Abstract
Due to the long wires between the solar master and solar slaves, we need I2C bus buffers.
High Capacitance
Long wires have high capacitance and I2C specifies the capacitance should be smaller than 400 pF (about 8 meters of 4-way cable). Given the approximately 5 meter length of MSXII and even greater lengths for wires, the capacitance may exceeds the 400 pF limit. However, the limitation of the capacitance can be raised by reducing the bit rate from 1 MHz to a slower rate.
Noise
In addition to the capacitance limitation, noise is also a limitation of long distance communication.