Maria, unless you are having trouble with other electronic devices in your home, the fire alarm nuisance tripping is likely not caused by solar flares. You may have brown outs in your area too, depending on the electrical grid demand.
The batteries could be low, the fire alarm device could be worn out, or dirty, or even if it is as you say, from solar flares, they may be damaged.
Here from the Fire Marshal:
Smoke Alarm Facts
How effective are smoke alarms?
Residential fire deaths have decreased steadily as the number of homes with smoke alarms increased. Reports from the National Fire Protection Association show that people have nearly a 50 percent better chance of surviving a fire if their home has the recommended number of smoke alarms.
When do I need to replace my smoke alarm?
Smoke alarms that are 10 years old are near the end of their service life and should be replaced. Some people think that their smoke alarm sits idle until smoke is present. But it is working every minute, constantly monitoring the air 24 hours a day. For example, an ionization smoke alarm goes through 3.5 million monitoring cycles in 10 years. In a photoelectric smoke alarm, a light operates 24 hours a day to check for smoke particles in the air.
Just like any electrical appliance, the components of smoke alarms wear out over time. When a smoke alarm reaches 10 years of use, the potential of failing to detect a fire increases substantially. Replacing them after 10 years reduces the likelihood of failure.
My smoke alarms are wired into my electrical system. Do I need to replace them as often as battery-operated alarms?
Yes. Both the hard-wired and battery-operated alarms are equally affected by age. http://firemarshals.org/rfsi/smokealarmfacts.html