Find multiple solutions in Pyomo with Gurobi

Question

I am fairly new to Pyomo and Gurobi. I'd like to find 20 sets of different solutions that meet the following constraints.

constraints：
10<=x1<=20 
12<=x2<=32 
5<=x3<=15 
5<=x4<=52 
x1+x2+x3+x4=100.

From here I learned Gurobi has PoolSolutions, so I decided to have a try.

from gurobipy import GRB
import numpy as np
from pyomo.environ import *
import matplotlib.pyplot as plt

generator={  
1 :{'down':10,  'up':20,},
2 :{'down':12,  'up':32,},
3 :{'down':5,   'up':15,},
4 :{'down':5,   'up':52,},
    }
G = generator.keys()

# create a new model
m = ConcreteModel()

# create variables
m.P = Var(G, domain=NonNegativeReals)

# set objective 
m.OBJ = Objective(expr = 0)

# add constraints
m.c = ConstraintList()
m.c.add(sum(m.P[g] for g in G)== 100)
for g in G:   
     m.c.add(m.P[g] <= generator[g]['up'])
     m.c.add(m.P[g] >= generator[g]['down'])

# try to get 20 sets of different solutions
n_of_s = 20
opt = SolverFactory('gurobi_persistent')
opt.set_instance(m)
opt.set_gurobi_param('PoolSolutions', n_of_s)
opt.set_gurobi_param('PoolSearchMode', 2)
opt.solve()

But it doesn't work properly. Hope somebody could teach me how to modify this and how to show the results of 20 solutions. Any suggestions are welcomed. THX