| Kent Renewable Energy Limited | Sandwich | 2010 |
| Kent Solar Limited | London | 2011 |
| Kent Supreme Heating Ltd | Sidcup | 2014 |
| Kentish Flats Limited | London | 2000 |
| Kentishes Solar Farm 3 Limited | Colchester | 2023 |
| Kentucky Energy Limited | Wallington | 2019 |
| Kenwyn Solar Limited | Kings Langley | 2013 |
| Keoma Energy Ltd | Sevenoaks | 2025 |
| Kernow Electric Heating Limited | Carharrack | 2018 |
| Kernow Thermal Ltd | St. Austell | 2025 |
| KES Electrics Services Ltd | Hornchurch | 2017 |
| Kesh Wind Ltd | Belfast | 2016 |
| Keska Ltd | London | 2025 |
| Kesteven Energy Ltd | Sleaford | 2022 |
| Kestral Renewable Energies Ltd. | Kilsyth | 2008 |
| Keswoodsparks Ltd | Camberley | 2014 |
| Kettering Energy II Limited | Bedford | 2017 |
| Kettering Energy Limited | Bedford | 2017 |
| Kevat Solar Limited | Macclesfield | 2012 |
| KEW GAS Ltd | London | 2023 |
| KEW Power Ltd | Richmond | 2025 |
| Key Integrated Services (Electrical) Limited | Manchester | 2017 |
| Keyingham Power Limited | Hull | 2004 |
| Keynsham Community Solar Limited | London | 2024 |
| Keystone Energy Partners Limited | Peterlee | 2025 |
| KF Energy Centre Ltd | Liverpool | 2020 |
| Kfworks Ltd | Porth | 2025 |
| Kfzm Limited | Elgin | 2014 |
| KG Utilities (NE) Ltd | Sherburn Village | 2024 |
| KH Electrotechnical Ltd | Hartlepool | 2026 |
| Khan & Brown Commercial Services Ltd | Bacup | 2026 |
| Khan Trading UK Ltd | Feltham | 2014 |
| Khawaja Energy Solution Ltd | Leighton Buzzard | 2026 |
| KHM Alpha Services Ltd | London | 2023 |
| KHM Power Limited | Ballymoney | 2014 |
| Kiaora Plumbing & Heating Limited | Dorchester | 2009 |
| Kickles PV Ltd | Saffron Walden | 2014 |
| Kidman Air Conditioning Ltd | Bedford | 2026 |
| Kids Road Wind Ltd | Belfast | 2016 |
| Kidzilla Services Limited | Cheadle | 2018 |
| KIE Property Ltd | Lanark | 2025 |
| Kieren Ryan Electrical Services Ltd | Stirling | 2024 |
| Kilbraur Wind Energy Limited | Edinburgh | 2003 |
| Kilbuck Lane Flexi Limited | Doncaster | 2017 |
| Kilda SM Limited | London | 2016 |
| Kildalloig Renewables Ltd | Campbeltown | 2023 |
| Kildrummy Wind Farm Limited | London | 2010 |
| Killail Hydro Ltd | Tighnabruaich | 2019 |
| Killean Bioenergy Ltd | Newry | 2019 |
| Killeter Wind Limited | Enniskillen | 2020 |
| Killington and District Sustainable Energy Trust | Sedbergh | 2009 |
| Killoch Resources Limited | Grays | 2023 |
| Killybeg West Wind Ltd | Belfast | 2016 |
| Killygordon Renewable Energy Ltd | Fivemiletown | 2022 |
| Killygore Wind Ltd | Cookstown | 2013 |
| Killymitten Wind Limited | Enniskillen | 2014 |
| Killyrudden Wind Ltd | Belfast | 2016 |
| Kilmac Energy (Finavon) Limited | Dundee | 2015 |
| Kilmarnock Energy Centre Limited | Edinburgh | 2023 |
| Kilmarnock Flexpower Ltd | Edinburgh | 2021 |
| Kilmaronock Energy Scotland Ltd | Glasgow | 2023 |
| Kilmoyle AD Limited | Ballymoney | 2016 |
| Kiln Power Limited | Bristol | 2016 |
| Kilnside Energy Park Limited | London | 2023 |
| Kilowatt Energy Limited | Derby | 2024 |
| Kilrea Wind Ltd | Belfast | 2016 |
| Kimberley Hydro Limited | Neath | 2010 |
| Kimblesworth Solar Limited | Bath | 2021 |
| Kimblewick Solar Limited | Liverpool | 2021 |
| Kimran Energy Limited | Londonderry | 2015 |
| Kincardine Grid 1 Ltd | London. | 2017 |
| Kincardine Grid 2 Ltd | London | 2021 |
| Kincardine Grid 3 Ltd | London | 2016 |
| Kincardine Offshore Windfarm Limited | Edinburgh | 2014 |
| Kincardine Storage Limited | London | 2015 |
| Kincardine Wind Partners Ltd | Edinburgh | 2025 |
| Kincorth Energy Storage System Ltd | Edinburgh | 2023 |
| Kincraig Energy Centre Limited | London | 2021 |
| Kindred Generation Limited | Woodbridge | 2011 |
| Kinecx Energy Limited | London | 2005 |
| Kinegar Wind Farm Limited | London | 2013 |
| Kinetic Power for Deep Engineering and Technologies Ltd | London | 2009 |
| Kinetic Power Solutions Ltd | Armagh | 2025 |
| Kinetic Renewables Ltd | Harwich | 2022 |
| Kinetic Surge Ltd | Manchester | 2026 |
| Kinetic Utilities Limited | Ilford | 2022 |
| Kinetica 846 Limited | Gatwick | 2014 |
| Kinetica 868 Limited | Gatwick | 2014 |
| Kingdom Powernet Limited | London | 2026 |
| Kingfisher Heating Ltd | Greenhithe | 2020 |
| Kings Lynn Heat and Power Ltd | Holme Next The Sea | 2022 |
| Kingsburn Wind Energy Limited | Edinburgh | 2004 |
| Kingsfort Developments Limited | Carryduff | 2011 |
| Kingsfort Energy Ltd | Carryduff | 2014 |
| Kingsmill Wind Ltd | Belfast | 2014 |
| Kingsnorth Peaking Power Limited | London | 2016 |
| Kingston Energy Storage Ltd | London | 2021 |
| Kingston Solar Limited | Kings Langley | 2019 |
| Kingsway Solar Farm Limited | London | 2023 |
| Kingswood Energy Ltd | Bodmin | 2013 |