household. Higher-quality light can also be provided through solar lan- terns, which can afford the same benefits achieved through solar home system-generated lighting. Solar lantern models can be stand-alone or can require central-station charging, and programs of manufacture, dis- tribution and maintenance can provide micro-enterprise opportunities. Use of solar lighting can represent a significant cost savings to house- holds over the lifetime of the technology compared to kerosene, and it can reduce the 190 Mt of estimated annual CO2 emissions attributed to fuel-based lighting (Mills, 2005). Solar-powered street lights and lights for community buildings can increase security and safety and provide night-time gathering locations for classes or community meetings. PV systems have been effectively deployed in disaster situations to provide safety, care and comfort to victims in the USA and Caribbean and could be similarly deployed worldwide for crisis relief (Young, 1996).
Solar home systems can also power televisions, radios and cellular tele- phones, resulting in increased access to news, information and distance education opportunities. A study of Bangladesh’s Rural Electrification Program revealed that in electrified households all members are more knowledgeable about public health issues, women have greater knowl- edge of family planning and gender equality issues, the income and gender discrepancies in adult literacy rates are lower, and immunization guidelines for children are adhered to more regularly when compared with non-electrified households (Barkat et al., 2002). Electrified house- holds may also buy appliances such as fans, irons, grinders, washing machines and refrigerators to increase comfort and reduce the drudgery associated with domestic tasks (ESMAP, 2004).
Indoor smoke from solid fuels is responsible for more than 1.6 million deaths annually and 3.6% of the global burden of disease.This mortality rate is similar in scale to the 1.7 million annual deaths associated with unsafe sanitation and more than twice the estimated 0.8 million yearly deaths from exposure to urban air pollution (Ezzati et al., 2002; see Sections 9.3.2 and 18.104.22.168). In areas where solar cookers can satisfacto- rily produce meals, these cookers can reduce unhealthy exposure to high levels of particulate matter from traditional use of solid fuels for cooking and heating and the associated morbidity and mortality from respiratory and other diseases. Decreased consumption of firewood will corre- spondingly reduce the time women spend collecting firewood. Studies in India and Africa have collected data showing that this time can total 2 to 15 hours per week, and this is increasing in areas of diminishing fuelwood supply (Brouwer et al., 1997; ESMAP, 2004). Risks to women collecting fuel include injury, snake bites, landmines and sexual violence (Manuel, 2003; Patrick, 2007); when children are enlisted to help with this activity, they may do so at the expense of educational opportunities (Nankhuni and Findeis, 2004). Well-being may be acutely at risk in refu- gee situations, as are strains on the natural resource systems where fuel is collected (Lynch, 2002). Solar cookers do not generally fulfil all house- hold cooking needs due to technology requirements or their inability to cook some traditional foods; however, even partial use of solar cookers
Direct Solar Energy
can realize fuelwood savings and reductions in exposure to indoor air pollution (Wentzel and Pouris, 2007).
Solar technologies also have the potential to combat other prevalent causes of morbidity and mortality in poor, rural areas. Solar desalination and water purification technologies can help combat the high preva- lence of diarrhoeal disease brought about by lack of access to potable water supplies. PV systems for health clinics can provide refrigeration for vaccines and lights for performing medical procedures and seeing patients at all hours. Improved working conditions for rural health-care workers can also lead to decreased attrition of talented staff to urban centres.
Solar technologies can improve the economic opportunities and work- ing conditions for poor rural populations. Solar dryers can be used to preserve foods and herbs for consumption year round and produce export-quality products for income generation. Solar water pumping can minimize the need for carrying water long distances to irrigate crops, which can be particularly important and impactful in the dry seasons and in drought years. Burdens and risks from water collection paral- lel those of fuel collection, and decreased time spent on this activity can also increase the health and well-being of women, who are largely responsible for these tasks.
Prospects for technology improvements and innovation7
This section considers technical innovations that are possible in the future for a range of solar technologies, under the following head- ings: passive solar and daylighting technologies; active solar heat and cooling; PV electricity generation; CSP electricity generation; solar fuel production; and other possible applications.
Passive solar and daylighting technologies
Passive solar technologies, particularly the direct-gain system, are intrinsically highly efficient because no energy is needed to move col- lected energy to storage and then to a load. The collection, storage and use are all integrated. Through technological advances such as low-emissivity coatings and the use of gases such as argon in glaz- ings, near-equatorial-facing windows have reached a high level of performance at increasingly affordable cost. Nevertheless, in heat- ing-dominated climates, further advances are possible, such as the following: 1) reduced thermal conductance by using dynamic exterior night insulation (night shutters); 2) use of evacuated glazing units; and 3) translucent glazing systems, which may include materials that change solar/visible transmittance with temperature (including a
Section 10.5 offers a complementary perspective on drivers and trends of techno- logical progress across RE technologies.