Adding a second (matching) solar panel in series would give you "24 volts" for charging your 24 volts battery bank (technically Vmp~35-36 volts). The big issue is your expectations on the amount of power you can expect from a couple of solar panels and a pair of 12 volt batteries.
Luckily, a 100W solar panel allows you to charge several batteries. Fundamentally, the only difference here is the length of time it takes to charge the batteries. Take in mind that you can fully charge a completely drained 12V 50 Ah LiFeP04 battery in ten hours with a 100w solar panel.
You need around 350 watts of solar panels to charge a 12V 120ah lithium battery from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller. Full article: Charging 120Ah Battery Guide What Size Solar Panel To Charge 100Ah Battery?
You need around 360 watts of solar panels to charge a 12V 100ah Lithium (LiFePO4) battery from 100% depth of discharge in 4 peak sun hours with an MPPT charge controller. What Size Solar Panel To Charge 50Ah Battery?
You need around 310 watts of solar panels to charge a 12V 150ah lead-acid battery from 50% depth of discharge in 4 peak sun hours with an MPPT charge controller. You need around 550 watts of solar panels to charge a 12V 150ah Lithium (LiFePO4) battery from 100% depth of discharge in 4 peak sun hours with an MPPT charge controller.
Make sure the solar panel is getting enough sunlight first; if it is shaded, it will need more electricity to recharge the battery. Also, connect the solar panel's positive lead to the battery's positive terminal and the panel's negative lead to the battery's negative terminal.
A 100 watts solar panel is an excellent power source to charge all your devices. Below are some benefits you can expect from 100W solar power panels. They are relatively compact so you can place the solar panel under a small roof section, over a window, or balcony. Hence, it is suitable for small-sized homes.