Solar energy in progress and future research trends

Solar radiation devices and collectors

The solar radiation can be used principally as a source of heat, particularly in the forms of domestic hot water consumption, crop dying, power heat engines, power for refrigerators and air conditioners, and ate photovoltaic cells operation for direct electricity production.

Solar energy is expected to be the foundation of a sustainable energy economy, because sunlight is the most abundant renewable energy resource. Additionally, solar energy can be harnessed in an almost infinite variety of ways, from simple solar cookers now used in different parts of the world. There is a vast literature about the solar energy concerning the engineering and architectural design procedures and projects [77]. It is not possible to present all these studies herein, but the proper references with brief description will be provided so that the reader can depend on himself for further information on the topic.

Most of the low-temperature solar heating systems depend on the use of glazing, because it has the ability to transmit visible light, but to block infrared radiation. High - temperature solar collectors employ mirrors and lenses. In order to gather radiation directly by devices, house roofs are constructed as discrete solar collectors. Solar thermal engines are extensions of active solar heating which help to produce high temperatures to drive steam turbines to produce electric power. On the other hand, solar ponds and even ocean thermal energy conversion devices that operate on the solar-induced temperature difference between the top and the bottom of the world’s oceans may cover many hectares.

Another way of benefiting from solar radiation is by passive solar heating devices, which have different meanings. For instance, in the narrow sense, it means the absorption of solar energy directly into a building to reduce the energy required for heating the habitable space. Passive solar heating systems are integral parts of the building, and mostly use air to circulate the collected energy without pumps or fans. In the broad sense, passive solar heating means low-energy building design, which is effective in reducing the heat demand to the point where small passive solar gains make a significant contribution in winter.

Careful building design makes the best use of natural daylight. In order to make the best use of solar energy, it is necessary to understand the climate of the region. Inappropriate buildings to local climate cause energy wastages [62].

It is possible to consider a south-facing window as a kind of passive solar heating element. Solar radiation will enter during daylight hours, and if the building’s internal temperature is higher than that outside, heat will be conducted and convected back out. Here, the main question is whether more heat flows in that out, so that the window provides a net energy benefit. The answer depends on the following several points. These are:

1. internal building temperature,

2. the average external air temperature,

3. the available solar energy amount,

4. the transmitting characteristics, orientation and shading of the window, and finally,

5. the U-value (Section 15.3) of the window whether it is single or double glazed.

The total amount of heat needed for supply over the year can be called as the gross heating demand. Such a demand may have three supply sources.

1. the body heat of people, heat from cooking, washing, lighting and appliances are together named as ‘free heat gains’ in a house or apartment. They are not significant individually, but collectively they may amount to 15 kW h per day. Free heat gains help for reductions in space heat loading,

2. passive solar gains occur mainly through the windows, and,

3. Fossil fuel energy exploitation from the normal heating system.