Solar water heating

By Flavian Rudolphe, Solar Dynamics

Energy is a major driving force of the global economy. It is a critical ingredient to development, providing fuel for electricity, transportation and communication. Energy therefore affects both the quality of life of a people and the level of productivity of a country. Any changes in the cost of energy will have ripple effects in most other key sectors in the economy.

Research shows that approximately 80% of the global consumption of primary energy is in the form of fossil fuels (oil, natural gas and coal). The availability of these resources is limited both in terms of geography and quantity. Countries with reserves of fossil fuels have an inherent competitive edge which allows them to attract more industries. However, the increased use of fossil fuels over the past century has resulted in a number of negative impacts on our environment. Emissions of sulphur dioxide and nitrogen oxide from fossil fuel combustion, results in air pollution and other environmental problems including acid deposition that affect water sources, as well as agriculture and forests. While such problems may be confined largely to countries in Europe and North America, the potential threat of Climate Change and global warming is expected to have world wide ramifications.

Unfortunately for us, it is also expected that small-islands like ours in the Caribbean would be particularly vulnerable to the anticipated effects of the resultant climate change even if our contribution to the problem is almost insignificant.

We are seeing a growing thrust towards the use of renewable energies, and these include wind, geothermal, water and of course, solar. Here in the Caribbean we are limited as to what extent we can develop these forms of energy. The French Department of Guadeloupe is one of the few islands with a significant contribution from renewable energy development. Dominica has managed to make hydro – electricity an integral part of their energy production over years, but generally renewable energy resources are grossly underdeveloped in our Caribbean Region.

The sun is the primary source for most forms of energy found on Earth. Solar energy is clean, abundant, widespread, renewable and free. Various technologies capture this solar energy, concentrate it, store it, and convert it into other useful forms of energy.

Now you may ask yourself how does solar heating work, and I am sure someone, somewhere, has a very detailed and complicated explanation. This is how it works in simplest terms;

The shallow water of a lake is usually warmer than the deep water. This is because the sunlight can heat the lake bottom in the shallow areas, which in turn, heats the water. It's nature's way of solar water heating. The sun can be used in basically the same way to heat water used in buildings and swimming pools.

Harnessing energy from the sun to heat water is nothing new. Solar water heaters have been commercially available since the late 1800s. What's remarkable is how prevalent solar water heaters have become today, in both domestic and commercial applications. Why? That is because solar water heaters are an environmentally sound way to reduce energy bills, and remain one of the most efficient and least expensive of the renewable energy technologies.

Solar water heaters save energy and use a renewable resource. By replacing electric energy or fossil fuel use for water heating, environmental carbon emissions associated with water heating are reduced or eliminated. A solar water heating system may result in immediate positive cash flow if the monthly cost of financing the system is less than the net savings. This is particularly applicable to commercial installations e.g. Hotels & Resorts.

 Each system has two separate components:

1. An insulated storage tank to keep the water hot until ready for use.

2. The collector which converts the sun's energy to heat.

There are two types of Installation in the industry, and both are practiced in our region.

The Thermosyphon System

Cold water enters the bottom of the storage tank and passes from the tank into the collector.  The highly efficient collector absorbs heat from the sun.  The radiation is then transferred to the tubes and the water inside of them.  As the water absorbs solar radiation via conduction from the fin tubes, it expands and, being less dense than the cool water, it rises from the collector to the storage tank by convection.  This thermosyphon action continually circulates the water in the tank until all the water in the tank is heated.

The thermosyphon system is a passive one and so its storage tank is elevated above the collector. 

Photovoltaic Powered D. C. Pump (PV/DC) system – Forced Circulation System

The PV/DC system is prescribed as an alternative when the weight of the tank or aesthetic consideration favors the placing of the tank out of sight. With this installation the storage tank is placed on the ground or in a concealed location and water is pumped up to the collector panel via a direct current (D. C.) water pump powered by a small photovoltaic (P. V.) panel. The PV panel is placed in the same plane with the collectors so that as long as there is sunlight for heating the water, the photovoltaic panel will power the pump to circulate the water between the collectors on the roof and the storage tank.

Throughout our Islands, we have seen the landscape of our roof tops change dramatically as home owners and Hoteliers make the “switch to solar”. Islands like Barbados, St. Lucia, Grenada and to a lesser extent Dominica now see provisions for Solar Water Heating as an integral part of the planning stage of residential and Hotel Construction.

Needless to say the recent increases in the price of fuel and the resultant increases in consumer’s electric bills has been a catalyst for growth in sales in the industry.

While Barbados has been a pioneer in the manufacturing of quality Solar Water Heaters in our region (Solar Dynamics led the way in June of 1974) thereafter other companies have come along even in other islands, thus keeping the regional markets competitive.

Our regional manufacturers have to a large extent done well to keep abreast of changes both in technology and consumer needs / requirements. The emphasis remains on accurate sizing, in both gallons of water in storage capacity and adequate square footage in collector area to maintain guaranteed temperatures.

Given the life span of the Solar Unit and the savings over the years, the product remains reasonably priced. In addition governments like St. Lucia who are environmentally conscious, have made accommodations for the purchase price to be claimed on employees’ Income Tax returns.