In August 2011, Mr Connolly was asked to assess a DETI business case for a body called Ofgem to carry out a feasibility study over whether it could administer the RHI scheme.

The economist made a number of points, including one in which he queries the cost of the study, saying: "£100,000 seems very expensive - what is the rationale for these costs?"

Mr Lunny describes the points raised as "value-for-money concerns".

He asks why he raised those concerns but didn't do the same about cost issues about the RHI scheme itself a month earlier, which Mr Connolly accepted in his evidence yesterday.

The witness says he believed there had been a rationale for the fact that the scheme "was going to cost a lot of money" and it "didn't seem anything out of the ordinary".

Picking up where he left off yesterday, the inquiry's junior counsel Donal Lunny asks Mr Connolly about a submission sent to the then DETI minister Arlene Foster on 5 July 2011.

Mr Connolly was copied into an email this was attached to, but did he read it?

"I would maybe have glanced at it but I very much doubt if I would have read it thoroughly or printed it off," he says.

Image source, RHI Inquiry

That briefing document for Mrs Foster did not contain any references to the "stark cost differences" between the two options for the RHI scheme - an up-front grants fund or an ongoing subsidy offer of that type that was ultimately adopted, Mr Lunny explains.

Does Mr Connolly think it should have included that information?

"I think that would be quite important, actually," replies Mr Connolly.

BBC News Northern Ireland

An economist who signed off on the RHI scheme accepted that he was "relatively inexperienced" and a more senior person should have been given the job.

Image source, Pacemaker

Samuel Connolly said he had done his best with the complex and novel scheme.

But he conceded to the inquiry that he had limited experience in dealing with such incentive projects.

BBC News Northern Ireland

An independent inquiry into the RHI scandal was established in January last year by the then finance minister Máirtín Ó Muilleoir.

He ordered it in the wake of the huge public concern and what was then a developing political crisis surrounding the scheme.

The RHI Inquiry began in November and Sir Patrick Coghlin (below), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

Image source, Pacemaker

It will look at:

• the design and introduction of the RHI scheme
• the scheme's initial operation, administration, promotion and supervision
• the introduction of revised subsidies and a usage cap for new scheme claimants in 2015
• the scheme's closure

For more information on the RHI Inquiry, you can read our handy Q&A.

When the scale of the overspend emerged, public and political concern rocketed.

As the minister in charge of the Stormont department that set up the RHI scheme, the Democratic Unionist Party (DUP) leader Arlene Foster (below) faced calls to resign from her role as Northern Ireland's first minister in December 2016.

Image source, PA

She resisted, and Sinn Féin's Martin McGuinness then quit as deputy first minister in protest at the DUP's handling of what had by then become a full-blown political crisis.

That move brought about the collapse of the Northern Ireland Executive. Now, a full year on from that, Northern Ireland remains without a devolved administration.

You can find much more detail on the RHI scheme in our need-to-know guide.

The budget of the RHI scheme ran out of control because of critical flaws in the way it was set up.

Claimants could effectively earn more money the more fuel they burned because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves.

The most recent estimate for the overspend was set at £700m, if permanent cost controls aren't introduced.

The massive overspend bill will have to be picked up by the Northern Ireland taxpayer.

The Renewable Heat Incentive scheme - or RHI for short - came to the fore of the Northern Ireland public's knowledge in autumn last year... and the fallout from the scandal attached to it is still being felt in the region's politics today.

Image source, Getty Images

The scheme was set up by the Northern Ireland Executive in 2012, as a way of encouraging businesses to switch from using fossil fuels to renewable sources for generating their heat.

Those who signed up were offered financial incentives to buy new heating systems and the fuel to run them.

We're back for the final day of RHI Inquiry proceedings this week - thanks for joining us.

Image source, AFP

We'll be hearing much more from former Department of Enterprise, Trade and Investment (DETI) economist Samuel Connolly today, who returns after his marathon session yesterday.

You can watch a live stream and follow our text updates throughout the day.