Solar Power for Houses: Your Residential Solar Power System

Solar pool heaters are the most common use of solar thermal technology in North America.   This is because they are extremely cost effective: a solar pool heater will typically pay for itself in 2 to 3 years (Can. Solar Industries). Even without considering the savings in greenhouse gas emissions, solar pool heaters make a lot of sense.   The total price of solar heating a pool is usually $3,000-$4,000 US including installation, but can range from $2,500 to $7,000 US (Costhelper.com).

Solar hot water panels used in pools are flat plate collectors. They are usually made of rubber or black plastic and are a very simple use of solar thermal technology compared to solar water heating systems for drinking water.

The solar hot water panels are usually about 50% of the pool’s service area.  If a pool is indoors or is not in direct sunlight, a larger area of solar heating panels must be used to reach the same temperature.   A pool cover should be used at night to reduce heat loss.  If you don’t use a pool cover, you’ll need to install twice the area of solar hot water panel.

While solar pool heaters make excellent sense for swimming pools, they don’t work as well for hot tubs.  The water temperature can be raised high enough using metal collectors used for heating domestic water, but if the jets in the hot tub are used, the water will swiftly cool down again.

Sources:

Canadian solar industries association.  Solar pool heating overview.  Retrieved June 20, 2009

Costhelper.com

Residential solar pool heating systems: a buyer’s guide 2001 retrieved June 20, 2009

In climates where there are freezing temperatures, the water in solar hot water panels is in danger of freezing.  No hot water is produced when this happens, and it’s possible that the panels or piping could be damaged when the water expands as it freezes.   However, it’s perfectly possible to get solar  hot water in a cold climate – even during the winter.

The most common way to prevent the solar hot water panels freezing is to use glycol-based solutions in the panels. This requires a closed loop system where the heat is transferred from the glycol solution into the water you use in your house via a heat exchanger.   These systems are more expensive than simpler systems, but they are much more resistant to freezing and can continue to produce heat through the middle of a cold winter.   You will probably want a tankless hot water heater as backup because they may not produce enough for your needs when there are long spells of cloudy weather, but they will still produce hot water.  Both active and passive heaters can be outfitted with glycol so long as there’s a closed loop system.

Four-Season Solar Thermal Systems

Glycol-based solutions are typically used in active solar thermal systems, but they are also used in some Thermosyphon systems.  In order to use glycol in a Thermosyphon system, it must be a closed-loop system in which the solution in the solar thermal panels does not mix with your household water supply.  The glycol acts as antifreeze, preventing the pipes from freezing.  These solutions are typically 50/50 glycol and water.  Active glycol systems tend to be expensive, but they are considered the best choice for very cold climates.

There is one type of water-based system that can be used in frost-prone areas.  This is the drainback system, which does not easily freeze so long as the piping is sufficiently inclined so that drainback can occur quickly.  However, I suspect that this system is less tolerant of extremely cold temperatures for long periods of time than a system that uses a glycol fluid.

Three Season Solar Hot Water Systems

It is also possible to use a very simple system such as the batch heater during the summer and drain it during the winter.  You will get no hot water from it in the winter, but it should still be usable the next summer.

As you can see, there are several choices of thermal hot water systems for homes in a cold climate. Whether active or thermosyphon glycol, drainback or summer-only batch, there is probably something available that will fit your needs and pocketbook.

Sources:

US Department of Energy. Energy Efficiency and Renewable Energy. Energy Savers: Solar Water Heaters. Retrieved June 19 2009

Homepower.com. Retrieved June 19 2009

Build it Solar: solar water heating. Retrieved June 19, 2009

To create hot water using solar thermal energy, the sun’s heat is used to heat water directly without converting it into electricity.   The most common use of solar hot water in North America is heating swimming pools, but solar thermal’s potential goes far beyond this.

Solar thermal is commonly used for water heating and for heating houses.  The cost of heating by a solar thermal system is usually lower than the cost of an equivalent amount of electricity supplied by photovoltaics because solar thermal is on average 3x more efficient at converting the sun’s heat into energy, although the savings depend on the type of solar thermal technology used.  Solar thermal systems are also low maintenance.

Types of Solar Water Heater

1) Collector (solar hot water panel) Types

There are three main collector types: flat plate, batch, and evacuated tube.  Evacuated tube technology is generally more expensive than flat plate and batch because it is mechanically more complicated.

2) System Type: Passive or Active

Active systems include a pump; passive systems do not.  Passive systems are less expensive and may be more reliable but are less efficient (Energy Savers: Solar Water Heaters).

Passive Solar Water Heating

Batch Heater

A batch heater is the simplest type of solar water heater available.  They are also sometimes known as breadbox heaters, since the tank of water on the roof is often about the size of a breadbox.  If you wish to build your own solar hot water system, a batch heater is probably your best bet.   Being water-based, they are not suitable for winter use in climates where freezing weather can be expected.  They also have the disadvantage that hot water cools overnight and usually isn’t hot early in the morning.   The Florida Solar Energy Center has a free set of plans and instructions for building one, which can be found here.  They give the materials cost as being US $70.00.

Thermosyphon

This design tends to be more expensive than batch heaters.  However, because there is an insulated storage tank hot water is available at all times of the day or night, unlike the batch filter.  This design is actually the world’s most popular solar water heater (Homepower.com).  It may be closed loop or open loop.  If it is a closed loop system, glycol can be used.  This modified design is suitable for using in climates with freezing temperatures.

Active Solar Water Heating

Drainback Heater

This type of heater is more complex, being a closed loop system where the water in the collector does not mix with the house’s water.  A heat exchanger is used to move the heat from the liquid in the collector to the house’s water.  Like most active systems, it is more expensive than a batch heater.  On the other hand, this system can be used in the winter in climates with freezing temperatures if the pipes are adequately sloped to ensure drainback occurs quickly.

Glycol-based Solar Thermal Systems

Systems containing glycol are primarily used in areas which have freezing temperatures during winter.  This is because they continue to work and provide hot water during such weather, unlike most systems that use water.  Water-based systems may also suffer damage when the collectors freeze that will then need to be repaired.  Glycol-based systems are more expensive than systems that use water, but in a cold climate this disadvantage is outweighed by their resistance to freezing (Homepower.com).

Overall, solar thermal hot water is a technology that is economical to install and run by renewable energy standards and can be used almost anywhere.  It has excellent potential for home use and should be perhaps the first alternative energy technology considered by a homeowner wanting to reduce dependence on the electricity grid.

Sources:

Build Your Own Solar Batch Water Heater. Florida Solar Energy Center Retrieved June 12, 2009.

http://www.builditsolar.com/Projects/WaterHeating/FSECFS36Batch11349.pdf

US Department of Energy. Energy Efficiency and Renewable Energy. Energy Savers:Solar Water Heaters. Retrieved June 12 2009

http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12850

Homepower.com

http://www.homepower.com/basics/hotwater/