v3.26.1
Document And Entity Information - shares
 9 Months Ended
Sep. 30, 2025
Apr. 24, 2026
Document Information [Line Items]    
Entity Central Index Key 0001883984  
Entity Registrant Name Alternus Clean Energy, Inc.  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q3  
Document Fiscal Year Focus 2025  
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Sep. 30, 2025  
Document Transition Report false  
Entity File Number 001-41306  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 87-1431377  
Entity Address, Address Line One 17 State Street, Suite 4000  
Entity Address, City or Town New York  
Entity Address, State or Province NY  
Entity Address, Postal Zip Code 10004  
City Area Code 212  
Local Phone Number 739-0727  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   724,658
Warrant [Member]    
Document Information [Line Items]    
Title of 12(b) Security Warrants, each whole warrant exercisable into one share of Common Stock  
Trading Symbol ACLEW  
Common Stock [Member]    
Document Information [Line Items]    
Title of 12(b) Security Common Stock, par value $0.0001 per share  
Trading Symbol ALCE