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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Courtyard lighting. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Alternative energy sources Regardless of the name (farm lighting, street lamp), outdoor lighting looks very attractive in every home. In addition to its aesthetic function, street lighting also serves to ensure safety. Everyone knows how dangerous an unlit path can become. What about the unfenced swimming pool? Small lights located along the path or around the pool can prevent accidents while walking. This chapter provides recommendations for installing outdoor lighting that uses solar energy.
System Features According to the principle of operation, external lighting is basically similar to the emergency lighting discussed in the previous chapter. Photovoltaics is also used to charge a lead-acid battery, which in turn powers the lamps. However, there is also a significant difference. The emergency lighting system is switched on only occasionally. In fact, it is required only during interruptions in the supply of electricity to the network; the rest of the time the system is idle. Outdoor lighting, in contrast, should be used during every night of the year. In this case, it is necessary to develop a system that has a sufficiently large battery capacity and photovoltaic converter power so that the system as a whole functions at any time of the year and under any weather conditions. These requirements were not taken into account when developing emergency lighting. System design Design begins with the fixtures themselves. They are designed for low voltage and therefore are very suitable for a power supply system that uses solar energy converters. Despite the fact that there are many different models of such lamps, they all operate on a voltage of 12 V. The lamps included in the set of lamps are designed, as a rule, for the same power of 12 W and, therefore, consume 1 A each. First you need to determine the required number of fixtures in the system. This number depends on each specific case. I chose five because this amount was enough to light up the front lawn and walkway. Therefore, my power source must feed a system that draws 5 A. If I chose six lamps, 6 A would be required. A current of 5 amps is not excessive and is easily obtained from several commercially available lead-acid batteries. The only question is the required size of the battery. This part of the development is somewhat more complicated. To correctly answer the question posed, it is necessary to perform some calculations and make several assumptions. First, consider what parameters the battery is characterized by. All batteries (lead-acid and others) are rated in amp-hours (often referred to as Ah). 1Ah means that the battery can supply 1A for 1 hour. Similarly, if a battery can supply 5A for 1 hour, it has a capacity of 5Ah. The same capacity is achieved at a current of 1 A for 5 hours. Regardless of the voltage, the battery capacity is numerically determined by the product of the current strength and the total time of its flow. So, it was found that the system will consume a current of 5 A. However, for a competent choice of battery, it is necessary to know the duration of the operation of the external lighting system per day. Let this duration for each evening be 4 hours. Now, multiplying the value of the current consumed by the lamps by the time they work per day, we get the required number of ampere-hours. In our case, 5 A x 4 h = 20 Ah. This is the daily energy consumption. It follows that a battery with a capacity of 20 Ah is enough for evening lighting. However, the battery will be completely discharged in the morning and will need to be charged again in order to use it again. Suppose it rains all next day. How do photovoltaic converters charge a battery? They don't work without sunlight. Given this fact, it will immediately become clear that it is necessary to increase the capacity of the battery. A 40 Ah battery will power the lighting system for 2 days and a 60 Ah battery for 3 days. Now you need to define one more condition: choose the average time between charge cycles and decide how long the battery should last without recharging. This parameter is not too critical in the case of lighting a personal plot. Let's assume that the energy reserve in the battery for 3 days will be quite enough. Therefore, a 60 Ah battery is required. Summarizing the above, we can formulate the sequence of a simple calculation of the required parameters of solar and storage batteries:
Now everything is all right. The number of lamps is selected, the duration of their operation during the day is set, and the battery capacity necessary to ensure this operation is calculated. It remains now only to dwell on a certain method of charging the battery. Requirements for photovoltaic converters The requirements for a solar battery are determined by the operating conditions of the lighting system. You can speculate a little; it does not take a lot of time. It was assumed that the lighting system required 20 Ah per day to operate. It is also known that the battery provides energy, therefore, the energy expended in the evening must be, figuratively speaking, returned the next day. Unfortunately, no battery is perfect. As a rule, to charge a lead-acid battery, it is necessary to supply 20% more energy than was released. Therefore, for every 20 Ah received from the battery, 24 Ah must be returned. The next step is the development of a photovoltaic array generating 24 Ah per day. To achieve this, it is necessary to know the available insolation. This value is determined by the number of useful hours of sunshine, in other words, the period of time (in hours) per day during which we can assume that the sun does the work we need. There are two ways to determine the number of useful hours of sunshine for any location. First, directly using the insolation meter described in Chap. 3. Or you can use a more general meaning based on the map given in the same chapter. The map has been compiled taking into account seasonal changes and the general nature of the weather. In the case of the described lighting system, the duration of useful lighting was chosen for calculations, corresponding to an average of 4,5 useful hours of sunshine per day. As you can see from the map, this figure is the same for most areas of the continental United States. Now, if we divide the number of ampere-hours (24 Ah) required to recharge the battery by the average useful hours of sunshine (4,5 hours), we can get the amount of current that the solar battery should generate: 5,3 A. Theoretically, this requirement is met by a battery that generates a current of 5,3 A at a voltage of 12 V. However, there are other factors that we have not yet considered. These include losses in connecting conductors, energy consumption by the regulator, etc. Therefore, to ensure reliability, it is not a bad idea to create a certain power margin; A 10% margin is fine, for example. Thus, the minimum current generated by the solar battery should be about 6 A. By doing the reverse calculation, i.e. multiplying 6 A by 4,5 hours, we get that the solar battery will produce an average of 27 Ah per day. On some days the return may be less, on others it may be more. It should be remembered, of course, that 27 Ah is not required for daily charging of the battery, the missing amount of solar energy on some days will be replenished by the battery. However, for the normal functioning of the lighting system, the average value should be 27 Ah. Solar battery A particular solar cell can be made in a variety of ways. It is possible to connect small modules in parallel and achieve the required power of 87 W, but this will be very expensive. As a rule, the larger the size of the modules from which the battery is assembled, the cheaper the cost of 1 W of electricity generated by the solar battery. For the described system, three modules were used, each of which generated a current of 2 A. All modules were made of round, relatively cheap solar cells with a diameter of more than 10 cm. If you independently assemble a solar battery from elements, then you can advise using round elements with a diameter of 10 cm from a single crystal or square elements 10x10 cm2 from a polycrystalline material. Although square cells are not as efficient as round monocrystalline cells, they are cheaper, but more will be needed. To ensure the cyclic operation of the lighting system (off during the day and on in the evening), a timer is required. Most lighting systems use mechanical clock timers that turn lights on and off at specific times; however, this seems to be a waste of energy. Why turn on the light before the sun goes down? The only way out in the case of conventional timers is to manually set the timer, adjusting to the solar cycle, which is done quite often. However, it's best to "force" the setting sun to start the timer. This is done using the electronic circuit shown in Fig. 1. Consider her work. As a light-sensitive photoresistor element, a PC1 photocell illuminated by direct sunlight is used. With a change in the intensity of light falling on a photocell, its resistance changes proportionally. In the daytime, its resistance is very small (about 100 ohms). However, with the onset of darkness, it increases by 100 or more times and reaches a value of more than 500 kOhm.
A resistor VR1 is connected in series with the photoresistor, forming a divider, the output voltage of which depends on the value of the resistance of the photoresistor PC1. The more light, the lower the output voltage, and vice versa. The voltage value is controlled by two comparators. It should be noted that the lower one is used in the non-inverting version of the inclusion, and the upper one - in the inverting one. This means that at zero input voltage, the lower comparator outputs a low level voltage, and the upper comparator outputs a high one. The comparators are connected in such a way that the lower comparator switches at a lower input voltage than the upper one. As soon as the voltage at PC 1 increases (when the sun sets), the first comparator switches, its output is set to a high voltage level. Now the outputs of both comparators are set to a high level voltage. In this case, a chain of two logic elements AND-NOT (7C2) outputs a high-level voltage to pin 11 of the /C3 chip. The /C3 chip is a programmable timer. It can measure time intervals up to a day. Inside this chip is a carry-through binary counter whose outputs can be used to set the time. By switching them, it is easy to increase the response time by 2 or 4 times. The nominal response time of the timer is determined by the resistance R8 and capacitance C1. With the values indicated on the diagram R8 and C1, the voltage at pin 8 increases after 4 hours. At pin 7 connected to the low-order digit of the counter, voltage will appear after 2 hours, at pin 6 - after 1 hour. The timer will start when a high potential is applied to pin 11. The timer operation time is selected by switch 51 "Time". At the beginning of the work cycle, all outputs are at low potential. The relay contacts RL 1 are closed under these conditions due to the transistor Q1 and the /C2 chip. Electricity is supplied to external lighting - and the lights are on. As night falls, the voltage on PC 1 continues to increase. Soon the upper comparator is triggered and a low voltage is set at its output. This changes the state of the inputs of IC2 and a low level voltage is applied to the input of IC3. However, this change does not affect the operation of the timer. At the end of the specified interval, IC3 automatically resets. Reset is performed by a feedback pulse coming from the output of the microcircuit. Since pin 11 is now low potential, the chip does not restart. In addition, as a result, the relay turns off and the lighting goes out. The next morning, as the sun rises, the resistance of PC 1 gradually decreases and, as a result, the input voltage of the comparators decreases. This could cause the upper comparator to fire before the lower one, to apply a high potential to the input of the timer and restart the timer. To prevent the timer from firing at sunrise, a small positive feedback is introduced into the upper comparator through the resistor R5. This results in a hysteresis that delays the response until the lower comparator switches. A high potential cannot be applied to both outputs at the same time and the timer will not start. Nevertheless, by evening the cycle will begin to repeat itself and the comparators will return to their "night" state. The level of operation of the comparators is set precisely by the variable resistor VR1 "Sensitivity". It is necessary to adjust the value of its resistance so that the outdoor lighting turns on immediately after dusk. Design The design of the timer uses printed wiring. The PCB configuration is shown in fig. 2, and the placement of circuit elements on it is shown in Fig. 3. The relay can be soldered directly to the board or placed in a socket to connect lighting.
The assembled timer must be placed in an opaque box, and the photoresistor PC1 must be placed on the lid so that it is exposed to sunlight. The timer has only three outputs: a common ground, a wire for connecting +12 V power from the battery and a phase wire connected to the lighting system. Make sure that all holes made in the housing are properly sealed and watertight to prevent moisture ingress.
Final connection of structural units Now all the elements necessary to create a lighting system are known, except for one. The system must also be equipped with a charge regulator. Without a charge regulator, the possibility of overcharging the battery and the resulting reduction in its service life cannot be ruled out. This probability is especially high in the summer, when the days are long and the nights are short. Under these conditions, there is a gradual accumulation of charge in the battery cells, which can easily lead to overcharging.
You can start assembling the system by placing lights on the site. There are no restrictions here, you can install lights where they will be more useful. Lamps are connected in parallel with thick wires. If an appropriate wire kit is used, then the necessary wire is necessarily included in its composition. If not, no. 18 flat lighting cable is recommended. The electrical wires leading to the lights are connected to the timer circuit. The timer must be placed so that it can be exposed to the sun's rays, and not to the headlights of passing cars or other external sources. The timer is connected to a 12 V battery. The battery life depends on the type of battery used. If you wish, you can use a car battery, but it will not last long in the harsh conditions of periodic work. It is better to use a boat battery. Such batteries are designed to work under conditions of repeated deep discharge cycles. Although they cost a little more, they will last much longer than a regular car battery. The charge regulator is connected between the solar and storage batteries. Great for a charge regulator. this regulator. You just need to connect the output of the regulator to the battery, and the input to the solar battery, observing the polarity. The front panel of the solar array is located in the south direction. The timer is set to the time during which lighting is needed after sunset. It may be necessary to adjust the timer when the seasons change to better match the weather. Now the paths near the house will be illuminated even after sunset. Author: Byers T.
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