i have been looking on this for an year+.. Here some current (online-shops) prices in Bulgaria.. say shop.chepakov.com / kameasolar.com

  - panel 490Wp 2sq.m chinese = ~80E
  - battery 5kwh Li chinese = ~1200E , non-chinese ~2000E+
  - hybrid invertor+charger 4kw = ~800E chinese , ~2000E non-chinese
  - grid and regulations:
  -- day price: 0.15E/kWh, night: 0.09E/kWh
  -- no such thing as spot prices - summer or winter, peak sun or midnight, no difference
  -- can install anything AS LONG AS Nothing goes back into grid - and does not break other city/dwelling rules

if one gets the electronics from Germany - geizheis.de - prices are half, coz a) no VAT, b) less middlemen . Even some smaller things come with free postage - from Germany to Bulgaria ; i did buy several smaller chargers/inverters (5kg), while local sellers here have no such ideas. But anyway.

The (proven) efficiency one can get is about 50-60% per Wp (if there is sun). So.. it depends how much panels one can install as that is the monie-source, all else is monie-sink :/

Rough Napkin math, electronics with german prices, ~5 hours per day sun on average: 10 panels (1000E) + 2 batteries (2000E) + inverter (1000E) ~~4000E yielding on average 440kwh/month i.e. pay itself in 5-7+ years, mostly for summer loads. While 5 panels + 1 battery + inverter ~2500E -> ~220kwh/month -> 6-8+ years

BUT only IF you can use that much electricity, otherwise it will take much longer to repay. And, batteries have to be replaced probably in 5-7 years, depending on depth-of-discharge.

In most places here everything is electrical. i have convectors, boilers, stove, etc. No A/C. (all other electrics is maybe under 2kw in total). i use like day/night 400/250kWh in summer, 1400/800 kWh in winter. Some people have noisy heat pumps but doubt that changes things much.

If it was a separate house - i would have done it long ago. But it's a block of flats.

So... small Balcony stuff makes no sense (a very expensive UPS?), big balcony stuff (like putting those 5 panels as balcony's shade.. a) probably won't be allowed, b) only a short balcony faces south-ish.

The roof of the building is empty - 250sq.m - and can hold about 75 panels - but dividing that into 15 (or 50+ in higher buildings).. is not pretty. a) Making one single farm and splitting the bill/output seems the only reasonable way but does not work without completely rewiring the building's grid input and measurings; not doable without bunch of permissions/certifications ; while b) making 15 separate 5-panels-packs - is not much economical, plus few kilometers of cables.. And c) If only few people want panels on roof, maybe some form of renting the roof space from others who don't want.. may work for a while but as any renting, may go crazy.

So.. been sitting and thinking.. and recently seems only sitting..