I think I know what you are asking but, I am not 100% sure that I know what you are asking so, I will take my "best shot" at giving you an answer.
Wow! I must have started writing 10 times and deleted it 10 times because all I could come up with is more questions of my own. Questions like; are you on or off grid? What is the nominal voltage of your solar yard lights? Do you want to wire them all in permanently to one power source? Are the solar cells built in or separate from the light? Are they all identical to one another?
Anything is possible but, without some base of reference it would be difficult at best for me to help you come up with a safe and viable lighting system. I assume that you are attempting to reuse existing lights without purchasing anything more than necessary to utilize them indoors. This would involve some sort of voltage supply equal to the nominal voltage of each light if they are all identical to one another.
http://www.powerstream.com/dc2.htmLook over this site and read the ratings carefully. Be sure the voltage range is not spread to far apart from what your lights need but keep in mind that the more lights there are on one string and, the longer the wire, the more of a voltage drop. Also the amperage. You will have to know how many amps are to be drawn from the power supply. Of course I don't know what the input voltage would be to the converter so... All in all, you may just have to experiment but, please practice safety. We wouldn't want to read about you burning yourself up now would we?