iphoto storage on icloud

No.

iCloud Photos is a syncing service. Any photo you delete from a device where iCloud Photos is turned on will also be deleted from iCloud and from any other device connected to iCloud Photos. You can potentially reduce the storage space required on a device by turning on Optimize Storage. See: Set up and use iCloud Photos - Apple Support

Apple does not currently offer cloud-only storage for photos. If that is what you want or need, you may want to explore 3rd party options such as Google Photos or Dropbox.

Are you using iPhoto or Photos? The iPhoto.app cannot use iCloud Photos, only its successor Photos can sync with iCloud Photos.

You can save storage with iCloud Photos, if you migrate your iPhoto Libraries to Photos for Mac, but do it only, if you always have a fast, affordable, and reliable internet connection. And if you go for iCloud Photos and "Optimize Mac Storage", your Time Machine backups of your Photos Library will no longer be complete and you have to find a will have to find an additional backup method to backup your Photos Libraries.

Some background information to help you decide, in addition to the spot-on posts by FoxFifth and Piqûre: Three Good Reasons for Using iCloud Photos and When not to use it… - Apple Community

If your goal is to save space on your drive which I assume is your main internal drive then you could just move your Photos or iPhoto library to an external drive. It will not affect syncing or any other feature of Photos or iPhoto. If you can afford it buy an external SSD, it will make opening and operating your library much faster. Even a cheap drive will read and write at 3-5 times the speed of your internal HDD.

Don't ever think of iCloud Photos as backup. Although it adds security to your photos and videos by copying them elsewhere it's not technically a backup. It's still worth doing.