Would it work if the script file first assembles the new segment and then performs a load that could autoconcatenate, like in:
FOR i = 1 to 28
LOAD Account_id RESIDENT Accounts;
Month(...) AS Month,
GROUP BY ...;
Lost_InstallersXX: // Will AUTOCONCATENATE?
LOAD * RESIDENT TempInstallerXX;
DROP Table TempInstallersXX;
[Edit] Sorry, I thought I got a very simple version that does the same, only to realise that I can't get my head around the LOAD/RIGHT JOIN logic. What is it's purpose? It won't reduce the data loaded from solar_field.