BBC News Northern Ireland

An independent inquiry into the 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.

Image source, Pacemaker

The RHI Inquiry began this week and Sir Patrick Coghlin (above), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

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.

Public and political concern erupted when the scale of the overspend emerged.

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.

For more details, here's our need-to-know guide to the RHI scheme.

Catastrophic errors in the way the RHI scheme was set up left it open to abuse and as time wore on the cost of the project rocketed far beyond what had ever been intended.

Crucial methods of controlling the scheme's cost were not installed, and claimants were able to earn more money the more fuel they burned, negating the whole point of the policy behind it.

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 huge projected overspend - the most recent estimate was £700m if cost controls are not introduced - and the bill will have to be picked up by the Northern Ireland taxpayer.

Need a quick refresher on what the Renewable Heat Incentive scheme - or RHI for short - is all about? Let us be your guides...

The disastrous green energy initiative came to the attention of the Northern Ireland public in autumn last year, and its consequences have been reverberating through the region's political sphere ever since.

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.

Welcome to Parliament Buildings at Stormont for week two of the Renewable Heat Incentive Inquiry.

Image source, AFP

Proceedings will kick off at 10:15 and we'll have a live video stream and text updates throughout the day - stick with us for the latest.