"Whether it actually sheds much light on it, we'll see in time."
Asked if Dr Elder's appearance would put the matter to bed, Mr Key said: "I don't think it will resolve those issues if that's what people want."
Dr Elder confirmed on Tuesday he would show up if Solid Energy permitted it. However, he also fuelled Opposition criticism that the company has been trying to gag him by saying he had always been willing to appear, and the fact he wasn't present during Solid Energy's financial review before the committee last week was the company's decision.
"I was advised that I was not required to be present".
That cut across what the committee was told by Solid Energy at the time. The committee had previously asked that Dr Elder attend if the company thought it "appropriate". However, acting chief executive Garry Diack told MPs that he was "not aware" that Dr Elder had approached the company about making himself available.
State Owned Enterprises Minister Tony Ryall said Solid Energy had written to the select committee to "clarify" that answer.
"They are making it clear that that response from the chief executive was incorrect ... He was confused in what he was answering."
Solid Energy said yesterday that Dr Elder remained an employee of the company "and as such would have been available to attend, if required, by Solid Energy or the Committee".
"Dr Elder did not make a direct request of Solid Energy to attend the hearing, but the evening before advised that he was willing to attend if required," a spokeswoman said. "Solid Energy did not believe at the time that the attendance of Dr Elder as a former, rather than current, chief executive would be in accordance with the protocols that usually apply."
Asked what he made of Solid Energy's decision not to get Dr Elder to appear last week, given the public interest in Solid Energy's problems, Mr Ryall simply said he was pleased Dr Elder would appear.
Labour MP Clayton Cosgrove said the question now was "whether he'll be released from their confidentiality obligations".
"You could have the farcical situation where he turns up willing to co-operate but says he can't answer anything because he has confidentiality obligations."