# DIY OFF GRID SOLAR SYSTEM

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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.

You can find all of my projects on :https://www.opengreenenergy.com/

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 a off grid solar system you need four basic components

3. Inverter

4.Battery

Besides the above components you need 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 any one know 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 product of power rating of your appliances and time ( hr) of run.

Example :

Lets you want to run a 11W CFL for 5hour from 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

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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 with your load requirement.

If you are not interested to doing the above maths then use a load calculator for this calculation.There are huge number of load calculator available in the internet.I am attaching a such link Off Grid Load Calculator.

## Step 2: SOLAR PANEL SELECTION

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

mono crystalline or poly crystalline.Mono crystalline are costlier and efficient than poly crystalline panel.

Solar panels are generally rated under standard test conditions (STC): irradiance of 1,000 W/m², 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 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 differ according to your location in 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.

## Step 3: BATTERY SELECTION

The out put from the solar panel is dc power.This power is generated during the 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 sun light.

>> If you want to run the appliances during 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 constant source of stable, reliable power.

There are 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 a deep discharge. But the solar battery is a deep-cycle lead-acid battery that allows for partial discharge and allows for deep slow discharge.Lead acid tubular battery is perfect for a solar system.

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

Note : Before going to choose the components 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.In most of the small home solar system 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 capacity more than 77.61 Ah.

You can round off to 80 Ah

## Step 4: CHARGE CONTROLLER SELECTION

A solar charge controller is a device which 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 over charging.

Usually, the solar power systems uses 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.

Types of Charge controller :

1.ON OFF

2. PWM

3. MPPT

Among the 3 charge controllers MPPT have 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 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, Charge controller is also 12V

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

By taking 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 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.

## Step 5: INVERTER SELECTION

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 tie or stand alone .In our case it is obviously stand alone.

RATING OF INVETER :

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 inverter.

## Step 6: MOUNTING THE SOLAR PANEL

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

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

Prepare the mounting stand : You can make it by 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 near by 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 any one can made it easily.

Tilting : To get the most from solar panels, you need to point them in the direction that captures the maximum sun light.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.

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

To get the south direction use this android app compass

Then make 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 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 back sides the solar panel have 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 positive and negative sign for polarity .In a large size solar panel this junction box have 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.

## Step 7: SERIES AND PARALLEL CONNECTION

After the calculating the battery capacity and solar panel rating you have to wiring them.In many cases the calculated solar panel size or battery is not readily available in the form of single unit in the market.So you have to add 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 solar panel or battery.

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

Example :

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

In series combination the current or amperage is 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 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 parallel connection the voltage is remain same but the current rating of the circuit is sum of all the devices.

Example :

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

## Step 8: INVERTER AND BATTERY STAND

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 back side I made a big circular hole just behind the inverter fan for fresh air suction from out side .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 out put to the appliances.At the 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 future I will installed my own made energy meter also.

## Step 9: WIRING

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 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 terminals 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 back side 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 red and black wire you may wrap red and black tap at the terminals.

Connect the dc load or dc light at last.

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 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 being consumed by your 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 have both metering and data logging capability.

After wiring every thing the off grid Solar system is ready for use.

## Step 10: Solar PV Design Worksheet

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

Thank you for reading my instructable.

53 Enrolled

## 186 Discussions

deba168, I want to thank you so much for posting this article. I am not an electrical engineer so many of the articles already on Instructables on this subject or on the internet seemed incomplete to me because they did not explain many of the details that you did. Perhaps for the electrically inclinded those finer points are common knowledge and not necessary, but for me it exactly what I needed. The step-by-step approach with explanations and links to products was fantastic.

I have never written an Instructable but I appreciate all the time and effort it requires to write something like this, so thank you very, very much.

Your kind words really motivate me to write an article like this in the future.
Thank you so much.

Hi,

If I know the max Amp battery I can fit in my sapce, how do I know what size panel/charge controller and inverter i need ?

We need to move our solar panels well away from trees. The optimal place is about 100 metres away from the batteries. Is this distance going to be a problem?

Hi Louise. For high distant instalations, it is advised to use higher Voltage systems.
Higher the voltage, lower the transmission losses and lower the cost of wireing

Does anyone know if it would be OK to house the batteries outside in an insulated box? If it stayed dry, could the controller also stay outside? I’m in the south so we don’t get much snow and temps don’t go below freezing very often.

Which circuit breaker should i choose for a small 300 w system...

Is there any way to build a system that pulls from a battery first, and then would pull from the grid after you used up all the electricity that got stored throughout the day from solar?

2 replies

Are you in the US? You can install solar panels and feed them into the grid if so. By law the power companies have to buy any electricity you produce. In some states it's much easier to implement than others though, check with local solar companies. You always use off the grid, but whatever you produce is fed into the grid during daytime. That offsets your electric bill. In most states the electric company just gives you a credit for whatever you produce, not a check in the mail.

There are automatic switches for generators that switch from grid to generator during a power outage. Shouldn't be hard to create something similar that will auto switch over when battery level is down. Those auto power outage switches aren't cheap though. Controlling the switch could be done with an Arduino or similar controleer, but you'd still need the heavy duty switch to switch over the load.

Important consideration: when you are selling your solar power into the grid the IRS gets involved and you will PAY taxes for the wonderful earnings of your solar array. If you are looking at ROI for your grid-tied system it might be a small thing or a large thing depending on your situation so just be aware especially if you are trying to save money over time.
Now at night when you draw energy from the grid... you're still paying the same rate as everyone without any panels, no tax refund.

Hey, one thing i see all the time with solar projects is all anybody uses is 12v deep cycle batteries. These batteries were mostly meant for boats, high cranking amps and could be discharged more without killing the life of the battery. The best battery to use is deep cycle 6v batteries wired in series to give you one big 12v battery. If you want lots of power stored for longer use, use 6v batts. Another thing that you need to think of if you are going off grid is your solar array needs to be big enough to not only run the things you want but also put out enough power to recharge the batteries at the same time or each time you start to use the batteries they will just be drained more and more until they are dead. System needs to be bigger than for just running the house. If you are totally off grid then your system needs to keep the batteries charged the whole time the house is draining power. Same thing either way you look at it.

2 replies

Thanks for the information, please i have a question if i am to use 2 6V instead of 1 big 12v battery, does the AH size matters? what i am interested in is getting lots of power power stored for longer use.

Having made something similar (though not yet solar powered) the capacity doesn't matter as long as both series batteries are the same. (Which is why I use 12v fire alarm rated sla batteries instead.) My total capacity on 12v is around 500Ah (about 6000wh...) with a 1000w inverter on it that I've never run past 500w.

Is there a battery for an off grid system that will power a 220v appliance?