How to select potential contractors for installation and/or maintenance of solar water heater
When screening potential contractors for installation and/or maintenance, ask the following questions:
* Does your company have experience installing and maintaining solar water heating systems?
Choose a company that has experience installing the type of system you want and servicing the applications you select.
* How many years of experience does your company have with solar heating installation and maintenance?
The more experience the better. Request a list of past customers who can provide references.
* Is your company licensed or certified?
Having a valid plumber’s and/or solar contractor’s license is required in some states. Contact your city and county for more information. Confirm licensing with your state’s contractor licensing board. The licensing board can also tell you about any complaints against state-licensed contractors.
Source: EERE, U.S. Department of Energy
In: Active Solar Heating · Tagged with: solar water heater
Installing and Maintaining a Solar Water Heating System
The proper installation of solar water heaters depends on many factors. These factors include solar resource, climate, local building code requirements, and safety issues; therefore, it’s best to have a qualified, solar thermal systems contractor install your system.
After installation, properly maintaining your system will keep it running smoothly. Passive systems don’t require much maintenance. For active systems, discuss the maintenance requirements with your system provider, and consult the system’s owner’s manual. Plumbing and other conventional water heating components require the same maintenance as conventional systems. Glazing may need to be cleaned in dry climates where rainwater doesn’t provide a natural rinse.
Regular maintenance on simple systems can be as infrequent as every 3–5 years, preferably by a solar contractor. Systems with electrical components usually require a replacement part after or two after 10 years.
Source: EERE, U.S. Department of Energy
In: Active Solar Heating · Tagged with: solar water heater
How to Select a Solar Water Heater
Before you purchase and install a solar water heating system, you want to do the following:
* Consider the economics of a solar water heating system
* Evaluate your site’s solar resource
* Determine the correct system size
* Determine the system’s energy efficiency
* Estimate and compare system costs
* Investigate local codes, covenants, and regulations.
Source: EERE, U.S. Department of Energy
In: Active Solar Heating · Tagged with: solar water heater
Two types of active solar water heating systems
* Direct circulation systems
Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.
* Indirect circulation systems
Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.
Illustration of an active, closed loop solar water heater. A large, flat panel called a flat plate collector is connected to a tank called a solar storage/backup water heater by two pipes. One of these pipes is runs through a cylindrical pump into the bottom of the tank, where it becomes a coil called a double-wall heat exchanger. This coil runs up through the tank and out again to the flat plate collector. Antifreeze fluid runs only through this collector loop. Two pipes run out the top of the water heater tank; one is a cold water supply into the tank, and the other sends hot water to the house.
Passive solar water heating systems are typically less expensive than active systems, but they’re usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:
* Integral collector-storage passive systems
These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.
* Thermosyphon systems
Water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems.
Illustration of a passive, batch solar water heater. Cold water enters a pipe and can either enter a solar storage/backup water heater tank or the batch collector, depending on which bypass valve is opened. If the valve to the batch collector is open, a vertical pipe (which also has a spigot drain valve for cold climates) carries the water up into the batch collector. The batch collector is a large box holding a tank and covered with a glaze that faces the sun. Water is heated in this tank, and another pipe takes the heated water from the batch collector into the solar storage/backup water heater, where it is then carried to the house.
Solar water heating systems almost always require a backup system for cloudy days and times of increased demand. Conventional storage water heaters usually provide backup and may already be part of the solar system package. A backup system may also be part of the solar collector, such as rooftop tanks with thermosyphon systems. Since an integral-collector storage system already stores hot water in addition to collecting solar heat, it may be packaged with a demand (tankless or instantaneous) water heater for backup.
Source: EERE, U.S. Department of Energy
In: Active Solar Heating · Tagged with: solar water heater
Solar water heaters – also called solar domestic hot water systems
Solar water heaters – also called solar domestic hot water systems – can be a cost-effective way to generate hot water for your home. They can be used in any climate, and the fuel they use – sunshine – is free.
How They Work
Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don’t.
Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.
Three types of solar collectors are used for residential applications:
* Flat-plate collector
Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors—typically used for solar pool heating—have a dark absorber plate, made of metal or polymer, without a cover or enclosure.
* Integral collector-storage systems
Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
* Evacuated-tube solar collectors
They feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications.
Source: EERE, U.S. Department of Energy
In: Active Solar Heating · Tagged with: solar water heater
Sizing a Solar Water Heating System
Sizing your solar water heating system basically involves determining the total collector area and the storage volume you’ll need to meet 90%–100% of your household’s hot water needs during the summer. Solar system contractors use worksheets and computer programs to help determine system requirements and collector sizing.
Collector Area
Contractors usually follow a guideline of around 20 square feet (2 square meters) of collector area for each of the first two family members. For every additional person, add 8 square feet (0.7 square meters) if you live in the U.S. Sun Belt area or 12–14 square feet if you live in the northern United States.
Storage Volume
A small (50- to 60-gallon) storage tank is usually sufficient for one to two three people. A medium (80-gallon) storage tank works well for three to four people. A large tank is appropriate for four to six people.
For active systems, the size of the solar storage tank increases with the size of the collector—typically 1.5 gallons per square foot of collector. This helps prevent the system from overheating when the demand for hot water is low. In very warm, sunny climates, some experts suggest that the ratio should be increased to as much as 2 gallons of storage to 1 square foot of collector area.
Source: EERE, U.S. Department of Energy
In: Active Solar Heating, Solar Electricity · Tagged with: solar water heater
Evaluating Your Site’s Solar Resource for Solar Water Heating
Before you buy and install a solar water heating system, you need to first consider your site’s solar resource. The efficiency and design of a solar water heating system depends on how much of the sun’s energy reaches your building site.
Solar water heating systems use both direct and diffuse solar radiation. Even if you don’t live in a climate that’s warm and sunny most of the time—like the southwestern United States—your site still might have an adequate solar resource. If your building site has unshaded areas and generally faces south, it’s a good candidate for a solar water heating system.
Your local solar system supplier or installer can perform a solar site analysis.
Source: EERE, U.S. Department of Energy
In: Active Solar Heating · Tagged with: solar water heater
Diffuse and Direct Solar Radiation
As sunlight passes through the atmosphere, some of it is absorbed, scattered, and reflected by the following:
* Air molecules
* Water vapor
* Clouds
* Dust
* Pollutants
* Forest fires
* Volcanoes.
This is called diffuse solar radiation. The solar radiation that reaches the Earth’s surface without being diffused is called direct beam solar radiation. The sum of the diffuse and direct solar radiation is called global solar radiation. Atmospheric conditions can reduce direct beam radiation by 10% on clear, dry days and by 100% during thick, cloudy days.
Source: EERE, U.S. Department of Energy
In: Solar Electricity · Tagged with: solar radiation
Solar Radiation Basics
Solar radiation is a general term for the electromagnetic radiation emitted by the sun. We can capture and convert solar radiation into useful forms of energy, such as heat and electricity, using a variety of technologies. The technical feasibility and economical operation of these technologies at a specific location depends on the available solar radiation or solar resource.
Basic Principles
Every location on Earth receives sunlight at least part of the year. The amount of solar radiation that reaches any one “spot” on the Earth’s surface varies according to these factors:
* Geographic location
* Time of day
* Season
* Local landscape
* Local weather.
Because the Earth is round, the sun strikes the surface at different angles ranging from 0º (just above the horizon) to 90º (directly overhead). When the sun’s rays are vertical, the Earth’s surface gets all the energy possible. The more slanted the sun’s rays are, the longer they travel through the atmosphere, becoming more scattered and diffuse. Because the Earth is round, the frigid polar regions never get a high sun, and because of the tilted axis of rotation, these areas receive no sun at all during part of the year.
The Earth revolves around the sun in an elliptical orbit and is closer to the sun during part of the year. When the sun is nearer the Earth, the Earth’s surface receives a little more solar energy. The Earth is nearer the sun when it’s summer in the southern hemisphere and winter in the northern hemisphere. However the presence of vast oceans moderates the hotter summers and colder winters one would expect to see in the southern hemisphere as a result of this difference.
The 23.5º tilt in the Earth’s axis of rotation is a more significant factor in determining the amount of sunlight striking the Earth at a particular location. Tilting results in longer days in the northern hemisphere from the spring (vernal) equinox to the fall (autumnal) equinox and longer days in the southern hemisphere during the other six months. Days and nights are both exactly 12 hours long on the equinoxes, which occur each year on or around March 23 and September 22.
Countries like the United States, which lie in the middle latitudes, receive more solar energy in the summer not only because days are longer, but also because the sun is nearly overhead. The sun’s rays are far more slanted during the shorter days of the winter months. Cities like Denver, Colorado, (near 40º latitude) receive nearly three times more solar energy in June than they do in December.
The rotation of the Earth is responsible for hourly variations in sunlight. In the early morning and late afternoon, the sun is low in the sky. Its rays travel further through the atmosphere than at noon when the sun is at its highest point. On a clear day, the greatest amount of solar energy reaches a solar collector around solar noon.
Source: EERE, U.S. Department of Energy
In: Solar Electricity · Tagged with: solar radiation
How to Evaluate Your Site’s Solar Resource for Solar Electricity
The solar resource across the U.S. is ample for solar electric systems—also known as photovoltaic (PV) systems—because they can use both direct and scattered sunlight. However, the amount of electricity generated at a particular site depends on how much of the sun’s energy reaches it. Thus, PV systems function most efficiently in the southwestern United States, which receives the greatest amount of solar energy.
Before you buy a PV system, you’ll want to be sure your site has enough solar energy to meet your electricity needs efficiently and economically. Your local system supplier can perform a solar site analysis for you or show you how to do so on your own.
When evaluating your site, you’ll also need to consider both the geographic orientation and the tilt of your solar panels—PV modules—as both can affect your system’s performance.
Source: EERE, U.S. Department of Energy
In: Solar Electricity · Tagged with: Solar Electricity