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Voltaic solar energy is obtained by the incidence of solar radiation on special plates, generating electricity. The raw material used and the manufacturing process give the plates a high cost/benefit ratio. As a result, voltaic solar energy is mostly used all over the world, when a governmental entity provides a subsidy. In Brazil, such subsidies are also given to thermal solar energy. As thermal solar energy, which entails converting solar energy into heat, presents a good cost/benefit ratio, it is the most used one and the one we shall write about:


By choosing to heat water in many types of building by solar energy, replacing conventional systems, we can achieve, among others, the following goals:

a) Electricity Saving:

By replacing the conventional systems within each unit of a building by a central solar water heating system, knowing that it will work, on cloudy days and/or on days of excessive hot water consumption, with the complement of a small auxiliary electric system (its use in the period of peak consumption, so critical for the concessionaries, is minimal), we will have an average consumption, by unit, 12% bellow that of the conventional systems annually. Hence, the total annual consumption of electric energy in residential buildings, hotels, hospitals, clubs and houses, can be reduced up to 50% by using solar energy.

b) Reduction of Installed Power:

With the introduction of solar energy in lieu of conventional systems, some buildings may have their installed power reduced to such an extent that one could dispense with one or even all the electric sub-stations usually required. Incidentally, it is a common practice in Brazil, faced with high electric energy bills, to disconnect one or more boilers to replaces it (them) with one or more electric showers, which increases the installed power at least twofold, jeopardizing the security of the fitting.

c) Reduction of Costs:

By using solar energy, to replace conventional systems that use electric energy, we reduce the number of circuit breakers, copper wires, cables, PVC electricity ducts, valve keepers and safety valves, copper pipes with connectors, electric heaters of boiler type and/or electric showers and/or transfer heater, manpower and administrative work linked to purchase and supervision, due to the reduction of countless items. In addition, space is gained in wall cabinets, ceilings of corridors, etc., when one eliminates heaters of boiler type. With the replacement of central gas systems, we dispense with boilers and tubes of significantly larger diameters. With the replacement of individual gas systems, we reduce the tubes and the boilers themselves. The solar water central heating system normally costs less. By eliminating one or more sub-stations, the cost of a solar system decreases significantly. Even if the cost of installing a solar system be higher than the cost of installing one of the above mentioned systems, the lower maintenance and significant reduction of electric energy or gas bill offer almost immediate returns on the investment.

d) Increase in Comfort and Safety With the Solar Heating System:

We can have hot water in all showers, baths, lavatories, bidets and kitchen sinks, at any time, day or night. Since such system is placed on the roof of the buildings, its low maintenance is confined to the cleansing of the collector glasses and spares the users the trouble and risk of damage within their appartments. The lower circulation of gas in the building increases safety to the user.


a) Builders

They can increase their margin of profit by the reduction of cost, offer more comfort to their clients and avoid the inconvenience caused by the maintenance of conventional systems.

b) Hoteliers and Hospital Owners

They can offer more comfort to their customers/patients and with substantial reduction of costs of electricity or gas.

c) Architects

Responsible for the success of a building (its beauty, function and comfort), they can offer their clients projects that use solar water heating systems (a modern inexpensive solution for water heating and air-conditioning) without altering their plans.

d) Users

By installing the solar water heating system, they would contribute to the preservation of the environment; the almost complete replacement of conventional systems by solar ones could avoid even the construction of new hydroelectric power plants. It would also contribute to their living standards, by having hot water in abundance at any time, day or night, and reducing the cost of the building and of the maintenance of their residences.


In order to install such a system, the decision should be taken even before the conception of the architectural project and the following stages be observed:

a) Techno economic feasibility study, taking into account the climate of the place where the building will be situated, its locality, its neighborhood and the maximum area available on the roof.

b) The integration of the various projects: the architect, the electric and hydraulic planners and, very often, the engineer in charge of the structural calculation must get together with the solar planner in order to proceed with the integration of their individual projects.

c) Calculation and Elaboration of the Project of a Solar Water Heating System: the calculation must take into account parameters such as the available area intended for the collection of energy and hot water storage, the local climate, shadows at each period of the day and each period of the year, the demand of hot water by the users, the building site.Sometimes, when such decisions have not been taken beforehand, as it should have been, the exact site of the construction on the building plot is a parameter to be taken into account by the calculation engineer. The result of the calculation will determine the dimensions and the ideal material of the collectors, their quantity, their position on the roof, their inclination, the volume of the tanks, the diameter of the tubes, the degree of the reduction obtainable in the installed power, the details of the electric auxiliary system and the necessity, or not, of calculating the re-circulation system.

d) The installation of the Solar System: in order that the central solar water heating system may work adequately, it is essential that the electric and the hydraulic projects, adapted according to the new situation, be carried out correctly, that the dimensions, coatings and protections of the collectors and the tanks comply with specifications of the project, and that its installation adhere rigorously to the distances, inclinations and positions as specified in the project.
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