Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 26, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-38995
Entity Registrant Name	Sunnova Energy International Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	30-1192746
Entity Address, Address Line One	20 East Greenway Plaza, Suite 540
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77046
City Area Code	281
Local Phone Number	892-1588
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	NOVA
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		111,970,130
Entity Central Index Key	0001772695
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false
Current Fiscal Year End Date	--12-31