The house is generally in very good condition mechanically (newer boiler and on demand hot water heater, PEX supply plumbing, new outlets, switches, light fixtures, updated electrical panel with breakers, fresh flooring, fresh paint, etc).

As far as the appraisal goes, it is the kind of thing I would mention.Updated electric service and panel, and per whoever the entire house was rewired.

Water heaters, dampness, foundation issues, control panels, the pricey stuff will show itself.

I have a property I am flipping and the home has solar panels on the front part of the roof.

In my BRRRR projects I tear out the kitchen and improve the layout, all stainless steel appliances, (the cost is minor compared to white appliances but looks so much better) open up walls for the open concept, gut the bath minus the tub (refinish the tub), new flooring (mostly hard woods), replace windows if necessary, new six panel doors, paint the entire house inside, possibly paint the outside if necessary.  

I in fact explored option to buy land and get the solar plant setup or lease to farmers etc. but seems hassle and no guarantee there.

Also his whole downstairs (basement) is wood-paneling which he valued at "70 bucks a square."

We put in a solar panel system for 19k they, gave us a 5k adjustment.Is there a guideline around certain types of improvements and what they generate in adjustments to an appraisal?

I have a detached garage that has power attached to unit one's service panel. 

For example- remove paneling, drywall, then paint.