20 pounds a month? Pretty much gotta do hydro and gotta do SOG. Figure average of 1 ounce per plant. OK so you have to do a perpetual grow and harvest once a month. 16 ounces per pound times 20 =320 plants harvested each month. Now it takes 3 months total on average to grow 1 plant all the way through to harvest so your gonna need 3 times the amount of plants you harvest...960 plants. might as well make it 1000 plants just for fun. Ok so now your gonna need lights, lots and lots of lights. Lets just figure 50W/plant to get the 1 ounce. Use light movers to get more efficiency and we will say for fun it will double your light capacity. 1000*50=50,000 total watts needed. Lets figure the amperage load shall we? 50,000/240 ( For a big setup like this you really have to use 240 volt ballasts) = 208 amps of power. thats almost 420 amps of 110v power. Thats a big fuggin load for sure, more on the lines of commercial use.
Even here where I live electricity can be as low as 4 cents per KWH at times, even then your bill is going to be in the neighborhood of 2 dollars per hour of lights on. The average rate for electricity is 13 cents per KWH, so then those lights are gonna cost about 6 dollars per hour of lights on....$72/day, BUT the big kicker is that the power companies can charge you more for using more, even here if I power hog I have to pay up to 4x the normal rate, so lets say those lights are now costing about $300 a day to run. BUT since your using light movers you only need half as much power to achieve about the same results, so in a perfect world you would half all your power costs.
Makes you think about the whole thing in a different perspective. Now imagine trimming out 20 pounds of weed by yourself.