For the first full year of the RHI scheme in Northern Ireland - which opened in November 2012 - Ofgem proposed that five audits of biomass boilers should be carried out - by that stage 30 installations had bee approved.

Twelve audits were carried out the 2014-15 and 2015-16 there were 14 audits - that amounts to 31 audits across the first three years of the scheme's operation.

Image source, Getty Images

In that time there had been 2,120 applications to the scheme.

The 31 audits amounted to 1.46% of those applications - far below the intended 7.5%.

The problem with applying the GB RHI scheme's approach of auditing 7.5% of installations to Northern Ireland was the smaller number of installations that there were through the NI scheme.

Dr Ward says that when he took over responsibility for the audits in 2015 he was told that the Ofgem team realised that "given the low numbers of audits... it is not possible to draw any statistically significant conclusions".

Ofgem's thinking was that lessons learned from the bigger GB scheme could be applied in Northern Ireland.

Image source, RHI Inquiry

Ofgem eventually adopted a statistically significant approach in 2016.

Inquiry chair Sir Patrick Coghlin puts it to Dr Ward that for four years DETI would not have been warned by Ofgem that "the number of audits we are doing shouldn't give you any confidence about what's going on on the ground".

Dr Ward says he can't comment on specific warnings but he can see where Sir Patrick is coming from.

Ofgem and the government department running the GB RHI scheme were content that auditing 7.5% of new biomass boiler installations would give them enough confidence about how the initiative as a whole was running.

The number of applications for the Northern Ireland RHI scheme was initially expected to be 3% of the uptake in the similar scheme in Great Britain scheme.

Therefore, audits of biomass boilers would run at 3% of the number of audits in the GB scheme.

If the uptake projection was correct, 7.5% of the installations in Northern Ireland should've been audited and Mr Lunny says he wants to look at whether that turned out to be correct.

Dr Edmund Ward, who was the was the head of Ofgem's technical team when the RHI scheme was open, is back for his third appearance before the inquiry.

You'll find Dr Ward's written statement to the inquiry in full here, external.

Image source, RHI Inquiry

The inquiry's junior counsel Donal Lunny begins today's session by saying this should hopefully be Dr Ward's last time in the hotseat.

He picks up from where things were left in Dr Ward's last session, with a look at Ofgem's audit strategy for the RHI scheme.

BBC News NI

A civil servant who managed the RHI scheme told the inquiry that he was never informed about articles in two national newspapers warning about abuse of the similar initiative that was running in Great Britain.

Stuart Wightman said if he had been aware he's sure the content would have been escalated to the minister.

The articles appeared in the Daily Mirror and Guardian in late 2014 and early 2015.

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 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, 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 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.

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 late-2016... 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.

It's another scorcher of a day up on the hill at Stormont - let's hope those dog walkers keep their shirts on.

In the more sedate surroundings of the senate chamber we've reached day 73 of the Renewable Heat Incentive Inquiry.

Image source, AFP

We're joined once again by Dr Edmund Ward of the scheme administrator Ofgem - he's a frequent flyer, having given evidence to the inquiry several times already, most recently on 11 May.

Stick with us - we'll have live coverage and commentary thoughout the day.