in my opinion you shouldn't be doing a 24/7. Plants need their rest just as you do. Sugar production is at a loss when doing 24/7. Your plants need the production of sugar for it's cell structure!
Some people swear by 24/7; some 24/7 for two weeks then 18/6; and some prefer only 18/6. Studies have been done and from most ive gathered 18/6 is just a sufficent as 24/7. I personally believe ive seen more growth using the method of 24/7 for 2 weeks then switching to 18/6. Its all up to you...but if electritcity is a issue then i would for sure just stick to 18/6