| IADYS | Roquefort-la-Bédoule, Bouches-du-Rhône | Visit site |
| IAV Poland | Opole, Opole Voivodeship | Visit site |
| IBIS Power | Eindhoven, North Brabant | Visit site |
| IBM | Armonk, New York | Visit site |
| IBP Ingenieure GmbH | München, Bavaria | Visit site |
| ICIS | London, England | Visit site |
| ICM | Colwich, Kansas | Visit site |
| ICO S.a.s. di Ing. Fornai & C | Alzano Lombardo, Bergamo | Visit site |
| ICSEL | Saint-André-de-Corcy, Ain | Visit site |
| IDCM | London, England | Visit site |
| IDE Technologies | Campus, Illinois | Visit site |
| IDEAL SOLAR ENERGY LTD. | Jerusalem, Jerusalem District | Visit site |
| IDOM Environment | Bilbao, Biscay | Visit site |
| IEA Constructors LLC, a MasTec Company | Indianapolis, Indiana | Visit site |
| IEC Pennsylvania | Harrisburg, Pennsylvania | Visit site |
| IEP Technologies | Marlborough, Massachusetts | Visit site |
| IES ENGINEERING SRL | Livorno, Livorno | Visit site |
| IESSA (Illumination Engineering Society of South Africa) | Johannesburg, Gauteng | Visit site |
| IFC - International Finance Corporation | Washington, District of Columbia | Visit site |
| IFM Investors | Melbourne, Victoria | Visit site |
| IFPL | Newport, England | Visit site |
| IG Renewables | London, England | Visit site |
| IG Windkraft | Vienna, Vienna | Visit site |
| IGEAM | Roma, Rome | Visit site |
| IGNES - Industriels des solutions électriques et numériques du bâtiment | · | Visit site |
| IGS Energy | Dublin, Ohio | Visit site |
| IHK für München und Oberbayern | München, Bavaria | Visit site |
| IJGlobal | London, England | Visit site |
| IKO International | Parsippany, New Jersey | Visit site |
| IKPT | Jakarta, Jakarta | Visit site |
| ILUM ENERGY SOLUTIONS | Sacramento, California | Visit site |
| IMARTEC ENERGIA | Lleida, Lleida | Visit site |
| IMB Energy Systems GmbH | Roth, Bavaria | Visit site |
| IMO Precision Controls Ltd | Hatfield, England | Visit site |
| IMT SOLAR | North Tonawanda, New York | Visit site |
| INDUS Environmental Services Pvt. Ltd. | New Delhi, Delhi | Visit site |
| INESC Microssistemas e Nanotecnologias | Póvoa de Santo Adrião, Lisbon | Visit site |
| INESC TEC | Porto, Porto | Visit site |
| INF Associates | New York, New York | Visit site |
| INGENIERIA Y OBRA CIVIL CHAVARRI SL | Burgos, Burgos | Visit site |
| INGETEK USA | · | Visit site |
| INL - International Iberian Nanotechnology Laboratory | Braga, Braga | Visit site |
| INNO ENERGY 2025 | Ouargla, Ouargla | Visit site |
| INNOVENTUM | Malmö, Skåne | Visit site |
| INNOVIS Consulting | Adelaide, South Australia | Visit site |
| INNOVX | Chelmsford, Massachusetts | Visit site |
| INSTRA Ingenieros | A Coruña, A Coruña | Visit site |
| INTECH Automation & Intelligence | Houston, Texas | Visit site |
| INTI-TECH | Santiago, Santiago Metropolitan Region | Visit site |
| INTO-R | Gimpo-si, Gyeonggi-do | Visit site |
| INVALL S.A. | Reus, Tarragona | Visit site |
| INVT Electric | Shenzhen Shi, Guangdong | Visit site |
| ION Chip Co., Ltd. | Seoul, Seoul | Visit site |
| IPD - BIM Services | Sheridan, Wyoming | Visit site |
| IPG Energy | Hoddesdon, England | Visit site |
| IPG Genesis Systems | Davenport, Iowa | Visit site |
| IPM Group | Bratislava, Bratislava | Visit site |
| IPOL Lubricants - GP Petroleums Ltd. | Mumbai, Maharashtra | Visit site |
| IREC - Institut de Recerca en Energia de Catalunya | Sant Adrià de Besòs, Barcelona | Visit site |
| IREDA Ltd. | New Delhi, Delhi | Visit site |
| IREX | Lancaster, Pennsylvania | Visit site |
| ISA Corporation | · | Visit site |
| ISC Constructors, L.L.C. | Baton Rouge, Louisiana | Visit site |
| ISC Konstanz | Yarrambat, Victoria | Visit site |
| ISCOM SPA - Roofing | Pescantina, Verona | Visit site |
| ISFH – Institut für Solarenergieforschung Hameln | Emmerthal, Lower Saxony | Visit site |
| ISG-MOOLEX | Heiligenbrunn, Burgenland | Visit site |
| ISGroup | Perth, Western Australia | Visit site |
| ISI Solar | Interconnection Systems, Inc. | Central City, Nebraska | Visit site |
| ISOLUX CORSAN | Madrid, Madrid | Visit site |
| ISRA VISION | Darmstadt, Hesse | Visit site |
| ISS Global Forwarding | Parauapebas, Pará | Visit site |
| ITC Guard | Las Vegas, Nevada | Visit site |
| ITI Powered | Victoria, British Columbia | Visit site |
| ITS WIND SERVICES LTD | Northern Ireland | Visit site |
| ITalConn | Bassano del Grappa, Vicenza | Visit site |
| IWEN Energy Institute gGmbH | Rostock, Mecklenburg-Western Pomerania | Visit site |
| IWNL Energy | Orlando, FL | Visit site |
| IWP - Ingenieurbüro für Systemplanung GmbH | Stuttgart, Baden-Württemberg | Visit site |
| IXYS Corporation | Milpitas, California | Visit site |
| IZI Solutions Durables | Courbevoie, Hauts-de-Seine | Visit site |
| IZIVIA - Groupe EDF | Courbevoie, Hauts-de-Seine | Visit site |
| Iberdrola México | General Manuel Ávila Camacho, Mexico | Visit site |
| Ice Industries | Sylvania, Ohio | Visit site |
| Iceland Geothermal | Reykjavík, Capital Region | Visit site |
| Iceland Renewable Energy Cluster | Reykjavík, Capital Region | Visit site |
| Icon Power | Tempe, Arizona | Visit site |
| Iconicx Services | Franklin, Wisconsin | Visit site |
| Idaho National Laboratory | Idaho Falls, Idaho | Visit site |
| Ideal Contracting | Detroit, Michigan | Visit site |
| Ideal New Energy | Wuxi Shi, Jiangsu | Visit site |
| Ideematec | Wallerfing, Bavaria | Visit site |
| IdentiFlight | Louisville, Colorado | Visit site |
| Ies Solare S.r.l. | Bibbona, Livorno | Visit site |
| Ifri-sol | Roseville, California | Visit site |
| Igloo Environmental Limited | Braintree, England | Visit site |
| Ijes Solar | Castalla, Alicante | Visit site |
| Ilios Integrators | Houston, Texas | Visit site |
| Illinois Green Alliance | Chicago, Illinois | Visit site |
| Illinois Solar Energy Association | Elk Grove Village, Illinois | Visit site |
| Illuminate USA | Pataskala, Ohio | Visit site |
| Illumine-i | Austin, TX | Visit site |
| Illuming Power Inc. | Vancouver, British Columbia | Visit site |
| Ilumisol Energia Solar | Cascavel, Paraná | Visit site |
| Imagine Instruments | Liberty Hill, Texas | Visit site |
| Imen Enerji Sanayi ve Ticaret Anonim Sirketi | İzmir, Bayraklı | Visit site |
| Imhotep.Industries | Freistadt, Upper Austria | Visit site |
| Impact Engineering | Vancouver, British Columbia | Visit site |
| Impact Hub Vienna | Vienna, Vienna | Visit site |
| Imperial Star Solar | Tomball, Texas | Visit site |
| Impresa Pizzarotti & C. S.p.A. | Parma, Parma | Visit site |
| Impuls Energy Trading GmbH | Köln, North Rhine-Westphalia | Visit site |
| In Phaze Electric | Orlando, Florida | Visit site |
| InEnergie | Utrecht, Utrecht | Visit site |
| InWarmte | Utrecht, Utrecht | Visit site |
| Inch Cape Offshore Limited | Edinburgh, Scotland | Visit site |
| Inclusive Green Growth in Egypt النمو الأخضر الشامل فى مصر | Piraquara, Paraná | · |
| Inclusive Prosperity Capital | Hartford, Connecticut | Visit site |
| Increase New Energy (Hunan) Co.,Ltd | Hunan | Visit site |
| Incubateur Savoie Technolac | Le Bourget-du-Lac, Savoie | Visit site |
| Independent Electricity System Operator (IESO) | Toronto, Ontario | Visit site |
| Independent Power Producers of New York | Albany, New York | Visit site |
| India Agrivoltaics Alliance (IAA) | Delhi | Visit site |
| Indie Energy, Inc. | Buda, Texas | Visit site |
| Indigenous Services Canada | Services aux Autochtones Canada | Gatineau, Quebec | Visit site |
| Indo-German Energy Forum Support Office (IGEF-SO) | New Delhi, Delhi | Visit site |
| Indonesia Infrastructure Finance | Jakarta, Jakarta | Visit site |
| Indovance Inc | Apex, North Carolina | Visit site |
| Indovance Pvt Ltd | Pune, Maharashtra | Visit site |
| Induscabos | Poá, São Paulo | Visit site |
| Industrial Automated Systems, Inc. | Wilson, North Carolina | Visit site |
| Industrial Batteries Australia | Sydney, New South Wales | Visit site |
| Industrial Networking Solutions (INS) | Richardson, Texas | Visit site |
| Infineon Technologies | Neubiberg, Bavaria | Visit site |
| Infinite Consulting Corp | Hicksville, New York | Visit site |
| Infisolar | Ronda, Málaga | Visit site |
| Influent Energy | Kansas City, Missouri | Visit site |
| Infra-Metals | Newtown, Pennsylvania | Visit site |
| InfraCredit | Lagos | Visit site |
| InfraRoad Trading & Contracting LLC | الشيحانية, Al-Shahaniya | Visit site |
| InfraVia Capital Partners | Paris, Île-de-France | Visit site |
| Infralogic | London, England | Visit site |
| Infranity | Paris, Île-de-France | Visit site |
| Infrastructure and Energy Alternatives, Inc. (IEA), a MasTec Company | Indianapolis, Indiana | Visit site |
| Infyos | London, England | Visit site |
| Ingenergía de México | San Juan Tehuixtitlán, Mexico | Visit site |
| Ingenieurbüro GEHLEN | Düsseldorf, North Rhine-Westphalia | Visit site |
| Ingenieurgesellschaft IDEAS mbH | Thundorf in Unterfranken, Bavaria | Visit site |
| Ingenieurgesellschaft Mengü Ingenieure GmbH | Westerbork, Drenthe | Visit site |
| Inglett & Stubbs | Mableton, Georgia | Visit site |