With Mr Moore's evidence at an end - for this first phase of the investigation, at least - the inquiry knocks off early for the day.

Given that we've spent several hours examining European state aid law, that might come as a welcome relief to some.

But Mr Moore says his work is "never boring" and he's "always enjoyed it"... and us RHI nerds found his evidence session perhaps weirdly intriguing.

Image source, AFP

Join us again tomorrow for a full day with senior DETI figure Trevor Cooper - we'll have the usual live stream and text commentary from start to finish.

Bye for now!

BBC News Northern Ireland

An RHI scheme tax write-off should have been part of the information sent to the European Commission in an application for the scheme to be approved, the inquiry heard.

The tax write-off was referred to in emails between two DUP advisers.

Image source, Getty Images

DETI's EU expert Stephen Moore had to review the application before its submission to the commission.

He said that if he had know about the tax issue, which could've been explicitly prohibited under European rules, he would've "almost certainly" raised it with the Treasury.

The discussion jumps forward to the period after the RHI scheme ran out of control and the European Commission's suggestions for dealing with the crisis in early 2016.

Mr Moore says Brussels did not advocate "clawing money back" from the beneficiaries.

Image source, Getty Images

It saw the scheme as worthwhile from an environmental perspective, and that it should be fixed "whilst also ensuring that the beneficiaries receive the level of compensation that they were due to receive".

The commission said that the Northern Ireland authorities would have to consider adjusting the subsidy tariffs.

"That's part of the review process that's currently ongoing," Mr Moore says.

The inquiry panel seems to be unimpressed by the DETI energy team's performance in applying for EU state aid approva for the RHI scheme.

"If they were hanging about in getting their application in one inference might be they don't know or appreciate the importance of getting it in," says chair Sir Patrick Coghlin.

Image source, RHI Inquiry

Mr Moore says he had "full confidence" in the team's ability and knowledge of the state aid rules and their importance, and the notification submitted was "very good" apart from the "critical error in the biomass tariff".

"Everything you got was at the last minute!" says Sir Patrick.

After the final state aid notification for the RHI scheme was submitted, the European Commission came back with a number of questions for DETI.

It wanted to know if there would be any tiering of tariffs, as existed in the Great Britain RHI scheme.

DETI's Mr Hutchinson replied to the effect that tiering was not required in the Northern Ireland scheme using a phrase that has become ominously familiar to the inquiry.

Image source, RHI Inquiry

"The subsidy rates were found to be lower than the incremental fuel expenses," he wrote. "Therefore no tiering is required."

Mr Moore confirms that there was evidence that that statement was incorrect.

The commission subsequently confirmed the scheme was compatible with state aid rules.

Image source, Getty Images

DETI's energy team continued its "prodding" of Mr Moore to find out when the EU state aid approval would be granted.

In one email he sent to an official in order to get a steer on the matter, he said that the energy team's "patience" was "wearing a bit thin".

There was "pressure" in early 2012 from the then enterprise minister Arlene Foster to get the RHI scheme open, says Mr Moore.

"We understood [from DETI's energy team] that the minister had committed to launch the scheme," says.

Image source, Reuters

Democratic Unionist Party (DUP) MLA Paul Givan asked a Northern Ireland Assembly written question in March 2012 about when the initiative would be introduced.

It was referred to Mr Moore, who was keeping across the EU state aid approval process, and he was happy to say that DETI would get the go-ahead before June.

We'll be back at about 14:05 to pick up the inquiry's afternoon session, when Mr Moore will have a few more questions to answer.

It was "pretty clear" that Mr Moore missed the tiering trigger in the RHI scheme, he accepts.

If he had suspected that the scheme had the potential to overcompensate claimant he "would've looked for it".

Image source, RHI Inquiry

Whenever it was pointed out to him after the scale of the scheme's disaster emerged it was "fairly obvious" to him, and he says: "I was thinking to myself: How did I miss this?'

"Undoubtedly, time was a factor in it."

There is a "lesson to be learned" for DETI in how it handles EU state aid appplications, says mr Moore.

"We would never want to be caught out like this in the future," he adds, making a colourful Sherlock Holmes reference, comparing himself to the dog in Sir Arthur Conan Doyle's The Adventure of Silver Blaze.

Image source, Getty Images

"The racehorse [in the story] is stolen and Holmes deduces by the fact that the dog doesn't bark that the person who stole the horse must've been known to the dog," he says.

"I kind of see myself as the dog [at DETI] to bark if I see anything unusual... and I trusted energy division colleagues that they had got it right."

He says that staff can become "complacent" and "overly trusting" in colleagues and "not as diligent as we might be in checking these things".

In February 2012, Mr Moore received two documents from Mr Hutchinson - an addendum to the state aid notification and a copy of CEPA's addendum to its economic appraisal of the RHI scheme.

Again, he was under severe time pressure to check the documents and says he "obviously" didn't have long enough.

He adds that it was a low-risk notification and shouldn't have included any anomalies.

Mr Lunny raises the by now well-known fact that the scheme's tariff for small biomass boilers was set at 5.9p while the cost of fuel was 4.3p, and that meant a tiering mechanism should have been applied.

That information was contained in the documents but Mr Moore didn't register it.

In his defence, he points out that it was buried in a table in an annex at the back of the CEPA addendum.

After Christmas 2011, Mr Moore began to chase up the state aid notification for the RHI scheme.

On 11 January 2012, he emailed the Foreign Office to see if there had been any progress and followed it up again a couple of weeks later but there had been no developments with the European Commission.

Image source, RHI Inquiry

Mr Lunny asks him if DETI had asked him to do this, and Mr Moore says he had been "proactive" in trying to push things along.

"I hope you got a nice Christmas card from Ms Hepper for all the work you put in to get it in before Christmas," says panel member Dr Keith MacLean.

"I don't think I've ever got a Christmas card from anybody," says Mr Moore rather sadly.

Matters move to tax relief linked to the RHI scheme that could've had implications for whether the RHI scheme was given EU state aid approval.

At the core of the scheme was a compensation for the cost difference between generating heat from fossil fuels and generating it from renewable sources.

But if the subsidy calculation was incorrect that would result in under- or overcompensaton; in the case of ovecompensation it would raise an issue regarding the European Commission's state aid approval.

True costs must therefore be ascertained, says Mr Lunny.

He outlines a July 2015 email from then DUP adviser Andrew Crawford to fellow party adviser Timothy Cairns, in which he says the "main problem" with the scheme was that DETI had been "caught out with the profile of applications".

DETI had received a spike in applications in the proceeding few months, he said, because poultry farmers buying biomass boilers for the scheme before the end of the last tax year could get the RHI subsidy and write off their boiler investment against tax.

Mr Moore said he didn't have time to "forensically look at that type of issue" when he was dealing with the scheme, and points out that this is the first time he's seen the email between the DUP advisers.

Had he known about the matter, he would have "had quite a bit of thinking about it and having discussions" with civil service solicitors and the Treasury around it.

"I would be concerned that this would be additional state aid," he says, adding that it could "be further overcompensation", which was prohibited by the European rules.

When Mr Moore received the draft he only had overnight to scrutinise it.

"It would normally be the case that I would have a lot more time to comment on a draft document," he says, adding that it would typically be "a couple of months during the drafting process".

Image source, RHI Inquiry

Mr Lunny puts it to him that he had little opportunity in that time to spot mistakes.

"I think that's obviously true, yes," he replies.

DETI's energy team boss ordered her staff to file the EU state aid notification for the RHI scheme even though Mr Moore - the department's expert on the issue - had not had time to assess it.

Peter Hutchinson finally sent the state aid notification to Mr Moore on 19 December, telling him that the department wanted it lodged with the European Commission before Christmas.

Mr Moore said that wouldn't happen because he was just about to go off on holiday.

Image source, Getty Images

Fiona Hepper, the DETI energy boss, sent him an email - copying in Mr Hutchinson and others - shortly afterwards saying: "I want this submitted before Christmas... Peter and Joanne, please proceed."

Mr Moore says that what Ms Hepper was instructing "would not have been normal".

"In fact, I don't even think Peter and Joanne could've proceeded without me," he adds.

Mr Moore was "surprised and I was concerned" about how long the team behind the RHI scheme was taking to submit a state aid notification.

Image source, Getty Images

"I was very conscious that it was a priority for the department," he says, adding that time lost can't be made up in dealings with the European Commission.

There were only two people working on the scheme at that stage, and inquiry chair Sir Patrick Coghlin points out that they "weren't short of work".

Mr Moore "prodded" Peter Hutchinson - one of the key people who worked on the set-up of the RHI scheme - to prepare the state aid notification for the project.

In an email in November 2011, he encouraged the DETI official to get the document drafted as soon as possible because "tempus fugit" - time flies.

Image source, RHI Inquiry

"Not a lawyer introducing Latin into this inquiry but an engineer," Mr Lunny observes.

In an email the next day to his line manager, Mr Moore said Mr Hutchinson told him he hoped to prepare a draft notification "within the next couple of days".

Mr Moore said he had made it clear to Mr Hutchinson that even if they got the notification to the European Commission before Christmas a decision before April 2012 "now looks very unlikely".

The potential of claimants being overcompensated through the RHI scheme was "uppermost in my mind" in his initial dealing with the project, says Mr Moore.

He says his focus would've been on whether DETI had got the "fundamentals of the tariff... right".

Image source, RHI Inquiry

But he didn't consider tiering, a cost control measure whereby the subsidy on offer is reduced when a claimant has run their boiler for a set number of hours.

He said he understood that the consultants at Cambridge Economic Policy Associates, which DETI contracted to draw up the basis of the scheme, were aware of what EU regulations would've required.

It appears that Mr Moore was "taking the initiative" on making DETI's energy team aware of the importance of the RHI scheme complying with the EU state aid rules, says inquiry panellist Dame Una O'Brien.

Image source, RHI Inquiry

That was the case, he says, and the scheme "was on my radar screen".

"I would have a work-in-progress list and I know that RHI featured in that."

In August 2011, Mr Moore obtained a copy of the state aid notification for the Great Britain RHI scheme.

It appeared to him to him that the GB scheme amounted to state aid, and given the similarities that would probably also be the case with the the NI initiative.

He contacted DETI official Peter Hutchinson, copying in the other members of the department's RHI team.

"You should expect state aid approval will also be required," he told them.

"Obtaining state aid approval for our scheme in time for the scheme going live on 1 April 2012 will probably be a struggle."