Photovoltaics

The word photovoltaic (PV) means “converting light to electricity.” PV panels, seen more and more often on Colorado roof tops, are composed of cells that contain a semi-conducting material, usually silicon. The semi-conducting material absorbs light energy from the sun and converts it into electricity.

Solar arrays, a system of PV panels, are designed specific to the needs of the site at which they are installed and can be used to meet most electricity needs depending on a few factors: the site’s exposure to the sun, the angle of the panels, and whether the system is connected to the utility grid. PV arrays are typically either mounted directly on a rooftop or on a pole on the ground.

It’s pretty simple: in order for it to work efficiently, a PV system must be exposed to the sun. Trees, roof overhangs, and neighboring buildings are all potential obstructions and should be evaluated by a professional installer; an evaluation called “siting.”

A PV array should never be blocked by an object at anytime of the year. It should also be oriented towards the south, and should be angled appropriately to take in as much light as possible as the sun moves from east to west during the day, and south to north throughout the year. An array can be installed so that the panels “follow” the sun as it moves, but most often they are mounted at an angle between 35 and 40 degrees (the optimum average angle for Colorado’s place on the map).

The PV array is accompanied by a system of electrical wires and a box, called an inverter. The inverter converts the energy coming in from the panels to the type of electricity that powers our lights, toasters, televisions, and computers. Inverters can show how much power the system is generating in real time; tracking the difference on a cloudy day vs. a sunny day often becomes a household science experiment.

What happens from there depends on whether the PV system is “grid-tied” or “off-grid.” The word “grid” is referring to the utility grid: the system of power plants, transmission lines, meter readers, and monthly bills that is responsible for keeping our lights on. The grid is owned and operated by a number of utility companies. Utility companies can be owned and operated by a group of private investors, by a municipality, or by its customers, which is called a cooperative. In Colorado, which company you pay for your electricity depends on where you live.

If the PV system is grid-tied, the electricity moves from the inverter and is either used right away, or sent to the grid. If the PV system is producing more power than is needed it is sent through the utility company’s meter to merge with the power in the grid. Excess power is “net-metered” which means you are credited for the excess power you generate.With net-metering, the meter will actually run backwards when power is being sent into the grid from the PV system. A meter running backwards means money is being taken off of a bill. In 2008 Governor Ritter spearheaded legislation that required utilities to provide net-metering to their customers making solar energy a viable option for Coloradans throughout the state.

If the PV system is off-grid, there is no utility company involved. The system functions completely separate from the power grid. In this situation, excess power is typically stored in batteries to be used later. Off-grid systems are most often used when connection to the grid is not possible due to location. Some grid-tied systems also use batteries to store power instead of sending it to the grid. This is typically done to provide a back-up system for power failures.

PV systems can provide power for almost anything. They are installed to generate electricity for general use in homes and commercial buildings. PV systems are also used to power specific items such as highway signs, garden lights, satellites and professional baseball stadium scoreboards. There are also large scale PV arrays that essentially function as a power plant.