1Kw flow rate ....
Approximate calculation of water flow that would be required in order to generate 1 kw, at 100 ft. vertical drop .....friction loss not included:
1kw=738 (ft-lbf)/sec = P lbf/in2 * 144in2/ft2 * Q ft3/sec
use P = 43 psi, corresponding to 100 ft, and solve for Q
giving Q = 0.12 ft3/sec = 54 gal/min
However, at 54 gpm flow rate, and a 400 ft. pipe run, using 1.5 in pipe, the head loss due to friction is prohibitive. See:
Pipe loss
By using 3" PVC the friction head loss at 50 gpm, and with a 400 ft pipe length is only about 3.6 ft, or equivalently, 1.6 psi loss.
Generator efficiency should be reasonably high, and not require any additional system modifications.