There is growing number of people DIYing solar/battery installs with or without the help of non MCS approved electricians. This number has drastically increased since the ending of the FIT tariff. Whils’t you can’t export to the grid or get funding, what they do become is self suficient.
As a good guide, a MCS registered installer will charge anywhere between £600 – £1000 per day. What we see all to often in the industry, especially where funding is concerned, is a growing number of installers see or believe some or all of that funding is theirs and can become greedy.
Being MCS registered also requires you to have an insurance backed guarantee of which HEIS is one such insurance. However, unlike say gas safe, MCS certificate is not a legal requirement, unless as outlined above.
@Brydo are you using the Sunsync connect app?