Compost is usually my answer for everything but grass clippings aren't especially good for compost tbh, you need to mix them in well with other stuff (ideally stuff high in carbon like dead leaves or even shredded paper - think I remember Elpenor mentioning having a shredder?) or they tend to just mat together into a soggy, smelly, yellow mess.
On the subject of compost, I know most people here won't have the time or space or enough waste for this - you need about a cubic metre or slightly more to build it in one go, then it needs turning every 48 hours or less - but I've been super impressed with the Berkeley method since trying it out recently. Even my first, very half-arsed
attempt is doing well and I'm about to hire a shredder (really need to buy one but I have plans to diy one out of a brushcutter and plastic barrel for now...) to start a second heap. Thinking I might stick it in one end of the polytunnel to act as a kind of low tech radiator.