How to Size Grid-Tied Solar System? (Step-by-Step)
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In this article, I will first explain the working principle of grid-tied solar systems, and fundamental system components and then show you how you can size grid-tied solar systems according to your monthly electricity usage. Let’s get started.
On-Grid solar photovoltaic systems or Grid-tied solar systems convert the electricity generated from solar panels into single-phase or three-phase by specially designed inverters and supply it to the electricity grid via a bidirectional electricity meter. Grid-Tied solar systems can be installed as high-power power plant systems or to meet domestic consumption. These systems have three main components: solar panels, on-grid solar inverters, and bidirectional electricity meters.
Grid-Tied Solar System Components
Solar Panel
Since grid-tied solar systems are grid-oriented, the voltage values of solar panels are significant. That is why you need to connect solar panels according to the voltage range that solar inverters can operate. Voltage and current values vary according to the power value of the panels. In new-generation systems, 350 W and above panels are preferred for the on-grid solar system. While determining the panel capacity for these systems, the average sunshine duration according to winter conditions is important as in off-grid system design.
On-Grid Solar Inverters
The inverter is like the heart of grid-tied solar systems. It converts the electricity from solar panels into single-phase or three-phase AC electrical energy according to the electricity grid. Grid-tied solar inverters have different models for three-phase and single-phase.
Solar inverters work together with the power from the solar panel and the power from the grid. The reason for this is to support the consumption load with grid electricity when a power drop occurs in the solar panel.
The capacity and model of grid-connected On-Grid inverters are determined depending on the following conditions.
- Grid-tied solar inverter’s power capacity should be the same as solar panels. (there may be a 10% tolerance margin). For example, if you have a 3 kW capacity of the solar panel then you need to choose a 3 kW on-grid solar inverter.
- You should know whether the power line in the place where the system will be installed is single-phase or three-phase.
Bidirectional Electricity Meter
Two-way electricity meters, like one-way electricity meters, transmit electricity from the grid to the household. The difference from a one-way meter is that it also transmits electricity generated from an external location to the electricity grid. With smart bidirectional meters, you can monitor the electricity produced and consumed on the digital display on the meter. If your production is the same or equal to your consumption at the end of the month, you will not pay a bill.
Sizing of Grid-Tied Solar System
We’ve learned the main components of grid-tied solar systems. Now, I will show you how to size a grid-tied solar system step by step. Let’s get started.
Daily Energy Consumption
First, let’s assume our monthly energy consumption is 150 kWh. So our daily electricity consumption is 360/30 = 12 kWh. You can easily find your monthly electricity consumption by checking your electricity bill.
Calculation of Total Solar Panel Capacity
Next thing we need to find the lowest sunshine duration in the region where we will install solar energy systems. You can find this value by checking the website regional meteorology station. We can get this value of 3 hours for our example.
To find solar panel capacity for our project, we need to divide daily energy consumption by the lowest sunshine duration in our region.
12 kWh/3h = 4 kW So we need 4 kWp total solar panel capacity. ,
The Number of Solar Panels
Now we need to calculate how many solar panels we need. Let’s say we’ve chosen 400 W monocrystal solar panels. (the new generation solar panels such as half-cut, bifacial, and flexible solar panels can be considered.) Then we can calculate the number of solar panels we need as shown below.
Total solar panel capacity / the power capacity of the single solar panel = 4 kW/0,4 kW = 10 pieces of solar panels we need for our solar system project.
Calculation of the On-Grid Solar Inverter Capacity
On-grid solar inverter capacity should be calculated according to the total solar panel capacity. Our total solar panel capacity is 4 kW so our on-grid solar inverter power capacity must be 4 kW or higher and close to this value depending on the model.
The Cost of Sized Grid-Tied Solar System
| Components | Adet | Adet Fiyatı | Maliyet |
| 400 W Monocrystal Solar Panel | 10 | 200 $ | 2.000 $ |
| 4 kW Grid-Tied Solar Inverter+Data Logger | 1 | 900 $ | 1.000 $ |
| Mounting Equipment of Solar Panels | – | – | 900 $ |
| Labor, Transportation, and Paperwork Process | – | – | 900 $ |
Total Cost: 4.800 $
You can consider the price range for a 4 kW system between $ 4.000-$ 5.000 according to the companies, and the document fees required for the permission of the electricity institution are also included in the price. The payback period of this system is around 7-8 years according to the increase in electricity prices.
In this article, I tried to explain the design of the grid-connected on-grid system. I will present you articles containing information about the cable connections of both off-grid and on-grid systems and the things to be considered during installation.
