Solar hot water systems collect the sun's radiant energy and use the energy to heat a home or building's water. Solar hot water is sometimes referred to as solar thermal.

One of the most cost-effective renewable technologies, the use of a solar hot water system on a home or office building can reduce or eliminate the building's need to use electricity or fossil fuels for hot water production.

Most solar hot water systems have two or three main parts: a solar collector and a storage tank, and when needed, a heat exchanger. There are two types of commonly used collectors; flat-plate collectors and evacuated tube collectors. The most frequently used collector in solar hot water systems is the flat-plate collector.

Solar hot water systems can be either active or passive:

• Active systems use electric pumps to circulate sun-heated liquid, such as glycol, through the collectors and the plumbing that leads to the building's potable water. There are two types of active systems.

• Direct circulation systems move potable water through the collector and into the domestic water system. This method is not recommended if you live in an area where temperatures get down to freezing or below, or where your water is hard or acidic. These type systems may or may not qualify for tax credits or rebates in your state. Check federal and your state requirements to see if direct circulation systems qualify.

• Indirect circulation systems move a heated fluid from the collectors to a heat exchanger that transfers the heat to the potable water. The most common indirect systems are:

• Antifreeze: In this application a non-toxic, freeze resistant fluid like a glycol-water mix is used to pump through the collectors and heat exchanger.

• Drainback: A drainback system, which usually uses water, allows the water to completely drain out of collectors and piping. Draining the water reduces or eliminates the possibilty of the water freezing, expanding and possibly causing the collectors and pipes to burst. These systems have to be carefully installed so that piping always slopes downward.

• Passive systems rely on gravity and the fact that water tends to naturally circulate when heated. This does not require electricity or electrical components. There are two types of passive systems:

• Integral collector storage systems that consist of one or more storage tanks in an insulated box that are placed glaze side up facing the sun. This type system is good for areas that rarely get below freezing. They work well in households that use most of the hot water during the day and in the evening. This doesn't work well for households that require lots of hot water in the early mornings, because the water isn't being heated when there isn't any sun.

• Thermosyphon systems rely on the natural convection of warm water. The warm water rises to circulate water through the collectors to a tank above the collectors. As water heats up, it becomes lighter and rises into the tank above. Cooler water then flows down the pipes to the bottom of the collector which enhances circulation of the water. Some thermosyphon systems storage tanks can be placed in a home's attic. There are also indirect thermosyphon systems, for freeze-prone climates, that use glycol fluid in the collector loop.

Uses for Solar hot water / Solar heating

• Reduce or eliminate the use of electricity or fossil fuels to heat hot water in your home or office

• Heat swimming pool water

• Heat water for an outdoor shower

• Hot water for a cabin or structure that does not have an electricity connection.

• Hot water for camping or RVing

• Hot water for radiant heating.

SOLAR PHOTOVOLTAIC (PV)

The definition of "photovoltaic": of, relating to, or utilizing the generation of a voltage when radiant energy falls on the boundary between dissimilar substances (as two different semiconductors). Source - Merriam Webster Dictionary

Simpler explanation...The word 'photo' is from the Greek word "phos" meaning 'light'. The word 'voltaic' means of, relating to, or producing direct electric current by chemical action (as in a battery). Therefore photovoltaic, also known as PV, means using light to produce electricity.

An easy way to remember what 'photovoltaic' is, is to relate it to another process that uses light to produce energy, photosynthesis.

Most people learned in elementary or middle school about photosynthesis, when plants absorb and process (synthesis) the sun's light (photo) into energy for the plant's chlorophyll-containing tissues.

Photovoltaic is when materials, like silicon, absorb and process the sun's light (photo) into energy, in this case electrical voltage (voltaic), otherwise known as electricity.

Solar photovoltaic or PV uses either wafers of sliced silicon (mono- or poly-crystalline) or a combination of silicon and other materials that are coated (amorphous) to capture energy. These materials are usually placed in a flat support structure to make a 'PV panel'. A PV panel can be used by itself or wired together with more PV panels in what is called an 'array' to produce more electricity.

SOLAR THERMAL

The term "solar thermal" is used when talking about the collection of the sun's radiant energy to produce heat. Solar thermal is most often used in conjunction with the terms "solar hote water" and "concentrated solar power".

• Solar Hot Water: Collectors filled with fluid use the sun's radiant energy to heat up the fluid in the collectors. This heat is then used to warm or heat a building's water supply, thus reducing or eliminating the need to use electricity or fossil fuels for hot water production. Solar hot water systems are used on homes, office buildings, and cabins.

• Concentrated solar power (CSP) - This is mostly for large-scale applications. It focuses on three main technologies: trough systems, dish/engine systems, and power towers. These technologies are used in CSP plants that use different kinds of mirror configurations to convert the sun's energy into high-temperature heat. In turn, the heat energy is then used to generate electricity in a steam generator.

PASSIVE SOLAR: HEATING AND COOLING

Passive solar is a design concept in which a home or building is designed and built to take advantage of nature's heat (passive heating) and cold (passive cooling). In passive heating, the sun's heat or the earth's heat (geothermal), is used to warm the interior of a building, all without the help of mechanical means. Passive cooling is the opposite, blocking the sun's heat, and using natural ventilation and air flow to keep the interior cool.

Passive solar design takes into consideration that in the winter you want as much of the sun's heat and light to stream into your living space for warmth, and in the summer you want very little or none of the sun's heat and direct light into your living space to keep your rooms cool.

Both passive heating and passive cooling use laws of nature. They incorporate the positioning of the sun at certain times of the year, the heating and cooling absorption properties of building materials, and natural air movement. Other factors that are considered in passive solar design: the positioning and size of walls and windows; open floor plans for air flow, ventilation, and light; and exterior shadings and overhangs. Solar passive heating and cooling can also be used in conjunction with geotheramal heating and cooling.

Passive solar designs can also utilize daylighting. Daylighting is the principle or practice of using natural daylight to light interior spaces during the day instead of lamps and fixtures that require electricity.