How it works

Home

How it works

Products

Services

Contact

Navigation

Solar

Key Partners

Solar

Blogs

How it works

Solar energy—power from the sun—is a vast and inexhaustible resource. Once a system is in place to convert it into useful energy, the fuel is free and will never be subject to the ups and downs of energy markets. Furthermore, it represents a clean alternative to the fossil fuels that currently pollute our air and water, threaten our public health, and contribute to global warming. Given the abundance and the appeal of solar energy, this resource is poised to play a prominent role in our energy future.

In 1839, French scientist Edmund Becquerel discovered that certain materials would give off a spark of electricity when struck with sunlight. This photoelectric effect was used in primitive solar cells made of selenium in the late 1800s. In the 1950s, scientists at Bell Labs revisited the technology and, using silicon, produced solar cells that could convert four percent of the energy in sunlight directly to electricity. Within a few years, these photovoltaic (PV) cells were powering spaceships and satellites.

The most important components of a PV cell are two layers of semiconductor material generally composed of silicon crystals. On its own, crystallized silicon is not a very good conductor of electricity, but when impurities are intentionally added—a process called doping—the stage is set for creating an electric current. The bottom layer of the PV cell is usually doped with boron, which bonds with the silicon to facilitate a positive charge (P). The top layer is doped with phosphorus, which bonds with the silicon to facilitate a negative charge (N).

The surface between the resulting "p-type" and "n-type" semiconductors is called the P-N junction (see the diagram below). Electron movement at this surface produces an electric field that only allows electrons to flow from the p-type layer to the n-type layer.

When sunlight enters the cell, its energy knocks electrons loose in both layers. Because of the opposite charges of the layers, the electrons want to flow from the n-type layer to the p-type layer, but the electric field at the P-N junction prevents this from happening. The presence of an external circuit, however, provides the necessary path for electrons in the n-type layer to travel to the p-type layer. Extremely thin wires running along the top of the n-type layer provide this external circuit, and the electrons flowing through this circuit provide the cell's owner with a supply of electricity.

Solar energy

Wind energy

The Sun heats our atmosphere unevenly, so some patches become warmer than others. These warm patches of air rise, other air blows in to replace them - and we feel a wind blowing. We can use the energy in the wind by building a tall tower, with a large propellor on the top. The wind blows the propellor round, which turns a generator to produce electricity.

We tend to build many of these towers together, to make a "wind farm" and produce more electricity. The more towers, the more wind, and the larger the propellors, the more electricity we can make.

It's only worth building wind farms in places that have strong, steady winds, although boats and caravans increasingly have small wind generators to help keep their batteries charged.

Small power systems that use both wind and solar photovoltaic power generation often work better than either one alone. Solar/wind hybrids use solar panels and small wind turbine generators to generate electricity in both grid-tied and stand-alone systems.

Solar

Solar power is most efficient in summer.
Solar energy image by lefebvre_jonathan from Fotolia.com Solar PV panels convert sunlight into electricity and send it into the home through a charge regulator that feeds batteries or an inverter unit that converts the DC output from the solar panels to AC house current.

Wind

Small wind turbines are most efficient in winter when solar panels don't work as well. A hybrid power system also uses a wind turbine generator to convert the mechanical energy of the windmill into electricity. According to the U.S. Department of Energy, hybrid systems are more efficient because they complement each other. In summer the winds are usually slow and the solar panels are most efficient. The wind turbine is more efficient in winter when winds are usually stronger and there is less sunlight.

The electricity from a hybrid system must be converted into usable AC current before it enters your home. The current from the wind turbine and solar panel is run through charge controllers and inverters to transform it into usable AC electricity.