A solar cell string having a plurality of solar cells (701, 801), wherein a front side of each of said solar cells has a light receiving surface; said solar cell string having: a first small cell string of first type (a', a) solar cells, and a second small cell string having first type solar cells and one second type (b") solar cell; wherein each of the first type solar cells is provided with a front electrode as a negative electrode and with a back electrode as a positive electrode, wherein said front electrode and said back electrode are respectively formed on opposite edges of each of said first type solar cells, wherein said solar cells of said first small cell string are connected in series by shingling manner, wherein said first small cell string has a first and a second end, wherein a solar cell (a') at said first end of said first small cell string has a second positive back electrode located in the middle of the back side of this solar cell; wherein said solar cells of said second small cell string are connected in series by shingling manner, wherein said second small cell string has a first and a second end, wherein a solar cell (a') at said first end of said second small cell string has a second positive back electrode located in the middle of the back side of this solar cell; wherein the first small cell string is formed by a same number of solar cells connected in series as the second small cell string; wherein said second type solar cell is provided with a first back electrode as a negative electrode located at an edge of said solar cell and having a same polarity as a back main grid of the second type solar cell, and is provided with a second back electrode as a positive electrode located at an opposite edge of said solar cell, and is provided with a third back electrode as a positive electrode located at the middle of said solar cell, wherein the front side of the second type solar cell is not provided with electrodes; wherein said second type solar cell is connected with its first back electrode to said front electrode of a solar cell (a) at said second end of said second small cell string, wherein this second type solar cell is connected with its second back electrode to a front electrode of said solar cell (a) at said second end of said first small cell string. wherein a front side of each of said solar cells has a light receiving surface; said solar cell string having: a first small cell string of first type (a', a) solar cells, and a second small cell string having first type solar cells and one second type (b") solar cell; a first small cell string of first type (a', a) solar cells, and a second small cell string having first type solar cells and one second type (b") solar cell; wherein each of the first type solar cells is provided with a front electrode as a negative electrode and with a back electrode as a positive electrode, wherein said front electrode and said back electrode are respectively formed on opposite edges of each of said first type solar cells, wherein said solar cells of said first small cell string are connected in series by shingling manner, wherein said first small cell string has a first and a second end, wherein a solar cell (a') at said first end of said first small cell string has a second positive back electrode located in the middle of the back side of this solar cell; wherein said solar cells of said second small cell string are connected in series by shingling manner, wherein said second small cell string has a first and a second end, wherein a solar cell (a') at said first end of said second small cell string has a second positive back electrode located in the middle of the back side of this solar cell; wherein the first small cell string is formed by a same number of solar cells connected in series as the second small cell string; wherein said second type solar cell is provided with a first back electrode as a negative electrode located at an edge of said solar cell and having a same polarity as a back main grid of the second type solar cell, and is provided with a second back electrode as a positive electrode located at an opposite edge of said solar cell, and is provided with a third back electrode as a positive electrode located at the middle of said solar cell, wherein the front side of the second type solar cell is not provided with electrodes; wherein said second type solar cell is connected with its first back electrode to said front electrode of a solar cell (a) at said second end of said second small cell string, wherein this second type solar cell is connected with its second back electrode to a front electrode of said solar cell (a) at said second end of said first small cell string.