It's been a long day for Ms McCay and the inquiry panel, but her evidence finally comes to an end and she'll not have to return to the Senate chamber for more questions.

Inquiry chair Sr Patrick Coghlin notes that today's proceedings have overrun by more than half an hour, and he tells Mr Aiken that it wouldn't need to become a habit.

Image source, Reuters

We'll be back tomorrow morning from 09:45, when the inquiry will be hearing from David Thomson, a former senior manager at DETI, about his role in the RHI scheme.

But for now it's good evening from us...

BBC News Northern Ireland

A civil servant who temporarily ran the DETI team dealing with the RHI scheme said she did not enjoy her time working on it.

Image source, Press Eye

Davina McCay had a seven-week spell between May and July 2014 working on the project, and told the inquiry she was relieved when her secondment was not made be permanent.

She said her role was "extremely busy" and was made all the more challenging because experienced staff had either left or were leaving the team.

In a year-end review in March 2015, Mr Wightman wrote that Ms McCay had "provided invaluable support and advice" to him and his colleagues in the team working on the RHI scheme.

She gave "comprehensive briefing advice" to him when he joined the team the previous June, and she continued to help out even after she had returned to her previous role.

Image source, Getty Images

In her written witness statement, Ms McCay raised several key points that proved to be problematic in her time working on the RHI scheme.

One of those was the staff resources, and she tells the inquiry that remains an issue at the Department for the Economy - formerly DETI - where she still works.

Ms McCay met Mr Hughes and Stuart Wightman at the end of June 2014, when they were taking over responsibility for renewable energy.

She does not remember telling either of them about the email from Ms O'Hagan, sometimes referred to as a whistleblower.

Image source, RHI Inquiry

Mr Aiken asks whether she told them about giving Ms O'Hagan the "assurance" that a review of the RHI scheme would begin within a few months

"I can't recall doing that, unfortunately, no," Ms McCay replies.

In July 2014, a new permanent secretary was appointed at DETI, when Dr Andrew McCormick (below) replaced David Sterling - now the head of the civil service - as the department's top official.

Ms McCay contributed the renewable heat section to the first-day brief for the permanent secretary, which Mr Aiken explains is a high-level summary document.

"Have you ever seen these where they actually spell out how dreadful something is?" he asks.

"Not in my experience," Ms McCay replies.

In March 2015, Ms O'Hagan emailed Ms McCay again because she felt there had been no progress regarding her concerns about the RHI scheme.

Ms McCay was no longer acting-up in the job she had working on the scheme the previous summer, so she passed it on to one of her successors, Seamus Hughes, and he informed Ms O'Hagan that a review was happening.

Image source, Getty Images

"With regard to tiered funding, whilst this is not being proposed as a specific issue under the review it may be introduced at a later date as a budgetary control measure," he wrote.

Mr Aiken suggests that means that what Ms McCay told Ms O'Hagan would happen is being "crashed into a wall".

"Yes, from her point of view she's been waiting for an answer," says Ms McCay.

The so-called whistleblower Ms O'Hagan sent a follow-up email to DETI on 9 June 2014 about the issues she'd raised the previous autumn with the RHI scheme.

It was forwarded to Ms McCay, who replied two days later, informing Ms O'Hagan that the DETI officials she had met in 2013 - Fiona Hepper, Joanne McCutcheon and Peter Hutchinson - had all left the department.

She also explained that DETI intended to "review elements" of the scheme, "including tariffs, within the next few months", adding that "the issues you've raised are on our radar".

Image source, Getty Images

In her evidence to the inquiry this month, Ms O'Hagan said that response left her relieved and hopeful that the department was finally doing something about the concerns she had raised about the initiative.

Asked is she had "any reasonable contemplation" that a review would begin in the timeframe she had suggested to Ms O'Hagan, Ms McCay says she "honestly believed" it was possible in spite of the enormous workload.

Sir Patrick probes why the witness didn't tell her successors that she had "given an undertaking" that the review would happen, especially when she had been told by her predecessor that it was "immediate and urgent".

Ms McCay says there was "a lot going on" and she agrees when Sir Patrick says "nothing was done" because she was "overwhelmed with work at the time without adequate resources".

In the document outlining the domestic RHI scheme for presentation to DETI's casework committee to assess in the summer of 2014, it says: "It was the minister who wanted an incentive scheme introduced."

Image source, Getty Images

Ms McCay says there was a "general impression within the department" that the the minister Arlene Foster wanted a similar initiative to the one that was running for domestic applicants in Great Britain.

But Ms McCay says she had no meetings with the minister.

Ms McCay was caught "in the eye of a storm" on 9 June 2014, with "three significant things happening at the same time," says Mr Aiken.

Image source, RHI Inquiry

They were:

• The casework committee process for the domestic RHI scheme
• Another email from Ms O'Hagan is sent to DETI
• Discussions with Ofgem about the issue of scheme applicants with Carbon Trust loans

The to-do list for the RHI scheme that Ms McCay was given was "wholly unrealistic", she has told the inquiry, and it left her "a little bit panicky".

She "wasn't fully aware of what was going to be involved" when Mr Hutchinson handed the project to her in May 2014.

Image source, Getty Images

She adds: "In my time working on the scheme it was very much just: 'Get as much done as you can.'"

She had "concern" that she wasn't going to get through as much of the work as she had wanted to in her temporary role on the scheme.

The so-called whistleblower Janette O'Hagan, who tried to draw then then DETI minister Arlene Foster's attention to a key flaw in the RHI scheme, gets a mention in Mr Hutchinson's handover note.

Ms O'Hagan (below) gave evidence to the inquiry this month.

In his note, Mr Hutchinson says that the point Ms O'Hagan raised when she met DETI officials the previous autumn relates to how claimants could use their renewable heat systems through the RHI scheme for "financial gain".

Image source, RHI Inquiry

There's no mention of Ms O'Hagan in Ms McCay's handwritten notes of the handover meeting, which the witness suggests means it wasn't mentioned.

Just before the handover meeting, Mr Hutchinson had received a follow-up email from Ms O'Hagan but hadn't replied to it - Ms McCay says she wasn't asked to reply to it on his behalf.

If she had been, she says she would've asked him to draw up a draft response because he had the experience of dealing with Ms O'hagan and knew about the issues she was raising.

There was sign that any work had been done to set the wheels in motion for a review of the subsides on offer through the RHI scheme, says Ms McCay.

"No - no drafting or terms of reference or liaison with economists about: 'Would you be able to do this for us?' - I didn't see any of that," she adds.

Image source, Getty Images

Asked to explain how she would have set about organising a review of the subsidies, she says it would've involved setting terms of reference for the process and that could've proved to be problematic.

"To tell someone what you want them to do you have to know it yourself - as a new team coming in it would have been difficult for us to do that," she says.

It may have led to the need to engage external consultants, a process Mr Aiken suggests could have led to a third report from Cambridge Economic Policy Associates (CEPA), with whom DETI had previously had a tense relationship after its earlier work on the scheme.

In Mr Hutchinson's handover note, he explains that the RHI scheme subsidies "can become overgenerous".

He explains that by adding a mechanism called tiering to the tariffs - which drops the subsidy rates offered whenever a certain limit of usage of a claimant's heat system has been reached - would be a solution.

He writes: "Certainly this should be considered for biomass under 100kW as a matter of urgency."

Image source, Getty Images

Mr Aiken notes that word "urgency" is only used in the document in context of the subsidies.

He also observes that Ms McCay's notes don't make mention of the apparent urgency of the matter.

Ms McCay says she can't remember Mr Hutchinson emphasising it in their handover discussion, adding that she "would've included it" in her notes of the meeting if it had been mentioned to her.

Sir Patrick notes the mention in the handover note's list of immediate actions of a "consideration of tiered tariffs to prevent excessive payments" through the RHI scheme.

He tells Ms McCay it would've been "strange to the point of careless" not to review that point until after the introduction of a domestic RHI scheme, which appears to have been prioritised by DETI.

Image source, Getty Images

"That would mean that excessive payments of public money were being made throughout that time," he adds.

Ms McCay says she "didn't get the significance of it" at the time.

She looks at her notes from the handover meeting she had with Mr Hutchinson in May 2014, and explains that if he had made the point that the review of excessive payments was "absolutely crucial, it has to be done straight away" she would have written it down.

When taking on the role in DETI's team working on the RHI scheme, Ms McCay was give a handover note from Mr Hutchinson, who had been working on the project from the start.

In it, seven bulletin points of actions that should be carried out by August 2014 - see some of them below - that included a review of the scheme.

In that the short period available to her she would only be able to carry out some of the actions, and Mr Aiken questions whether it was realistic for a review of the scheme to take place "in a six-week period".

Image source, Peter Hutchinson

She says that when in a new to a job "it can be difficult from a looking at a series of bullet points to understand and comprehend what exactly's involved".

Within the note was a lengthy reading list that he suggested for Ms McCay to bring herself up to speed with the details and background of the scheme.

But she says "there just wasn't time" to get through all of it.

In June 2014, Ms McCay met John Mills, the head of DETI's energy division, to raise an issue regarding the Carbon Trust loans.

She says that Mr Mils had a mannerism of running his hands through his hair when he was thinking.

Image source, RHI Inquiry

"I remember him standing at his window in his office and saying: 'I was told RHI would look after itself'," she says.

Sir Patrick asks Ms McCay if she thinks Mr Mills's reaction Indicated "surprise heading towards despair".

"He had a heavy remit, to be fair," she replies.

Ms McCay took on her temporary promotion to the Department of Enterprise, Trade and Investment's (DETI) team working on the RHI scheme in mid-May 2014.

"Four very significant issues that the inquiry has been grappling with" took up much of Ms McCay's time, explains Mr Aiken.

Image source, Getty Images

Those were:

• Presenting the domestic RHI scheme to DETI's casework committee
• A dispute over loans from the Carbon Trust for RHI scheme applicants
• Getting arrangements in place for data-sharing between DETI and Ofgem, the scheme's administrator
• Interaction with and fielding queries from the renewable heat industry

Ms McCay says the "main problem" was there was no staff remaining on the team who had been involved in the policy-making for the scheme.

"There really was just me replacing two long-term members of staff."

Ms McCay says that when she took over the reins on the RHI scheme she hadn't been expecting that so much needed to be done on it.

"There was nowhere near enough resource - I was one person trying to cover essentially two posts," she says.

Image source, RHI Inquiry

It's a complaint the inquiry has heard numerous times.

All the while, Ms McCay continued to do some work in her previous role, which was ongoing - transposing an EU directive - and on top of that she also had line management responsibilities in both roles.

Ms McCay was "very relieved" when her seven-week spell working on the RHI scheme came to an end and she returned to her previous role.

Asked by inquiry chair Sir Patrick Coghlin if the work had been "a bit of a disaster", she tells him it was "just extremely busy".

Image source, Getty Images

She points to the lack of continuity in the team - two key figures who had been working hands-on with the RHI scheme since its inception had just left, leaving virtually no experience of the project within the team.

"Everything I wanted to do seemed to take longer because I had to go back and research," she adds, saying there was no-one to turn to who knew the background of the scheme.

There was also a "high volume" of calls about the scheme from the general public for her to deal with.

Davina McCay acted-up as DETI's head of renewable heat briefly, having won a temporary promotion after the departure of Joanne McCutcheon and Peter Hutchinson.

Her written witness statement can be found on the inquiry's website, external.

Image source, RHI Inquiry

The inquiry's junior counsel Joseph Aiken tells the panel Ms McCay is quite nervous.

Today's session will be covering "a seven-week period which she probably regrets having anything to do with", he adds.