This is really on foot of a question asked by one of our regular commenters Ted. It’s not a definitive answer (the Public Inquiry report should give us that) but more of an educated guess.
First thing is to ask why for the first three years of the existence of this thing it was vastly under-subscribed. Well then, so why? In fact, the “free money” only comes in after you’ve made the initial capital outlay.
These things are not cheap (hence the scheme). A commercial boiler is going to set you back between 25k to 55k, with the average in the mid 30ks. So you need a lot of cap ex in hand to buy before you can avail of the scheme.
Not many people are in that sort of position so as a proposition on the face of it doesn’t look great. It’s only when you can afford the initial outlay that the benefits of the gearing kicks in.
The spike, of course, comes when officials get the word out that the scheme looks like closing and presumably speeds up the decision making out with a prompt to get in quick before it ends, that the rush comes.
Importantly it does not fit the classic corruption profile, where people would have been told to get in from the start.