photovoltaic systems أنظمة الطاقة الشمسية
إظهار الرسائل ذات التسميات Off-grid. إظهار كافة الرسائل
إظهار الرسائل ذات التسميات Off-grid. إظهار كافة الرسائل
الخميس، 13 فبراير 2020
الأحد، 16 أبريل 2017
Download :Off Grid Solar Power System Design (7) : Step 5 Inverters .mp4
Off Grid Solar Power System Design
Step 5 : Inverters
Download :Off Grid Solar Power System Design (6) : Step 4 Charge Controllers .mp4
Off Grid Solar Power System Design
Step 4 : Charge Controllers
Download :Off Grid Solar Power System Design (5) : Step 3 Solar Array Sizing .mp4
Off Grid Solar Power System Design
Step 3 : Solar Array Sizing
Download :Off Grid Solar Power System Design
Download :Off Grid Solar Power System Design (4) : Step 2 Battery Bank Sizing.mp4
Off Grid Solar Power System Design
Step 2:Battery Bank Sizing
Download :Off Grid Solar Power System Design (3)Step 1Loads List .mp4
Off Grid Solar Power System Design
Step 1:Loads List.mp4
Step 1:Loads List.mp4
الأحد، 31 يوليو 2016
Planning an Off-Grid Electric System
Planning an Off-Grid Electric System
Off-grid solar systems operate from the stored energy in a battery bank. Solar panels are used to keep a battery bank charged on a daily basis. Some part of the cabin or tiny house electricity loads, during the daytime, will usually end up running directly off the array via the electricity passing across the battery connectors. At night, the inverter is pulling directly off the batteries. Your solar system has to be sized to support your daily loads and replace the stored energy pulled from the batteries on a daily basis.
Defining Your Load
The first step in determining how many solar panels you will need or how big your inverter should be is to figure out how many watts of power you need per day. Since you determine what you are trying to run, and how long each day you want to run the items, the first place you have to start, after reducing your loads, is to determine your daily energy budge or daily loads. You are going to want to reduce your daily energy demands first before you start to calculate your loads because it is cheaper to save energy than to make energy.
All the Parts Needed; Looking at The Whole System
A typical stand-alone system consists of solar panels usually connected in series of 2 or 3 which product DC electricity from the sun. The solar panels are connected to a charge controller which controls the pace at which batteries are recharged which is connected a 24VDC or 48VDC battery bank. You will then need an off-grid inverter to convert the DC (Direct Current) electricity stored in the battery bank to AC (Alternating Current) electricity which is more commonly used in home appliances. (Click on the 2nd sub-tab above "Planning Design & Installation Tips" to learn more.)
Where to Get Started; Cheaper to Save Energy Than to Make Energy
The trick to off-grid living is energy conservation and efficiency. The starting point in planning your system is to first reduce demand. (Need Tips? Click on the 3rd sub-tab above "Off-Grid Living Energy Conservation") Most people in America can easily cut their electricity consumption in half. Reducing your family's energy consumption by conserving and investing in watt saving home lights and efficient appliances means you are putting your money in your pocket and can substantially reduce the amount of off-grid equipment and or battery bank. As you begin your journey towards freedom from the grid, start by conserving as much as possible first. Its always cheaper to save electricity than to generate electricity. Most off-grid generation is used for lighting, appliances like refrigerators and water pumping. Lighting is the easiest to tackle. Don't stop at compact florescent lights, go all the way to LED which can use 1/6th the watt consumption of compact florescent lighting.
The BIG Questions You Need to Answer First:
- List your loads. How many watts per day does your household consume? The most important challenge in an off-grid system is to balance your energy consumption with your supply of energy required. You cannot begin to do that without first knowing how much energy you need each day.
Energy Load Worksheet (Excel)
Energy Load Worksheet
IE: 5 - 13 watt light bulbs X 5 hours per day = 65 watts. 18 CF refrigerator @ 5 amps x 120VAC = 600 watts x 6 hours per day = 3,600 watts. THIS IS IMPORTANT: When we say "list your loads", we mean all your loads. From the cell phone chargers to a hair dryer. Need Help? If you download the Excel worksheet you will only have to indicate how much of each piece of equipment you have and how long your run it.
- Daily energy budget? It is NOT based on a homes sq. ft. It is NOT based on how many people are living in the house. It is based on the equipment or appliances you want to run and how long each day you typically run them. It does not get more individual than that. The amount of energy you and your family consumes each day will vary among individuals habits and personal choices.
- How many days of limited sun do you want to be able to run? (Days of Autonomy) Typical is a minimum of 3 day to 5 days. The more days, the more energy storage required or the bigger the battery bank needed.
- What is the largest load you expect to run (Watts / Amps / Volts IE: 240V Well Pump @ 9.5 Amps)
- Click on the sub-tab above "Planning Design & Installation Tips" directly below the buySafe emblem to learn more
https://www.bluepacificsolar.com/off-grid.html
الأحد، 10 يوليو 2016
Designing a Stand-Alone PV System By: Khanti Munro
Living off the grid is a romantic ambition for some, a practical necessity for others. But whatever your motivation for off-grid living, cutting the electrical umbilical cord from the utility shouldn’t be taken lightly. Before you pull out the calculator, size up the realities and challenges of living off the grid. Then, once you’re convinced it’s the way for you, use this guide to design a successful stand-alone system.
Design Considerations
Designing a stand-alone PV system differs substantially from designing a batteryless grid-direct system. Instead of meeting the home’s annual demand, a stand-alone system must be able to meet energy requirements every day of the year. The PV system must be able to keep the battery bank charged—or include a generator for backup—because once the last amp-hour is drawn, the lights go out (see “Backup Generators” sidebar).
Efficiency first! This long-standing mantra for PV system design still holds true and is especially important for off-grid systems. Using energy efficiently should always be a prerequisite to energy design and production. Every $1 spent on energy efficiency is estimated to save between $3 and $5 on PV system costs. As a system designer, it’s virtually impossible to mandate wise energy use by the end user, but we can specify efficient appliances, such as Energy Star refrigerators and clothes washers, and strategies, such as shifting loads to non-electric sources during times of low solar insolation. For more on efficiency and load-shifting, see “Toast, Pancakes & Waffles: Planning Wisely for Off-Grid Living” in HP133.
Energy Consumption and the Solar Resource. Carefully comparing the home’s daily and seasonal energy usage with the daily and seasonal availability of the sun will help prevent energy production shortages. This important step involves a careful analysis of the home’s changing seasonal load profile and the corresponding solar resource throughout the year. Paramount to this analysis is the presence or absence of a backup charging source, such as a generator. If a backup charging source is not incorporated, the designer should choose as the design target the time of year when energy consumption is expected to be highest and the solar resource at its lowest—usually during the depths of winter.
Without a backup generator, a PV system must produce every watt-hour required, at all times of the year. This is often a tall task during the winter months and typically results in a costly system that is oversized for the rest of the year. For this reason, stand-alone systems without a backup charging source are often limited to smaller, nonresidence applications, such as seasonal cabins.
For systems with a backup charging source, more design flexibility means designers can use average consumption numbers and peak sun-hour values. For example, they can choose to size the system at a time of year when energy consumption is not at its highest or lowest, but in the middle—say, a typical day in the fall or spring. In addition, they might use the specific location’s average solar resource. Using the average for both consumption and sun-hours will strike a good balance between an affordable array size and generator run time. If minimal generator run time is desired, the array and battery bank may need to be upsized based on more conservative consumption and sun-hour values.
Size it Up: A Case Study
Let’s explore an example sizing scenario, component by component, with a method Solar Energy International (SEI, see Access) uses in its classes to size stand-alone systems using an maximum power point tracking (MPPT) controller:
Who: The Ackerman-Leist family
Where: Pawlet, Vermont, approximately 3/4 mile from utility service
Solar window: 8 a.m. to 4 p.m.
Average daily solar resource: 4.6 peak sun-hours*
System backup: 4 kW backup engine generator
System voltage: 24 VDC
Projected energy use (AC and DC): 2.2 kWh per day
Expected avg. ambient temperature for batteries: 60°F
Record low temperature: -35°F
Desired days of autonomy: 3
Desired battery depth of discharge: 50%
Battery: 6 V nominal, 225 Ah, deep-cycle flooded lead-acid
PV modules: 12 V nominal, 80 W STC , array tilt equal to the latitude (43°)
Charge controller: MPPT, 60 A
Array mounting: Pole-mount
*Peak sun-hours are based on Concord, New Hampshire, values, which more accurately reflect the site’s latitude and weather patterns.
Step 1: Estimate Electric Load
Determine the amount of energy (kWh or Wh) that will be consumed on a daily basis. If it is for a home not yet built, this can be a very involved and time-consuming step. A designer will need to work closely with the homeowner/builder to realistically estimate the daily and seasonal energy requirements.
The power (W) of individual loads and their estimated energy consumption (Wh) can be tallied to calculate the household’s average daily load. This step will help identify opportunities for efficiency improvements and pave the way for sizing the system components. The table below lists the electrical loads found in the Ackerman-Leist household. The family heats their home with wood, cooks with wood and propane, uses a propane refrigerator, and heats their water with a solar thermal system and a backup propane boiler, so those are not factors in the load analysis.
According to the table, daily household loads average 1.8 AC kWh and 0.36 DC kWh (from the chest freezer), totaling almost 2.2 kWh a day.
Step 2: Battery Bank Sizing
The average daily load is then used to calculate the battery requirements. The batteries must be able to store the total daily load, in addition to the extra energy lost by inverting from direct current (DC) to alternating current (AC). Dividing the AC average daily load by the inverter efficiency (90% standard), inflates the average daily load that the batteries must store to account for efficiency losses from the inverter. While inverter manufacturers will commonly list “peak efficiency” (generally ranging from about 92% to 95%), we use a more conservative 90% to account for the fact that the actual operating efficiency depends on the AC load, which is constantly fluctuating. Hence, an inverter will rarely operate at the load level which results in peak efficiency.
The battery bank’s ambient operating temperature is also taken into consideration, since temperature affects a flooded lead-acid battery’s internal resistance and ability to hold a charge. As temperatures fall below 80°F, battery capacity is reduced. A battery temperature multiplier table can be used—check with the battery manufacturer for their specific correction factors.
Days of autonomy is also an important design criterion, as it dictates how many days the battery bank will need to sustain the average daily load when there is little or no sunshine to recharge it. It’s a compromise between having energy during overcast spells, how much time the generator will run, and the added cost of a larger battery bank. The more days of autonomy desired, the larger the battery bank. Generally three to five days of autonomy provides a good balance. Keep in mind that the larger the battery bank, the larger the PV array will need to be to recharge the bank sufficiently on a regular basis—or the more the generator will be needed to pick up the slack.
The last major design criterion for sizing batteries is the depth of discharge (DOD). While deep-cycle lead-acid batteries are designed to discharge 80% of their capacity, the deeper they are discharged on a regular basis, the fewer charge/discharge cycles they can provide over their lifetime. When choosing a DOD, strike a balance between longevity, cost, and the significant hassle of replacement. Many system designers will specify a 50% DOD to be used in the worksheet. Because several days of autonomy are accounted for, which increases the battery bank size, the actual depth of discharge during sunny weather will often be less than 20%. The DOD design value can greatly affect the cost of the battery bank. (For simplicity, the numbers from the load table have been rounded in the following equations.)
(1,800 AC Wh Avg. Daily Load ÷ 0.9 Inv. Eff.) + 360 DC Wh Avg. Daily Load = 2,360 Wh/day
2,360 Wh/day ÷ 24 DC System Volts = 98.3 Avg. Ah per day
98.3 x 1.11 battery temperature multiplier x 3 days autonomy ÷ 0.5 DOD = 654.7 total system Ah
654.7 ÷ 225 Ah individual battery capacity = 3 parallel battery strings (rounded up from 2.9)
24 V system voltage ÷ 6 V battery voltage = 4 batteries in series
3 parallel strings x 4 batteries in series = 12 total batteries
The battery calculations indicate that a battery bank made up of 12 of the chosen 6 V, 225 Ah, flooded lead-acid batteries will provide adequate storage to meet daily energy requirements, inverter efficiency losses, operating temperature effects, days of autonomy, and the desired average depth of discharge. The number of batteries or series-strings of batteries connected in parallel should be kept to a minimum, preferably three or less. This minimizes the chance of unequal charging from one battery or string to the next. While using higher-capacity batteries would have resulted in fewer parallel strings, the Ackerman-Leists chose lower-capacity batteries for budgetary reasons.
Batteries are rated by their capacity in amp-hours and at the rate that they are charged/discharged. In most PV systems, the appropriate Ah rating to use is based on a discharge over 20 hours. Unlike shallow-cycle vehicle batteries, deep-cycle batteries in PV systems are charged and discharged over 24 hours, and the weather, level of solar irradiance, and energy usage patterns all influence the charge/discharge scheme. In this system example, the battery could provide 225 Ah of stored energy—if discharged 100% over 20 hours. If it were discharged faster, the capacity would be less, and vice versa. Be sure to check with the battery manufacturer, as they provide battery-specific Ah capacity values based on different charge/discharge rates. Choose the 20-hour rate when sizing and selecting batteries, unless a specific load profile dictates otherwise.
Step 3: Array Sizing
Now that we have calculated loads and storage, next calculate the array size in watts, and the number of PV modules needed. The array calculations must include Wh per day (calculated from the average daily load), the location’s solar resource, expressed in daily peak sun-hours, battery efficiency losses (about 20%), module temperature losses (about 12%), possible array shading, and a conservative derate multiplier to account for things like wire losses, module soiling, and production tolerance.
Peak sun-hours are the equivalent number of hours per day when solar irradiance (intensity) averages 1,000 watts per square meter, as derived from the National Solar Radiation Database (http://rredc.nrel.gov/solar/pubs/redbook/). Dividing the Wh required by the location’s peak sun-hours leaves us with the initial PV array watts needed. For this sizing example, the solar data for Concord, New Hampshire (at 43.2°N) provides the closest estimate of the solar resource for Pawlet, Vermont (at 43.3°N) at an array tilt angle equal to latitude. Since this system is using a backup generator, the average daily peak sun-hours can be used (4.6), as the generator can cover energy shortages during periods of low insolation or high energy consumption—or both. If less generator run time is desired, the array size must be increased or daily energy consumption must be reduced appropriately (or both).
Battery efficiency: Since batteries are not 100% efficient in converting electrical energy into chemical energy and back again, the array size must be increased to account for energy lost in the storage process. A common battery efficiency is 80%.
PV temperature losses: Module standard test conditions (STC) ratings, which are based upon a cell temperature of 77°F (25°C), don’t reflect real-world operating conditions. To account for losses due to higher cell temperatures, a derating value of 0.88 can be used. This assumes an average daytime ambient temperature of 68ºF and an estimated cell temperature of 122°F. (Another way to calculate temperature losses would be to use the specific module’s maximum power temperature coefficient, in conjunction with a cell temperature based on the record high daytime local temperature.)
Shading coefficient: Although 9 a.m. to 3 p.m. is often considered the ideal solar window, site-specific shading should always be evaluated for the whole day. Even moderate shading can have a substantial impact on array output. In the case of this sizing example, with a shade-free solar window of 8 a.m. to 4 p.m., an average shading coefficient of 0.90 was determined with a Solar Pathfinder array siting tool.
Derate factor: A 0.85 derate factor (from NREL’s PVWatts online performance calculator) accounts for other system losses, including module production tolerances, module mismatch, wiring losses, dust/soiling losses, etc. An experienced designer can adjust this value to reflect conditions for your specific site. See the table for a summary of these values.
2,360 Wh daily load ÷ 4.6 peak sun hours ÷ 0.8 battery efficiency ÷ 0.88 temp. losses ÷ 0.9 shading coefficient ÷ 0.85 system derate = 953 W peak array
953 ÷ 80 W STC individual module = 12 modules needed
48 V nominal array voltage ÷ 12 V nominal module voltage = 4 modules per string, 3 strings total
The resulting 12-module array will have a capacity of 960 W STC, rounded up slightly from the 953 W specified in the calculations. Although the DC system voltage and the battery bank are 24 VDC, this array can be wired at a higher voltage of 48 VDC, because of the “step-down” feature of the charge controller being used. Since the modules are nominally rated at 12 V, they will have to be wired into three series-strings of four modules each.
If these calculations seem conservative, it is because they are. It is imperative to design a system that will operate reliably and efficiently—and that will produce, on average, the expected amount of energy required. In other words, it is the designer’s job to give the system manager/homeowner a realistic idea of what to expect.
Step 4: Controller Sizing
With an array size specified, a charge controller is next—sized to safely handle and regulate the array’s incoming power to prevent overcharging the batteries. A charge controller needs to be selected based on the maximum array watts, nominal battery voltage, and desired features. A MPPT controller allows the array to maximize the energy put into the batteries, particularly under cold conditions (high array voltage) and low battery voltage. These controllers also have the ability to step down a higher array voltage to a lower battery bank voltage which, in turn, helps keep wire size and costs down for long wire runs. It can also reduce the number of series fuses and the size of the combiner box. To prevent damaging the controller and potentially voiding its warranty, the maximum open-circuit voltage (Voc) of the array must never exceed the charge controller’s maximum voltage rating at the lowest expected ambient temperature.
12 modules x 80 W each = 960 W (max. W controller must handle)
960 W ÷ 1,500 W max. controller W rating at nominal battery voltage (24 V) = 1 charge controller required (rounded up from 0.64)
22.1 V module Voc x 4 modules in series x 1.25 temp. multiplier (per NEC Table 690.7 for record low temp. of -35°F) = 110.5 VDC maximum PV array Voc
110.5 max. Voc < 150 VDC, the controller’s maximum Voc rating
*Max. system voltage was calculated using the module’s Voc temp. coefficient
Although charge controllers are most commonly rated by the amount of current (amps) they can deliver to the battery bank, it is often simpler to compare the calculated array watts with the controller manufacturer’s recommendation for maximum array watts (STC) at the applicable battery bank voltage. More often than not, the maximum array watts for different battery bank voltages are listed on the controller’s spec sheet, allowing the designer to simply divide the system’s array size (in watts) by the controller’s maximum allowable watts, to determine how many controllers will be needed.
Another option, especially when a controller spec sheet does not list the maximum allowable watts, is to use the manufacturer’s controller string-sizing tool on its Web site to determine allowable array configurations. If no string-sizing tool is available, make sure that the calculated array size meets the given controller specifications, mainly “maximum input current.” In the example here, the controller spec sheet does specify an STC nameplate rating of 1,500 W for a 24 VDC battery bank. Lastly, the above calculations also verify that at the coldest expected low temperature, the maximum array voltage will not exceed the controller’s maximum open-circuit voltage rating.
Step 5: Inverter Sizing
A battery-based inverter must handle all the household AC electrical loads that could be on simultaneously (AC total watts). An inverter must also be able to handle the expected surge or in-rush of current that some large loads draw upon startup. While a conservative method for estimating surge requirements is simply to multiply the total AC watts by three, realistically, many household loads do not surge. In this sizing example, likely only the clothes washer and well pump will surge significantly, although we also include the base load of the other appliances that may also be consuming power. Always be sure to compare the surge rating of an inverter with the expected surge requirements of the system.
Other design criteria include matching the inverter’s input voltage with the nominal battery voltage, choosing the desired AC output voltage (120 or 240 VAC), considering environmental conditions (indoor or outdoor, mountainous or coastal, etc.), and weighing different optional features, such as an internal battery charger.
2,356 W total AC loads = minimum inverter continuous watt rating (round up to 2,500 W typical inverter size)
[(1,560 W pump + 480 W washer) x 3] + 316 W base load = 6,436 W minimum surge rating
Desired AC output: 120 VAC
Desired features: Integrated AC-DC battery charger, digital display
An inverter with a continuous rating of 2,500 W and a minimum surge rating of 6,436 W will meet the household’s instantaneous power and surge requirements. The inverter model chosen must have an input voltage of 24 VDC to match the nominal voltage of the battery bank, and have an AC output voltage of 120 VAC to meet the needs of household loads. There are no 240 VAC loads in the Ackerman-Leist home, but if there were, the following options would be available: specify an inverter with 120/240 VAC output; stack two 120 V inverters in series; or use a step-up transformer for the loads that require 240 VAC. Inverter features are also important to consider, such as an inverter-integrated AC-DC battery charger. This feature is convenient for use with a backup generator when the batteries need supplemental charging. A digital interface can also be a helpful feature.
System Recap
This system was sized appropriately given the design parameters and, along with the backup generator, should provide the family with a reliable and long-lasting PV system. The daily and annual energy production of any PV system is largely dependent on how much available sunlight there is and weather patterns, which vary from year to year.
It is interesting to examine how the system design would change if a backup generator was not incorporated. Using the month with the lowest peak sun-hours (December, 2.8 daily sun-hours) and increasing the days of autonomy from three to five would require 20 batteries and 20 modules—a 66% increase! Of course, higher-capacity batteries and larger modules could be used, but the increase in cost would still be substantial.
Since it was installed in May 2004, the Ackerman-Leist system has performed well and has provided the family with almost all of their electrical needs—minus about 30 hours per year of generator run time to equalize the batteries and make up for occasional shortages during the winter months. Although the system was sized for 12 modules, they started out with 10 for budgetary reasons. But with the addition of two children to the family (making them a family of five) and a few new loads, they will be adding the other two PV modules soon. In addition to the use of efficient appliances, the family is also in-tune with the weather and their energy usage patterns; they only do laundry on sunny days and only use a clothesline to dry their clothes. The system powered the entire construction of their three-level home and has since served as an educational model for them, their community, and students at Green Mountain College, where Philip Ackerman-Leist teaches.
It’s inspiring to see a family of five use so little energy and yet live so comfortably—a system of this scale would be vastly undersized for almost any other full-time residence, at least here in the United States. A testament to energy conservation, efficiency, and awareness, the Ackerman-Leist family lives with their system, paying close attention to the ebb and flow of energy.
Access
Khanti Munro is a Green Mountain College alum, an ISPQ-certified PV instructor, and SEI’s PV online coordinator and instructor trainer. Tied to the grid since childhood, Khanti lives vicariously through his off-grid friends and clients, with ambitions to someday unplug.
The sizing method presented is the sole intellectual property of Solar Energy International (www.solarenergy.org), which acknowledges that there are many sizing methodologies available today, and assumes no liability for systems sized using this method. Omitted from this sizing exercise were some technically complex aspects including nonoptimal tilt and orientation derate factors, conductor and conduit sizing, overcurrent protection sizing, grounding, and PV mount selection.
http://www.homepower.com/articles/solar-electricity/design-installation/designing-stand-alone-pv-system?v=print
الأربعاء، 15 يونيو 2016
نظام الطاقة الشمسية - OFF GRID باسم خريس
نظام الطاقة الشمسية - OFF GRID
نتيجة للأزمات التي نعيشها في عالمنا العربي من حروب في العديد من الدول بدءا من العراق وليبيا و سوريا و السودان و انتهاء باليمن كما لا يخفى عليكم الحصار الخانق الذي يعاني منه الفلسطينيين في غزة الحبيبة التي خاضت ثلاث حروب طاحنة في أقل من عقد من الزمان ضد العدو الصهيوني كان أخرها و أشدها العام الماضي. برزت في هذه الدول أزمة نقص في الطاقة الكهربائية مما زاد من معاناة مواطني هذه الدول و أصبح شغلهم الشاغل هو كيفية توفير مصادر بديلة للطاقة الكهربائية لتدبير احتياجاتهم اليومية منها و لو بشكل جزئي.
وكنت قد دونت سابقا عن موضوع الطاقة الشمسية وحسب طلب العديد من الأخوة متابعي المدونة من خلال تواصلهم معي عبر الشبكات الاجتماعية على اختلافها و جدت أنه من الضروري الكتابة عن نظام الطاقة الشمسية بنوعيها ON GRID و OFF GRID و اليوم سأتناول النوع الثاني OFF GRID.
الصورة من على سطح مبنى في غزة.
وكنت قد دونت سابقا عن موضوع الطاقة الشمسية وحسب طلب العديد من الأخوة متابعي المدونة من خلال تواصلهم معي عبر الشبكات الاجتماعية على اختلافها و جدت أنه من الضروري الكتابة عن نظام الطاقة الشمسية بنوعيها ON GRID و OFF GRID و اليوم سأتناول النوع الثاني OFF GRID.
OFF GRID:
في العديد من الدول حتى المتقدمة منها كالولايات المتحدة الأمريكية و غيرها توجد مناطق نائية مأهولة بمجموعات قليلة من السكان هذه المناطق لا تصلها الشبكة العامة للكهرباء أو حتى المناطق التي يقصدها الأغنياء لقضاء إجازاتهم في الجبال و الغابات أصبحت الطاقة الشمسية الخيار الأمثل للتزود بالكهرباء في هذه المناطق رغم التكلفة العالية في البداية إلا أن الأسعار بدأت في النزول بشكل ملحوظ وخاصة لمكونات هذا النظام. كما أن نظام الطاقة الشمسية انتشر في دولنا العربية وهناك العديد من الخيارات والعروض المتوفرة في الأسواق ومن خلال هذه التدوينة أريد عرض فكرة ولو بسيطة عن نظام الطاقة الشمسية.
مكونات النظام:
مكونات النظام:
1- الخلايا الشمسية
2-وحدة الشحن و التحكم
3- الإنفرتر
4- البطاريات
كيف نصمم هذا النظام كي يلبي احتياجاتنا المطلوبة . سأشرح ذلك خطوة خطوة.
كيف نصمم هذا النظام كي يلبي احتياجاتنا المطلوبة . سأشرح ذلك خطوة خطوة.
الخطوة الأولى - حساب الأحمال:
قبل أن نفكر حتى بشراء أي من مكونات النظام يجب أن نقوم بحساب الأحمال و ببساطة الأحمال هي قدرة الأجهزة التي أريد تشغيلها و تحسب ب الوات و كم من الوقت سوف يعمل كل جهاز ويحسب ب الساعة وهنا العملية حسابية بحتة فكل ما علينا عملة حصر هذه الأجهزة ( ثلاجة - غسالة - تلفزيون - رسيفر - مروحة - لمبات إنارة - و غيرها من الأجهزة ) و تحديد كم من الوقت أريد تشغيل كل جهاز.
كل جهاز من الأجهزة المنزلية له لائحة مواصفات مذكور فيها قدرة هذا الجهاز بالوات بالإمكان رؤية هذه اللائحة على ظهر الجهاز أو مكتوبة في الكتالوج المرفق مع الجهاز.
الآن لحساب الوات ساعة لكل جهاز= قدرة الجهاز بالوات X عدد ساعات التشغيل.
مثال:
لمبة موفرة ذات قدرة 28 وات أُريد تشغيلها 5 ساعات
وات ساعة = 28 * 5 = 140
و هكذا نقوم بالحساب لباقي الأجهزة
مثال:
لمبة موفرة CFL عدد 4 بقدرة 15 وات للواحدة تشغيل 5 ساعات = 4*15*5=300 وات ساعة
مروحة بقدرة 60 وات تشغيل 3 ساعات = 60*3 = 180 وات ساعة
تلفزيون بقدرة 80 وات تشغيل 5 ساعات = 80*5 = 400 وات ساعة
رسيفر بقدرة 25 وات تشغيل 5 ساعات = 25*5 = 125 وات ساعة
مضخة مياه 1500 وات تشغيل 1 ساعة = 1500*1 = 1500 وات ساعة
غسالة مع تسخين 3000 وات تشغيل ساعة = 3000*1 = 3000 وات ساعة
جهاز كمبيوتر مكتبي 350 وات تشغيل 3 ساعات = 350*3 = 1050 وات ساعة
ثلاجة متوسط 275 وات تشغيل دائم 24 ساعة تحتاج إلى 1900 وات ساعة
إجمالي الوات/ ساعة للأجهزة المذكورة أعلاه = 300+180+400+125+1500+3000+1050+1900= 8455 وات ساعة
بعد إتمام هذه العملية الحسابية الناتج يساعدنا على تحديد مكونات النظام.
الخطوة الثانية - اختيار البطاريات:
من الضروري هنا أن نقرر الفولت المستخدم للنظام المراد تشغيله 12 فولت أو 24 فولت أو 48 فولت حيث كلما زاد الفولت قل التيار وبالتالي يمكننا استخدام كوابل نحاسية ذات قطر أقل.
سأختار نظام 24 فولت في حساباتي و هو الدارج في معظم المشاريع المنزلية.
لحساب سعة البطاريات المراد استخدامها كالتالي:
القدرة = الفولت * شدة التيار ( أمبير )
الوات ساعة = الفولت * أمبير * الزمن (ساعة )
فولت البطارية = 24 فولت
سعة البطارية = مجموع الأحمال / الفولت
إذا سعة البطارية لمجموع الأحمال المذكورة في المثال أعلاه = 8455 / 24 = 352 أمبير ساعة
من المعروف أن البطاريات حتى و إن كانت جديدة تكون كفاءتها بنسبة 80%
سعة البطارية المطلوبة = 352/0.8= 440.36 أمبير ساعة. بتقريب الناتج سيكون سعة البطارية 450 أمبير ساعة هو الخيار المناسب.
طبعا من عنده المقدرة لشراء بطاريات ذات سعة أعلى فهذا خيار جيد
إذا يمكن عمل بنك بطاريات مكون من 6 بطاريات سعة كل منها 150 أمبير ساعة توصل كل اثنتان على التوالي للحصول على 24 فولت ثم توصل الثلاث مجموعات على التوازي للحصول على سعة 450 أمبير ساعة و ينصح هنا باستخدام بطاريات عميقة الدورة
Deep cycle batteries .
الخطوة الثالثة - اختيار الألواح:
عدد الألواح يعتمد على مقدار ساعات الاستفادة من ضوء الشمس بكفاءة في منطقتك و الحمد لله منطقة الشرق الأوسط غنية بأشعة الشمس وتصنف من الأعلى توليدا للطاقة في المتوسط 7 كيلو وات ساعة / للمتر المربع يوميا.
إجمالي قدرة الخلايا = 24 فولت * 450 أمبير سعة البطارية = 10800 وات ساعة
على فرض إمكانية الاستفادة من ضوء الشمس بكامل طاقتها مدة 6 ساعات إذا القدرة المراد توليدها من الألواح =
10800/6= 1800 وات .
يوجود لدينا في السوق المحلي ألواح 24 فولت 300 وات
عدد الألواح المطلوب = 1800/300 = 6 لوح
أي 6 ألواح نظام 24 فولت 300 وات.
الخطوة الرابعة - اختيار و حدة التنظيم و الشحن:
يمكن تنظيم عملية الشحن يدويا بواسطة مفتاح ON/OFF. و هو الخيار الأقل تكلفة أما الخياران الآخران هما استخدام منظم شحن جاهز الأول PWM أو MPPT و الأخير هو الأعلى تكلفة و الأكثر كفاءة و هنا يجب مراعاة استخدام منظم يستطيع تمرير شدة تيار تزيد عن 75 أمبير حيث أن قدرة الألواح1800 وات نقسم على 24 فولت .
الخطوة الخامسة - اختيار الإنفيرتر:
لقد شرحت في موضوع سابق عن الإنفيرتر و في أنظمة الطاقة الشمسية يفضل استخدام الإنفيرتر ذو الموجة الجيبية النقية Pure sine wave و الأسواق مليئة بهذا النوع و منها المخصص للطاقة الشمسية كما أن يعض الأنواع تحتوي على وحدة الشحن والتنظيم مبنية داخل الجهاز و هو ما يعرف بثلاثة في واحد و لتحديد قدرة الإنفيرتر الذي يجب استخدامه في نظامي يجب أن نعود للمثال الذي وضحته في الخطوة الأولى وهو حساب كمية الأحمال المراد تشغيلها حيث نلاحظ أن أعلى قدرة لجهاز هو الغسالة مع استخدام التسخين الداخلي لها ( 3000 وات ) يليها مضخة المياه ( 1500 ) وات عادة قدرة الإنفيرتر يجب أن تساوي مجموع الأحمال أو أكثر و لكن نحن نتحدث عن الطاقة الشمسية المتوفرة فقط في النهار وبالتالي لجأنا لتخزين هذه الطاقة في بطاريات لاستخدامها في حال غياب ضوء الشمس ليلا وهنا لا أحتاج لإنفيرتر بقدرة تزيد عن 8000 وات فأنا لن أستعمل الغسالة على مدار اليوم وكذلك العديد من الأجهزة الأخرى و في الليل أحتاج للإنارة و نوع من التسلية عبر الوسائل المختلفة من تلفاز و راديو أو كمبيوتر و لحساب قدرة الإنفيرتر لنظام معتدل يفي بمعظم احتياجاتنا يمكن استخدام إتفيرتر قدرته تعادل أعلى قدرة من الأجهزة التي سوف أستخدمها مع زيادة بعض الشيئي لترك مساحة من الأمان لحاجة أي جهاز لقدرة أعلى أثناء التشغيل.
إذا الغسالة 3000 وات سيكون خياري هو إنفيرتر بقدرة 4500 وات لنظامي و هنا يجب مراعاة أنه يجب تشغيل الأجهزة عالية القدرة كالغسالة و المضخة و المكواة و الميكروويف ومجفف الشعر أو حتى مكيف هواء صغير و غيرها من الأجهزة المنزلية حسب برنامج وجدول معين أثناء النهار و تلافي تشغيل هذه الأجهزة ليلا كما يجب عدم تشغيل أكثر من جهاز في آن واحد.
إذا الغسالة 3000 وات سيكون خياري هو إنفيرتر بقدرة 4500 وات لنظامي و هنا يجب مراعاة أنه يجب تشغيل الأجهزة عالية القدرة كالغسالة و المضخة و المكواة و الميكروويف ومجفف الشعر أو حتى مكيف هواء صغير و غيرها من الأجهزة المنزلية حسب برنامج وجدول معين أثناء النهار و تلافي تشغيل هذه الأجهزة ليلا كما يجب عدم تشغيل أكثر من جهاز في آن واحد.
طبعا لن أذكر ماركة معينة أو نوع بعينه وذلك لاختلاف المتوفر في الأسواق كل حسب بلده.
الخطوة السادسة – تركيب الألواح:
و هذا متروك للمتخصصين في هذا المجال و أصحاب الخبرة حيث يجب تركيب الألواح على السطح بتوجيه و زوايا معينة للاستفادة من أكبر قدر ممكن من أشعة الشمس.
الخطوة السابعة – وضع البطاريات و الإنفيرتر على حامل أو رف بعيدا عن الرطوبة وكذلك بعيدا عن أيدي الأطفال أو أي شخص لا يستطيع التعامل مع الأجهزة الكهربائية وذلك لخطورة العبث بالأجهزة الكهربائية.
الخطوة الثامنة – التوصيلات:
وهذا العمل متروك للعاملين في هذا المجال مع مراعاة عمل التوصيلات طبقا للمعايير القياسية لأنظمة الطاقة الشمسية و لن أخوض في تفاصيلها من ألوان الكوابل و قطرها و الفيوزات و قواطع التيار إلى أخره من هذه الأمور .
الخاتمة:
أي نظام طاقة شمسية يجب أن تكون مكوناته مبنية على حساب احتياجاتنا من القدرة اللازمة لتشغيل الأجهزة المنزلية الدارج استعمالها في أي بيت بحيث يلبي هذا النظام معظم هذه الاحتياجات دون قصور في الكفاءة و الأداء مع مراعاة كل توصيات المنتج للحفاظ على الجودة و طول عُمر المكونات.
تنبيهات:
الألواح الشمسية تقل كفاءتها مع تراكم الغبار عليها بفعل الأحوال الجوية و بالتالي يجب مسحها من وقت لأخر.
يجب عدم تفريغ البطاريات بالكامل في أي حال من الأحوال هذا يؤدي إلى قصر عمرها الزمني و كفاءتها.
معظم الأجهزة المنزلية تحتاج لضعف القدرة المخصصة لها عند بدء التشغيل و هذا يؤخذ في الحسبان عند ثحديد قدرة الإنفيرتر.
معظم الأجهزة المنزلية تحتاج لضعف القدرة المخصصة لها عند بدء التشغيل و هذا يؤخذ في الحسبان عند ثحديد قدرة الإنفيرتر.
المصدر http://basemkhrais.blogspot.com/2015/09/off-grid.html
الاشتراك في:
الرسائل (Atom)