Sunlight is a powerful force, it gives life to so many things, and can take life just as easily. So of course this can be an incredibly powerful cleansing method.
Do be careful with sunlight as many crystals (like Rose Quartz or Amethyst) are known to fade if left in direct sunlight. You can find a list of some of them here.
If your crystals are sun safe then this can be a very simple cleansing and charging method.
You can leave your crystals in the sunlight for a few hours, maybe on a windowsill or somewhere safe that gets some lovely gentle morning sun to cleanse and charge.
If the weather allows for it you can put your crystals in a nice spot in your garden or on your balcony as the sun rises or sets to capture that specific rising/setting energy.
We recommend cleansing your crystals every 1-2 months.