Inquiry panellist Dame Una O'Brien asks Mr Connolly whether he ever felt "under pressure to sign these (projects) off, or an expectation that you would sign off the value for money at the end".

Mr Conolly says no - he felt that if ever there was a problem "usually the approach was to sort it out".

Image source, RHI Inquiry

Dr MacLean says it appears from Mr Connolly's written evidence that he was working under an "inappropriate or insufficient" time pressure at times.

"I certainly did work under a time pressure for this project," he replies, adding that with the benefit of hindsight he would have asked for longer to work on it.

Inquiry panel member Dr Keith MacClean also picks up on the seeming contradiction in the economists' dual role in DETI, adding: "I struggle to see how that is compliant."

Mr Lunny asks how many times Mr Connolly refused to sign off on a project during the four years he was performing this role.

Image source, RHI Inquiry

"I don't think, from recollection, it happened ever," he replies.

Mr Lunny says that could mean either the system worked very well, or that the value-for-money assurance role lacks independence "and as we all know that if you're marking your own homework you're not going to give yourself a bad mark".

"Potentially yes, Mr Connolly replies.

Mr Connolly helped DETI's energy team to develop the RHI scheme and he also later checked that the policy provided value for money.

That could be viewed as a case of "marking your own homework", says Mr Lunny, and he "may be perceived to lack a bit of independence".

Image source, Getty Images

The guidance in the NIGEAE is that it is "important that the role of the economist was independent of the advice" provided to the policymakers.

The witness accepts that there are risks in one economist being involved in both aspects, but he says the "normal working practice" was that the economist who began working on a project would see it right through and his view is that he was independent of the DETI energy team.

Mr Connolly's work was carried out under a standard guide for executive departments known as the Northern Ireland Guide to Expenditure Appraisal and Evaluation (NIGEAE), external.

His role included the provision of independent quality assurance and advice; another role was the provision of a value-for-money sign-off.

Mr Lunny questions Mr Connolly's involvement in the drafting of the economic appraisal carried out by CEPA in 2011, saying that the witness notes there are potentially two roles.

Image source, RHI Inquiry

"There's the role at the end when you look at it and say: 'Does this come up to scratch? Can I be assured? Do I say it's value for money?' There's that independent scrutiny or assurance role at the end".

But there was also the role where Mr Connolly was "involved in the production of the economic appraisal," he says.

Mr Connolly says the two are related as in order to be able to sign off on the economic appraisal "If there are points of challenge you have to be able to raise them".

Mr Connolly is an economics graduate and began working in at DETI as an economist in 2008, where he remained until 2014, when he moved to Stormont's finance department.

Asked if he considers himself an "energy specialist", he says: "No, far from it."

Image source, RHI Inquiry

His role at DETI was to review business cases and economic appraisals, as well as providing support to other civil servants working on policy projects.

He says he believes he spent about 80 hours working on the development of the RHI scheme, including considering reports by the consultants at Cambridge Economic Policy Associates (CEPA) and giving the project a value-for-money sign-off.

Mr Connolly takes the oath and he confirms his written evidence to the inquiry's junior counsel Donal Lunny, as is usual with new witnesses.

Image source, RHI Inquiry

Unfortunately, the inquiry has yet to publish Mr Connolly's written statements.

But inquiry chair Sir Patrick Coghlin has seen them and he raises a slight problem with them that could cause problems - there are six of them, and they are not signed or dated.

BBC News Northern Ireland

There was something "fundamentally dangerous" about communication structures surrounding the set-up of the RHI scheme, the inquiry heard.

Image source, Getty Images

Inquiry panellist Dr Keith MacLean said more effort should have been made to find out how the £25m granted by the Treasury for the scheme in Northern Ireland would be used.

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, centre), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

Image source, Press Eye

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 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.

Critical mistakes were made in the way the RHI scheme was set up that left it open to abuse and that later saw its budget spiral out of control.

Crucial cost curbs that existed in a similar scheme in Great Britain were not replicated and claimants could effectively earn more money the more fuel they burned.

That was because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves.

As a result, the scheme racked up a huge projected overspend - one recent estimate put the figure at £700m if permanent cost controls aren't introduced - and the bill will have to be picked up by the Northern Ireland taxpayer.

Before today's inquiry proceedings begin, a quick reminder of why we're here...

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 few people, if anyone, would have expected it to have the consequences it has done in the months that followed.

Image source, Getty Images

It 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.

It's another nice blue-skied morning up here at Stormont as politicians gather for the second day of their talks to restore power-sharing and lawyers pile in to the Senate chamber for the RHI Inquiry.

Image source, AFP

Today we'll be hearing from Samuel Connolly, an economist at the Department of Enterprise, Trade and Investment at the time the RHI scheme was being set up.

We've heard a lot about Mr Connolly's role in the proceedings so far, so this is likely to be an intriguing session - stick with us for our live video stream and text commentary.