DIY OFF GRID SOLAR SYSTEM

Day by day the price of the solar panel falls gradually. But still, installation of a complete off-grid solar system is costly. So I write this instructable to get all the components of your solar system separately and assemble it all by yourself.

Checkout my updated V2.0 Instructables on Off-Grid Solar System

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If you are decided to install a solar panel system to cover your home power needs. This tutorial is for you.

I have tried my best to guide you step by step from buying different components to wiring everything by yourself.

Only you have to know some basic electrical and math for designing the entire system. Instead of this, I have attached links of my other Instructables to make the charge controller and energy meter.

For an off-grid solar system, you need four basic components

1. Solar Panel (PV Panel)

2.Charge Controller

3. Inverter

4.Battery

Besides the above components you need a few more things like Copper Wire, MC4 Connector, breaker, meter, and fuses, etc.

In the next few steps, I will explain in details how you can choose the above components according to your requirement.

Note: In the picture I have shown a big solar panel of 255W @ 24V, two batteries of 12V @ 100Ah each, 30A @ 12/24V PWM solar charge controller and a 1600 VA pure sine wave inverter. But during the calculation, I have taken a smaller solar system example for better understanding.

Before choosing the components you have to calculate what is your load, how much time it will run etc. If anyone knows basic maths then It is very simple to calculate.

1. Decide what appliances (light, fan, tv, etc ) you want to run and how much time (hour).

2. See the specification chart in your appliances for power rating.

3. Calculate the Watt Hour which is equal to the product of power rating of your appliances and time ( hr) of the run.

Example :

Lets you want to run an 11W CFL for 5hour from the solar panel, then the watt-hour is equal to

Watt Hour = 11W x 5 hr = 55

4. Calculate the total Watt Hour: Just like a CFL calculate the watt-hour for all the appliances and add them together.

Example :

CFL =11W x 5 hr = 55

Fan = 50 W x 3hr = 150

TV = 80W x 2hr = 160

------------------------------------------------

Total Watt Hour = 55+150+160 = 365

Considering 30% energy lost in the system.

So total Watt Hour per day = 365 x 1.3 = 474.5 Wh which can be round off to 475 Wh

Now the load calculation is over. The next thing is to choose the right components to match your load requirement.

If you are not interested to do the above maths then use a load calculator for this calculation. You can use this nice Load Calculator.

The Solar Panel converts the sunlight into electricity as direct current (DC). These are typically categorized as

monocrystalline or polycrystalline. Monocrystalline is costlier and efficient than the polycrystalline panel.

Solar panels are generally rated under standard test conditions (STC): irradiance of 1,000 W/m², the solar spectrum of AM 1.5 and module temperature at 25°C.

RATING OF SOLAR PANEL :

The solar panel size should be selected in such a way that it will charge the battery fully during the one day time.

During the 12hr day time, the sunlight is not uniform it also differs according to your location around the globe. So we can assume 4 hours of effective sunlight which will generate the rated power.

Total Wp of PV panel capacity needed = 475Wh /4 = 118.75 W

By taking some margin you can choose a 120 Watt, 12v solar panel.

Here you should not confuse with the 12V. I wrote 12V as it is suitable for charging the 12V battery. But actually the Solar panel voltage is around 17V or more.

The output from the solar panel is dc power. This power is generated during day time only. So if you want to run a dc load during day time then it seems to be very easy. But doing this is not a good decision because


>> Most of the appliances need a constant rated voltage to run efficiently. Solar panel voltage is not constant it varies according to the sunlight.


>> If you want to run the appliances during the night then it is impossible.


The above problem is solved by using a battery to store the solar power during the day time and use it according to your choice. It will provide a constant source of stable, reliable power.


There is various kind of Batteries. Car and bike batteries are designed for supplying short bursts of high current and then be recharged and are not designed for deep discharge. But the solar battery is a deep-cycle lead-acid battery that allows for partial discharge and allows for deep slow discharge. The lead-acid tubular battery is perfect for a solar system.


Ni-MH batteries and Li-Ion batteries are also used in many small power applications.


Note: Before going to choose the components to decide your system voltage 12/24 or 48 V.Higher the voltage lesser the current and lesser will be the copper loss in the conductor. This will reduce your conductor size also. Most of the small home solar systems have 12 or 24 V.


In this project, I am selecting the 12 V system.

RATING OF BATTERY:


Batteries capacity are rated in term of Ampere Hour.


Power=Voltage X Current


Watt Hour =Voltage (Volts) x Current (Amperes) x Time (Hours)


Battery Voltage = 12V ( as our system is 12V)


Battery capacity= Load /Voltage = 475/12 = 39.58 Ah

Practically battery are not ideal, so we have to consider the loss. Let the battery loss is 15%.

So battery capacity required is 39.58 / 0.85 =46.56 Ah

For better battery life, they are not allowed to discharge fully (100% ). For flooded lead-acid battery 60% depth of discharge (DOD) is considered as good practice.


So Capacity Required = 46.56 /0.6 = 77.61 Ah

You can select a deep cycle lead-acid battery with a capacity of more than 77.61 Ah.

You can round off to 80 Ah

A solar charge controller is a device that is placed between a solar panel and a battery. It regulates the voltage and current coming from your solar panels. It is used to maintain the proper charging voltage on the batteries. As the input voltage from the solar panel rises, the charge controller regulates the charge to the batteries preventing any overcharging.

Usually, the solar power systems use 12-volt batteries, however, Solar panels can deliver far more voltage than is required to charge the batteries. By, in essence, converting the excess voltage into amps, the charge voltage can be kept at an optimal level while the time required to fully charge the batteries is reduced. This allows the solar power system to operate optimally at all times.

You can read my latest article on selecting the right charge controller for your Solar PV System

Types of Charge controller :

1.ON OFF

2. PWM

3. MPPT

Among the 3 charge controllers, MPPT has the highest efficiency but it is costly. So you can use either PWM or MPPT.

MPPT Charge Controller is most effective under these conditions :

1. Cold weather, cloudy or hazy days

2. When the battery is deeply discharged

Try to avoid the ON/OFF charge controller as it is the least efficient.

RATING OF CHARGE CONTROLLER :

Since our system is rated 12V, the Charge controller is also 12V

Current rating = Power output of Panels / Voltage = 120 W/ 12V = 10 A

By taking a 20% margin, you can choose a 10 x1.2 = 12A charge controller. But the next rating controller available in the market is 15A. So choose a Charge Controller of 12 V and a current rating of 15 A.

If you like to reduce your system cost you can make a PWM charge controller. For step by step instruction, you can see my instructable on PWM CHARGE CONTROLLER.

You may also like my new design on Solar Charge Controller.

The solar panel (PV) that receive the sun’s rays and convert them into electricity called direct current (DC). DC is then converted into alternating current (AC) through a device called an Inverter. AC electricity flows through every outlet of your home, powering the appliances.

Types

1. Square Wave

2. Modified Sine Wave

3. Pure Sine Wave

Square wave inverter is cheaper among the all but not suitable for all appliances. Modified Sine Wave output is also not suitable for certain appliances, particularly those with capacitive and electromagnetic devices such as a fridge, microwave oven and most kinds of motors. Typically modified sine wave inverters work at lower efficiency than pure sine wave inverters.

So as per my opinion choose a pure sine wave inverter.

It may be grid-tied or stand-alone. In our case, it is obviously stand alone.

RATING OF INVERTER :

The power rating should be equal or more than the total load in watt at any instant.

In our case the maximum load at any instant = Tv (50W) +Fan (80W) +CFL (11W) =141W

By taking some margin we can choose a 200W inverter.

As our system is 12 v we have to select a 12V DC to 230V/50Hz or 110V/60Hz AC pure sine wave inverter.

Note :

Appliances like fridge, hair drier, vacuum cleaner, washing machine, etc likely to have their starting power consumption several times greater than their normal working power (typically this is caused by electric motors or capacitors in such appliances). This should be taken into account when choosing the right size of the inverter.

After calculating the battery capacity and solar panel rating you have to wire them. In many cases, the calculated solar panel size or battery is not readily available in the form of a single unit in the market. So you have to add a small solar panel or batteries to match your system requirement. To match the required voltage and current rating we have to use series and parallel connection.

1. Series Connection :

To wire any device in series you must connect the positive terminal of one device to the negative terminal of the next device. The device in our case may be a solar panel or battery.

In series connection the individual voltages of each device are additive.

Example :

lets 4 12V batteries are connected in series, then the combination will produce 12 + 12 + 12 + 12 = 48 volts.

In a series combination, the current or amperage is the same.

So if these devices were batteries and each battery had a rating of 12 Volts and 100 Ah then the total value of this series circuit would be 48 Volt, 100Ah. If they were solar panels and each solar panel had a rating of 17 volts(Osc voltage) and were rated at 5 amps each then the total circuit value would be 68 volts, 5 amps.

2. Parallel Connection :

In a parallel connection, you must connect the positive terminal of the first device to the positive terminal of the next device and negative terminal of the first device to the negative terminal of the next device.

In a parallel connection, the voltage remains the same but the current rating of the circuit is a sum of all the devices.

Example :

Lets two batteries of 12v,100Ah are connected in parallel then the system voltage remains 12 volts but the current rating is 100+100=200Ah. Similarly, if two solar panels of 17V and 5 amps are connected in parallel then the system will produce 17 Volts, 10 amps.

The first component we are going to wire is the Charge Controller. At the bottom of the Charge Controller, there are 3 signs in my charge controller. The first one from the left is for the connection of the Solar Panel having positive (+) and negative (-) sign. The second one with plus (+) and minus (-) sign is for the Battery connection and the last one for the direct DC load connection like DC lights.


As per the charge controller manual always connect the Charge Controller to the Battery first because this allows the Charge Controller to get calibrated to whether it is 12V or 24V system. Connect the red (+) and black (-) wire from the battery bank to the charge controller.

Note: First connect the black /negative wire from the battery to the charge controller's negative terminal, then connect the positive wire.


After connecting the battery with charge controller you can see the Charge Controller indicator led lights up to indicate the Battery level.


After connecting this inverter terminal for battery charging is connected to corresponding positive and negative terminals of the battery.


Now you have to connect the solar panel to the charge controller. At the backside of the Solar Panel, there is a small junction box with 2 connected wires with positive(+) and negative (-) sign. The terminal wires are normally smaller in length. To connect the wire to the charge controller you need a special type connector which is commonly known as MC4 connector. See the picture. After connecting the solar panel to the charge controller the green led indicator will light if sunlight is present.


Note: Always connect the Solar Panel to Charge Controller while facing the Panel away from the sun or you may cover the panel with a dark material to avoid sudden high voltage coming from the solar panel to the Charge Controller which may damage it.

SAFETY :


It is important to note that we are dealing with the DC current. So the positive (+) is to be connected to positive (+) and negative (-) with negative (-) from Solar Panel to Charge Controller. If it gets mixed up, the equipment can go burst and may catch fire. So you need to be extremely careful when connecting these wires. It is recommended to use 2 color wires i.e. red and black color for positive (+) and negative (-). If you don't have a red and black wire you may wrap red and black tap at the terminals.


Connect the dc load or dc light at last.

Additional Protection :


Though charge controller and inverter have inbuilt fuses for protection, you can put switches and fuses in the following places for additional protection and isolation.


1. In between solar panel and charge controller


2. In between the charge controller and battery bank


3. In between battery and inverter

Metering and Data logging :


If you are interested to know how much energy is produced by your solar panel or how much energy is consumed by the appliances you have to use energy meters.


Besides this, you can monitor the different parameters in your off-grid solar system by remote data logging


For DIY based energy meter you can see my instructable on ENERGY METER which has both metering and data logging capability.


After wiring everything the off-grid Solar system is ready for use.

Updated on 22.07.2019

The current generated from the solar panels should reach the Battery with minimum loss. Each cable has its own ohmic resistance. The voltage drop due to this resistance is according to Ohm’s law

V = I x R (Here V is the voltage drop across the cable, R is the resistance and I is the current).

The resistance ( R ) of the cable depends on three parameters:

1.Cable Length: Longer the cable, more is the resistance

2. Cable Cross-section Area: Larger the area, smaller is the resistance

3. The material used: Copper or Aluminum. Copper has lesser resistance compared to Aluminium

In this application, copper cable is preferable.

You can calculate the cable size by using RENOGY online calculator.

You need to enter the following parameters :

1. Solar Panel Operating Voltage (Vmp)

2. Solar Panel Operating Current (Imp)

3. Cable Length from Solar Panel to Battery

4. The expected loss in percentage

The first two parameters ( Vmp and Imp) can be easily found from the specification sheet on the backside of the solar panel or from the datasheet. The cable length depends on your installation. The loss percentage considered for good design is around 2 to 3%.

In the earlier step, we have already finalized the Solar panel, the rating. From the Solar panel specification sheet Vmp = 36.7V and Imp = 6.94A ( rounded off to next higher number i.e 37V and 7A). Let the distance between the Solar panel and the Battery is 30 feet and the expected loss is 2%. By using the above values in the online calculator by RENOGY, The cable size is 12 AWG.

The calculation screenshot is also attached for reference.

You can buy the Solar cables from Amazon or Aliexpress

You can read my Instructables on Selecting Solar Cables and How to Make MC4 Connector.

Note: The voltage grade of the cable should be matched with the Solar Panel maximum system voltage.

Image Credit: Banggood

Updated on 17.12.2019

It is very important to be sure you are using the appropriate cable size for your inverter/battery. Failing to do so could lead to your inverter not supporting full loads and overheating, which is a potential fire hazard. Use this as a guide for choosing the proper cable size, and be sure to contact a professional electrician or our tech team with any additional questions you may have.

1. What size inverter do you have?

2. What is the DC voltage of your battery bank?

3. Now divide the inverter’s wattage by your battery voltage; this will give you the maximum current for your cables.

Example Calculation

Current (Amps ) = Power (Watts ) / Voltage (Volt)

Consider 1500 Watt inverter connected to the 24V battery bank.

(1500 W)/(24 Vdc)=62.5 A

So, 62.5 A is the maximum current that the cable needs to support in order to properly provide the current to the inverter. The next higher size available on the table is 100A.

Use the above chart as a guide to determine which size cable will be best for your application.

In our example, we can see that 2/0 AWG cable would be appropriate.

NOTE: For distances over 10 feet, the voltage drop over the cables will occur due to resistance through the wiring. If you will need to run cables longer than 10 feet, it is recommended that you increase the cable size in order to compensate for voltage loss. If you are unsure about your application feel free to give us a call and we will be able to assist you in finding the right cable.

After design the solar system. Buy all the components with an appropriate rating as per the previous steps.

Now it is time to mount the solar panel. First, choose a suitable location on the rooftop where there is no obstruction sunlight.

Prepare the mounting stand: You can make it on your own or it is better to buy one from any store. In my case, I have taken the drawing from the solar panel company and made it at a nearby welding shop. The tilt of the stand is nearly equal to the latitude angle of your location.

I made a small wooden mounting stand for my 10 Watt solar panel. I have attached the pictures so that anyone can make it easy.

Tilting: To get the most from solar panels, you need to point them in the direction that captures the maximum sunlight. Use one of these formulas to find the best angle from the horizontal at which the panel should be tilted:

>> If your latitude is below 25°, use the latitude times 0.87.

>> If your latitude is between 25° and 50°, use the latitude, times 0.76, plus 3.1 degrees.

For more details on tilting click here

First place the stand in such a way that the face is directed towards the south.Mark the leg position over the roof.

To get the south direction use this android app compass

Then make a rough surface at each leg of the stand by using a sharp object. I made around 1Sq feet size rough surface over the roof at each leg. This is helpful for perfect bonding between the roof and concrete.

Prepare concrete mix: Take cement and stones with a 1:3 ratio then add water to make a thick mix. Pour concrete mix at each leg of the stand. I made a heap shape concrete mix to give maximum strength.

Mounts the panels to the stand: At the backsides, the solar panel has inbuilt holes for mounting. Match the solar panel holes with the stand/platform holes and screw them together.

Wire the solar panel: At the back sides of the solar panel a small junction box is there with a positive and negative sign for polarity. In a large-size solar panel, this junction box has terminal wires with MC4 connector but for small size panel, you have to connect the junction box with external wires. Always try to use red and black wire for the positive and negative terminal connection. If there is provision for earth wire the use a green wire for wiring this.

I made the above inverter and battery stand by the help of a carpenter. The design idea I got from this instructable. The design is really helpful for me.

At the backside, I made a big circular hole just behind the inverter fan for fresh air suction from outside. Later I covered the hole by using plastic wire mesh. Few small holes are also made for inserting the wires from solar panel, charge controller and inverter to the battery and ac output to the appliances. At both sides panel, 3 horizontal holes are provided for sufficient ventilation. A glass window is provided at the front side to view the different led indications in the inverter.

In the inclined plane of the inverter stand, I have mounted the charge controller. In the future, I will install my own made energy meter also.

I found a nicely documented worksheet on Solar PV Design from Renewable Energy Innovation page.

This is a simple design worksheet for stand-alone solar PV systems. It explains the design process and explains some of the practicalities of building a system.

I hope it will be useful. The full credit goes to the authors of Re-Innovation