you would be surprised on getting cheap batteries.  If you are near a golf course "dead" golf cart batteries are cheap.

If I was going to do a small play system I would add 1 panel a bigger one say 300watts. blend it into the 300 watts he has. source some batteries he does not need to run system all the time.

Run it 9 hours a day.   600 watts of panels to charger to batteries to inverter to s9 set to 300 watts. which would be 8 volts and 225  on brains.

way cheaper then a 24 hour setup. and for 6 hours a day he has a shot to hit a block on solo.ckpool

since he is subject to seasonal change.  He could do 4 hours in winter 6 hours in spring 8 hours in summer.

If he really looked around I would think he could do this for 500 dollars.

this never lets batteries run down as he only runs an hour after sunrise. and shuts down 1 hour before sundown.

it would be a fun project.
I will be doing a thread soon on s9 upgrades here is the link

https://bitcointalk.org/index.php?topic=5253561.0

note:

it is a teaser so no info is on it.