At the same time, as with some other forms of RE, issues of variable pro- duction profiles and energy market integration as well as the possible need for new transmission infrastructure will influence the magnitude, type and cost of solar energy deployment.
Finally, the regulatory and legal framework in place can also foster or hinder the uptake of direct solar energy applications. For example, minimum building standards with respect to building orientation and insulation can reduce the energy demand of buildings significantly, increasing the share of RE supply without increasing the overall demand, while building and technical standards can also support or hinder the installation of rooftop solar systems. Transparent, stream- lined administrative procedures to site, permit, install and connect solar power sources can further support the deployment of direct solar energy.