Ok. if you're not experienced, do not answer this. From your experience, how much did your electricity bill go up from using a 250w Mh bulb 20/4? I am growing with cfl's, but they are growing very slow due to the lack of lumens.
I am experienced, specifically with 250w HID, but you really can't tell that by looking at your bill -- if it's higher or lower than last month was that because of your grow? More or less use of your furnace or air conditioner? Etc. And the answer is all of the above because you can't break out on your bill which kilowatt hour was used by what (unless you have separate meters). But there is an easy way to calculate. You need to arrive at two numbers, the electrical use of your grow op and how much you are charged per kilowatt hour. Electrical use of your grow op: 250w x 20 hours a day usage = 5,000 watt-hours used. Times average 30 days per month = 150,000 watt-hours used per month. Divided by 1,000 equals 150 kilowatt hours per month. Now, look at your electric bill. Some electric companies actually print the kilowatt hour rate on the bill, if not you can get a close-enough average by taking the total charge of your bill and divide by the total kilowatt hours the bill says was used. For example, if your bill was $100 and it says you used 800 kilowatt hours then your rate is about 12.5¢ per kilowatt hour. Multiply the kilowatt hour usage of your grow times the rate and get the electrical cost of your grow -- in my example, 150 x $0.125 = $18.75 per month. If you want the electrical cost for your entire grow op then don't forget to include the usage by fans, pumps, heaters, etc.