A method for storing and recovering renewable energy, which was generated offshore, wherein use is made of: • a first reservoir connected to a first well, and a second reservoir connected to a second well, wherein each of the first reservoir and the second reservoir is an offshore underground reservoir from which natural gas or oil was previously extracted and which has been made ready for injection and storage of CO2, and wherein said CO2 is defined as being a mixture of pure carbon dioxide and other substances, wherein the share of carbon dioxide is at least 50%, and wherein each of the first well and the second well is an opening, which has previously been drilled for the purpose of extracting natural gas or oil, and which has been made ready for injection and storage of the CO2 in the first reservoir and the second reservoir, respectively, and wherein the CO2 is stored in the first reservoir and in the second reservoir, and wherein the CO2 in the first reservoir is kept at a lower pressure than in the second reservoir; • a ducting structure (19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30), which is configured for displacing a portion of the CO2 from the first reservoir, successively via the first well, the ducting structure and the second well, to and into the second reservoir, and vice-versa; and • an electrically driven compressor, a turbine and an electric generator; and wherein said storing of said generated renewable energy is achieved by causing a portion of the CO2 to flow, successively via the first well, a part of the ducting structure (19, 20, 21, 22, 24 and 23) and the second well, from the first reservoir to and into the second reservoir, wherein said causing a portion of the CO2 to flow is realized by the compressor being driven by said generated renewable energy; and wherein said recovering of the generated renewable energy is achieved by allowing a portion of the CO2 to flow, successively via the second well, a part of the ducting structure (23, 24, 25, 26, 27, 28, 29, 30, 20 and 19) and the first well, from the second reservoir to and into the first reservoir, wherein said portion of the CO2, during said allowing a portion of the CO2 to flow, is expanding and is driving, via the turbine, the electric generator. • a first reservoir connected to a first well, and a second reservoir connected to a second well, wherein each of the first reservoir and the second reservoir is an offshore underground reservoir from which natural gas or oil was previously extracted and which has been made ready for injection and storage of CO2, and wherein said CO2 is defined as being a mixture of pure carbon dioxide and other substances, wherein the share of carbon dioxide is at least 50%, and wherein each of the first well and the second well is an opening, which has previously been drilled for the purpose of extracting natural gas or oil, and which has been made ready for injection and storage of the CO2 in the first reservoir and the second reservoir, respectively, and wherein the CO2 is stored in the first reservoir and in the second reservoir, and wherein the CO2 in the first reservoir is kept at a lower pressure than in the second reservoir; • a ducting structure (19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30), which is configured for displacing a portion of the CO2 from the first reservoir, successively via the first well, the ducting structure and the second well, to and into the second reservoir, and vice-versa; and • an electrically driven compressor, a turbine and an electric generator; and wherein said storing of said generated renewable energy is achieved by causing a portion of the CO2 to flow, successively via the first well, a part of the ducting structure (19, 20, 21, 22, 24 and 23) and the second well, from the first reservoir to and into the second reservoir, wherein said causing a portion of the CO2 to flow is realized by the compressor being driven by said generated renewable energy; and wherein said recovering of the generated renewable energy is achieved by allowing a portion of the CO2 to flow, successively via the second well, a part of the ducting structure (23, 24, 25, 26, 27, 28, 29, 30, 20 and 19) and the first well, from the second reservoir to and into the first reservoir, wherein said portion of the CO2, during said allowing a portion of the CO2 to flow, is expanding and is driving, via the turbine, the electric generator. and wherein said storing of said generated renewable energy is achieved by causing a portion of the CO2 to flow, successively via the first well, a part of the ducting structure (19, 20, 21, 22, 24 and 23) and the second well, from the first reservoir to and into the second reservoir, wherein said causing a portion of the CO2 to flow is realized by the compressor being driven by said generated renewable energy; and wherein said recovering of the generated renewable energy is achieved by allowing a portion of the CO2 to flow, successively via the second well, a part of the ducting structure (23, 24, 25, 26, 27, 28, 29, 30, 20 and 19) and the first well, from the second reservoir to and into the first reservoir, wherein said portion of the CO2, during said allowing a portion of the CO2 to flow, is expanding and is driving, via the turbine, the electric generator.