A solar water heating system is a good start for those looking to become energy independent and/or environmentally friendly. It’s one of the cheapest alternative energy systems you can install, and in most cases it’s clearly a long term money saver (check out this article for more detail on the cost of installing a solar water heater). It really is a no brainier, so let’s get started and learn what they’re all about.
Solar water heating (SWH) systems use solar energy to heat the water a household uses. Some cheaper systems can cover 50-70% of the water heating needs, while some of the more efficient and expensive models can cover over 90%. Considering that around 25% of the average household’s energy consumption each year is on water heating, this can lead to large savings on your energy bill.
TYPES OF SOLAR COLLECTORS
There are various forms of solar collectors that can be used in a SWH system.
Flat Plate Collectors: Metal boxes with a clear glass or plastic top, and a dark-coloured, sunlight-absorbing bottom which heats a series of pipes containing the heat-transfer fluid. This model is simpler and cheaper.
Evacuated Tube Collectors: A series of tubes within tubes. The outer tube absorbs and locks in heat, while the inner tube contains the heat transfer fluid. This model is more efficient, especially in colder climates, but is more expensive.
Batch Collectors: A water tank that serves as water storage as well as a solar collector, located within an insulated box to maximize heat absorption.
TYPES OF SOLAR POWER SYSTEMS: ACTIVE vs PASSIVE
There are also two types of SWH systems available: Active systems and passive systems.
Active (or pumped) systems use a pump to move water through the heating cycle, requiring a second power source. They allow much more flexibility in design, allowing the water tank to be located inside and hidden from view. They also may be a necessity in climates that experience freezing temperatures.
An active system stores the water tank inside of the house, with a tube running through it containing a non-freezing liquid (usually propylene glycol). The non-freezing liquid is pumped out to the heating panels, where it is warmed. It flows back to the water rank, warming the water, which can then be used for washing and bathing.
Active systems are more expensive than passive, but are more efficient, more reliable, and can be used in climates that experience freezing.
Passive (or compact) systems use no pumps or secondary electrical sources. They use natural convection currents to move warm water to the water tank and cold water to the collector to be heated. They are generally cheaper than active models, and due to their simpler nature last longer, but are less efficient, less reliable and sometimes require setting up a water tank on your roof. They are better suited for warmer climates, where freezing isn’t a concern.
There are two types of passive systems:
Integral Collector-Storage Passive Systems (ICS): In this model, the batch collector is used, making it simpler and cheaper than other model. It works best in warmer climates and households with daytime/early evening demand for hot water. It requires the water tank to be stored on the roof, though, so the roof must be able to support the weight (400-700lb) of the water tank.
Convection Heat Storage Systems: In this model the tank and collectors are separated, and natural convection currents are used to allow heated water to flow into the water tank, and cold water to flow to the collector to be heated. As warm water flows up, the water tank must be located above the collector. This model is more expensive than ICS’s, but is more efficient and reliable.
At times when there isn’t enough solar power (at night, or overcast days), your traditional water heater will switch on the heat the water.
After installation, maintenance is a must. Consider having an active system inspected every couple years, a passive system ever 3-5 years.
Solar water heating is becoming more popular worldwide. China is the largest user overall, with 3/4 of the world’s units. Israel is the highest per capita user, with 85% of households having a solar thermal heating unit, and was the first country to require the installation of solar water heating systems. Spain was the second.
Click here if you’d like to read our article DIY: How To Build A Solar Water Heater For Your Home.
Good luck and stay prepared!