Actually, it's simple: there is no special case for speech, so you use the tense that's appropriate to locate the event in time, just like any other sentence.
- [future] When it is published later this year, the report's introduction will say "There is a need for more bio-compostable plastics"
- [simple present] In its executive summary, the report says "There is a need for more bio-compostable plastics"
- [simple past] The previous edition said "There is a need for more bio-compostable plastics"
- [conditional past perfect] Without that last-minute edit, the report's summary would have said "There is no need for more bio-compostable plastics"
Note that Number 3, the word "previous" hints that the report is no longer current. Because of this sense of no longer being in the present, the simple past tense is appropriate. For reasons of style, this sentence would normally be written as reported speech rather than a quotation ("...said that more ... were needed"), but it is grammatically correct as written above.
When quoting from documents that are still considered to be "current" (and that includes literary works), Number 2, the simple present is the preferred tense. Generally, you don't see the past tense used as in Number 3 unless the author is contrasting one source with one she/he considers to be "newer" (or better informed, or more advanced).
For speech, it's much easier to get the tense correct - just ask yourself: when were the words spoken? The answer to that question will give you the correct tense to use.