Copy of Pv Design Software

SOLAR ELECTRICTY SYSTEM SIZING AND DESIGN SOFTWARE

DIGIBITS SOLAR EMPIRE

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NOFF-GRID SOLAR ELECTRICITY SYSTEM DESIGN

STEP 1: LOAD EVALUATION 1 Electrical Appliances DC(Watts) AC (Watts) Qty

Ceiling Fan (50watts) 50 1 Energy saver Light Bulb(18watts) 40 3Television(32")(150watts) 150 1DVD Player(40watts) 40 1Radio Player(40watts)Sattelite Dish decoder(30watts) 30 0LapTop Computer(90watts) 90 0Desktop Computer/ Monitor(180watts) 180 0Refrigerator(1140watts) 1140 0

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Deep Freezer(1200watts)Airconditioner(1500watts) 0Blender(1200watts)Microwave Cooker(1200watts)Pumping Machine 2HP(1200watts) 0Water Heater(1200watts) 0Iron(1200watts)Shaver/clipper(20watts)security light 75 0.0

miscellaneous(1200watts) 200 1



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Total watt-hr/dayTotal Connected Load (Continous Load) watts) 0 1,995

Load Correction factor(1.25)

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2 Convert to DC watts-hours per day. Multiply result from 1 above by 1.15 to correct for inverter loss3 Inverter DC Input voltage ; usually 12-,24-, or 48-volts. This is the DC system voltage4 Divide line 2 by line 3. This is the Total DC Amp-Hours per day used by AC Loads (Ah)5 Total DC loads from load evaluation in 1 above6 DC system voltage usually 12-,24-, or 48-volts.7 Find the Total Amp-Hours per day used by DCLoads: Divide line5 by line6

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STEP 2: SOLAR ARRAY SIZING FOR NON-MPPT CHARGE CONTROLLER

1 Total average Amp-Hours per day needed(line8 from step 1 above) (Ah)2 Multiply line 1 by 1.25 to compensate for loss from battery charge /discharge (Ah)

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3 Average sun-hour per day (yearly insolation of site):(this figure is from insolation map)4 Total Solar Array Amps required: Divide line2 by line3

5 Peak-Power Amps(A) of the solar module selected. Check module specification (STP280-24Vd Suntech solar)

6 Total number of solar modules required in parrallel: Divide line4 by line57 Round off to the next highest whole number

Total Amp-Hours per day used by all loads(AC LOADS and DC LOADS). This is the Total average Amp-Hours needed to be supplied by the battery bank. Add line4 and line7



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8Number of modules in each series string to provide DC battery voltage(see table below

9 Total Number of Solar Modules required for the system (Multiply line7 by line 8)

Volts 12V Modules 24V Modules12 1 N/A24 2 148 4 2

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N STEP 3: SOLAR ARRAY SIZING FOR USE WITH MPPT CHARGE CONTROLLER4 Total Solar Array Amps required: from line4 step 2 above

5Enter average charging voltage: use 13.5V for 12V Systems, use 27V for 24V Systems, 54V for 48V Systems

6 Calculate the Total PV Array wattage required: multiply line4 result by line5 result

7 Enter thePeak-Power Wattage of the chosen PV module. (Use the module's Peak power wattage at STC(STP-180S-24Ab-1)

8Total number of solar modules required (Divide the result in line6 by the wattage in line7)

9Round up to the nearest whole number(Note: this number may need to be adjusted in line11 below)

10 Number of modules in each series string (see table below and enter number here)

Nominal System Voltage

Number of Series Connected Modules Per String



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Module 12V 24V 48VEvergreen ES 1 to 3 2 to 3 3REC SCM -210 1 to 3 2 to 3 3

SolarWorld SW175 1 to 2 1 to 2 2MitsubishiUD185MF5 1 to 3* 2 to 3* 3*

12V Norminal Modules 1 to 5 3 to 5 4 to 5

12V Norminal Modules w/appolo controllers 2 to 5 3 to 5 5

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Table for 150VDC Maximum Controllers. (For Controllers with other Maximum Voltages, see Controllers instructions)

*In climates that never have freezing temperatures below 10oF Four MitsubishiUD185MF5 Module may be used in series.

Total number of series string: (Divide the Total number of modules in line9 by the number of modules per series string from line10 above). If this is not a whole number, either increase or decrease the number of module in line 9 to obtain a whole number of series strings. WARNING: Decreasing the total number of modules may result in insufficent power production

Determine the wattage of each series string. Multiply module wattage from line7 by number of module per string on line10. This is the total wattage per string.



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System Norminal Voltage12V 24V

15A 200W 400W30A 400W 800W50A 650W 1300W60A 750W 1500W80A 1000W 2000W

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STEP 4: BATTERY SIZING FOR YOUR SYSTEM

1 Total average Amp-Hours needed to be supplied by the battery bank. (line8 of step 1 )

2 Maximum nunber of expected cloudy Days for which storage is required(2-5 days)

Determine the number of module string per Controller. Divide appropriate Wattage figure from the chart below by the wattage per string from line12. Round up to a whole number. This is the total number of module string per controller. If you have more module strings(from line11) than can be handled by the chosen controller, either use a larger controller, or use multiple controllers.

Maximum watts that can be used with an MPPT Controller

Controller Amp Rating

Determine the number of Controllers needed by dividing the total number of strings from line11 by the number of strings per controller from line13. Round up to a whole number.



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N3 Multiply line1 by line2: Total Maximum average Amp-Hours for storage

4 Determine depth of discharge by dividing line 3 by 0.5. This will increase the battery shelf life(50%-80%)

if no special conditions below apply, skip to line 9

Special condition #1: Heavy Electrical Load

5 Maximum Amperage that will be drawn by the loads for 10 minutes or more

6 Multiply line5 by 5.0

Special condition #2: High- Charge Current

7 Maximum Output amperage of PV Array or other battrey charger.OFF-G

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8 Multiply line7 by 5.0

9 Amp-Hours from line 4, 6, or 8, whichever is largest.

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11 Optimum Battery size in amp-hours : Multiply line9 by line10 (Ah)

12 Amp-Hours of chosen battery(100Ah, 200Ah, 130Ah, 150Ah, 75Ah, e.t.c)

13 Total number of batteries in parallel required: (Divide the result in line11 by theAh of chosen battery in line12)

14 Round off to the next highest whole number:This is the number of parallel string required

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16 Total number of batteries required by the system battery bank: (Multiply the result in line14 by the result in line15)

If you are using Lead Acid Battery, select the multiplier from the battery temperature table below which correspond to the battery's wintertime average ambient temperature

Determine the number of batteries required in series: Divide the system voltage(12,24,or 48) by the chosen battery voltage(2, 6 or 12)



Multiplier1

1.041.111.191.31.4

1.59

STEP 5:SIZING PMW SOLAR CHARGE CONTROLLERS FOR YOUR SYSTEM

1 System sizing and Nominal Voltage

Battery Temperature

80OF/26.7OC70OF/21.2OC60OF/15.6OC50OF/10.05OC40OF/4.4OC30OF/-1.1OC20OF/-6.7OC

In sysytems using the one-voltage-in and and -out charge controller type, all three main components must have the same nominal voltage throughout the system(PV array, charge controller, and the battery bank). For these situations, the first step in charge controller sizing is voltage selection



2 Selected module's short-circuit current(Isc)

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4 Selected array's short-circuit current(Isc)

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The next step in pmw charge controller sizing involves the current. PV modules' current output varies with changing conditions of temperature and sunlight intensity, so we must add a prudent safety margin to ensure that the charge controller is not subjected to potentially damaging amperage. This is called "de-rating". this calculation is based on the solar module/array's rated output current. This rating is easily obtained for a single-module system by looking at the label on the back of the module. Current output is listed there in at least two ratings: current at maximum power(Imp), and short-circut current(Isc). Isc is always higher than Imp and sizing calculations should always be based on Isc even though a short-circuit in the system may seem like an unlikely occurance. The important point here is that there are conditions under which a module can produce more than it's rated current. we must protect the charge controller against those circumstances. We use a standard factor to account for all PV output-boosting circumstances. That factor is 1.25 or 125%. so our formula for current safety margin(de-rating) will look like this:

De-rated Minimum charge controller amperage(A) rating for a single module is module Isc multiplied by de-rating factor(1.25).Select a charge controller with a rating equal to or higher than your de-rated value. Always "round" upward.

If the array consists of more than one module, we must be sure to take the array wiring scheme into account as we calculate voltage and amperage, since the wiring method affects these figures. Series wiring produces additive voltage and constant amperage; while parralel wiring produces additive amperage and constant voltage. Calculate total array current accordingly.

De-rated Minimum charge controller amperage(A) rating for array is array Isc multiplied by de-rating factor(1.25).Select a charge controller with a rating equal to or higher than your de-rated value. Always "round" upward.

For systems in continuous operation, additional protection must be included to allow for heat and equipment stress(according to the National Electric Code[NEC]). Continuous operation is defined as three hours or longer of continuous use, which would include most PV systems. This second de-rating factor is also 1.25 or 125%.



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STEP 6:SIZING MPPT SOLAR CHARGE CONTROLLERS FOR YOUR SYSTEM

Fully De-rated Minimum charge controller amperage(A) rating for a single module is result from line3 above multiplied by de-rating factor(1.25).Select a charge controller with a rating equal to or higher than your de-rated value. Always "round" upward.

Fully De-rated Minimum charge controller amperage(A) rating for array is result from line5 above multiplied by de-rating factor(1.25).Select a charge controller with a rating equal to or higher than your de-rated value. Always "round" upward.

The reason for pointing out these two de-ratings seperately is that some charge controller manufacturers already include this second de-rating(for continuous use) in their products' rating figures. A typical example is morningstar brand of charge controllers. Their charge controllers are essentially already rated for continuous use. with morningstar controller, a total de-rating factor of 1.25 is all that's needed for a given system. if you are unsure whether the controller you are considering has already been de-rated for continuous use, err on the side of caution and use the double de-rating factor in your calculations.



1 Solar Panel array Wattage2 Solar Panel array Voltage3 Battery bank Voltage

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Solar charge controllers are rated and sized by the solar panel array current and system voltage. Most common are 12, 24, and 48-volt controllers. Amperage ratings normally run from 1 amp to 60 amps, voltages from 6-60 volts. For example, if one module in your 12-volt system produces 7.45 amps and two modules are utilized, your system will produce 14.9 amps of current at 12 volts. Because of light reflection and the edge of cloud effect, sporadically increased current levels are not uncommon. For this reason we increase the controller amperage by a minimum of 25% bringing our minimum controller amperage to 18.6. Looking through the products we find a 20-amp controller, as close a match as possible. There is no problem going with a 30-amp or larger controller, other than the additional cost. If you think the system may increase in size, additional amperage capacity at this time should be considered. Traditionally, you would assume that the nominal voltage of your battery and your solar panel array would be the same and that you would also choose that voltage for your charge controller. However, in recent years, a more efficient charging technology called Maximum Power Point Tracking (MPPT) has become available on some models of charge controllers. One of the interesting features of this technology is that it usually allows you to have a solar panel array with a much higher voltage than your battery bank's voltage. The MPPT charge controller will automatically and efficiently convert the higher voltage down to the lower voltage. A big advantage to having a higher voltage solar panel array is that you can use smaller gauge wiring to the charge controller. And since a solar panel array can sometimes be over a 100 feet away from the charge controller, keeping the cost of the wiring down to a minimum is usually an important financial goal for the whole project. When you double the voltage (e.g. from 12 to 24 volts), you will decrease the current going through the wires by half which means you use a quarter as much copper (or cable with half of the diameter).

Output amperage(A) required from the MPPT Charge controller: divide the solar array power(watts) by the battery bank voltage(volts)



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Another Benefit of MPPT Charge Controllers

How Charge Controllers Work

Allow for boosting(25%) to take into account special conditions that could occur causing the solar panel array to produce more power than it is normally rated for. Round up and choose the appropriate mppt charge controller.

Because MPPT charge controllers can handle a different (but higher) input voltage from the solar panel array than the battery bank's voltage, you can also use these charge controllers with solar panels that have odd voltages that don't match any typical system voltage (i.e. 12, 24 or 48V). For instance, you could have a solar panel that has a nominal voltage of 57 volts and charge and battery bank that's 24 volts efficiently with an MPPT charge controller. Be aware that MPPT charge controllers have an upper voltage limit that they can handle from the solar panel array. It's important that you make sure than there is no condition that the solar panel array voltage will go above this limit or you will like burn out the controller. You want to make sure that the open circuit voltage of the solar panel array does not go above this limit. You also want to give yourself a little bit of a margin for an error to take in account the possibility that a solar panel array's voltage will actually increase the colder it gets. If you give yourself a 10% margin of error you should be fine.We'll use four 12 volt Evergreen 102 Watt solar panels all run in series for a nominal voltage of 48 volts and our battery bank is at 12 volts. We'd like to use BZ Product's MPPT500 charge controller. If we look at the panel's specification page we see that each panel has an open circuit voltage of 21.3V. That means the array has four times that (because there are 4 panels in series). So the array open circuit voltage is 21.3V x 4 = 85.2V. We'll boost this up by 10% for safety and we get 93.7V. Now we'll look at the MPPT500's specifications and we see that it can take a maximum of 100 volts. So we're ok!



Functions of Charge Controllers

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Solar charge controllers are an essential element to any solar electric panel system. At a most basic level charge controllers prevent batteries from being overcharged and prevent the batteries from discharging through the solar panel array at night. A charge controller is an essential part of nearly all power systems that charge batteries, whether the power source is PV, wind, hydro, fuel, or utility grid. Its purpose is to keep your batteries properly fed and safe for the long term.

The basic functions of a controller are quite simple. Charge controllers block reverse current and prevent battery overcharge. Some controllers also prevent battery over discharge, protect from electrical overload, and/or display battery status and the flow of power. Let's examine each function individually.

Blocking Reverse Current Photovoltaic panels work by pumping current through your battery in one direction. At night, the panels may pass a bit of current in the reverse direction, causing a slight discharge from the battery. (Our term "battery" represents either a single battery or bank of batteries.) The potential loss is minor, but it is easy to prevent. Some types of wind and hydro generators also draw reverse current when they stop (most do not except under fault conditions). In most controllers, charge current passes through a semiconductor (a transistor) which acts like a valve to control the current. It is called a "semiconductor" because it passes current only in one direction. It prevents reverse current without any extra effort or cost. In some controllers, an electromagnetic coil opens and closes a mechanical switch. This is called a relay. (You can hear it click on and off.) The relay switches off at night, to block reverse current. If you are using a PV array only to trickle-charge a battery (a very small array relative to the size of the battery), then you may not need a charge controller. This is a rare application. An example is a tiny maintenance module that prevents battery discharge in a parked vehicle but will not support significant loads. You can install a simple diode in that case, to block reverse current. A diode used for this purpose is called a "blocking diode."

Preventing Overcharge



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When a battery reaches full charge, it can no longer store incoming energy. If energy continues to be applied at the full rate, the battery voltage gets too high. Water separates into hydrogen and oxygen and bubbles out rapidly. (It looks like it's boiling so we sometimes call it that, although it's not actually hot.) There is excessive loss of water, and a chance that the gasses can ignite and cause a small explosion. The battery will also degrade rapidly and may possibly overheat. Excessive voltage can also stress your loads (lights, appliances, etc.) or cause your inverter to shut off. Preventing overcharge is simply a matter of reducing the flow of energy to the battery when the battery reaches a specific voltage. When the voltage drops due to lower sun intensity or an increase in electrical usage, the controller again allows the maximum possible charge. This is called "voltage regulating." It is the most essential function of all charge controllers. The controller "looks at" the voltage, and regulates the battery charging in response. Some controllers regulate the flow of energy to the battery by switching the current fully on or fully off. This is called "on/off control." Others reduce the current gradually. This is called "pulse width modulation" (PWM). Both methods work well when set properly for your type of battery. A PWM controller holds the voltage more constant. If it has two-stage regulation, it will first hold the voltage to a safe maximum for the battery to reach full charge. Then, it will drop the voltage lower, to sustain a "finish" or "trickle" charge. Two-stage regulating is important for a system that may experience many days or weeks of excess energy (or little use of energy). It maintains a full charge but minimizes water loss and stress. The voltages at which the controller changes the charge rate are called set points. When determining the ideal set points, there is some compromise between charging quickly before the sun goes down, and mildly overcharging the battery. The determination of set points depends on the anticipated patterns of usage, the type of battery, and to some extent, the experience and philosophy of the system designer or operator. Some controllers have adjustable set points, while others do not.

Control Set Points vs. Temperature The ideal set points for charge control vary with a battery's temperature. Some controllers have a feature called "temperature compensation." When the controller senses a low battery temperature, it will raise the set points. Otherwise when the battery is cold, it will reduce the charge too soon. If your batteries are exposed to temperature swings greater than about 30 F (17 C), compensation is essential. Some controllers have a temperature sensor built in. Such a controller must be mounted in a place where the temperature is close to that of the batteries. Better controllers have a remote temperature probe, on a small cable. The probe should be attached directly to a battery in order to report its temperature to the controller. An alternative to automatic temperature compensation is to manually adjust the set points (if possible) according to the seasons. It may be sufficient to do this only twice a year, in spring and fall.



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Control Set Points vs. Battery Type The ideal set points for charge controlling depend on the design of the battery. The vast majority of RE systems use deep-cycle lead-acid batteries of either the flooded type or the sealed type. Flooded batteries are filled with liquid. These are the standard, economical deep cycle batteries. Sealed batteries use saturated pads between the plates. They are also called "valve-regulated" or "absorbed glass mat," or simply "maintenance-free." They need to be regulated to a slightly lower voltage than flooded batteries or they will dry out and be ruined. Some controllers have a means to select the type of battery. Never use a controller that is not intended for your type of battery. Typical set points for 12 V lead-acid batteries at 77 F (25 C)

(These are typical, presented here only for example.) High limit (flooded battery): 14.4 V High limit (sealed battery): 14.0 V Resume full charge: 13.0 V

Low Voltage Disconnect (LVD)



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7 Displays and Metering

The deep-cycle batteries used in renewable energy systems are designed to be discharged by about 80 percent. If they are discharged 100 percent, they are immediately damaged. Imagine a pot of water boiling on your kitchen stove. The moment it runs dry, the pot overheats. If you wait until the steaming stops, it is already too late! Similarly, if you wait until your lights look dim, some battery damage will have already occurred. Every time this happens, both the capacity and the life of the battery will be reduced by a small amount. If the battery sits in this over-discharged state for days or weeks at a time, it can be ruined quickly. The only way to prevent over-discharge when all else fails, is to disconnect loads (appliances, lights, etc.), and then to reconnect them only when the voltage has recovered due to some substantial charging. When over-discharge is approaching, a 12 volt battery drops below 11 volts (a 24 V battery drops below 22 V). A low voltage disconnect circuit will disconnect loads at that set point. It will reconnect the loads only when the battery voltage has substantially recovered due to the accumulation of some charge. A typical LVD reset point is 13 volts (26 V on a 24 V system). All modern inverters have LVD built in, even cheap pocket-sized ones. The inverter will turn off to protect itself and your loads as well as your battery. Normally, an inverter is connected directly to the batteries, not through the charge controller, because its current draw can be very high, and because it does not require external LVD. If you have any DC loads, you should have an LVD. Some charge controllers have one built in. You can also obtain a separate LVD device. Some LVD systems have a "mercy switch" to let you draw a minimal amount of energy, at least long enough to find the candles and matches! DC refrigerators have LVD built in. If you purchase a charge controller with built-in LVD, make sure that it has enough capacity to handle your DC loads. For example, let's say you need a charge controller to handle less than 10 amps of charge current, but you have a DC water pressurizing pump that draws 20 amps (for short periods) plus a 6 amp DC lighting load. A charge controller with a 30 amp LVD would be appropriate. Don't buy a 10 amp charge controller that has only a 10 or 15 amp load capacity!

Overload Protection A circuit is overloaded when the current flowing in it is higher than it can safely handle. This can cause overheating and can even be a fire hazard. Overload can be caused by a fault (short circuit) in the wiring, or by a faulty appliance (like a frozen water pump). Some charge controllers have overload protection built in, usually with a push-button reset. Built-in overload protection can be useful, but most systems require additional protection in the form of fuses or circuit breakers. If you have a circuit with a wire size for which the safe carrying capacity (ampacity) is less than the overload limit of the controller, then you must protect that circuit with a fuse or breaker of a suitably lower amp rating. In any case, follow the manufacturer's requirements and the National Electrical Code for any external fuse or circuit breaker requirements.



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STEP 7:SIZING WIRE AND CABLE FOR YOUR SYSTEM

Charge controllers include a variety of possible displays, ranging from a single red light to digital displays of voltage and current. These indicators are important and useful. Imagine driving across the country with no instrument panel in your car! A display system can indicate the flow of power into and out of the system, the approximate state of charge of your battery, and when various limits are reached. If you want complete and accurate monitoring however, spend about US$200 for a separate digital device that includes an amp-hour meter. It acts like an electronic accountant to keep track of the energy available in your battery. If you have a separate system monitor, then it is not important to have digital displays in the charge controller itself. Even the cheapest system should include a voltmeter as a bare minimum indicator of system function and status.

Have It All with a Power Center If you are installing a system to power a modern home, then you will need safety shutoffs and interconnections to handle high current. The electrical hardware can be bulky, expensive and laborious to install. To make things economical and compact, obtain a ready-built "power center." It can include a charge controller with LVD and digital monitoring as options. This makes it easy for an electrician to tie in the major system components, and to meet the safety requirements of the National Electrical Code or your local authorities. Conclusion The control of battery charging is so important that most manufacturers of high quality batteries (with warranties of five years or longer) specify the requirements for voltage regulation, low voltage disconnect and temperature compensation. When these limits are not respected, it is common for batteries to fail after less than one quarter of their normal life expectancy, regardless of their quality or their cost. A good charge controller is not expensive in relation to the total cost of a power system. Nor is it very mysterious. I hope this article has given you the background that you need to make a good choice of controls for your power system.



Universal Wire Sizing Chart A 2-Step Process

STEP 1: CALCULATE VOLTAGE DROP INDEX(VDI)1 Load in amperes(A)2 Distance(one-way wiring distance[measure in feet; 1 meter is 3.28ft]A3 % Voltage drop(usually 2-3%) but safe to use 2%4 DC System Voltage(12,24,48)B5 Voltage Drop Index(VDI)

STEP 2: DETERMINE APPROPRIATE WIRE SIZE FROM CHARTCompare your calculated VDI with the VDI in the chart to determine the closest wire size. Amps must not exceed the AMPACITY indicated for the wire size.

Wire Size Area mm2

COPPER

AWG VDI Ampacity

Properly sized wire can make the difference between inadequate and full charging of a battery system, between dim and bright lights, and between feeble and full performance of tools and appliances. Designers of low voltage power circuits are often unaware of the implications of voltage drop and wire size.In conventional home electrical systems (120/240 volts ac), wire is sized primarily for safe amperage carrying capacity (ampacity). The overriding concern is fire safety. In low voltage systems (12, 24, 48VDC) the overriding concern is power loss. Wire must not be sized merely for the ampacity, because there is less tolerance for voltage drop (except for very short runs). For example, at a constant wattage load, a 1V drop from 12V causes 10 times the power loss of a 1V drop from 120V.

This chart works for any voltage or voltage drop, American (AWG) or metric (mm2) sizing. It applies to typical DC circuits and to some simple AC circuits (single-phase AC with resistive loads, not motor loads, power factor = 1.0, line reactance negligible).



16 1 10

14 2 15

12 3 20

10 5 30

8 8 55

6 12 75

4 20 95

2 31 130

0 [1/0] 49 170

00 [2/0] 62 195

000 [3/0] 78 225

0000 [4/0] 99 260

Metric Size COPPER ALUMINUM

by cross-sectional area (VDI x 1.1 = mm2)

EXAMPLE:

20 Amp load at 24V over a distance of 100 feet with 3% max. voltage drop

VDI = (20x100)/(3x24) = 27.78

1.31(1.5mm2)

2.08 (2.5mm2)

3.31 (4mm2)

5.26 (6mm2)

8.37 (10mm2)

13.3 (16mm2)

21.1 (25mm2)

33.6 (35mm2)

53.5 (70mm2)

67.4 (70mm2)

85.0 (95mm2)

107 (120mm2)

(VDI x 1.7 = mm2)

Available Sizes: 1 1.5 2.5 4 6 10 16 25 35 50 70 95 120 mm2

NOTES: AWG=American Wire Gauge. Ampacity is based on the National Electrical Code (USA) for 30 degrees C (85 degrees F) ambient air temperature, for no more than three insulated conductors in raceway in free air of cable types AC, NM, NMC and SE; and conductor insulation types TA, TBS, SA, AVB, SIS, RHH, THHN and XHHW. For other conditions, refer to National Electric Code or an engineering handbook.

For copper wire, the nearest VDI=31.

This indicates #2 AWG wire or 35mm2



OFF-GRID SOLAR ELECTRICITY SYSTEM DESIGN

STEP 1: LOAD EVALUATION Hrs/day usage

Watt.Hrs/day6.0 300.0 506.0 720.0 1206.0 900.0 1506.0 240.0 40

0.0 010.0 0.0 05.0 0.0 05.0 0.0 06.0 0.0 0

0.0 05.0 0.0 0

0.0 00.0 0

2.0 0.0 02.0 0.0 0

0.0 00.0 0

10.0 0.0 00.0 0

2 400.0 200

inverter sizing



Total watt-hr/day 2,560.0 560.0

Convert to DC watts-hours per day. Multiply result from 1 above by 1.15 to correct for inverter loss 2,944Inverter DC Input voltage ; usually 12-,24-, or 48-volts. This is the DC system voltage 12Divide line 2 by line 3. This is the Total DC Amp-Hours per day used by AC Loads (Ah) 245Total DC loads from load evaluation in 1 above 0DC system voltage usually 12-,24-, or 48-volts. 12Find the Total Amp-Hours per day used by DCLoads: Divide line5 by line6 0

245

STEP 2: SOLAR ARRAY SIZING FOR NON-MPPT CHARGE CONTROLLER

Total average Amp-Hours per day needed(line8 from step 1 above) (Ah) 245Multiply line 1 by 1.25 to compensate for loss from battery charge /discharge (Ah) 307

Average sun-hour per day (yearly insolation of site):(this figure is from insolation map) 4.5

Total Solar Array Amps required: Divide line2 by line3 68Peak-Power Amps(A) of the solar module selected. Check module specification (STP280-24Vd Suntech solar) 7.13

Total number of solar modules required in parrallel: Divide line4 by line5 9.6

Round off to the next highest whole number 10

Total Amp-Hours per day used by all loads(AC LOADS and DC LOADS). This is the Total average Amp-Hours needed to be supplied by the



Number of modules in each series string to provide DC battery voltage(see table below1

Total Number of Solar Modules required for the system (Multiply line7 by line 8) 10

48V ModulesN/AN/A1

STEP 3: SOLAR ARRAY SIZING FOR USE WITH MPPT CHARGE CONTROLLER

Total Solar Array Amps required: from line4 step 2 above 68

Enter average charging voltage: use 13.5V for 12V Systems, use 27V for 24V Systems, 54V for 48V Systems13.5

Calculate the Total PV Array wattage required: multiply line4 result by line5 result 920

Enter thePeak-Power Wattage of the chosen PV module. (Use the module's Peak power wattage at STC(STP-180S-24Ab-1) 142

Total number of solar modules required (Divide the result in line6 by the wattage in line7)6.5

Round up to the nearest whole number(Note: this number may need to be adjusted in line11 below) 6Number of modules in each series string (see table below and enter number here) 1

Number of Series Connected Modules Per



6

142

Total number of series string: (Divide the Total number of modules in line9 by the number of modules per series string from line10 above). If this is not a whole number, either increase or decrease the number of module in line 9 to obtain a whole

Decreasing the total number of modules may result in insufficent power production

Determine the wattage of each series string. Multiply module wattage from line7 by number of module per string on line10.



2.8

80A

char

ge c

ontro

ller

System Norminal Voltage48V

800W1600W2600W3000W4000W

2

STEP 4: BATTERY SIZING FOR YOUR SYSTEM

Total average Amp-Hours needed to be supplied by the battery bank. (line8 of step 1 ) 245Maximum nunber of expected cloudy Days for which storage is required(2-5 days) 1

Determine the number of module string per Controller. Divide appropriate Wattage figure from the chart below by the wattage per string from line12. Round up to a whole number. This is the total number of module string per controller. If you have more module strings(from line11) than can be handled by the chosen controller, either use a larger controller, or use multiple

Maximum watts that can be used with an MPPT Controller

Determine the number of Controllers needed by dividing the total number of strings from line11 by the number of strings per



Multiply line1 by line2: Total Maximum average Amp-Hours for storage 245Determine depth of discharge by dividing line 3 by 0.5. This will increase the battery shelf life(50%-80%) 491

Special condition #1: Heavy Electrical Load

Maximum Amperage that will be drawn by the loads for 10 minutes or more 0Multiply line5 by 5.0 0Special condition #2: High- Charge Current

Maximum Output amperage of PV Array or other battrey charger. 55.65Multiply line7 by 5.0 278Amp-Hours from line 4, 6, or 8, whichever is largest. 491

1.19

Optimum Battery size in amp-hours : Multiply line9 by line10 (Ah) 584Amp-Hours of chosen battery(100Ah, 200Ah, 130Ah, 150Ah, 75Ah, e.t.c) 200Total number of batteries in parallel required: (Divide the result in line11 by theAh of chosen battery in line12) 2.9Round off to the next highest whole number:This is the number of parallel string required 3

1

Total number of batteries required by the system battery bank: (Multiply the result in line14 by the result in line15) 3

If you are using Lead Acid Battery, select the multiplier from the battery temperature table below which correspond to the

Determine the number of batteries required in series: Divide the system voltage(12,24,or 48) by the chosen battery voltage(2,



STEP 5:SIZING PMW SOLAR CHARGE CONTROLLERS FOR YOUR SYSTEM

System sizing and Nominal Voltage 12

have the same nominal voltage throughout the system(PV array, charge controller, and the battery bank). For these situations, the first step in charge controller sizing is voltage selection



Selected module's short-circuit current(Isc) 7.84

9.80

Selected array's short-circuit current(Isc) 78.4

98.0

PV modules' current output varies with changing conditions of temperature and sunlight intensity, so we must add a prudent safety margin to ensure that the charge controller is not subjected to potentially damaging amperage. This is

this calculation is based on the solar module/array's rated output current. This rating is easily obtained for a single-module system by looking at the label on the back of the module. Current output is listed there in at least two ratings: current at maximum power(Imp), and short-circut

Isc is always higher than Imp and sizing calculations should always be based on Isc even though a short-circuit in the system may seem like The important point here is that there are conditions under which a module can produce more than it's rated current. we must

PV output-boosting circumstances. That factor is

factor(1.25).Select a charge controller with a rating equal to or higher than your de-rated value. Always "round" upward.

If the array consists of more than one module, we must be sure to take the array wiring scheme into account as we calculate voltage and amperage, since the wiring method affects these figures. Series wiring produces additive voltage and constant amperage; while parralel wiring produces additive amperage

De-rated Minimum charge controller amperage(A) rating for array is array Isc multiplied by de-rating factor(1.25).Select a charge

For systems in continuous operation, additional protection must be included to allow for heat and equipment stress(according to the National Electric Code[NEC]). Continuous operation is defined as three hours or longer of continuous use, which would include most PV systems. This second de-rating



12.3

122.5

STEP 6:SIZING MPPT SOLAR CHARGE CONTROLLERS FOR YOUR SYSTEM

Fully De-rated Minimum charge controller amperage(A) rating for a single module is result from line3 above multiplied by de-rating factor(1.25).Select a charge controller with a rating equal to or higher than your de-rated value. Always "round" upward.

Fully De-rated Minimum charge controller amperage(A) rating for array is result from line5 above multiplied by de-rating factor(1.25).Select a charge controller with a rating equal to or higher than your de-rated value. Always "round" upward.

The reason for pointing out these two de-ratings seperately is that some charge controller manufacturers already include this second de-rating(for continuous use) in their products' rating figures. A typical example is morningstar brand of charge controllers. Their charge controllers are essentially already rated for continuous use. with morningstar controller, a total de-rating factor of 1.25 is all that's needed for a given system. if you are unsure whether the controller you are considering has already been de-rated for continuous use,



Solar Panel array Wattage 1420Solar Panel array Voltage 12Battery bank Voltage 12

118

Solar charge controllers are rated and sized by the solar panel array current and system voltage. Most common are 12, 24, and 48-volt controllers. Amperage ratings normally run from 1 amp to 60 amps, voltages from 6-60 volts. For example, if one module in your 12-volt system produces 7.45 amps and two modules are utilized, your system will produce 14.9 amps of current at 12 volts. Because of light reflection and the edge of cloud effect, sporadically increased current levels are not uncommon. For this reason we increase the controller amperage by a minimum of 25% bringing our minimum controller amperage to 18.6. Looking through the products we find a 20-amp controller, as close a match as possible. There is no problem going with a 30-amp or larger controller, other than the additional cost. If you think the system may increase in size, additional amperage capacity at this time should be considered. Traditionally, you would assume that the nominal voltage of your battery and your solar panel array would be the same and that you would also choose that voltage for your charge controller. However, in recent years, a more efficient charging technology called Maximum Power Point

One of the interesting features of this technology is that it voltage. The MPPT charge controller

will automatically and efficiently convert the higher voltage down to the lower voltage. A big advantage to having a higher voltage solar panel array is that you can use smaller gauge wiring to the charge controller. And since a solar panel array can sometimes be over a 100 feet away from the charge controller, keeping the cost of the wiring down to a minimum is usually an important financial goal for the whole project. When you double the voltage (e.g. from 12 to 24 volts), you will decrease the current going through the wires by half

Output amperage(A) required from the MPPT Charge controller: divide the solar array power(watts) by the battery bank



148

Another Benefit of MPPT Charge Controllers

How Charge Controllers Work

Allow for boosting(25%) to take into account special conditions that could occur causing the solar panel array to produce more power than it is

Because MPPT charge controllers can handle a different (but higher) input voltage from the solar panel array than the battery bank's voltage, you can also use these charge controllers with solar panels that have odd voltages that don't match any typical system voltage (i.e. 12, 24 or 48V). For instance, you could have a solar panel that has a nominal voltage of 57 volts and charge and battery bank that's 24 volts efficiently with an MPPT charge controller. Be aware that MPPT charge controllers have an upper voltage limit that they can handle from the solar panel array. It's important that you make sure than there is no condition that the solar panel array voltage will go above this limit or you will like burn out the controller. You want to make sure that the open circuit voltage of the solar panel array does not go above this limit. You also want to give yourself a little bit of a margin for an error to take in account the possibility that a solar panel array's voltage will actually increase the colder it gets. If you give yourself a 10% margin of error you should be fine.We'll use four 12 volt Evergreen 102 Watt solar panels all run in series for a nominal voltage of 48 volts and our battery bank is at 12 volts. We'd like to use BZ Product's MPPT500 charge controller. If we look at the panel's specification page we see that each panel has an open circuit voltage of 21.3V. That means the array has four times that (because there are 4 panels in series). So the array open circuit voltage is 21.3V x 4 = 85.2V. We'll boost this up by 10% for safety and we get 93.7V. Now we'll look at the MPPT500's specifications and we see that it can take a maximum of 100 volts. So we're ok!



Functions of Charge Controllers

Solar charge controllers are an essential element to any solar electric panel system. At a most basic level charge controllers prevent batteries from being overcharged and prevent the batteries from discharging through the solar panel array at night. A charge controller is an essential part of nearly all power systems that charge batteries, whether the power source is PV, wind, hydro, fuel, or utility grid. Its purpose is to keep your

The basic functions of a controller are quite simple. Charge controllers block reverse current and prevent battery overcharge. Some controllers also prevent battery over discharge, protect from electrical overload, and/or display

Photovoltaic panels work by pumping current through your battery in one direction. At night, the panels may pass a bit of current in the reverse direction, causing a slight discharge from the battery. (Our term "battery" represents either a single battery or bank of batteries.) The potential loss is minor, but it is easy to prevent. Some types of wind and hydro generators also draw reverse current when they stop (most do not except under fault conditions). In most controllers, charge current passes through a semiconductor (a transistor) which acts like a valve to control the current. It is called a "semiconductor" because it passes current only in one direction. It prevents reverse current without any extra effort or cost. In some controllers, an electromagnetic coil opens and closes a mechanical switch. This is called a relay. (You can hear it click on and off.) The relay switches off at night, to block reverse current. If you are using a PV array only to trickle-charge a battery (a very small array relative to the size of the battery), then you may not need a charge controller. This is a rare application. An example is a tiny maintenance module that prevents battery discharge in a parked vehicle but will not support significant loads. You can install a simple diode in that case, to block reverse current. A diode used for this purpose is called a "blocking diode."



When a battery reaches full charge, it can no longer store incoming energy. If energy continues to be applied at the full rate, the battery voltage gets too high. Water separates into hydrogen and oxygen and bubbles out rapidly. (It looks like it's boiling so we sometimes call it that, although it's not actually hot.) There is excessive loss of water, and a chance that the gasses can ignite and cause a small explosion. The battery will also degrade rapidly and may possibly overheat. Excessive voltage can also stress your loads (lights, appliances, etc.) or cause your inverter to shut off. Preventing overcharge is simply a matter of reducing the flow of energy to the battery when the battery reaches a specific voltage. When the voltage drops due to lower sun intensity or an increase in electrical usage, the controller again allows the maximum possible charge. This is called "voltage regulating." It is the most essential function of all charge controllers. The controller "looks at" the voltage, and regulates the battery charging in response. Some controllers regulate the flow of energy to the battery by switching the current fully on or fully off. This is called "on/off control." Others reduce the current gradually. This is called "pulse width modulation" (PWM). Both methods work well when set properly for your type of battery. A PWM controller holds the voltage more constant. If it has two-stage regulation, it will first hold the voltage to a safe maximum for the battery to reach full charge. Then, it will drop the voltage lower, to sustain a "finish" or "trickle" charge. Two-stage regulating is important for a system that may experience many days or weeks of excess energy (or little use of energy). It maintains a full charge but minimizes water loss and stress. The voltages at which the controller changes the charge rate are called set points. When determining the ideal set points, there is some compromise between charging quickly before the sun goes down, and mildly overcharging the battery. The determination of set points depends on the anticipated patterns of usage, the type of battery, and to some extent, the experience and philosophy of the system designer or operator. Some controllers have adjustable set points, while others do

The ideal set points for charge control vary with a battery's temperature. Some controllers have a feature called "temperature compensation." When the controller senses a low battery temperature, it will raise the set points. Otherwise when the battery is cold, it will reduce the charge too soon. If your batteries are exposed to temperature swings greater than about 30 F (17 C), compensation is essential. Some controllers have a temperature sensor built in. Such a controller must be mounted in a place where the temperature is close to that of the batteries. Better controllers have a remote temperature probe, on a small cable. The probe should be attached directly to a battery in order to report its temperature to the controller. An alternative to automatic temperature compensation is to manually adjust the set points (if possible) according to the seasons. It may be



The ideal set points for charge controlling depend on the design of the battery. The vast majority of RE systems use deep-cycle lead-acid batteries of either the flooded type or the sealed type. Flooded batteries are filled with liquid. These are the standard, economical deep cycle batteries. Sealed batteries use saturated pads between the plates. They are also called "valve-regulated" or "absorbed glass mat," or simply "maintenance-free." They need to be regulated to a slightly lower voltage than flooded batteries or they will dry out and be ruined. Some controllers have a means to select the type of battery. Never use a controller that is not intended for your type of battery. Typical set points for 12 V lead-acid batteries at 77 F (25

(These are typical, presented here only for example.) High limit (flooded battery): 14.4 V High limit (sealed battery): 14.0 V



The deep-cycle batteries used in renewable energy systems are designed to be discharged by about 80 percent. If they are discharged 100 percent, they are immediately damaged. Imagine a pot of water boiling on your kitchen stove. The moment it runs dry, the pot overheats. If you wait until the steaming stops, it is already too late! Similarly, if you wait until your lights look dim, some battery damage will have already occurred. Every time this happens, both the capacity and the life of the battery will be reduced by a small amount. If the battery sits in this over-discharged state for days or weeks at a time, it can be ruined quickly. The only way to prevent over-discharge when all else fails, is to disconnect loads (appliances, lights, etc.), and then to reconnect them only when the voltage has recovered due to some substantial charging. When over-discharge is approaching, a 12 volt battery drops below 11 volts (a 24 V battery drops below 22 V). A low voltage disconnect circuit will disconnect loads at that set point. It will reconnect the loads only when the battery voltage has substantially recovered due to the accumulation of some charge. A typical LVD reset point is 13 volts (26 V on a 24 V system). All modern inverters have LVD built in, even cheap pocket-sized ones. The inverter will turn off to protect itself and your loads as well as your battery. Normally, an inverter is connected directly to the batteries, not through the charge controller, because its current draw can be very high, and because it does not require external LVD. If you have any DC loads, you should have an LVD. Some charge controllers have one built in. You can also obtain a separate LVD device. Some LVD systems have a "mercy switch" to let you draw a minimal amount of energy, at least long enough to find the candles and matches! DC refrigerators have LVD built in. If you purchase a charge controller with built-in LVD, make sure that it has enough capacity to handle your DC loads. For example, let's say you need a charge controller to handle less than 10 amps of charge current, but you have a DC water pressurizing pump that draws 20 amps (for short periods) plus a 6 amp DC lighting load. A charge controller with a 30 amp LVD would be appropriate. Don't buy

A circuit is overloaded when the current flowing in it is higher than it can safely handle. This can cause overheating and can even be a fire hazard. Overload can be caused by a fault (short circuit) in the wiring, or by a faulty appliance (like a frozen water pump). Some charge controllers have overload protection built in, usually with a push-button reset. Built-in overload protection can be useful, but most systems require additional protection in the form of fuses or circuit breakers. If you have a circuit with a wire size for which the safe carrying capacity (ampacity) is less than the overload limit of the controller, then you must protect that circuit with a fuse or breaker of a suitably lower amp rating. In any case, follow the manufacturer's requirements and the National Electrical Code for any external fuse or circuit breaker requirements.



STEP 7:SIZING WIRE AND CABLE FOR YOUR SYSTEM

Charge controllers include a variety of possible displays, ranging from a single red light to digital displays of voltage and current. These indicators are important and useful. Imagine driving across the country with no instrument panel in your car! A display system can indicate the flow of power into and out of the system, the approximate state of charge of your battery, and when various limits are reached. If you want complete and accurate monitoring however, spend about US$200 for a separate digital device that includes an amp-hour meter. It acts like an electronic accountant to keep track of the energy available in your battery. If you have a separate system monitor, then it is not important to have digital displays in the charge controller itself. Even the cheapest system should include a voltmeter as a bare minimum indicator of system function and status.

If you are installing a system to power a modern home, then you will need safety shutoffs and interconnections to handle high current. The electrical hardware can be bulky, expensive and laborious to install. To make things economical and compact, obtain a ready-built "power center." It can include a charge controller with LVD and digital monitoring as options. This makes it easy for an electrician to tie in the major system components, and to meet the safety requirements of the National Electrical

The control of battery charging is so important that most manufacturers of high quality batteries (with warranties of five years or longer) specify the requirements for voltage regulation, low voltage disconnect and temperature compensation. When these limits are not respected, it is common for batteries to fail after less than one quarter of their normal life expectancy, regardless of their quality or their cost. A good charge controller is not expensive in relation to the total cost of a power system. Nor is it very mysterious. I hope this article has given you the background that you need to make a good choice of controls for your



Universal Wire Sizing Chart A 2-Step Process

Load in amperes(A) 68Distance(one-way wiring distance[measure in feet; 1 meter is 3.28ft] 30

2,044% Voltage drop(usually 2-3%) but safe to use 2% 2DC System Voltage(12,24,48) 12

24Voltage Drop Index(VDI) 85.19

Compare your calculated VDI with the VDI in the chart to determine the closest wire size. Amps must not exceed the AMPACITY indicated for the wire size.

ALUMINUM

VDI Ampacity

Properly sized wire can make the difference between inadequate and full charging of a battery system, between dim and bright lights, and between feeble and full performance of tools and appliances. Designers of low voltage power circuits are often unaware of the implications of voltage drop and wire size.In conventional home electrical systems (120/240 volts ac), wire is sized primarily for safe amperage carrying capacity (ampacity). The overriding concern is fire safety. In low voltage systems (12, 24, 48VDC) the overriding concern is power loss. Wire must not be sized merely for the ampacity, because there is less tolerance for voltage drop (except for very short runs). For example, at a constant wattage load, a 1V drop from 12V causes 10 times the power loss of

This chart works for any voltage or voltage drop, American (AWG) or metric (mm2) sizing. It applies to typical DC circuits and to some simple AC circuits (single-phase AC with resistive loads, not motor loads, power factor = 1.0, line reactance negligible).



Not Recommended

20 100

31 132

39 150

49 175

62 205

NOTES: AWG=American Wire Gauge. Ampacity is based on the National Electrical Code (USA) for 30 degrees C (85 degrees F) ambient air temperature, for no more than three insulated conductors in raceway in free air of cable types AC, NM, NMC and SE; and conductor insulation types TA, TBS, SA, AVB, SIS, RHH, THHN and XHHW. For other conditions, refer to National Electric

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