Green open access refers to the possibility to make subscription-based journal articles open access by uploading the peer-reviewed and accepted author manuscript to an institutional repository (such as DiVA). This article version is also known as post-print. In most cases, you are not allowed to use the publisher's typeset PDF version of the article. This option is offered by most publishers. Green open access doesn't involve any costs and also meets the research funders' open access requirements as long as the embargo period is not too long. This type of open access is also called parallel publishing or self-archiving.
In many cases, however, there is a time embargo from its publishing date to when you can make it open access. Such an embargo can vary between 6 to 48 months depending on the publisher and to which discipline the journal belongs. The humanities and social sciences have usually longer embargo periods than such disciplines as medicine, physics and biomedicine.
The database used by the library when checking publishers' copyright policies, especially their green open access possibilities is SHERPA/RoMEO. In this database you can find out the following details about a journal's or publisher's open access possibilities:
SHERPA/RoMEO uses colour codes to distinguish the different types of archiving policies (remember that the most important thing is to look at the basic information about the policy since the colour coding might be a bit misleading in some cases):
Let us look at an example of a journal published by Elsevier:
From the information above we then know the following:
Browsing through this list we can then see that there is a 12-month embargo for this journal. You can therefore make it freely available in DiVA 12 months after it has been published.