Now a familiar face to the inquiry, Fiona Hepper is here for her third appearance before the inquiry.

She played a key role in the RHI scheme, running the division within DETI that set it up.

Image source, RHI Inquiry

You can find our coverage of Ms Hepper's earlier evidence sessions before the inquiry here and here.

Putting the questions to her today is the inquiry's senior counsel David Scoffield QC.

A familiar setting with a familiar cast of characters greets regular viewers of our RHI coverage as we pick up after the Christmas break.

Inquiry chair Sir Patrick Coghlin wishes everyone a happy new year and he makes some housekeeping announcements aimed at pushing on the inquiry's progress.

He and his panel has decided it would be best to hear from more senior individuals with responsibility in DETI, including former minster Arlene Foster, at an earlier time than originally planned.

Image source, RHI Inquiry

"We will now aim to hear from witnesses such as the former permanent secretary, special adviser and minister towards the end of phase two in order to allow them to deal with phase one and phase two issues," he says.

Those phases cover the design and introduction of the RHI scheme, and the scheme's initial operation.

They will also be recalled at a later date to deal with issues in phases three and four.

The inquiry will also now meet on Friday afternoons and will run for three consecutive weeks from 22 January.

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An independent inquiry into the RHI scandal was established in January 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 last year.

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, and as we near 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.

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 projected overspend of hundreds of millions of pounds and the bill will have to be picked up by the Northern Ireland taxpayer.

Before we start into today's inquiry proceedings, 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 2016, 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.

Happy new year!

We're back for the first hearing in 2018 of the Renewable Heat Incentive Inquiry on this bright, frosty morning at Stormont.

Former Department of Enterprise, Trade and Investment (DETI) energy boss Fiona Hepper, who has already appeared before the inquiry twice, is in the hotseat again today, and proceedings will begin shortly.