Charging a 36V battery set with a 255W solar panel
More info, e.g. battery specs.  I would almost certainly guess the batteries can handle much more input current than the panel will ever be able to put out, though.  You'd be concerned about overvoltage.

From this SO Answer (referring to a single 12V, but you can extend it here):

"The maximum is typically around 14.4V to 14.8V at 21C temperature. If the maximum is exceeded for minutes to hours, the battery will be permanently damaged. The damage occurs around the same time that flammable gas is generated and vented, so there is a risk of gas explosion near the battery.

Your setup would require constant monitoring, especially if the load is disconnected or turned off. Check the voltage every hour, and disconnect the solar panel as the voltage approaches the maximum.  

To find the maximum voltage, check the manufacturer's label or datasheet for the battery." (Emphasis added)

Based on the three stages of 36V battery charging described here, it seems a reasonable maximum voltage for your setup might be 40.5V.  I don't know your batteries though, and I am also assuming that you are using a lead-acid chemistry.