While Congress' Solyndra probe may have hit a dramatic peak when Energy Secretary Steven Chu testified on Capitol Hill last month, Republicans on the House Energy and Commerce Committee reminded the secretary and the White House yesterday that its investigation is far from over.

The panel sent a trio of letters yesterday demanding more cooperation on document requests and access to Obama administration staffers, and warning of more subpoenas and other consequences if cooperation is not forthcoming.

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Solyndra, a solar manufacturer that was given a $535 million loan guarantee and touted by the White House as a model for the clean energy economy, has filed for bankruptcy. E&E examines how it got there and what it means. Click here to read the report.

"When you issue a subpoena to the White House you've got to be prepared to back it up and that's what I think our letters are showing, that we're prepared to back it up," Rep. Cliff Stearns (R-Fla.), who is heading the panel's investigation, said last night. "If they don't do anything and they continue to slow walk then we have to sit down with leadership to see if they want to take the next step."

When it comes to a possible contempt of Congress resolution, which would be the next step the committee could take if it determines the administration has refused to comply with its subpoenas, Stearns said last night that "we're not there yet."

Instead, he said the panel could seek to interview former and current top White House advisers who have appeared in Solyndra-related emails including Larry Summers, Carol Browner, Ron Klain and Valerie Jarrett.

Yesterday, former White House chief of staff and current Chicago Mayor Rahm Emanuel told an NBC affiliate in Chicago that he would testify if he was called.

Stearns said testimony from Emanuel is something he would consider but that he is concentrating right now on the other five top White House staffers.

In the committee's letter to Chu yesterday, Republicans asked the Energy secretary to expedite his promised responses on several issues raised during his testimony last month.

For instance, during the hearing Republicans pointed to emails that indicated DOE officials pressured Solyndra to delay an announcement regarding layoffs at the company until after the 2010 midterm elections.

Late last October, after Solyndra informed DOE that the company was planning to shut down some operations and lay off staff, an adviser for one of the company's private investors said DOE tried to manage the timing of that announcement.

"They did push very hard for us to hold our announcement of the consolidation to employees and vendors to November 3rd -- oddly they didn't give a reason for that date," the adviser wrote in an email.

But Chu testified that he was surprised as anyone else to learn about that email.

"Something like that was not discussed with me," Chu said. "I would have not approved it."

Chu vowed to have DOE's general counsel look into the matter.

In their letter yesterday, committee Republicans instructed Chu to inform the panel in writing no later than Dec. 6 about the results of that investigation.

DOE spokesman Damien LaVera said last night that the agency is being "fully open and transparent" in response to the investigation.

"To date, we have provided more than 180,000 pages of documents to congressional investigators, made the secretary and the head of the loan program available for congressional hearings and made more than half-a-dozen department officials available over the course of this 10-month long investigation," LaVera said. "The record confirms what we have consistently said: that every decision on the Solyndra loan was made here at the department on the merits based on extensive review by our loan program experts."

Click here to read the letter to Chu.

Click here to read the letter to the White House counsel.

Click here to read the letter to the vice president's chief counsel.