The letter to banks became a "subject of considerable media speculation as to the minister's motives in doing it", says Mr Aiken.

Ms Hepper said in her submission that the letter had come about as a result of an interdepartmental meeting attended by the minister three-and-a-half months earlier.

The inquiry team has located the minutes of the meeting in September 2012, which show that Peter Scott of the Department of Agriculture and Rural Development (DARD) was asked how the RHI scheme would impact on a DARD biomass processing grants scheme.

Image source, RHI Inquiry

He said that some applicants for the DARD grants were experiencing difficulties obtaining loans for renewable energy equipment.

At that point in proceedings, Mrs Foster said she would write to the banks at an appropriate time to explain how the schemes worked and to encourage a more positive response from them.

The letter was also to cover renewable energy generation schemes, so "it's not just about RHI", Mr Aiken points out.

No-one had applied to the RHI scheme by the end of November 2012, the month when it opened.

At the end of December 2012, Ms Hepper sent a submission to the minister in relation to a letter from Mrs Foster to banks regarding renewable incentive schemes generally.

Image source, Getty Images

In addition to the RHI, it was to cover electricity generation schemes such as the Northern Ireland Renewables Order and the Feed-in Tariff.

Mr Aiken reminds the inquiry panel that: "The minster didn't write this letter. The letter was written for her by her officials."

When the existence of the letter emerged to the public at the end of 2016, Mrs Foster faced calls to resign as Northern Ireland's first minister, and you can find out a bit more background about it by clicking here.

When the submission was received by Mrs Foster's officer her adviser Andrew Crawford was the first to see it, and in an annotated version of the document he asked whether the cost of engaging the consultants could be reduced.

Image source, RHI Inquiry

That query was endorsed by the minister and was referred back to Ms Hepper.

In response, DETI's energy team boss said the work would be "complex" but she would "proceed on the basis of pressing down on the costs as best as possible".

At the end of October 2012, DETI's energy boss Fiona Hepper made an "urgent" submission to the then minister Arlene Foster outlining the plans for the next stage of the RHI scheme's development.

It outlines the intention to engage consultants at a cost of between £80,000-£120,000, with the plan of expanding the scheme and introducing the domestic initiative by summer or autumn 2013.

Image source, Getty Images

But there is no written reference to cost controls, says Mr Aiken, and he tells the inquiry panel to consider "how important the issue of budget management was to DETI" at the time.

In the document, Ms Hepper says that it would be a "very tight schedule" and it is "possible there may be some slippage", but it's "essential that this project goes ahead as soon as possible".

But Mr Aiken adds that "less [than what was planned] was done over a much longer time period".

Mr Aiken compares the situation with the GB and NI RHI schemes as they stood in November 2012.

"We have already six GB RHI consultations, two sets of RHI regulations" and also the interim cost controls introduced as a result of problems encountered with the Feed-in Tariff - a domestic electricity generation scheme.

"There seems to have been no equivalent Northern Ireland reaction" Mr Aiken says.

There was "virtually a wholesale change of personnel" in DETI's energy branch between the end of 2013 and through 2014, says Mr Aiken.

Image source, Getty Images

That change went right from the permanent secretary to the deputy principal in the branch that was dealing specifically with the RHI scheme.

Given the "complexity" of the scheme, the inquiry will want to look at handovers between staff, Mr Aiken adds.

There were no cost controls in the domestic RHI scheme when it was introduced in December 2014, says Mr Aiken.

Had it done, the control that had been consulted on would've applied to the entire budget for both domestic and non-domestic schemes.

Image source, RHI Inquiry

The barrister says that the "events of 2015 and 2016" - when the scheme's cost spiralled out of control - "may have been considerably different".

Budget protectors were in place in the equivalent Great Britain scheme, but Northern Ireland had none in its initiatives.

He says the decision-making about not adding that control is a matter the inquiry will want to investigate.

In planning the Northern Ireland RHI scheme, DETI had decided not to follow interim cost controls introduced to the Great Britain initiative in July 2012.

Instead, the NI scheme was to follow a long-term cost control scheme to be introduced in GB at a later date.

Those long-term controls were introduced in GB in April 2013 in the form of digression, which allowed the subsidy on offer to be lowered in response to increased demand, keeping the initiative's budget on course.

Image source, Getty Images

As Mr Aiken explains, DETI did not introduce a long-term digression measure, instead wanting to introduce an interim measure of the kind it had earlier rejected.

That was to remain in place while DETI worked on a degression mechanism.

Mr Aiken says that may seem "somewhat convoluted" but its importance will become clear.

A "disturbing deja vu or groundhog day" will become apparent to the inquiry when it looks at how the domestic RHI scheme was being developed in Northern Ireland, says Mr Aiken.

He tells the inquiry panel that there are "several reasons" why it "cannot ignore" the domestic RHI scheme for Northern Ireland, because the two were woven together.

Among those is that the funding for the domestic scheme was coming from the same pot as the non-domestic scheme.

An initial plan for the RHI scheme to be developed was curtailed and pushed back by more than a year, Mr Aiken reveals.

The plan that DETI initially had was for the three issues to be addressed by summer or autumn 2013, including:

• the expansion of the non-domestic RHI scheme;
• the introduction of the domestic RHI scheme;
• other issues, including adding cost controls to the non-domestic RHI scheme.

But that to-do list was reduced to just introducing the domestic scheme by December 2014, rather than more than a year earlier.

Mr Aiken tells the inquiry: "You will want to examine why that happened and what effect that had on the problems that would subsequently emerge."

Image source, RHI Inquiry

The inquiry's junior counsel Joseph Aiken opens proceedings by explaining what he'll be presenting today.

This second phase of four broad phases of the inquiry roughly covers the period from November 2012 to July 2015.

It coincides with the initial operation of the RHI scheme, and Mr Aiken describes his presentation today as "a staging post along our journey".

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 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, more than a 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

Image source, Getty Images

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.

Welcome along to what is a wonderful morning up here on Stormont hill, where we've got a lovely view of the snow on the Black Mountain overlooking Belfast.

Today, the RHI Inquiry moves on to its second phase, even though the first one isn't quite complete.

Image source, AFP

We'll hear evidence from some significant figures later this week, including a woman who tried to draw the then enterprise minister Arlene Foster's attention to the scheme's overgenerosity.

Today and tomorrow the inquiry's counsel will be giving us a broad overview of what's to come in this part of the inquiry, so expect some juicy details...