It is one of the most cost-effect solar technologies on the market and can provide year round heating of your water.  There are many state and federal incentives to subsidize the cost of your solar hot water system.

The basics

The principles are simple.  The sun shines on a collector that heats up.  This heat is transferred to a liquid that is is then stored in tanks for use in your house.

Open or Closed?

All solar hot-water heaters fall into one of two categories: open loop or closed loop. The difference is simple. Open-loop systems heat the water that you actually use, while closed-loop systems heat an antifreeze-water solution (water and glycol) that transfers its heat to the domestic hot water.

If you live in a region where the temperature stays above freezing, you can get by with the simpler open-loop type. If you live in an area that experiences freezing temperatures for much of the year, you’ll need to go with a closed-loop system.

The most basic open-loop type is called a batch collector, or integral collector storage system. Large-diameter pipes or one or more tanks are mounted in an insulated box with double or triple glazing. Batch collectors are plumbed into the household water system and feed hot water to the domestic water heater, or bypass it when there’s ample sunshine. The disadvantage of a batch collector is that it is also a storage tank. That means that if you don’t use the hot water quickly, you’ll lose the heat it contains.

A more efficient open-loop system is a flat-plate collector type that transfers water to an insulated storage tank. These insulated and glazed panels contain water in rows of copper tubes mounted in a heat-absorbing black plate. Most systems use an electric circulator, but photovoltaic pumps are available also.

The thermosiphon system shown at right is an open-loop type that uses a collector and a storage tank, but it takes advantage of convection to move heated water through the system. In most cases, the insulated tank is located in the attic. From the attic tank, the water is piped to the household hot-water system.

If you live in an area that experiences occasional freezing, either type of open-loop system can be set up to circulate warm water from the storage tank to the collector when the temperature drops to prevent freezing. However, this is risky since it can wreak havoc with the system’s temperature sensors. Also, it wastes heat and uses electricity; hence, these systems are not a good fit for many areas of the United States.

Closed-loop systems are inherently more complex than open-loop types. In the system shown on the lead page, the heated antifreeze-water solution flows from the collector to a coil in a tank. Domestic water in the tank is heated by the coil. In the drainback system shown at right, just the opposite occurs. In it, heated water flows directly into the tank, transferring its heat to the house’s domestic water in the coil. The system, which uses distilled water or a blend of water and glycol, is designed so that the collector has water in it only when the circulator is running. When the circulator shuts off, water drains into the storage tank. The design is popular in cold regions because it prevents freeze damage to the system.

The Heat Collector

There are several types of heat collectors used in modern solar hot water systems.  Each has advantages and disadvantages.

Flat plate collector

Consists of a thin absorber sheet (usually copper, to which a black or selective coating is applied) backed by a grid or coil of fluid tubing and placed in an insulated casing with a glass cover. Fluid is circulated through the tubing to remove the heat from the absorber and transport it to an insulated water tank, to a heat exchanger or to some other device for using the heated fluid.

As an alternative to metal collectors, some new polymer flat plate collectors are now being produced in Europe. These may be wholly polymer, or they may be metal plates behind which are freeze-tolerant water channels made of silicone rubber instead of metal. Polymers, being flexible and therefore freeze-tolerant, are able to contain plain water instead of antifreeze, so that in some cases they are able to plumb directly into existing water tanks instead of needing the tank to be replaced with one with extra heat exchangers.

Evacuated (or vacuum) tubes panel.

Evacuated tube collectors

Are made of a series of modular tubes, mounted in parallel, whose number can be added to or reduced as hot water delivery needs change. This type of collector consists of rows of parallel transparent glass tubes, each of which contains an absorber tube (in place of the absorber plate to which metal tubes are attached in a flat-plate collector). The tubes are covered with a special light-modulating coating. In an evacuated tube collector, sunlight passing through an outer glass tube heats the absorber tube contained within it. The absorber can either consist of copper (glass-metal) or specially-coated glass tubing (glass-glass).

Two types of tube collectors are distinguished by their heat transfer method: the simplest pumps a heat transfer fluid (water or antifreeze) through a U-shaped copper tube placed in each of the glass collector tubes. The second type uses a sealed heat pipe that contains a liquid that vapourises as it is heated. The vapour rises to a heat-transfer bulb that is positioned outside the collector tube in a pipe through which a second heat transfer liquid (the water or antifreeze) is pumped. For both types, the heated liquid then circulates through a heat exchanger and gives off its heat to water that is stored in a storage tank (which itself may be kept warm partially by sunlight). Evacuated tube collectors heat to higher temperatures, with some models providing considerably more solar yield per square metre than flat panels. However, they are more expensive and fragile than flat panels.

For a given absorber area, evacuated tubes can maintain their efficiency over a wide range of ambient temperatures and heating requirements. However, due to the design the absorber area only occupies about 50% of the collector panel. In most climates and for the majority of domestic hot water services, flat-plate collectors will generally be a more cost-effective solution than evacuated tubes. Unless employed in large arrays, the efficient but costly evacuated tube collectors have only marginal net benefit in winter and give little real advantage in the warmer months. They are most suited to extremely cold ambient temperatures or in situations of consistently low-light. They are also used in industrial applications, where high water temperatures or steam need to be generated.

A wind turbine collects kinetic energy from the wind and converts it to electricity that is compatible with a home’s electrical system.  Typically the turbine is installed on top of a tall tower to clear any obstructions in the area.

Today the most popular type of system is called a grid-intertie system where power from the wind turbine and the electrical utility both power the home.  If the wind speeds are below cut-in speed (7-10 mph) there will be no output from the turbine and all of the needed power is purchased from the utility. As wind speeds increase, turbine output increases and this power used in your home.  Power pulled from the utility is decreased during this period.  When the turbine produces more power than the house needs, the extra electricity is sold to the utility. All of this is done automatically. There are no batteries in a modern residential wind system.

Hydro power drums up images of huge dams such as hoover dam.  However there are many smale scale hydro power systems that can generate energy day and night throughout the year for your home.

If you are fortunate enough to have a small stream, river or creek on your property there are several ways you can generate energy.  As long as the water source doesn’t dry up you can have a very affordable electrical plant.  This is often more affordable than wind power or solar voltaic power.

What do you need?

There are two things you need to generate electricity with hydro. Those are flow and head.  Flow is the amount of water passing through the unit, and head is the height difference between the top of the water run and where your hydro unit is located.  The higher the drop and greater the flow the more electricity you can generate.

 The Units

Pelton Wheel

The most popular type of residential hydrogenerator is a pelton wheel turbine. Pelton wheels work best for high-head, low flow sites. The water that is channeled through a pipe is focussed on a series of cups that spin a wheel. The wheel in turn is connected to a turbine that generates electricity.

Submersible Propeller

The submersible propeller works best for fast running streams. A stream that flows between 6 mph and 9 mph are adequate. They can also operate in as little as 1 foot of water.  A major advantage of a propeller system is the fact that it doesn’t require any modifications to the stream (a dam) to generate electricity.

 Geothermal heat pumps use the natural temperature from the earth in your yard to heat or cool your home. 

Ground temperatures about four to six feet below the Earth’s surface remain relatively moderate and constant all year. That’s because the Earth absorbs 47% of all the heat energy that reaches its surface from the sun. A geothermal system circulates a water-based solution through a buried loop system to take advantage of these constant temperatures.

 Heating Cycle

During the heating cycle the heat pump circulates the fluid through the loop extracting heat from the ground.  The heat pump compresses the extracted heat to a high temperature and delivers it to your home through a normal duct system or radiant heat system.

Cooling Cycle

For cooling, the process is simply reversed. Because the earth is much cooler than the air temperatures on a hot day, the geothermal system removes heat from the home and deposits it into the ground. The fluid is cooled by the ground temperatures and returned to the unit for cooling your home.

Uses

Geothermal sytems can be used for forced air heating and cooling, radiant flooring and hot water systems.

Passive Solar

The first method is called Passive Solar. This method utilizes the sun directly to heat your home. Typically this involves the design and layout of your house and is best used when building a new home. The results can be very dramatic, with many homes achieving 90% of their heating directly from the sun with little to no supplemental heating.

Active Solar

The second method is active solar. Active solar uses more complex systems to harvest the energy from the sun and turn it into electricity or heat. The two main uses for active solar are photovoltaic electrical generation and solar hot water.

Closed Loop

 A closed loop system is the most common type of geothermal heating/cooling system.  In a closed loop system the heat exchanger, a loop of tubing filled with antifreeze is buried underground or under water.

The antifreeze circulates continuously inside the buried pipe, absorbing heat from the earth during the winter for use inside your home or business. In warmer months, the antifreeze takes heat from indoors and transfers it back into the earth.

Horizontal Loop Field

 If your home has adequate space and a sand or clay based soil then a horizontal loop field is the most efficient and affordable option.   In a horizontal loop field trenches are dug leading from the home outward.   I single or multiple tubes are then buried in these trenches.  Trenches should be below the frost line, and 8-10 feet deep is recommended in cooler climates.

There are several options for trenches. 

• Invidividual trenches with a single pipe run in the trench.
• Narrow trenches with multiple pipes run in the trench.
• Wide trenches with multiple pipes run in the trench.

In areas with rocky ground, a horizontal loop field should have sand layered at the bottom of the trench, and a layer of sand put on top of the loop field to protect the piping.

Vertical Loop Field

A vertical loop field is typicall used when there is limited land space.  In a vertical loop field multiple wells are drilled to accomodate the total length of pipe.  For example if 2000 feet of pipe are required two 500 foot wells may be drilled, or four 250 foot wells may be drilled.  Typically cost is the determining factor of the number and depth of the wells.

A length of pipe, hairpinned, is then dropped into the well and the well is backfilled or grouted to ensure good contact with the earth and the pipe.

Drilling a well for a vertical loop is often cheaper than drilling a well for water.  Finding water is not necessary so the driller can simply go for depth.  Additional no casing is needed for the well as the tubing is the casing for the fluids and the hole will simply be backfilled.

Coil Loop Field

A coil loop field is becoming more popular, especially in residential applications where land space is limited.

In a coil loop field a trench is dug, similar to the horizontal loop field.  Instead of a long straight run of piping, a flexible piping is used and it is coiled on top of itself, somewhat like a slinky.  The trench is typically 3 feet wide and should be 8-10 feet deep.   The advantages of this is that a much shorter trench can be dug, often 2/3rds shorter than a standard horizontal system.   The disadvantage of a coil loop field is that since more fluid is concentrated in a smaller area the heat transfer is less efficient. 

As with a horizontal field if the ground is rocky the trench should be layered with sand to protect the piping

Water Loop Field

A water based loop field utilizes water instead of earth as the heat source.  A trench is dug from the home to the water source, typically a pond or a lake.  Tubing is then coiled at the bottom of the water source.  This system can be very economical as very little trenching is needed. 

Water loop fields work well as long as the water source is deep enough to prevent complete freezing of the water.

Open Loop

Instead of using an antifreeze solution sealed inside the buried piping, an open loop system uses water from a surface or underground source - such as a pond, lake or well.

This water is piped through your heat pump and the heat extracted from it.  The water is then returned to the pond, lake or well.  In some cases the water is simply discharged onto your lawn, but this is not recommended.

Well water systems are most often used with an open loop system.  The well water provides both your household water, and the input to the geothermal heat pump.  With a well driven open loop system  you need to ensure your well can support 10-15 gallons per minute water draw.  Often this means using a larger pump and water tank.

A major concern of an open loop system is the water quality.  Because a continuous flow of freshwater is pumped through your heat pump mineral deposits may build up within the system.  Before going with an open loop system you should have your water tested for hardness, iron, acidity and other impurities.

Local regulations should be checked before implementing an open loop system as some areas prohibit such systems.  In general open loop systems are not recommended due to the potential environmental issues such as depletion of the aquifer and release of the water if not reinjected into a well.  Additionally open loop systems can increase the ownership costs by shortening the life of your heat pump.