Solar H20 Heater

Solar hot wate rGas and electric water heaters are one of the single biggest domestic energy users. They can be responsible for up to a third of all energy use, and subsequently, greenhouse gas emissions, in the average Australian home. However, this need not be the case.

A simple way to reduce those bills, and the greenhouse gas emissions that they represent, is to install a solar water heater. Using the suns energy to provide some or all of your hot water requirements can have an enormous effect on reducing your greenhouse gas contribution. Instead of using electricity or gas, solar water heaters use the suns rays to heat water. Like most water heaters, they store the water to be heated in a tank. But instead of heating the water with an electric element or a gas flame, the water flows through a solar collector panel, where the suns rays are used to heat it.

How do they work?The solar collectors are usually a flat metal box with pipes inside. These pipes are attached to a metal sheet which is painted black to help it absorb the sun’s heat. The top of the box is covered with a sheet of glass, and the box is insulated to reduce heat losses.

There are several variations on this type of collector, including an all-plastic collector, and collectors made by several manufacturers filled with a special anti-freeze liquid that transfers heat into the water. When the sun shines on the collector panels, heat is absorbed by the water in the collector panels pipes. As the water heats up, it starts to rise up the pipes, in the same way that hot air rises. When it gets to the top of the collector panel, it flows out of the panel and back into the storage tank.

Colder water from the bottom of the tank then flows down to the bottom of the collector panels. Water continues to cycle through the system, and on sunny days can easily exceed the temperature required for home hot water.

The water storage tank is similar to that of most gas or electric water heaters. The tank is usually made of either stainless steel or enamel-coated mild steel, though some tanks are made of copper or even plastic.

Boosting All solar water heaters come with some sort of backup boosting for periods of low sunshine, such as during cloudy days. Most systems have an electric booster element fitted which can be operated on a cheap night rate tariff.

Other boosting methods are gas or a slow combustion wood stove. The amount of boosting required will depend on the location. Some gas boosted solar water heaters have a special controller to only allow boosting at certain times of the day. This prevents boosting occurring in the morning when large amounts of water are drawn off, allowing the water to be heated by the sun during the day, with boosting only occurring at night.

Another option is to use an instantaneous gas water heater as a booster. These heat water as it passes through them, and can be installed between a solar water heater and the house taps to heat the water to a predetermined level if there has been insufficient sunshine to do so.

It is also possible to use your existing gas or electric hot water system and connect one or more solar collector panels to it. The water heater would need to have a suitable capacity, and be less than five years old to make it worthwhile.

Heat pumps: Heat pumps work in a different way to a conventional solar water heater. Instead of using the sun’s rays to heat the water directly, the heat pump collects the heat using a refrigerant gas, pumped through a coil on the roof, just like that found in refrigerators and air-conditioners.

The heat is then transferred to the water in the storage tank by a heat exchanger in the tank. As they are heat concentrators, heat pumps have the advantage that they work even when the sun is not shining, as they can even extract heat from cold air. They can also be used in situations where sunlight is limited, such as when there is no north-facing roof area.

Which water heater? Which solar water heating system you choose depends on several factors, including the availability of gas for boosting, the design of your house, and your available budget.

Solar water heaters come in several different system configurations. The most common is the lose couple system, with the panels mounted on the roof and the storage tank mounted horizontally directly above them. These are usually mains pressure systems, though some close-coupled systems are gravity feed systems.

Some systems have the tank within the roof space so that only the collector panels can be seen from outside. These systems are nearly always gravity feed systems. It is also possible to have the collector panels mounted on the roof, and the tank located at ground level. Water is pumped around the system by a small electric pump. This type of system is always a mains-pressure system, as a gravity feed system needs the tank to be well above tap level in order to work.

This split-level system has less visual impact, which may be desirable if the water heater needs to be discrete, such as when heritage laws govern home modifications. Determining the correct size for a solar water heater unit is most important.

On average, each person will use around 50 litres of hot water per day. It is advisable to have 1? days reserve capacity. The system should be sized for the dwelling, and not necessarily its occupants-people sell houses and move on, but the hot water system stays.

A three bedroom house can comfortably accommodate four people, so should have a 300 litre system, even though it may be occupied by a retired couple. An undersized system will have a disappointing output and require excessive boosting from non-renewable sources.

Mains pressure solar hot water systems have become very popular over the last thirty years and are strongly promoted by the manufacturers. Mains pressure systems allow the use of flick-mixer taps and give a strong flow in the shower.

They are suitable for use with water supplied by a pressure pump, a tank high up on a hill (provided the pressure is great enough) and, of course, water supplied from the mains. With gravity feed systems, the pressure at the taps is supplied at a constant rate governed by the height of the header tank. Larger diameter water pipes are often required in the house to allow for the reduced water pressure, though this also depends on the position of the water heater and the height of the roof.

The advantages of gravity feed systems include longer tank life due to the greatly reduced pressure and the ability of these systems to be connected directly to the heat exchanger (wet back) of a slow combustion stove, which provides auxiliary heating. Gravity feed systems are also generally less expensive to purchase.

Installation: For the majority of installations, the tanks are fitted on or in the roof, and the panels are fitted on the roof. The roof should face north with a margin of approximately 20? east or west.

If this is not possible then a proportional loss in performance can be expected. At 45? off north the loss is 10 per cent and at 90? the loss is 20 per cent. Some manufacturers provide mounting frames which provide for rooftops that face south, east and west. In some cases adding an extra collector panel can compensate for the poor orientation.

Ideally there should be no shading of the collectors from vegetation or nearby structures between 8am and 4pm. The installation should be done by an experienced installer,and all plumbing connections must be done by a licensed plumber.

The heater is normally installed on top of the existing roof. Installation will generally take around half a day to complete in most cases. Some roofs require strengthening in order to support the extra weight of a solar water heater safely. The installer will know what to look for, and how to do this.

Frost protection: Wherever there is a possibility of a frost, the system should be fitted with a freeze protection system. This is because water expands as it falls below 4?C and turns into ice. If there is no ability to absorb this expansion or prevent it happening, the result will be ruptured pipes in the collectors. Repairing collectors can be difficult and replacement is expensive.

Virtually all solar water heaters available in Australia today include some form of frost protection, often in the form of valves that open to drain the panel of water when the temperature falls below 4?C. Others use a heat exchange system, where anti-freeze fluid circulates through the panels and passes the collected heat to the water in the tank through a heat exchanger.

Cost payback and environmental benefits: A common question about solar hot water is What is the payback period? To make an evaluation, the cost of an equivalent non-solar system must be deducted from the cost of a solar unit. The running costs of both systems must also be evaluated, which will vary depending on the patterns of usage and the geographic location.

From these guesstimations we can get paybacks from 4 to 14 years, the average payback being around 8 to 9 years. Some states, such as Queensland, have rebate schemes to reduce the cost of installing solar water heaters.

The average amount of hot water that can be gained from solar heating for home use ranges from 50 per cent in southern states to more than 90 per cent in northern Australia. However, energy (and therefore money) saved by a properly sized system is roughly the same across Australia. Because the initial temperature of the water to be heated is lower in southern states, the energy supplied from the sun is more valuable in the heating process.

The environmental benefits of solar hot water systems are well known. By replacing fossil fuel energy from burning coal or gas with solar energy, solar hot water systems can reduce the amount of greenhouse gas generated.

As an example, if you were to replace an electric hot water system with a gas-boosted solar unit, you could reduce the amount of greenhouse gases produced by water heating by over 75%. The annual saving in greenhouse gas emissions would be around 2 tonnes, which is equivalent to driving a small car from Sydney to Perth and back again.

However, a solar hot water system will not always be the most environmentally friendly option for water heating, depending upon the location and boosting method used. An electric-boosted solar water heater can actually produce more greenhouse gas emissions than a high-efficiency gas-only water heater in cooler climates where a solar system is more reliant on boosting. This means that replacing a gas water heater with an electric boosted solar water heater can actually have a detrimental effect on the environment. If mains gas is available, a gas boosted solar water heater is the best option.

The exception will be where the electricity used for boosting is generated without fossil fuel, such as in Tasmania, where electricity is produced by hydro generators.