Even a tub deicer on solar is going to cost a fortune in batteries and panels to power. And unless your hot tub is inside a building it isn’t going to keep pipes from freezing in SOUTH FRICKING DAKOTA! I lived in Newell for 3 miserable winters... nope, nuh-huh...
to keep a hot tub from freezing there, and the pipes inside it, you will need a building around the tub, and a large heat pump running keeping that space warm.
Resistive heating water is crazy demanding of energy...
1500W x 24 hours is 36KWh of batteries... at 48V that is 750AH for one day... and you will need 5 days minimum due to lack of sunshine IN WINTER in SFD... SO, 3750Ah of batteries...
using average Battleborn pricing (I know... you can build for less yourself... but not a lot less... figure a BEST case of 1/3 Battleborn pricing...)
50Ah 24V BB IS ABOUT $900 each... on sale, with coupon... so, carry the one... um... 38K in batteries...
Now... you need enough solar to recover the 36KWh daily use... divide by 3hours of average winter sunlight... that’s 12000 watts of panels for one day of recovery...
you would need to double that so you can cover the daily use, and recharge the bank some... 24,000 watts of panels... just to keep a 1500W heater going one day...
and a hot tub that isn’t in ground... is going to need way more than 1500W to keep the pipes from freezing.
it’s been a while since I lived there... maybe global warming has softened the winters there since I left in 83... but if I remember correctly, the frost line was 6’ there... so, the tub would need to be below that to keep from freezing...
“Beef up the insulation” is not realistic... build a building around the hot tub, and have THAT built with significant insulation... keep a minisplit running to keep the building above 32F... might be possible on solar...