basically it works like that:
for the application, of course, muhtar, title deed, site plan, kibtek, installer, electric plan.. aso, all this needs to be done.
to do this "on yor own" is a challangea and "some things" you are not permitted to do anyway. eg electric plan, electric installation.
for the size of a solar system the following rules are in power:
you take your last 12 month consumption in kWh and divide by 1700.
eg, 5900 kWh / 1700 = 3,49. so, you are permitted to install a 3 kW inverter. the box
say, 6000 kWh / 1700 = 3,52, so, you can install a 4 kW inverter.
to any inverter you can install as many solar panels as you like, but i would say no more as factor 1,25 = approx 3,7 kWp to a 3 kW inverter and 5 kWp to a 4 kW inverter. installers here often take factor 1,5. why? just to "squeeze" more out of the system, but thats not good for the inverter.
meaning, the difference of 100 kWh a year only (or 8,5 kWh a month or 0,27 kWh a day) "permits" you to install a bigger inverter + additional solar panels which can produce 2200 kWh (more) a year.
=it is important how many kWh you used!! and you may use a 100 kWh additinally next month to get a permission for a bigger inverter.
for "new" houses (eg, solar system supplied from developer) a 4 kW inverter is max. but you can install 5 kWp solar power.
today, solar panels are available in different sizes, say, 380Wp or eg, 500Wp.
but, they also differ in size, eg, 1,70 x 1 or 2 x 1 or 2,2 x 1,2 meter.
the question "how many panels you got" is irrelevant. better would be: how many square meters you got?
and, most manufacturers offer different models lines of same power size which can be 50-100% more expensive as the cheaper version!
so,
we differ inverter power in kW and installed solar power in kWp. but you also can scrap that all and ask:
how many kWh your system will produce in first year? and how many kWh will be produced after 10 or 15 years?
because, there are quality differences. inverter wise, panel wise and also installation wise.
you should not believe in promises.
what are 200 GBP or a bit more when "somebody independent" explains you whats going on and evaluates offers (for you) as well?
anyway, cont:
the produced solar energy will be used immediately and excess will be deducted from your bill and you may get credit for next month.
thats the regulation.
but, there are rumours that this regulation will change. many expect "not for the better".
as the political situation is, say it politely, difficult, no one knows when it may change and what will come.
it seems that hundreds of applications are waiting for permission from ministery of energy and nothing is going on.