# Getting Started¶

Carousel helps you build complicated models quickly. The Quickstart and Tutorials that follow will guide you through the steps to making and simulating an example Carousel model.

## Quickstart¶

Carousel adds the script carousel-quickstart to quickly start a project.

\$ carousel-quickstart.py MyCarouselProject.


This creates a new folder for MyCarouselProject, a Python package with the same name, and a data folder.

MyCarouselProject
|
+-+- mycarouselproject
|
+- __init__.py
|
+- data


The quickstart script adds the constant mycarouselproject.PROJ_PATH that refers to the project path MyCarouselProject/mycarouselproject. This path is useful, as we’ll see in the next tutorial, and should be imported into the project package modules. The script also adds version, author and email information that you can complete if you want.

## Tutorials¶

The following Tutorials will go through an example of how to implement a Carousel model. There are are five tutorials that cover the different steps in making a Carousel model.

### PV System Power Example¶

The example in this tutorial demonstrates using a Python package called PVLIB to simulate a photovoltaic (PV) power system. It follows the example in the Package Overview section of the PVLIB documentation. A working version of the demonstration model is included in the examples folder of both the Carousel Git repository and the archive distribution of the Carousel Python package.

### Quickstart¶

To start the tutorial, first execute carousel-quickstart PVPower from your OS terminal (EG: BaSH on Linux, CMD on Windows). This will create a new Carousel project named PVPower containing the following folders: pvpower, data, formulas, calculations, outputs, simulations and models. A Python package is created with the same name as the project in lower case, ie: pvpower, and a file called my_model.json is created in the models folder. These folders will be used to create Carousel models in the tutorials that follow. For more information about carousel-quickstart see the Quickstart section in Getting Started.

The next tutorial covers specifying outputs for your Carousel model.

## Parameters¶

Model parameters are items that are declared in each layer of a Carousel model. For example a model’s data layer might declare data parameters called “direct_normal_irradiance” and “ambient_temperature” with attributes like “units” and “uncertainty”. Carousel’s goal is to make entering model parameters intuitive, quick yet flexible, so there are currently two different styles for entering model parameters.

### Class Attributes¶

The preferred way to specify model parameters in each Carousel layer is to declare them as class attributes equal to an instance of Parameter. Each Carousel class has its own Parameter class to set the items for that layer. Behind the scenes Carousel collects parameters and instantiates them without needing to write dunder methods such as __init__. Therefore model parameters are declared in a simple and concise way. Please see the tutorials for examples.

### JSON File¶

Originally Carousel collected all parameters from JSON files because it was meant to be used entirely from a graphic user interface, therefore the application state was saved and reloaded using JSON. This legacy style still works in the current version of Carousel and can even be combined with the class attribute style by specifying the parameter files as class Meta options.

### Model Class Instance¶

There is a third method for entering model parameters that can only be used when creating a Carousel model directly from a model parameter JSON file by calling Model with the filename as the argument. Therefore Carousel models can be created three different ways.

1. Specifying the model parameters as class attributes of a subclass of Model:

class MyModel(models.Model):
"""
Layers specified as class attributes. This is the preferred way.
"""
data = ModelParameter(
layer='Data',
sources=[(MyModelData, {'filename': 'data.json'}), ...]
)
outputs = ModelParameter(
layer='Outputs', sources=[MyModelOutputs, ...]
)
formulas = ModelParameter(
layer='Formulas', sources=[MyModelFormulas, ...]
)
calculations = ModelParameter(
layer='Calculations', sources=[MyModelCalculations, ...]
)
simulations = ModelParameter(
layer='Simulations', sources=[MyModelSimulations]
)

class Meta:
modelpath = PROJ_PATH  # path to project folder

m = MyModel()

2. Specifying the path to the model parameter file as Meta class options:

class MyModel(models.Model):
"""
JSON parameter file specified as Meta class options.
"""
class Meta:
modelpath = PROJ_PATH  # path to project folder
modelfile = MODELFILE  # path to model parameter file

m = MyModel()

3. Calling Model with the model parameter file as the argument:

m = models.Model('path/to/project/models/parameter_file.json')


The Carousel model is the only class that can be instantiated directly by the user. The other classes, data, formulas, calculations, outputs, and simulations, are instantiated by the model class automatically.

## Meta Class Options¶

Model options that apply to an entire Carousel class are listed separately in a nested class that is always called Meta. For each layer, there are a few options that are typically listed in the Meta class. For example, the model class has an attribute called modelpath that is listed in the Meta class and refers to the project path created by carousel-quickstart. Please read the tutorials to learn more about what Meta class options can be used in each Carousel layer.