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How to define the size of your PV plant

Got some project size specifications you need to abide by? You came to the right place!

Introduction

Whether it's installing as much power as possible within a designated area, trying to reach a target capacity, or having to abide by certain delivery point limitations, pvDesign can do all three!

Maximum capacity

So, you have just decided that you want to install as much power as possible inside your defined plot area. Well, say no more! In pvDesign's Electrical tab, you'll simply have to select the Maximum Capacity option as shown in the image below.

With the maximum capacity option selected, all you'll need to do is choose your target DC/AC ratio. This value will be used to generate the List of Electrical Configurations from which one configuration must be selected. To know more about this topic, check out How to define your electrical configuration.

For this article, we will take a DC/AC ratio of 1.209 as an example.

The Layout tab will allow us to check how much maximum power can be installed in our PV plant.

Now let's say that the DC/AC ratio proposed by pvDesign is different from what we need, what should we do to go around this?

If you are using central inverters, enable the secondary central inverter option and select the same inverter again. In the list of electrical configurations, two different DC/AC ratios will appear thus allowing you to reach your target ratio. But wait! How are we supposed to know the exact number of inverters of each type that must be installed in our PV plant?

Let's take a look! Assume that you would like to have an exact value of 1.2 as your DC/AC ratio.

First, check the maximum peak power that can fit in the PV plant by reviewing the Layout tab. In our example, this would be 130.9 MWdc.

Next, enable the secondary central inverter option in the Equipment tab and select the same inverter as the primary one.

After that, selectins Specific Capacity in the Electrical tab. Here, you'll need to fill the number of inverters needed to reach the target power. In this case, it's 60 inverters, and with a DC/AC ratio of 1.2, the peak power would be 129.1 MWdc.

Now, we must go to the List of Electrical Configurations and see all the available options to select from.

To achieve your target DC/AC ratio, you must select a configuration that has a DC/AC ratio above your desired value and another one right below it. In this case, the second configuration would be a good option to reach an overall ratio of 1.2.

To obtain the number of inverters of each type that must be installed, the following operations can be done:

In our example, we are targeting a DC/AC ratio of 1.2 and a total of 60 inverters, thus 54 primary inverters and 6 secondary inverters are needed.

Specific Capacity

What if I want to install a specific power? Simply select the Specific Capacity option in the Electrical tab.

Using the design from before, we define our PV plant with 50 inverters, thus obtaining 89.65 MWac. 

To ensure that we reach the exact specific power that we ant, we will first calculate the DC/AC Ratio associated with our peak power. If, for example, we want 100 MWdc, a DC/AC ratio of 1.115 must be included as a power requirement.

With this, the same process as before must be followed. We first select an adequate configuration.

After that, we calculate the number of primary and secondary inverters needed, which in this case are 46 and 4 respectively. With this, we obtain the specific peak power in our design.

If our desired power is not achieved, the process must be repeated with another configuration until reaching our goal.

Power limitation at the delivery point

What if I want to define a power limitation in my PV plant instead of reducing the installed capacity? In pvDesign, you can set a power limitation at the delivery point, by enabling the following option in the Energy tab and specifying the active power limit.

This way, pvDesign will design your PV plant based on your inputs (the power limitation option is available for both Maximum Capacity and Specific Capacity), and the energy yield results will take into consideration this power limitation. This means that if our plant can generate energy at a higher power than this limit, pvDesign will cap the plant's energy generation.


For any other questions or for more information, you can contact us at the following email: support@ratedpower.com.