With the questions for Mr Ellis at an end, the inquiry closes its doors for today.

We're back tomorrow morning for more from the Senate chamber, with Andrew Crawford, the ex-special adviser to the former DETI minister Arlene Foster, due to give evidence.

His witness statement is already available on the inquiry's website, external, so there's some bedtime reading for you.

It promises to be an intriguing day, so join us then and we'll keep you across the details.

Goodnight for now!

BBC News Northern Ireland

An official denied that civil servants at Stormont's agriculture department kept the lucrative nature of the RHI scheme to themselves as their "interests lay with farmers".

Cathal Ellis, a renewable energy expert in the department, told the inquiry that suggestion had no foundation.

Image source, Press Eye

It emerged that the department understood the overgenerous nature of tariffs eight months after the scheme opened in 2012.

Its officials attended a 2014 event that showed a biomass boiler costing £36,000 had earned £35,000 in subsidies in its first year of operating.

Image source, Getty Images

Figures provided to the inquiry by Moy Park show that 943 out of 1,526 of its growers' poultry houses in Northern Ireland are being heated by the RHI scheme.

Mr Lunny says that huge uptake among poultry farmers is reflected in the spike in the number of applications to the initiative in autumn 2015, which burst the initiative's budget and eventually led to its closure.

DARD was still promoting the scheme as far on as October 2015 - Mr Ellis says that was done "with DETI's knowledge".

Mr Ellis contacted Moy Park when he was preparing his paper for DETI but he "wasn't able to obtain any information" from the firm.

He confirms that he spoke to David Mark of the Moy Park's agri-projects team and "would have run the average figures that we had generated past him" - those were the figures of 360,000 to 380,000 kWh.

Pressed to say when he spoke to Mr Mark, the witness says he thinks it was after he met Mr Forgrave.

"I think the first anybody here has been aware that Moy Park had an involvement or an input into your paper is now - you haven't mentioned that before." says Mr Lunny.

It wasn't mentioned in his witness statement or in the paper for DETI, he adds.

Mr Ellis sent his final research paper on the poultry sector's use of the RHI scheme to Mr Forgrave.

In the email containing the paper, he told the farmer that he could share it with the UFU's poultry committee but said it was "probably wise if DETI don't know you've seen final version".

Image source, Getty Images

Looking back now, Mr Ellis says that was a "strange thing to have said".

He puts it down to panicking and a "lack of experience in dealing with organisations", but Mr Lunny queries whether that was actually the case, saying that the witness had been in the civil service for 31 years at that stage.

"I can't explain why I would've said that," adds Mr Ellis.

Tom Forgrave (below), a major poultry farmer for Moy Park and chairman of the Ulster Farmers' Union's poultry committee and a claimant on the RHI scheme, met Mr Ellis in July 2015.

They discussed the contents of the paper that was being prepared for DETI and Mr Forgrave shared data from his farm, which the DARD official incorporated into his research paper on the poultry sector's use of the RHI scheme.

Mr Lunny points out that Mr Forgrave had "vested interests" in relation to the scheme.

The witness says he "didn't really have any concerns that he was trying to game the scheme or make things better" for himself.

He says he may have told the farmer that he was seeking information to "assist" DETI in making decisions about the future budget for the RHI scheme.

Mr Ellis says that when speaking to boiler installers in preparing his paper for DETI he wouldn't have raised the matter of cost controls on the RHI scheme.

About that this time, DETI began receiving queries from installers asking about possible changes to the scheme.

Mr Lunny wants to know if Mr Ellis's dealings with suppliers could have been a "catalyst" for this.

Image source, RHI Inquiry

"It may well have been - I don't recall the actual conversations," he says.

"I was fairly specific in my requests not going outside of looking for technical information." the witness says.

He says he contacted boiler installers to get information for DETI because they were the ones carrying out the work at the farms and that would've given them a "reasonable idea" of the requirements of poultry farmers.

Mr Ellis heard "rumours" from fuel suppliers in July 2015 that changes to the RHI scheme - including the addition of cost controls - could be on the cards.

At that stage, the uptake on the scheme was rising fast and a few months later it spiralled totally out of control.

Image source, Getty Images

DETI official Seamus Hughes emailed Mr Ellis in June 2015 to get a "better understanding" of how the poultry sector was using the scheme because they department has been "led to believe that some [poultry] houses are running 24/7".

Mr Ellis drew up a paper for the department and in doing so contacted installers of biomass boilers to find out information about heat production costs, etc.

Asked what told them when he contacted them, Mr Ellis says he would've explained that he was seeking information for DETI on the use of heat in the poultry sector.

Mr Lunny turns to a statement given by the poultry firm Moy Park, indicating that it was expanding quite rapidly in the years after 2010.

It was also providing support to its farmers - known as poultry growers - in Northern Ireland from 2013 onwards.

Mr Ellis attended a meeting with the firm and boiler suppliers in September 2013, and he says his role was that of independent technical adviser.

He could have seen from that meeting that Moy Park's suppliers "were likely to opt for the RHI in large numbers", says Mr Lunny, who asks the witness if he sent his note of the meeting to DETI.

The witness says it was only passed to his own line management and he can't remember if there was any discussion of whether or not it should be handed to DETI.

Image source, Getty Images

Some claimants who were signed up to a DARD subsidy scheme for renewable energy wanted to hand the money from that back to the department in order to join the RHI scheme instead.

Within weeks of the RHI scheme opening, one wrote to the department to outline their intention.

They said their reason for wanting to switch was that the RHI scheme was "much more lucrative" than the one they was benefitting from.

Civil servants at DETI and DARD had been "completely incapable of picking up what the common-sense commercial market was doing and saying" at the energy events, says Sir Patrick.

Mr Ellis tries to explain by saying that he had no commercial background but the inquiry chair says that wasn't relevant.

Image source, RHI Inquiry

"You wouldn't need a commercial background - you would need common sense," adds Sir Patrick.

The witness says he has no explanation as to why civil servants didn't see the scheme in the same way that those within the renewable energy did.

Sir Patrick notes that Mr Ellis said at the beginning of his evidence that his contact was with "frequently with installers and suppliers - that was the major part of my work".

The inquiry chair therefore struggles to understand why the witness remained in the dark about how lucrative the RHI scheme was.

"You missed it when everyone else seems to have seen it," he says.

Image source, RHI Inquiry

Mr Ellis says his contact with the installers was concerned with technical issues.

"Were they trying to keep you out of the loop?" Sir Patrick asks.

Perhaps the businesspeople were wary of highlighting those issues to a government department, responds Mr Ellis.

Mr Ellis says he can't remember ever seeing material or displays promoting the RHI scheme as "cash-for-ash" at the DARD-run events.

"If I had seen that it would've triggered some sort of alarm," he explains.

He would've been giving lectures at the events or "dashing" through the trade stands to make sure exhibitors' needs were met but he wouldn't have noticed their leaflets.

In Mr Elliott's evidence in February, he said that the only way someone couldn't have noticed what energy firms like his were advertising would've been if they were "blind and deaf".

Picking up after lunch, Mr Lunny returns to DARD's promotional events and the presence of commercial boiler suppliers and installers at those.

One company present at those events was Solmatix, and he displays one of the firm's leaflets from the time advertising the RHI scheme as "cash-for-ash".

Image source, RHI Inquiry

Mr Lunny also refers to the evidence given to the inquiry by County Fermanagh businessman Neil Elliott (above) back in February.

Mr Elliott, who runs Future Renewables Energy Systems Ltd, told the inquiry: "It was widespread knowledge within the renewable industry that the incentive was too good to be true."

He also exhibited at the DARD events and said that promotional material - including posters and leaflets - outlining the benefits of the scheme were displayed and would've been obvious to anyone attending.

Image source, Getty Images

The inquiry will be back in session in the Senate chamber at 14:00 after everyone gets a bite to eat, so join us again then.

Inquiry chair Sir Patrick Coghlin says he finds it "very difficult to understand why" the rapid paybacks for many farmers on the RHI scheme "did not at least engender questioning" from DARD officials.

"This is not something that's theoretical, it's not in the sky - it's something that is happening in rural Northern Ireland," he adds.

Image source, RHI Inquiry

Sir Patrick says the impression he's getting is that is was considered "simply very good for farmers" and officials thought: "'Let's keep it going - this is very good for [farmers].'"

He adds that the short amount of time it took for claimants to recoup their costs should have "started alarm bells of considerable volume ringing" and it "was obvious to everybody."

Mr Ellis says DARD officials did not keep the knowledge of the scheme's lucrative nature to themselves and they would've had "no reason to do so".

It "doesn't take a genius" to work it out that the RHI scheme would offer massive profits to claimants over its 20-year lifespan, says Mr Lunny.

Asked it it ever stuck him that the scheme was "too good to be true", Mr Ellis says he and fellow DARD officials thought it was "an exceptionally good scheme".

Image source, Getty Images

A low uptake in the first year suggested to him that farmers believed it was too good to be true and they were waiting to see what others did before jumping in themselves.

Mr Ellis admits that he didn't tell civil service colleagues at DETI that the scheme looked to be so lucrative because he didn't have the "knowledge to make that judgement".

He says he assumed that DETI would've already known and he acknowledges that he "didn't pick [it] up" that the scheme wasn't representing good value for taxpayers' money.

One particularly stark case study was from a presentation by John Gililand at an event at his Brook Hall farm in December 2014, which was attended by Mr Ellis.

A 99kW boiler costing £36,000 was operated for 7,000 hours out of the 8,760 hours in the year and produced 560,000 kWh each year.

Mr Lunny notes that that would have resulted in an RHI tariff income of £35,000 in the first year, and payback within just over one year.

"That would have been very clear to you at that event," he says.

Mr Ellis says he would have seen it but adds: "I might not have just twigged the significance of it during the event."

Mr Ellis met representatives from the major poultry production firm Moy Park in September 2014, and says it indicated that it expected 200 to 300 farmers to sign up for the scheme.

Mr Lunny observes that that could have represented numerous installations per farm.

He puts it to Mr Ellis that DARD was particularly targeting farmers in sectors with high heat demands.

Image source, Reuters

Mr Ellis says he and DARD were not "deliberately pushing RHI" for farmers to jump on board but were "trying to encourage farmers to uptake heat from biomass technology".

"As part of that process, the RHI scheme was there," he adds.

"We were aware that those with low heat demands were unlikely to uptake an extremely expensive technology."

In a DARD booklet produced in 2014, Mr Ellis wrote about the RHI scheme, saying that "if heat demand is very high, payback periods can be very short".

He went on: "If demand is low and capital replacement costs are high, then biomass heating may not be suitable."

Mr Lunny puts it to him that that was a way of promoting the scheme to agricultural users who had a high demand for heat and would be using their heating systems for long periods of time, therefore collecting more money that had been intended.

Mr Ellis accepts that it "could be interpreted that way".