UKH

I'm having solar PV fitted next week as part of larger project. Due to location and time constraints the DNO is unlikely to accept >16A feed-in so we've gone with a 4kW array, but I have roof space for 17kW.

The roof is due E and W at 45 degree, with 2 kW on each side. Because of this I would have though the theoretical maximum (which is what I believe is used for the calculation of inverter size) is not 4kW, but lower. Does anyone have a link to the calculation of peak theoretical output hour-by-hour through the day, so I can add 2kW W to 2kW E and see what I get.

From this website ( http://www.photoscot.co.uk/info/SolarPanels.aspx ) They achieve only about 2.1 kW peak from 1.8 and 1.9 kW on E and W. If I can get the calculations and convince the installer then I can probably fit 3 kW on each side and not exceed 4kW.

At the end of the day, as long as the inverter can't do more than 16A it won't affect whether I need DNO approval. I just need the inverter manufacturer to accept that there is no risk to the inverter.


Note, I've used 4W as shorthand for the exact figure of 3.68kW that gives 16A at 230V.

In reply to Philip:
Sadly its not the installer that is the issue.

The law does allow for large arrays capped under 16amps. However the people that implement the law have chosen to ignore it (the law) & are implementing their own version.

You also have the issue that the tax free income status could come into doubt if your system has been designed to make more than you can use.

If you want lots of info re this then sign up on this forum
http://www.navitron.org.uk/forum/index.php

The above assumes that you will want to claim FITs at the 4kw rate.

In reply to Philip:

We have 4kWp installed due east (there's solar hot water on the W side)

The max this summer has been 25kW in a day, so must be nudging the full output at optimum.

It's the installed capacity, not the actual output that determines the FiT.

One thing I can't recommend too highly is one of these:
http://www.apollosolarproducts.co.uk/products/

Essentially channels any excess of generation over demand into our thermal store and, when that's at max temp, into a dehumidifier/heater in the (damp) cellar.

In reply to Philip:

If you have panels in series you get the current output from the dimmest panel. Having panels on E and W facing roofs is great for the network extending peak generation times away from noon but only if the system actually produces what it's capable of from the sun facing side and isn't limited by the dark panels. I'm sure your installer will have considered this.

Are you going to use the power or mainly export it for the FIT? If you're mostly looking for the FIT then adding panels is a bit pointless so long as the installer is willing to write 16A on the bottom of the paperwork they submit. You get paid for the paperwork not the power.


You may find adding a couple of panels exceeds the voltage input limit. I'd speak to the installer, see what they have to say.
jk

In reply to jkarran:

Some inverters (ours does) take 2 inputs so you can have a set on each side.

I'll have air source heat pump and solar immersion, so I will use more than the 50% export value.

I'm only looking to use 6kW not 4kW, on the basis that 6kW as 2 x 3kW half E half W will have a maximum output equivalent to 4kW South.

I'm just trying to maximise the generation without exceeding 16A as it's generation not F-i-T I'm after. E and W suits me as I will get twice the output from E+W than due S in the time period I'm at home (and using electricity).

In reply to Philip:


In that case with no FIT's the DNO will be happy with a 2 x 3kWp install as long as the inverter is capped at 16 amps.


How do the install cost verses elec savings numbers stack up if your not going to claim the FIT's?

I didn't get anywhere and so gave up (temporarily).

They agreed that 2 x 3kW E and W would not overload the inverter, and the inverter would limit the load anyway. But the exemption from DNO approval is based on total installation size as is the F-i-T level. So although I'd get what I want, I'd have to get the DNO to agree that I was only 16A, rather than not needing their agreement at all.

In reply to Philip:

That might be the response of one installer. Try asking on the forum I mentioned & also look for an installer there too.

The DNO accepting a G83/2 (I think its /2 now) inverter is standard practice re 16 amp limit.