You can use CertBot to install free SSL Certificates on servers with or without hosting panels.
You can follow instructions here for various setups https://certbot.eff.org/instructions
I use Centos 7 & Nginx with one setup, this presumes you have added running sites to nginx and want to enable SSL.
Enable Epel-Release for Centos 7
yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
yum install certbot python2-certbot-nginx
echo "0 0,12 * * * root python -c 'import random; import time; time.sleep(random.random() * 3600)' && certbot renew -q" | sudo tee -a /etc/crontab > /dev/null