... looking for a sanity check... in the UK....
... constant daytime use of about 200w... 10% light I would need a 2kw system in order to generate that 200w.
If you had a good net-metering agreement (e.g., sell power to the grid at the rate you get charged for it) then 200 watts x 24 hours = 4.8 kWh/d.
Assuming a winter insolation of 1.5 (you'd have to look up your actual worst value) then 4.8 / 1.5 / .96 inverter efficiency = 3.6 kW array. In the summer, with an insolation of 5, that 3.6 kW array would generate 18 kWh of energy per day (over 4x what you need). You could just size for the summer (4.8 / 5 = 1 kW array) and take what you can get in winter. With a good net-metering agreement you pick somewhere inbetween to zero out the yearly bill.
Since you'd still be on grid you'd have power when you needed it, and since it's the average you don't have to worry about the 10%.
But, since you're in the UK, most places don't have net-metering agreements and you might not be able to "give" power to the grid (that is they might have laws against it - no worries, most inverters have some sort of zero-export feature).
If you put a battery into the mix, prices are going to go up and there's a round trip loss so you need more solar to accommodate it.
I would like to start very small at 330w and scale out from there.
Microinverters provide the ultimate in scalability. You don't need to plan much, you can scale to any size, they usually have 25-year warranties. Enphase can be set to zero-export (you need the envoy module). Unfortunately, AFAIK only Enphase currently places nice with batteries, other systems need to be
AC coupled.
The good news is, a single 330W panel will cover your 200W energy needs for most of your daylight hours. Without a battery or a net-metering agreement, anything else won't do you any good.
I don't plan on having the inspections and certifying it to local regulations ( despite it being compliant ) and selling electricity back to the grid.
Most meters don't run backwards - so when you export to the grid, they run forwards - that is, without contacting your power company to get a bidirectional meter (which will probably require inspections), they will charge you for the power you put on the grid as if you were consuming it.
There is a 350w Chinese Y&H inverter at around £55 pounds, example:
https://www.ebay.co.uk/itm/403087824719 that would match this panel.
I wouldn't skimp on that (I have Enphase), especially as you need so few. But, the things to check are: is it certified by a lab (e.g., CE, that's not a guarantee it won't set fire to your house; but better than nothing), can it be set to zero export, what's the warranty, do you get the data from an API that you need, do you get the support you need to operate it?
Price per ( potential ) KW would be about £720
In Australia, professionally installed costs are $0.50 to $1.00/w. In U.S. installed DIY typically runs around $1/W. Not sure what the UK costs are, but a $/W in U.S. dollars seems like it should be about .75£/W.
The initial system setup seems almost too simple, it this right ?
Usually, there's some setup through the API to program them. You'll also need over-current protection and to select the proper gauge using the temperature correction factors (see the
FAQ). Microinverters like Enphase have all sorts of training and tools to help you, not sure what others like AP Systems have. Whatever system you pick should have documentation illustrating the right way to hook it up.