The 32-year-old has not played since flying home early from the tour of New Zealand with a right knee injury in March.
Having been pencilled in to make his international return in the second of a two-match Twenty20 series against New Zealand on Thursday Pietersen is easing himself back into action in the LV County Championship.
Solanki's decision to insert the Division One leaders did not pay immediate dividends in the morning session of their Division One clash as Adam Lyth (33 not out) and Alex Lees (13no) put on 50 without loss.
Somerset captain Marcus Trescothick's decision to insert Derbyshire proved more fruitful as the hosts were reduced to 84 for three.
Jamie Overton, Alfonso Thomas and Craig Meschede shared the wickets with only Wayne Madsen (30no) and Chesney Hughes (25) making any contribution with the bat.
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