By uniting energy reaper with rechargeable battery, we can make battery-based power beginning of infinite life-time ideally.
Figure 2. Block diagram of solar energy system.
The paradigm system designed for this undertaking is shown in Fig.2. It consists of solar panel, charge regulator, energy shop device which is a 1.2 Vs rechargeable battery, DC-DC convertor and solar tracker. Solar cells can be either connected in series or parallel to supply a coveted value of end product electromotive force or current. The solar panel for this undertaking is designed to supply an end product electromotive force of 4 Vs ( 200mA ) . It can be achieved by utilizing four 2V ( 100mA ) solar cells. Four solar cells are divided into two groups. Each group consists of two solar cells which are connected in series supplying an end product electromotive force of 4 Vs. Since the current will drop as the electromotive force subsequently being boosted to a higher degree, the two groups of solar cells are hence connected in analogue to increase the end product current to 200 ma. Since the outright available energy collected by solar panel is normally non plenty to power the electronic device therefore it is desirable to be accumulated and stored in the battery until the energy is adequate to make something practical. The energy stored in the battery subsequently can be boosted to a higher electromotive force degree by DC-DC convertor in order to power the DC tonss, such as the motor of solar tracker.
Figure 3. How the Si solar cell works.
As one method that has been widely used for electricity coevals from solar energy is photovoltaic coevals. Photovoltaics is the term used to depict the electricity from solar energy by giving off negatrons when the atoms of light-sensitive stuff are struck by visible radiation, which is besides known as the photovoltaic consequence. Silicon solar cell is basic generator for little sum of electric power since Si is the most normally used stuff in the electronic industry. As the semiconducting material engineering advanced, the belongingss of such element become reasonably good known and pure Si is hence doped or contaminated with other elements in order to make a field, besides known as possible difference, leting the valency negatrons ejected from Si atoms to roll through the crystal lattice organizing a steady negatron flow, or current. Such semiconducting material is capable of keeping a much greater negatron flow than would be possible with the metal in its pure province. The stuff used for solar cells is called polycrystalline Si or polysilicon. The single-crystal Si is produced based on polysilicon in order to better the electrical belongingss of Si. Numerous thin-film engineerings, such as crystalline Si ( c-Si ) or multicrystalline Si ( mc-Si ) , every bit good as thin movie CdTe and Cu In Ga diselenide and related stuffs are presently being developed to make an energy transition efficiency of at least 10 % . Due to the fresh countries between cells, the working efficiency of existent solar faculties is merely approximately 10 to 12 per centum even the mass-produced single-crystal Si solar cells can hold an efficiency higher to 14 or 15 per centum. Since crystalline solar cells are rather common on the market and comparative cheap, it is hence chosen to be the energy aggregator of this undertaking. The Fig. 1 has to the full represented the action of a Si solar cell that millions free negatrons are ejected from Si atoms due to photon barrage. These free negatrons are accelerated across the P-N junction of the cell to the forepart face where they are collected by metallic grids and enter a way formed by grid lines to the external circuit and supply current to the burden. Electrons so return to the dorsum of the cells to finish the circuit by make fulling the waiting holes in the P-silicon. The procedure is clean since there is either no noise or pollution, merely a little sum of heat dissipated to the ambient milieus [ 4, 5 ] .
Figure 4. Equivalent circuit of a solar cell.
The internal opposition Rs could impact the public presentation of solar cell by doing the internal electromotive force bead harmonizing to the Fig. 2 which shows the tantamount circuit for a solar cell. The Eq. ( 1-3 ) below show that the net electrical current through the Rs and burden RL is the difference between the light-generated current and the current through rectifying tube junction.
Due to proper design of the metallization and the conduction of the stuff, Rs is frequently assumed to be equal to zero and hence the internal electromotive force bead in a cell can be minimized [ 8 ] .
Since merely a 1.2V rechargeable battery is selected to be the energy shop device, it is non necessary to add a charge accountant. Alternatively, a electromotive force regulator which is capable of forestalling the high electromotive force that could damage the battery or cut down its life-time is used to supply a stable electromotive force of 1.45V to bear down the battery safely. As shown in Fig. 5, the is 1.45 Vs and the electromotive force bead between base and emitter of a Si transistor is ever 0.6 Vs if the transistor is “ on ” . Therefore, the electromotive force clamped by the zener rectifying tube is 2.05 Vs. Since the input electromotive force is 4 Vs, the electromotive force across is 1.95 Vs and therefore the opposition of is equal to be
Fig 6. Hike convertor utilizing MAX756.
A dc-dc convertor is besides needed to supply an end product electromotive force that is higher than the input for certain power demands. The probe undertaken into dc-dc convertor has revealed the fact that a step-up ( encouragement ) convertor which converts the lower input electromotive force to a higher electromotive force degree is more suited for the circuit [ 3 ] . The advantage of utilizing this constituent is that the end product electromotive force can be increased to a higher degree from a individual battery thereby salvaging infinite alternatively of utilizing multiple batteries to carry through the same undertaking. Furthermore, it can avoid the state of affairs that the electromotive force provided by solar panel is non high plenty to bear down the battery if two or more batteries are used in series to hive away the electricity. Furthermore, following this constituent can cut down the size and cost of the circuit. A type of circuit diagram has been analyzed as shown in Fig. 2. It has a MAX756 CMOS step-up DC-DC shift regulators for little, low input electromotive force or battery-powered systems, change overing a positive input voltage down to 0.7V to a higher pin-selectable end product electromotive force of 3.3V or 5V [ 6 ] .
Figure 6. Block diagram of solar tracker.
The solar tracker is used to track the Sun in order to let the cells face towards to the entrance sunshine, ensuing in much-improved efficiency. There are two types of sun-tracking systems. The two-axis trailing system can let up to 50 per centum more energy collected by solar panel. However, the climb and mechanism of this type are rather dearly-won. Single-axis trailing system has emerged as it offers a good via media between capital costs and energy delivered [ 20 ] . Therefore, solar tracker is of critical importance in the public presentation of solar energy reaping system. The design of solar tracker of this undertaking is inspired from an on-line picture [ 15 ] . As shown in Fig.6, the motor is powered by a 4AA rechargeable battery which is 4.8 Vs. Two exposure resistances are soldered to the corresponding pins of potentiometer in the servo motor. The rule is simple that the opposition of exposure resistances will alter as they sense the alteration of way of incoming Sun visible radiation. The servo motor will therefore rotate harmonizing to the potentiometer which is a three-pin resistance moving as a electromotive force splitter.