Solar Sisters are bounty plants in Plants vs. Zombies: Battle for Neighborville. They resemble Sunflowers wearing the "Sunshine Rocketeer" Costume. They can be hunted in Weirding Woods and come in a group of three. Defeating them unlocks the Sun Burned medal.
Solar Sisters are unique in that they will respawn eight seconds after one of them is defeated, hinted by the "a sister regrows" message when it happens. This makes it an extremely difficult bounty hunt to attempt in single player. It is recommended to have at least three players perform this bounty hunt as each players can try to defeat all three of them at the same time.
The easiest way to defeat them is to use the Super Brainz, as he is suited for close quarters combat, not to mention that the Sunflowers have a rather weak firepower. Have each players attack all of them simultaneously. Once one of them is defeated, the other players will only have eight seconds to defeat the rest of the Sunflowers before she respawns. Use the Super Ultra Ball ability to finish them off quickly.
Attempting this bounty hunt in single player is possible, but is very difficult. You need to defeat them all within a very small time frame. A good way to defeat them is to use the Space Station, then lure them all so that they get closer together. After that, use the Crater Maker and beam them up quickly until all of them die. If the timer for the Crater Maker runs out, quickly dispatch the rest of the Sunflowers with the laser before the others respawn. Another great zombie to use in this bounty hunt is the Engineer as his Bullhorn Swarm can prevent the Solar Sisters from healing each other and combined with his Heavy Helper, the Engineer can easily wipe out a sister to low HP though beware that the turret may defeat a sister too early and cause them to respawn with full HP.
Coin, marshmallow, and XP farming
Please note that this method is no longer efficient. The XP and coin yield of bounty hunts has been reduced by 10x and marshmallows from bounty hunt completion are no longer awarded due to an unlisted nerf in the November 2019 Patch.
This particular bounty hunt can be exploited to farm coins, marshmallow, and XP. However, it requires at least three players due to the aforementioned difficulty in defeating them with less than three players. Simply use the Super Brainz with Fearless and Leveling Up upgrades, and defeat them multiple times until you get the desired amount of them. Beating this bounty hunt gives you at least 500 coins, 6-12 tacos (from enemy loot drops), and 275 XP (301 XP with Leveling Up), and defeating the Solar Sisters takes around 15-20 seconds; the quickest to perform compared to Bitey Brothers or Queenigma.
This farming method allows you to earn roughly 72,000 coins, 864 tacos, and 39,600 XP per hour (43,344 XP with Leveling Up). You can also earn about 2-3 prize bulbs per hour with this method.