DIFFERENT SOURCE OF SOLAR ENERGY

While I have wandered from the main subject of the sun, to consider the source of stellar energy, the two topics are so intimately related that their solutions are identical. I consider that I have demonstrated the reasonableness of Jeans's theory by the manner in which it seems to fit the observed facts. There is, as I can see, no important objection to the hypothesis. It is too much to hope that the foregoing analysis is rigidly complete, but I confidently believe that the main points are established and that further modification will consist in the clearing up of details. The application of astrophysics and atomic theory to a new field appears to have met with considerable success. In spite of this success, however, caution is necessary. The present position of the theory advocated in this paper is somewhat analogous to the place once held by the theory of Helmholtz—i.e., it is the only one sufficiently elastic to stretch over the region of known facts. Our knowledge is yet limited and, with our vision thus impaired, we can not predict the future. Some unforeseen event may upset our present hypothesis as completely as that of Helmholtz; we have built as securely as possible upon observation, and it remains for the future to test the accuracy of this or any other theory so established.

In an attempt to discover a reasonable explanation of the origin and duration of the solar radiation, all possible sources of energy are examined. The following hypotheses are reviewed and discarded, the arguments against their validity being too well known to necessitate a review at this place;

(1) Original Heat;

(2) Chemical;

(3) Gravitational,

(a) Meteoric, (b) Contraction;

(4) Radioactive.

THE SOURCE OF SOLAR ENERGY

The source of all energy radiated by the Sun lies in its core, a central region comprising only 1.5% of the total solar volume. This is a very large thermonuclear reactor where Hydrogen atoms are fused together to form Helium, releasing energy at the rate of 3.86 x 1026 Joules per second. The fusion reactions in the solar core take place because of the very high temperatures and very large pressures present in this region of the Sun. Although there is no way of measuring these quantities directly, physical models of the Sun suggest that the core temperature is around 15 million degrees and the central pressure is about 250 billion atmospheres (250 billion times the pressure on the Earth at sea level).
It is the massive gravity of the Sun that compresses the core to such a high pressure and resultant high temperature, which then is sufficient to ignite the fusion reactions which take place. The overall result is to convert 4 Hydrogen atoms into one Helium atom (see below). For every 1 kilogram of hydrogen that is consumed, most is turned into Helium but a small portion, 0.007 kg, is turned into pure energy. Using the famous energy-mass equivalence formula (E = m c2) developed by Einstein, we can calculate that this mass amounts to a little over 600 trillion Joules (6 x 1014 J). When related to the total energy output of the Sun, this means that the solar fusion reactions are consuming mass at almost 5 million tons per second!
There are two distinct reactions in which 4 H atoms may eventually result in one He atom. The first of these is:
(1) 1H + 1H → 2D + e+ + ν
then 2D + 1H → 3He + γ
then 3He + 3He → 4He + 1H + 1H
This reaction sequence is believed to be the most important one in the solar core. The total energy released by these reactions in turning 4 Hydrogen atoms into 1 Helium atom is 26.7 MeV.
The second reaction generate less than 10% of the total solar energy. This involves carbon atoms which are not consumed in the overall process. The details of this "carbon cycle" are as follows:
(2) 12C + 1H → 13N + γ then 13N → 13C + e+ + ν then 13C + 1H → 14N + γ
then 14N + 1H → 15O + γ then 15O → 15N + e+ + ν
then 15N + 1H → 12C + 4He + γ
All the energy that is generated in the solar core escapes mostly in the form of very high energy gamma rays. This energy is absorbed and re-emitted many many times by the layers overlying the core, as the photons (bits of electromagnetic energy) diffuse out toward the surface. In doing so, the energy is degraded; gamma photons are turned into X-ray photons, and then into UV photons, and finally into visible light and infrared photons. And so it is light and heat that is finally radiated from the surface of the Sun into interplanetary space. This same heat and light has a flux density of 1370 watts per square metre by the time it arrives at the upper atmosphere of the Earth. It is this energy that makes life possible on the surface of the Earth, that produces our terrestrial weather, and that photovoltaic cells can convert into electrical energy. Solar energy is, in actuality, nuclear energy.

Solar water heating

Solar water heating, where heat from the Sun is used to heat water in glass panels on your roof. This means you don't need to use so much gas or electricity to heat your water at home. Water is pumped through pipes in the panel. The pipes are painted black, so they get hotter when the Sun shines on them. The water is pumped in at the bottom so that convection helps the flow of hot water out of the top.

This helps out your central heating system, and cuts your fuel bills. However, with the basic type of panel shown in the diagram you must drain the water out to stop the panels freezing in the winter. Some manufacturers have systems that do this automatically. Solar water heating is easily worthwhile in places like California and Australia, where you get lots of sunshine.

Water heating

Solar hot water systems use sunlight to heat water. In low geographical latitudes (below 40 degrees) from 60 to 70% of the domestic hot water use with temperatures up to 60 °C can be provided by solar heating systems. The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools.

As of 2007, the total installed capacity of solar hot water systems is approximately 154 is the world leader in their deployment with 70 GW installed as of 2006 and a long term goal of 210 GW by 2020. Israel and Cyprus are the per capita leaders in the use of solar hot water systems with over 90% of homes using them. In the United States, Canada and Australia heating swimming pools is the dominant application of solar hot water with an installed capacity of 18 GW as of 2005.

Solar Cells

(really called "photovoltaic", "PV" or "photoelectric" cells) that convert light directly into electricity.

In a sunny climate, you can get enough power to run a 100W light bulb from just one square metre of solar panel. This was originally developed in order to provide electricity for satellites, but these days many of us own calculators powered by solar cells.

Solar lightening

A preview for solar lightening.

Solar lighting

the history of lighting is dominated by the use of natural light. The Romans recognized a right to light as early as the 6th century and English law echoed these judgments with the Prescription Act of 1832. In the 20th century artificial lighting became the main source of interior illumination but daylighting techniques and hybrid solar lighting solutions are ways to reduce energy consumption.

Daylighting systems collect and distribute sunlight to provide interior illumination. This passive technology directly offsets energy use by replacing artificial lighting, and indirectly offsets non-solar energy use by reducing the need for air-conditioning. Although difficult to quantify, the use of natural lighting also offers physiological and psychological benefits compared to artificial lighting Daylighting design implies careful selection of window types, sizes and orientation; exterior shading devices may be considered as well. Individual features include sawtooth roofs, clerestory windows, light shelves, skylights and light tubes. They may be incorporated into existing structures, but are most effective when integrated into a solar design package that accounts for factors such as glare, heat flux and time-of-use. When daylighting features are properly implemented they can reduce lighting-related energy requirements by 25%.

Hybrid solar lighting is an active solar method of providing interior illumination. HSL systems collect sunlight using focusing mirrors that track the Sun and use optical fibers to transmit it inside the building to supplement conventional lighting. In single-story applications these systems are able to transmit 50% of the direct sunlight received.

Solar lights that charge during the day and light up at dusk are a common sight along walkways.

Although daylight saving time is promoted as a way to use sunlight to save energy, recent research has been limited and reports contradictory results: several studies report savings, but just as many suggest no effect or even a net loss, particularly when gasoline consumption is taken into account. Electricity use is greatly affected by geography, climate and economics, making it hard to generalize from single studies