THALL I found it really hard to find out what " all the paperwork " was. Being a first4solar customer has forced me to look hard at this :-(. A lot of the documentation, Napit/MCS actually comes straight from the installer, once they have the " badge" from the organisations, and paid their fees, they self certify. Make of that what you will. The insurance backed guarantee comes from HIES, again if the Installer is registered/pays the fees to them...
The EIC needs to be produced by the qualified electrician who was present at the install for the electrical work.
The DNO is responsible for approving the G98/G99, issuing the acceptance letter. It is also responsible for providing the Export MPAN ( the application for that can either be via the installer on day 1, or via supplier ( e.g. octopus) when you apply for SEG). Are we all confused yet ? : -)
If you want SEG payments:
You need the MCS cerificate. [ provided by installer as an MCS
You need the letter from the DNO to say that they accept your g98/g99. [ This is required whether you want SEG or not, as long as the install connects to the mains supply Note that g99 needs to be applied for BEFORE install and commissioning.]
Some SEG suppliers want to see:
A proof of ownership document.
For your safety/ selling your house
You need an EIC for any mains electrical install, (missing from many first4solar packs.)
You should have a building Compliance certificate, thats says that things like roofwork has not compromised the property. ( which I thought covered the EIC, but does not)
For ongoing warranty:
You (probably) need the 10 year Givenergy Inverter upgrade, if promised it. The new battery already have 10 years, Inverters only 5 years standard.
You probably should have an Insurance Backed Guarantee, that is supposed to provide the financial support to cover any work that the Installer would have put right if the installer folds.
[ I haven't personally seen any documentation on how to claim on the 25+ year panel warranties, anyone enlighten me ? ]
Hope that helps.