This is Dermot Nolan's second appearance at the inquiry - he was here a few weeks ago and was asked probing questions about whether his organisation did enough to flag up key problems with the energy scheme.

He's the boss at Ofgem - it's primary function is as a regulator but a subdivision administers energy schemes, as it did with the RHI.

Image source, RHI Inquiry

Mr Nolan has been the head of it since 2014, having previously worked as a commissioner at the Republic of Ireland's independent energy regulator.

His statement on behalf of Ofgem can be found in two parts here, external and here, external.

Mr Nolan's booked in for an all-day session and posing the questions will the inquiry counsel Joseph Aiken.

Jayne McCormack
BBC News NI politics reporter

A DUP adviser anonymously sent civil servants' "explosive" emails to the media and to his department's top civil servantin order to take pressure off the party at the height of the RHI scandal, it emerged.

Simon Hamilton, a former Stormont economy minister, admitted his adviser had taken the action with his knowledge.

He conceded it had not been his "proudest moment" and claimed it was done because his party had been under a sustained attack by political rivals and the media over the cash-for-ash affair.

BBC News NI

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 major political crisis surrounding the scheme.

The RHI Inquiry began in November last year and Sir Patrick Coghlin (below), a retired Court of Appeal judge, is its chair and has been given full control over how it operates.

Image source, Pacemaker

It is looking 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 autumn 2015
• the scheme's closure in February 2016

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, well beyond a year-and-a-half 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 the initiative 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.

At one point the estimate for the overspend was set at £700m if permanent cost controls weren't introduced - temporary cuts have since pulled the budget back on track for now.

Whatever the scale of the bill, it 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 late 2016.

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 people 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.

After yesterday's drama at the Renewable Heat Incentive Inquiry, today is likely to be a bit more sedate but you never know what's around the corner.

In a few minutes, the inquiry will hear from Dermot Nolan, the chief executive of Ofgem, the cash-for-ash scheme's administrator.

We'll bring you every minute of the proceedings on our live stream and you can follow our text updates throughout the day.