Solar Hot Water Systems

In many areas of the world, such as in the Mojave Desert and southern Spain, solar energy generates heat and electricity for tens of thousands of homes. Powering TVs, computers, lights, and heaters, the sun meets much of people’s everyday needs in these regions.

Solar heating is another way to heat water and your home. Collecting solar energy for heating can be accomplished using two types of systems—passive and active.

Passive and Active Solar Heating
Passive solar heating systems simply collect electromagnetic energy without the use of any moving mechanical parts, such as pumps and fans. Have you ever stood in the sun in a black t-shirt? What did you notice? The sun’s energy was pas sively absorbed by the dark shirt and your body. This absorbed energy is transformed into thermal energy, which then warms your shirt and your body.

Architects and engineers design walls, windows, floors, and roofs that can passively collect and transform the sun’s energy into thermal energy. They do this by facing more windows towards the sun in cooler climates. This allows more electromagnetic energy onto floors and walls that then absorb the energy and transform it into heat. Dark stones or tiles are often used to maximize this energy transformation. This way homes and buildings can cut down on energy bills with minimal environmental impact.

The difference between passive and active solar heating systems is that active systems collect and move solar energy with the use of moving mechanical parts, such as a pump or a fan. The addition of a pump or a fan increases the efficiency of the collection, storage, and distribution of thermal energy within the system. Often, thermal energy from active solar systems can be stored in rock bins or in water tanks. This energy can then be used later when the electromagnetic energy from the sun is no longer available. So, when the sun is not shining, the solar energy is still available for use!

Solar Power Plants
Scientists are also now able to transform solar energy into electrical energy. At a solar power plant, the sun’s energy is first collected and concentrated by reflective troughs, dishes, or towers. This energy is then used to heat a fluid, such as water, which produces steam. The steam is then used to spin a turbine which turns a generator to produce electrical energy.

Photovoltaics
You do not necessarily need an entire solar power plant to transform the sun’s energy into electrical energy. In fact, most often when we talk about generating electrical energy from electromagnetic energy, we are referring to using photovoltaic systems.

Photovoltaic (PV) technology focuses on transforming electromagnetic energy from the sun into electrical energy. You may be familiar with the small, light-sensitive strip that powers some calculators. Or maybe you have seen a solar panel on a road sign or a garden light. Most PV technologies use similar concepts in order to produce electrical energy.

Layers of a PV Cell
PV cells can transform electromagnetic energy into electrical energy because of the properties of two specially treated materials. When these materials are placed on top of one another, an electric field develops. Sunlight passes through the top layer (n-layer) and strikes the bottom layer (p-layer). The bottom p-layer of the PV cell is specially treated to release electrons whenit absorbs a certain amount of electromagnetic energy. Electrons released from the bottom p-layer follow the electric field through a junctionand are collected by the top n-layer. This top n-layer has been specially treatedto accept electrons. Because of the direction of the electric field created by the junction of both materials,it is harder for electrons to return back through the junction to the bottom p-layer. As more electromagnetic energy reaches the bottom p-layer, and as more electronsmove to the top n-layer, a voltage builds. A metal conductor strip creates a circuit that carries electrons away from the topn-layer back to the bottom p-layer. This is an easier pathway for electrons to returnback to the bottom layer. This flow of electrons is the electrical energy that can be used to charge batteries and light lamps.

Most photovoltaic systems use a photovoltaic array. A photovoltaic array consists of multiple photovoltaic cells linked together to generate a higher energy output.

Today, products such as PV plastics, fibers, and paints, called thin-film photovoltaics, are changing the way we look at and think about electromagnetic energy collection.

Advantages and Limitations
Solar power is popular because it comes from a free and inexhaustible source. In addition, once installed, solar energy systems do not produce any air or water pollution. PV cells and arrays can also be designed to fit most size or shape requirements, making them extremely useful in different situations.

Major limitations of solar power include the initial cost of the equipment and installation. Large scale solar arrays and power plants also require large amounts of land. Additionally, the amount of electrical energy produced depends on the amount of sunlight available.

Individual photovoltaic cells are composed of silicon sheets. Linking these cells together creates a photovoltaic array, which produces levels of electrical energy high enough to be distributed to the power grid.