NABCEP is the North Amercian Board of Certified Energy Practitioners.
NABCEP is the only large, nationally recognized certification for solar energy which is sometimes either considered a plus or an actual requirement in some states or on certain contracts to be able to do certain types of work or to work at all as a primary installer responsible for the job.
NABCEP creates credentialing programs as well as entry level exams for installers and other practitioners in several renewable energy technology areas. They do not normally give classes, independant parties do the training and in most cases the tests are administered by NABCEP or by NABCEP authorized entities after applicants meet whatever the pre-requisites were and pay a fee to NABCEP. Certifications are not permanent, they need to be renewed periodically and maintained often via actual work in the field and or continuing education.
The big four currently are:
Certified Solar PV Installer
NABCEP PV Entry Level Exam (this last is confirmation you passed a test, it is not a 'certification')
Certified Solar Thermal Installer
Certified Small Wind Installer
They are considering certifications for PV Technical Sales, for companies and also various credentials for other renewable energy technologies and positions.
The NABCEP website contains a wealth of educational materials, references, study guides and links which are extremely helpful to consumers and energy professionals alike.
OSHA is the United States Occupational Safety & Health Administration.
For some projects, varying levels of safety certifications may or may not be called for. As an example, some municipalities or rebating entities require that all workers on a jobsite have taken a 10 hour OSHA safety course. These are often offered by local training centers, schools or instructors.