ExportAllReports.ps1

#Log in to Power BI Service
Login-PowerBI  -Environment Public 	

#First, Collect all (or one) of the workspaces in a parameter called PBIWorkspace
$PBIWorkspace = Get-PowerBIWorkspace 							# Collect all workspaces you have access to
#$PBIWorkspace = Get-PowerBIWorkspace -Name 'My Workspace Name' 	# Use the -Name parameter to limit to one workspace

#Now collect todays date
$TodaysDate = Get-Date -Format "yyyyMMdd" 

#Almost finished: Build the outputpath. This Outputpath creates a news map, based on todays date
$OutPutPath = "C:\PowerBIReportsBackup\" + $TodaysDate 

#Now loop through the workspaces, hence the ForEach
ForEach($Workspace in $PBIWorkspace)
{
	#For all workspaces there is a new Folder destination: Outputpath + Workspacename
	$Folder = $OutPutPath + "\" + $Workspace.name 
	#If the folder doens't exists, it will be created.
	If(!(Test-Path $Folder))
	{
		New-Item -ItemType Directory -Force -Path $Folder
	}
	#At this point, there is a folder structure with a folder for all your workspaces 
	
	
	#Collect all (or one) of the reports from one or all workspaces 
	$PBIReports = Get-PowerBIReport -WorkspaceId $Workspace.Id 						 # Collect all reports from the workspace we selected.
	#$PBIReports = Get-PowerBIReport -WorkspaceId $Workspace.Id -Name "My Report Name" # Use the -Name parameter to limit to one report
		
		#Now loop through these reports: 
		ForEach($Report in $PBIReports)
		{
			#Your PowerShell comandline will say Downloading Workspacename Reportname
			Write-Host "Downloading "$Workspace.name":" $Report.name 
			
			#The final collection including folder structure + file name is created.
			$OutputFile = $OutPutPath + "\" + $Workspace.name + "\" + $Report.name + ".pbix"
			
			# If the file exists, delete it first; otherwise, the Export-PowerBIReport will fail.
			 if (Test-Path $OutputFile)
				{
					Remove-Item $OutputFile
				}
			
			#The pbix is now really getting downloaded
			Export-PowerBIReport -WorkspaceId $Workspace.ID -Id $Report.ID -OutFile $OutputFile
		}
}

Hey! thanks for sharing! I was wonder if you would like to include dataflows as well

#Collect all (or one) of the dataflows from one or all workspaces 
  $PBIDataflows = Get-PowerBIDataflow -WorkspaceId $Workspace.Id 				# Collect all dataflows from the workspace we selected.
  		
  	#Now loop through these reports: 
  	ForEach($Dataflow in $PBIDataflows)
  	{
  		#Your PowerShell comandline will say Downloading Workspacename Reportname
  		Write-Host "Downloading "$Workspace.name":" $Report.name 
  		
  		#The final collection including folder structure + file name is created.
  		$OutputFile = $OutPutPath + "\" + $Workspace.name + "\" + $Dataflow.name + ".json"
  		
  		# If the file exists, delete it first; otherwise, the Export-PowerBIReport will fail.
  		 if (Test-Path $OutputFile)
  			{
  				Remove-Item $OutputFile
  			}
  		
  		#The Power BI Dataflow(json) is now really getting downloaded
  		Export-PowerBIDataflow -WorkspaceId $Workspace.ID -Id $Dataflow.ID -OutFile $OutputFile
  	}``