how much light will keep them in veg?

im putting some clones out in 2 weeks and dont want them to go right into flowering so whats the minimum amount of light that will keep them in veg?
they will be in a hoophouse in the bay area, the site does not have electicity so im looking to use 12 volt dc cfl or 12vdc led which will be powered by a car battery(either solarcharged or replaced with afresh charged bat)

in the camping dept. they have 4-AA powered 24 led round lights for $7 would this be enough light?

the plants will be in a 100sq ft. space

i have my mothers outside in a box. vegging. running 2, 26 watt clfs, but using the sun during the day. my understanding is as long as just a slp of light under the door will keep them in veg. remember thought, they may stretch alot.