Solar energy

In 2009, the global solar industry remains in a very strong position, despite the faltering global economy. A number of factors are driving strong growth in the global solar industry today: government policy incentives and carbon regulation; volatility in the fossil fuels markets; climate change, energy security issues; and the need for increased energy production to meet growing demand.

Solar photovoltaic (PV) is the direct generation of electricity from sunlight, using solar cells packaged in photovoltaic modules. Each cell is made from semiconductor materials and creates an electrical charge in reaction to sunlight that can be transformed into a current of electricity. PV modules can be placed on rooftops or adjacent to buildings for distributed power, or organised into arrays for large-scale deployment.

There are many commercial solar products on the market today. These include battery chargers, portable electronics, garden lights, solar appliances and even solar clothing. These products all employ the basic application of PV energy. As technology advancement continues and material prices drop, the opportunities seem endless!

Solar heating and cooling systems (solar thermal - active and passive) are becoming more prevalent in residential and business applications. Solar heating converts the sun’s power into heat for hot water, space heating and swimming pools. Passive solar heating uses large windows to let in more light and warmth, while active solar heating uses specially designed mechanical systems to intensify the sun’s heat for use indoors.

Solar PV technology

There are many advantages of PV technology: the fuel is free; there are no moving parts to wear out, break down, or replace; only minimal maintenance is required to keep the system running; the systems are modular and can be quickly installed anywhere; and it produces no noise, harmful emissions or polluting gases.

The most important parts of a PV system are the cells that form the basic building blocks of the unit. These collect the sun’s light and include the modules that join large numbers of cells into a unit, and, in some situations, the inverters used to convert the electricity generated into a form suitable for everyday use.

The modules are clusters of PV cells incorporated into a unit, usually by soldering them together under a sheet of glass. They can be adapted in size to fit the proposed site and are quickly installed. They are robust, reliable and weatherproof. Module producers usually guarantee a power output of 80% of the nominal power, even after 20-25 years.

Inverters are used to convert the direct current (DC) power generated by a PV generator into alternating current (AC) compatible with the local electricity distribution network. This is essential for grid-connected PV systems. Inverters are offered in a wide range of power classes, from a few hundred watts through the most frequently used range of several kilowatts (3-6 kW) up to central inverters for large-scale systems with 100 kW and above.

Other components for standalone (off-grid) PV systems include a battery to store the energy for future use. New high-quality batteries designed especially for solar applications, with lifetimes of up to 15 years, are now available. The battery is connected to the PV array via a charge controller. The charge controller protects the battery from overcharging or discharging and can also provide information about the state of the system or enable metering and pre-payment for the electricity used. If AC output is needed, an inverter is required to convert the DC power from the array.

Concentrating solar power

Concentrating solar power (CSP) plants are utility-scale generators that produce electricity by using mirrors or lenses to efficiently concentrate the sun’s energy. CSP technologies include parabolic trough systems, power towers, dish/engine systems, linear concentrators and thermal storage, which concentrate the thermal energy of the sun to drive a conventional steam turbine.

Smaller CSP systems can be located directly where the power is needed. Single dish/engine systems can produce 3-25 kW of power and are well suited to such distributed applications. Larger, utility-scale CSP applications provide hundreds of megawatts of electricity for the power grid. Both linear concentrator and power tower systems can be easily integrated with thermal storage, helping to generate electricity during cloudy periods or at night. Alternatively, these systems can be combined with natural gas and the resulting hybrid power plants can provide high-value, dispatchable power throughout the day. These attributes, along with world-record solar-to-electric conversion efficiencies, make CSP an attractive renewable energy to ‘sun belt’ locations worldwide.

Solar supply chain

The ability to provide plug-and-play solutions, providing ease of installation and maintenance, is important, regardless of the solar application being considered. As an example, housings are equipped and wired entirely in accordance to end-user specifications; all you have to do is connect them in the field. However, be forewarned, lack of standardisation can mean that a product solution approved for one end-user may not work for another. As standards continue to be developed and refined, industry-leading connector manufacturers should use this as an opportunity to get involved with the standards committees serving this industry.

The higher up the PV value chain one travels, the fewer companies are involved. At the upper end of the chain, silicon production requires substantial know-how and investment, as does the production of wafers. On the other hand, at the level of cell and module producers, there are many more players in the market. At the end of the value chain, the installers are often small, locally based businesses.

In 2007, there were major bottlenecks in the silicon PV supply chain, driving up PV prices. However, those higher prices initiated considerable investment in silicon production, cell production and module manufacturing. Since the third quarter of 2008, module prices have fallen 25%. While this is likely to produce a shakeout in PV manufacturing and eliminate some of the high-cost producers, it will also likely result in significant savings to consumers. Modules typically constitute half the cost of PV systems.

In larger-scale solar installations, such as CSP, the supply chain continues to be refined. Industry guidelines do exist; however, end-user requirements for applications, product design and testing continue to vary due to a lack of standards in the industry. There is considerable focus on the need for delivery of fully tested cable assemblies, allowing for quick installation, few connections and little maintenance. Interconnect content is likely to increase as the application of motor drives continues to be incorporated into moving solar towers and panels.

Product solutions, common between most solar applications, are typically designed for harsh climatic and environmental conditions. For PV applications, exterior modules and other PV components, such as connection wires and cables, should be used with UV radiation and ozone-resistible insulation. The temperature range is also important. Exterior cables should allow for a temperature range from -45 to 80 °C, or more. Life expectancy is typically 20 years. Connectors are designed for high voltage and high current-carrying capacity, in addition to the IP67 sealing requirement. Surge protection, due to potential lightning strikes, requires energy supply lines to be designed in accordance with IEC 60364-7-712.

Solar innovation

Research and development by companies and research labs is continually discovering new techniques and materials that improve efficiencies and cut the cost of capturing solar energy. The industry seeks to commercialise the most promising technology to improve delivery of solar power generation for homes, business and government. Examples include: applying different materials for thin-film PV applications; solar cooling systems; and incorporating PV into building materials such as roofing, windows, and even painted surfaces.

Other areas being aggressively pursued are storage systems (thermal and electrical); solar hybrid lighting; improved manufacturing techniques; nanotechnology; low-cost semiconductor alternatives to polysilicon; and improving concentrating solar power systems.

Solar standards

Interconnection standards dictate the administrative process and technical specifications a homeowner or installer must follow to install solar electric property (solar panels, solar hot water heater, etc) and connect that property to the local utility’s distribution system. Not only do these standards vary by state, they may vary from utility to utility and country to country.

The IEEE Standards Coordinating Committee (SCC21) is responsible for continued progress on the interconnect standard to address interconnection of all distributed generation.

In closing, the promise of a solar future beckons. Solar power competes effectively today for peak power production, in grid-constrained territories, and for applications that are off the grid. Solar power offers a number of advantages over conventional energy sources. Among them, the ability to deliver energy at or near the point of use, zero fuel costs, minimal maintenance requirements and zero carbon-based source emissions. The current surge of activity in the solar electricity sector represents a fraction of the transformation and expansion expected to occur over the coming decades. Much work still needs to be done to turn potential into reality, but for those who do, solar electricity will result in socioeconomic, industrial and environmental benefits.