My journey to Off Grid Solar systems part 1

As some of you might already know, I’m from a tiny island in the Indian ocean called “Sri Lanka”. Due to the current economy crisis in Sri Lanka, government started power cuts throughout the country hoping to save some fuel which was used to generate power. (Yes, fossil fuel plays a large role in my country) Please check the following graph related to daily electricity generation in Sri Lanka.

 

Source : https://cebcare.ceb.lk/gensum/details

Currently daily power cuts last 3 hours and few months back we have hit 9 hours power cuts per day. Due to Covid, I was working from home since early 2020 and these power cuts directly affect my ability to work during working hours. First, I have managed to work with UPS (Uninterrupted power supply) but due to increased hours of power cuts led me to discover newer ways of dealing with this problem.

 

I have discovered this local Facebook group called “DIY Off Grid Sri Lanka group” https://www.facebook.com/groups/diyoffgrid accidentally and started my journey towards free solar energy. I spend hours reading the guides provided in the group and read every single conversation happening in there. This helps me to identify main components we need to build an off grid solar system and where to buy them.

 

But before you buy any component there is this important task, we should do first. That is to measure how much power your house is consuming throughout the day. This step was bit easy for me since I’m running a smart home which include a gadget which check total energy consumption 24x7. I used this device to measure how much power each my household consumes. Don’t worry, if you don’t have any device you can simply check the labels on your electric devices and get an idea of their power consumption or maybe you can check your power bill for last few months.  Look at below example.

 

Look at the highlighted values. You have,

• Voltage

•  Frequency

•  Maximum Power

Where you will use to decide the capacity of the components of your solar system.

 

You must add the maximum power of all the electrical components that you’re going to use on solar system. For example, you must include lights, refrigerator, TV, Fans, Air conditioners or heaters, Computers ... etc. If you’re not using all of these at the same time you can scale down your system and if you let the high-power consumption items (Air conditioners or heaters, refrigerator) to run using the grid and let the other’s run through solar.

With all this information you can safely buy an inverter which is the heart of your system to match to your need and electricity standard. What Inverter does is to convert DC battery power to AC current which you can power your house. The total power requirement is helping you to decide the Inverter capacity. As a best practice it’s best if you can leave some head room when buying the inverter. For example, imagine you will need 1500W to power up your house. It’s best to buy at least 2000W inverter so, you have some head room for the future, and it release the stress on the electronic components in the inverter making them work for long time.

Mostly used for mobile applications (RV's, Boats)

Mostly used in houses

There are two types of inverters.

• Pure sine wave inverters 

• Modified sine wave inverters

We'll further discuss on these in a later post but, my recommendation is you should get a pure sine wave inverter.

When you’re buying the inverter it’s best to decide the battery voltage that you’re going to use in this inverter. The higher the battery voltage you will draw less amps from the batteries and your system will be more efficient, less stress on batteries & you can save some money using smaller gauge DC wires.. For 2000W system I’m recommending at least 24V batteries. If you’re going for 3500-5000W I’m recommending going with 48V. If you use lead acid batteries (Usual vehicle battery) you will need 2 batteries in series to generate 24V and 4 batteries in series to have 48V.

I'm recommending Lifepo4 batteries over Lead Acid batteries due to usable capacity, cycle life, weight & safety. You can buy pre-built batteries (easy way) or cells & BMS to build your own battery (DIY). Lifepo4 cells comes with 3.2V therefore you will need 4 cells in series to create a 12V battery. (8 cells for 24V & 16 cells for 48V)

Your battery capacity will decide how long you can run your electrical devices in this system. You will see this capacity in AH on the battery.  Higher the number you will have more time also you can parallel connect same capacity battery to increase the capacity. We'll discuss further about batteries in a later post.

Lead-Acid Battery

Lifepo4 Battery

The next component you need is a solar charge controller. Solar charge controller connects to your solar panel and controls the battery charging making sure that it will not overcharge the batteries and destroy them. When deciding on Solar charge controller you must consider battery voltage, battery capacity, Solar panel capacity which you’re going to use. There are two types of controllers PWM & MPPT.

• PWM – Old technology / Cheap / Less efficient 

 

• MPPT – New technology / Expensive / More efficient

 

 

 

 

 

 

 

 

 

 

 

 

For my case since I’m running a 12V system and because of that I can only go with max solar power of 720W. I have one 100AH and one 120AH lead acid batteries in parallel so, to safely charge it 20A Solar charge controller would be enough. But thinking about future expansions I have settled with a device which can handle up to 60A and 48V system. So, when I decided to upgrade my system, device in it will be ready and I don’t have to buy something new.

 

Final piece is to buy Solar panels. There are multiple brands and multiple capacity in Solar panel. Currently the biggest single solar panel you can find in Sri Lanka is 540W in capacity. Solar panels were the hardest and most expensive component in my system due to the high demand and import restrictions in my country. Since you will need many of these depending on your power requirement this should cost you a lot.I was able to purchase Canadian Solar 445W new single panel for my project.

 

 

There are two types of solar panels

• Monocrystalline (More efficient / Bit expensive)
  
• Polycrystalline (Less efficient / Cheap)
   

You need to check the data sheets or the sticker on the back of the solar panel to grab some important details. Here’s what’s in my sticker.

 

The important numbers on this data sheet would be,

• Nominal Maximum Power (Pmax)
  

• Open Circuit Voltage (Voc)
  

• Short Circuit Current (Isc)
  

 

These values would help you to decide the capacity of your solar charge controller or minimum number of panels you need to turn on an inverter which has a built in solar charge controller.

Alright, Now we know all the main components we need. I will be writing the part 2 of this article explaining how all these parts connects soon. Until then stay tuned and stay safe.