Glossary - City & Infrastructure

Solar Photovoltaic (PV) system

Solar Photovoltaic systems convert sunlight directly to electricity

They work in daylight, especially when the sun is shining, but more electricity is produced when the sunlight is more intense and strikes the PV modules directly. Solar PV systems work best in energy-efficient homes and buildings. The Department of Energy recommends adding energy-efficient lighting, insulation, appliances and windows to reduce your home or facility’s electric use before you install a PV system. And taking advantage of regional tax credits can further enhance the economics of solar power. Photovoltaic cells look similar to solar panels but they work in a different way. Solar panels are used to produce hot water or even steam. Photovoltaic panels convert the sunlight directly into electricity. A typical example of a device powered by photovoltaic cells is a solar-powered calculator. Silicon is a material known as a ‘semiconductor’ as it conducts electricity and it is the main material for photovoltaic cells. Impurities such as boron or phosphorus are added to this base material, which create the right environment for electrons to be freed when sunlight hits the photovoltaic panel. The freeing of electrons leads to the production of electricity because when sunlight shines on the cell it creates an electric field across the layers. The power of a PV cell is measured in kilowatts peak (kWp). That's the rate at which it generates energy at peak performance in full direct sunlight during the summer. PV cells come in a variety of shapes and sizes. A photovoltaic array (also called a solar array) consists of multiple photovoltaic modules. Optionally, a photovoltaic system may include any or all of the following:

• renewable energy credit revenue-grade meter
• maximum power point tracker (MPPT)
• battery system and charger
• GPS solar tracker
• energy management software
• solar concentrators
• solar irradiance sensors
• anemometer
• task-specific accessories designed to meet specialised requirements for a system owner.

Decentralisation brings millions of small generators producing power where it is needed, and solving the problem of large energy losses during transmission.

Wind power

Wind power is the conversion of wind energy into a useful form of energy, such as by using wind turbines to make electrical power

The generation of wind-produced electrical power begins when the force of the wind pushes against the turbines’ blades, causing them to rotate and thereby creating mechanical energy. The spinning blades attached to a hub and a low-speed shaft, turn along with the blades. Connected to the rotating low-speed shaft is a gearbox that in turn connects to a high-speed shaft on the opposite side of the gearbox. This high-speed shaft connects to an electrical generator that converts the mechanical energy from the rotation of the blades into electric energy. Spinning between 11 and 20 times per minute, each turbine can generate 1.5 megawatts of electricity, or even more – enough to power, on average, more than 500 residential homes. Large wind farms consist of hundreds of individual wind turbines that are connected to the electric power transmission network. Offshore wind is steadier and stronger than on land, and offshore farms have less visual impact but construction and maintenance costs are considerably higher. Small onshore wind farms provide electricity to isolated locations. Utility companies increasingly buy surplus electricity produced by small domestic wind turbines, and direct this surplus to the power network for general electric consumption. As of 2011, Denmark has been generating more than a quarter of its electricity from wind, and 83 countries around the world are now using wind power on a commercial basis. In 2010 wind energy production of electricity was more than 2.5% of total worldwide electricity usage, and growing rapidly at more than 25% per annum. The monetary cost per unit of energy produced is similar to the cost for new coal or natural gas installations.