Off-Grid PV Solar system
DO IT YOUR WAY WITH DAILY POWER
It became easy to install a PV solar system in homes today because there are many engineers who can do it, but did you know that it is easy to do it on your own?
Solar energy is one of the most important sources from which electrical energy can be produced due to its high performance, ease of installation, as well as being cheap compared to other sources (wind energy for example).
Yes, you can do that alone and save costs when you make the following steps.
In this article, we will talk about how to install a PV solar system isolated from the network for combining houses or for people who do not have an electricity network close to their housing complex.
WHAT S THE PURPOSE OF SIZING?
The purpose behind the sizing of installation is to fix the modalities of implementation according to technical and financial criteria.Technical studies concern the design and sizing of photovoltaic fields and system components.
These components are mainly:
- Regulators (or converters)
- The dimensioning allows:
- An evaluation of the energy produced.
- Optimization of the PV system taking into account the factors influencing the system (shading, loss of energy, dirt, temperature, ct)
- The sizing aid tools are software like Homer, RETSCREEN, PV-CHART, TRNSYS, etc.
- sizing of a PV Solar system requires knowledge of :
- The nature of the installation (autonomous, injection into the network or hybrid)
- The nature of the load and the energy requirements
- The characteristics of PV modules.
- The characteristics of the site (sunshine weather conditions, etc.
- The modes of use of PV modules (fixed or mobile orientation (solar tracking)
- The angle of inclination.
- The technology and characteristics of the storage system (battery)
- Characteristics of regulators
- Characteristics of inverters.
ENERGY BALANCE OF PV SOLAR SYSTEM
Sizing a system is a fairly complicated task due to:
- The random and intermittent nature of solar radiation reaching the photovoltaic modules.
- Shading effects
- The effects of soil reflection (albedo).
- The orientation of the PV module (tilt, rotation, and azimuth orientation)
- Soiling of the modules …. etc
Therefore, there are several models for sizing a PV Solar system; among these models are:
- The simplified model .
- The pressure drop probability model.
STEP1:SIZING TOTAL LOADS
1.Determine Power consumption demande
Let s suppose for example you want run on theses devices :
freezer,6 lampes , a TV , a satelate etc..
The first step you goona do is to know the power for each device and hou many hour this device will be working .
- Where I can found the power of the device ?
Every electrical device has a datasheet on the back that says the power, amperes, and some information about the device, so it is easy to know the power of the device you want, and it is wrong to estimate that without referring to the datasheet because it is possible that the device can have a capacity of 100 watts and you put 150 Watts calculations.
- Determine the start-up current ( peak power ) of the freezer and air conditioners
The start-up current is one of the important things that you must know because it is one of the things that determines whether the device that needs start up current will cause a problem with regard to disconnecting the charging regulator from the system . I will give an example:
What is Peak power (Surge Power ) ?
When the freezer starts it draws a current greater than the value of the current it has been operating on during its entire period of operation, and therefore it needs a large take-off capacity called Peak power
In the table below you can see how to calcul total loads loads.
|Device||Power(W)||Time of work (h)||Load(Wh)|
Total loads = 5000+3600+750+200=9550wh=9.55kwh
Note: 9550wh is the quantity of power we need in our house every day to run theses devices but its not the final quantity we need, we have to add energy loss.
2.Add Enegry Loss of all the system
A percentage of 20 to 30 percent is added in order to compensate for the loss resulting from the components( Panels, batteries, controller, and the inverter ) of the following PV solar system must be added to the energy consumed in the day.
What causes energy loss ?
No device is 100 % efficient, there are lots of reasons why your PV solar system will not 100 % efficient and theses are some factors that affect the output (nominal ) energy :
- The accumulation of dirt on the panels causes a decrease in the amount of energy produced by the solar panel and the high temperature, as well as a little affect the efficiency of the panels.
- Overheating affects the amount of energy stored in the battery
- The total discharge of the batteries affects the efficiency of the battery’s energy storage… etc
- The inverter also is not 100 % efficience .
- Loss in wires.
In our case we estimate 30 % (1.3) of energy loss we get:
9550*1.3= 12415 wh/day per
12415 wh is the Final total power consumed by the devices everyday
3. Determine the system voltage
- Superior to 1200 w : 12 V PV solar System
- 1200-2400 :24 V PV solar System
- 2400 – 4800 :48 V PV solar System
12000w <12415w <2400 w
According to the result we get Our system is 24 V.
4.Total Capacity (Ah)
The Total capacity lead to sizing batteries and number of modules neccesairy
Capacity(Ah)=Final Total loads (total lods*loss)[ Wh] / System Voltage 24[V]
12415/24 = 517.3 Ah / day @24V
STEP2 : SIZING THE BATTERY BANK
- Daily Solar radation on the site for each meter square equals 2kwh/m2/day ( minimum value in winter )
- The System is 24 V.
- Days without radiation or days of storage (0-2 days) in winter .
- Depth of discharge is 80 %( required rate) .
- Temperature compensation 70 % ( at 0 degre)
1.Usual energy storage
Usual energy storage(Ah)= Total Load (ah/day) * number of days
Usual energy storage(Ah)= 517.3*2 = 1034.6 Ah
2.Depth of discharge
It is known that over-discharging reduces the life of the battery, so if we withdraw energy from the battery more than 80 percent several times, the battery will be damaged, but withdrawing a small percentage of energy from the battery necessitates the need for more batteries This means an increase in costs and this rated value must not pass 80 % .
Storage Capacity = Total capacity /0.8
Note : The depth od discharge must not be superior than 80 % ; capacity of the battery must not equal 0 Ah because this minimize the lifspan of the battery .
The picture below show relation between depth of discharge and number of cycles .
3.Pick up the capacity of battery (Ah)
Let s suppose you chosed a solar battery from Trojan company (trojan is an American company ) you choosed this brand or maybe mighy max anyway and you don t know what exactely you need for your system ? ;
1.The first thing you goona do is to look for a 12/24 V solar battery ( Because The system is 24 V)
Note : 6 v solar batteries are for small systems while the quantity of power you need is more than 1200 Wh ) .6V battery required lots of battery to achieve the 24 V .
The battery capacity is affected by the temperature as well, and not only by the discharge rate. Whenever the temperature is below zero, the battery capacity is affected. Let s take for example a temperature in the site is for winter months 00 C .
From the following picture, we note that the battery capacity decreases as the temperature decreases, and this is often in the months of winter.
Final Storage capacity = 1293.25 / 0.7
Final Storage capacity= 1847.5 Ah
5.Number of batteries
As you see the battery we choosed is [email protected]
Now we have to size the bank battery( number of batteries)
Number of Batteries = usual energy stored/ capacity of the battery
N = 1841.65/200= 10 Battery
10 Battery [email protected] 12V
STEP3 : PV MODULE SIZING
1.PEAK SUN HOURS (PSH)
This map helps to determine the number of hours that can be used from sunlight during the day in winter and summer and the number of hours in which sunlight can be used varies from one place to another, therefore x hours is a good rate that can be worked on.
Total Power given by modules = Total loads / number of hours (PSH)
12376 wh/ 5h=2475.2 w
3.NUMBER OF MODULES
The selection of the panels is not random, but rather according to the system, and the details of the panel must be known through the datasheet to see if the panel fits the batteries or not.
N = 2475.2/280= 9 Modules
Note( you have to make an eye on the system voltage because there are panels for 24 v systems and others for 12 v sytems also there exist solar panels for On-grid and off-Grid systems ) .
- If the module Vmp is 18 V that means the module can work on 12 V system .
- For 12V system : 36 Cell module.
- For 24 V System : 72 Cell module means The panel is 24 V .
4. HOW TO CONNECT MODULES?
The 9 modules which we have must be connected on parallel why ? because the system is 12 v so connecting 9 modules on parallel give us 12 V.
5.DIRECTION OF MODULES
How do you FIX the angle of the panels?
In the summer it is known that the position of the sun is high in the sky while the sun becomes low in the winter, and this means that the rays coming from the sun are not constant.
The ideal case in which the solar panel produces maximum energy is when the rays of the sun are perpendicular to the surface of the solar panel, i.e. practically forming a 90 degree angle with the surface of the solar panel
In general, you have three options :
- Once you place the solar panels at an angle equal to exactly the latitude of the location you are in
- Or to place the panels at an angle so that the station’s production is greater in winter
- Or to place the panels at an angle so that the plant’s production is greater in the summer
However, the angle remains exclusively related to the site. There is no fixed rule in the solar energy world regarding the angle of installation of the panels
Knowing that the angle has a very large impact on the panels’ electricity productivity
STEP4 : SIZING THE CHARGE CONTROLLER
The specifications of the charging regulator are calculated based mainly on the characteristics of modules I mean specifically on the value of the short circuit current of the module through the datasheet of the module, and thus you can know the value of the current ( Icc) that the module gives, and by that you choose the appropriate controller.
In the picture below you can see some informations of a module.
In our case , we have :
- MPPT Solar conroller
- Input Voltage 24 V
- Isc =8.87 A
- The conversion efficiency of 98%. (1.02)
Solar charge controller = Total short circuit current *Number of Modules *1.25
8.87*9*1.02 = 81.42 A
Note : we multiple in 9 because the 9 modules are on parallel ( Itotal=9*Isc)
That means a controller rated between ( 80 – 100 Amps)
Although the solar charge controller works on 12 and 24 volts, it alone automatically recognizes the voltage it is working on through the installed modules.
STEP 5:SIZING THE INVERTER
1.The role of the inverter
Solar panels generate DC electricity which must be converted to alternating current (AC) electricity and This will be done primarily with the role of the solar inverter.
Picking up the Total power (watt) of all appliance
Total Watt of All Appliance= 500+75+20+(6*50)=895 W
for safety ; the inverter should be considered 25-30 % bigger size because this allow you to add more devices in future if you decided to make your system more power producing and also for security .
The inverter should be about 895*1.3=1163.5w
Note: One of the most important things you should take when picking up an inverter is; the inverter should be 3 times surge power when the system starts working)
2.Which inverter I have to choose
The solar inverter is the most sophisticated part of any grid-tie PV solar system and unfortunately, it’s also the part most likely to have issues. This is not surprising considering inverters are usually located outside in harsh weather conditions including rain, humidity, and extreme heat, all while generating thousands of watts of power for up to 10 hours a day. This is why it’s important to use a quality inverter and mount it in a sheltered location if possible.
Characteristics of the inverter you must look for :
- 1.5 kW solar inverter
- Surge power 3.5 kW (3*1.16 kW)
- Pure sine wave
- Top Brand: SMA (Sunny boy series) / Fronius / SolarEdge / Sungrow /Huawei / Fimer / Victron/Reongy
- Continuous Power: 2000W
- Surge Power: 4000W
- Input Voltage: 12V
- Output Voltage: 115V AC
- Output Frequency (Nominal): 60 Hz
- USB Power Port: 5V/2.1A
- AC Output Sockets: 3
- Dimensions: 17.5 x 8.7 x 3.7 In
- Weight: 11.7 lbs
STEP6: SIZING CABLES (wires clip, length)
(Sizing will be performed on the basis of single phase current)
Assuming the following:
- Permissible voltage losses 3 %
- Wire length will be determined later.
- A.Wires Between modules and the controller
The 9 modules were connected in two chains (strings) on parallel and each string consist of 7 modules connected on series respectively.( 2 strings of 7 panels)
Assuming the specifications of one panel (8.7 amps, 18 volts”280 W”), the system specifications are as follows:
Vtot of modules =18 *7 = 126V
Itot of modules=8.7*2=17.4 A
Let s Say The length of the wire is 20 meters.
Wire clip= 2 * The length*Current intencity *0.03(0.01724 For aluminum and copper cables ) /(Voltage drop ratio* Voltage)
Wire clip =2*20*17.4*0.03/(0.03*126)
Wire clip=5.52 mm2 (3-4 AWG)
- B . Between The charge controller and bank of batteries
- 24 V System
- 90 A ( output voltage 24 v)
- The lengh of the cable 4 m
- Permissible voltage losses 3 %
Wire clip =2*4*90*0.03/(0.03*24)
wire clip = 30 mm2 (2.4 AWG)
- C.Between The inverter and Battries
Assuming the highest stable value is 1200W
- Battries voltages 24 V
- I=P/V = 1200/24V = 50A
- The lengh of the cable 4 m
- Permissible voltage losses 3 %
wire clip =( 2*4*50*0.03)/(0.03*24)
wire clip=16.66 mm2 (0.4 AWG)
- D.Wires between batteries
The wires between batteries in a battery bank tend to be the largest in the system since they are used in conjunction with a power inverter that can at times demand more current than that the PV system can supply on its own. These same wires will also have to carry current used simultaneously for charging and for power inversion. A typical battery bank wire size is 1/0 or “one-ought.”
Choosing the right wire sizes in your PV system is important for both performance and safety reasons. If the wires are undersized, there will be a significant voltage drop in the wires resulting in excess power loss. In addition, if the wires are undersized, there is a risk that the wires may heat up to the point in which a fire may result.
For more informations about this point read Choosing the Right Wire Size for every component in the system .
This video is also helpful
Description: This video explains the main things you need to keep in mind when purchasing wire for your solar panel system. There are numerous kinds and sizes of wires so it can be confusing and making a mistake can be expensive or hazardous to your health.
To check out the wire size calculator :free sun power
Inventory of components
- 9 Solar Panels of 280 W/36 Cell.Mono
- DC circuit breaker between Modules and charge controller.
- Solar charge controller 24 V (90-100 ) A.
- 10 Batteries 200 Ah/12
- .Inverter 2000W.
PV SOLAR SYSTEM – QUALITY SAFETY AND MAINTENANCE
One of the important things in the world of solar energy that the customer must know is the quality of the components and elements of the solar system, including solar panels, batteries, wires and charging regulators.
- SOLAR PANELS COSTS AND QUALITY
Regarding solar panels, I talked in a previous topic about the quality of the panels and the prices. You can view it from here. In short, you should avoid cheap panels that do not contain datasheet.
- SOLAR BATTERIES
Regarding solar batteries, I talked in a previous topic about matters related to batteries and how you can avoid expired batteries and how you can know the date of manufacture of the battery. You can view the post from here
- SOLAR PANELS -ANTI THEFT DEVICES
1.Akraboot 4 physically locks adjacent panels while attaching
them inseparably to the construction array. The Akraboot 4
system also allows all panels to be interconnected using any
electronic security system, guaranteeing immediate detection of any theft attempt. Advanced versions of the system
include integral electronic protection devices.
Akraboot 4 is suitable for existing PV systems as well as for
new plants Akarboot 4 units are also:
• Compatible with nearly all panel types.
• Seamlessly integrated with existing security measures
• Manufactured from extremely strong yet flexible
composite materials, ensuring maximum endurance and
• Easily installed causing no panel damage.
The Akraboot 4 system is cost effective and requires minimal
A plastic fiber cable protects every single solar panel, like a chain. The LiteSUN Plus analyser triggers an alarm when the fiber is bent or cut. As is is insensitive to vibrations (e.g. wind, rain, snow…) the system is very robust to false alarm. Plastic fiber LiteWIRE is very easy to handle, terminate and repair. Engineered and manufactured by Naria Security.
Watch this video : Anti-theft system for solar panels and do it your way .
There is no system that does not require maintenance and monitoring, and solar energy systems also need some kind of maintenance, which is cleaning panels, monitoring batteries and cables, and measuring the voltage between batteries. You can get more details in this article.
Regarding solar batteries, I talked in a previous topic about matters related to batteries and how you can avoid expired batteries and how you can know the date of manufacture of the battery.
Some Components Reviews
- The controller
- The inverter