If you are using a 24V Battery or have created a 24V Battery Array by connecting two 12V Batteries in Series you will want a Solar Array that is also 24V. You can accomplish by using one 24V Solar Panel, or by wiring two 12V Solar Panels in Series.
Series vs Parallel
Connecting two Solar Panels in Series doubles the Voltage and the current (amperage) remains unchanged. Likewise, connecting two Solar Panels in Parallel doubles the Amperage and the Voltage remains unchanged.
Example: A 100 Watt Solar Panel designed to produce 12 Volts in various weather conditions will have a Max Power Current (IMP) of approximately 5.75 Amps.
Connecting (2) 12 Volt, 5.75 Amp Solar Panels in Series results in a 24 Volt, 5.75 Amp Solar Array.
Connecting (2) 12 Volt, 5.75 Amp Solar Panels in Parallel results in a 12 Volt, 11.5 Amp Solar Array.