It depends a lot on how much they like your porch area - in Source, below, I provide a link to an exterminator's opinion on one way that I have hard works.
There are commercial bat repellent sprays and ultrasonic devices that some people say work, some say not so much - google "bat repellent" or look some up on Amazon or similar website.
I have also tried and had success with placing a very strong-smelling soap on top of joists or beams in the area where they try to roost - I have used Fels Naptha soap cut into 3 or so pieces (a very hard, strong-smelling laundry soap made by Purex) successfully, though it does make for a bit of a naptha chemical smell around the front door. Needs replacement yearly as it loses potency over time.
Hanging a bunch of foot-long strips of tin foil in the area is unsightly but supposedly works well - the extreme echoes confuse them, and they don't like flying where their wings hit things. Bat netting will NOT stop overnight roosting like this unless the net itself puts them out in the open (they like cavities and protected areas) - it can keep them from getting into attics and such, but they will just cling to it to hang - provides a nice porous surface for them to grip into. The only way I see that working is to place a bat netting continuous under the porch roof, across the bottom of the beams so if they hang on it they are fully exposed - of course, that will be pretty visible to visitors.
Some people just put in a lot stronger light bulb (150W flood lamp pointing up into underside of porch roof) and say it works, though of course you are burning a half a dollar or so a night in electric cost.
In a house in Buffalo I just spray coated the underside of the eaves and porch with Raid Wasp and Hornet Killer (the jet spray type) once a year, and it eliminated wasp and hornet nest and bat problems for a full season. Just don't do it with windows open, do it on a morning when you and any kids will be out of the house for the day, and of course be cautious if you have small children - the residual smell is pretty strong for a couple of days, so you may not want to open windows near the prorch for several days.
Other people have perched a fake owl on ones of the beams and say it works - but then I have seen a clump of bats clinging at night to the underside of a neighbor's fake barn owl's open wings, too. About as funny as seeing a flock of crows perching on a scarecrow.
If you are a persistent cuss, shooting the bat with a squirt gun filled with vinegar a couple of times also worked at a summer camp I worked at decades ago, though vinegar can stain paint. If you try this, use white instead of brown vinegar and wash it off after squirting. Visualize a water pistol of vinegar, and a super-soaker fiull of rinse water after the bat has flown. In some jurisdictions bats are protected, and in some states (like FLorida and NM), all are protected, so this action could get the Fish and Wildlife service on your case.
My advice, since you are not talking a serious infestation, is start with the simplest and cheapest solution that appeals to you, and work up from there till you find one that works for you.
Another long-term solution, though not so simple, is putting in a metal ventilated soffit panel to close in the underside of the porch roof - google "porch soffit panel images".