In this easy to read guide, we will break down how to design and install a grid tied solar system including solar panels, racking, batteries, inverter and many more.
We will explain it in simple English without speaking to you like an senior level electrical engineer, so you comprehend everything and go on with your project to cut your electric bill.
Here we go.
Basic Grid Tied System Diagram
A basic grid tied system is the most common system installed in locations where electricity are already available from the local utility company.
Cutting electrical bill is the number 1 reason why we do this.
Collects Sunlight Energy - This type of system takes the energy from the sun during the day (Assume peak sunlight hours), and uses it REAL TIME for your RV, home or other facilities.
Get Credit For Left Over Power - Any left over power will be sold to the city power grid for credit.
Buy Grid Power - If sunlight isn't enough to generate the solar power you need, then you can buy power using the credit from the grid.
Size Your Grid-Tied Power System
You can pay a local service to do this for you, or you can design it yourself.
Here are 8 questions you must ask before starting this project:
- Determine monthly power usage
- Calculate the annual daily average
- Analyze Insolation Maps for solar potential
- Calculate solar array wattage
- Pick out solar panels to buy
- Size an inverter
- Identify string sizing
- Determine mounting platforms
- Size breakers and fuses
The Easiest Way To Determine Your Home’s Power Usage
Look at your electric bill for the past 12 months and take into account all whether trends for an accurate estimation.
How much solar power you need to power a house? the math all starts right here
Calculate monthly power usage
For this example, we assume the following:
- Annual power usage: 19120 kWh,
- Location: Las Vegas, NV
- Annual sunlight average for Vegas: 6.4 hrs
- System Loss: 21%
Let's get started
First we have to calculate the annual daily average
Annual Daily Average – 19120 kWh / 365 days = 52.38 kwh / day
To see more examples, please check out this guide.
The next step is to take this number to size your solar panel required!
Analyze Insolation Maps
The insolation map will show you the regions of the world exposed to the most amount of sunlight.
It shows the visitor an average 3 - 6 peak sun hours every day and the lowest sun exposure region.
Get the annual average sun peak hours from this chart
Cities like Honolulu, Phoenix and Las Vegas do get a lot of sunlight, but northern states still get enough sunlight on average to still leverage solar power.
When we size our solar array for a grid-tied system, we are designing the requirement around the annual average number, and the maximum average for max sun exposure.
If you follow the chart, the chart will tell you if you need an roof tilt mount for your solar panels for not.
Dealing With Inefficiency
Nothing in the real world is consistent, so we need to take system inefficiency into account for a grid system.
Generally there are roughly 18 - 21 % loss in the system due to:
- Wiring
- Component qualities
- Shading
- Sun exposure
- Diodes
- Voltage drop
Determine Solar Panel Size Required
If we follow the example above
- Annual Daily Average = 52.38 kwh / day, that's about 52380 W annual average
- Annual Region Average = 52380 Wh / 6.41 hrs = 8171 W
- Offset Loss = 8171 W / 0.79 = 10343 W
10343 W total solar panel output is needed!
Here is the important part to factor in:
Most grid tie systems aren't 100% solar, we just want to cut our electric bill.
So we are going to cut the 10343 W number in half in this example.
10343 W / 2 = 5171 W
You can check out our best solar panel guide to select
Now let's use this number to size the rest of our system, we go after inverter first.
Size Solar Panel Inverter
The size of the grid-tied inverter is based on the size of the solar panel. There are certain numbers of panels in series or parallel connection that will work with the inverter.
The inverter converts DC power from the solar panel to AC power, and the easiest way to understand how to size it is look at how much power you consume.
For example: 4000 W consumption, please use an inverter with continuous watts and surge watts rating slightly bigger that.
Learn More: How to size solar inverter in depth
To make this easy, we use a string sizer to determine what we need.
Most inverter companies have this simple to use calculator on their websites to help the buyers make buying decisions.
Click here to learn how to configure the calculator.
Once you know which inverter you need, we figure out the mounts needed for your solar panels
Determine Mounting System
Solar panel mounting design can differ from people to people.
If your roof is ready for it, you can hire professionals to design the mount for you.
Add Over Current Protection
Over current protection prevents cataphoric things from happening.
For a grid-tied system, there are two locations to install over current protection
- DC side by the solar panels
- AC side in the main breaker box
We also need a combiner box so we can control the power coming in and off from the solar panels to meet safety requirement.
So what size fuse do you use?
Look at the solar panel you have chosen, and plug the short circuit current into the equation below to calculate the fuse size
For example: an Renogy 300W 12V solar panel with a short circuit current spec of 6.24 Amp.
Fuse Size - 6.24 Amp X 1.56 = 8 A
To learn more in-depth please click here.
So what size breaker do you use?
The AC output inverter goes with dual pole breaker in your home's main breaker box.
To calculate the size do the following:
8000 W inverter (Assume) / 240 V X 1.25 (ratio to oversize it) = 41 A (round it to 50 A)