Solar system expansion - anyone done it, few questions

Pulpdiction

I was looking to add some additional panels to my existing system and got a local company to ask the DNO, they've come back with an offer of an additional 750w of inverter allowance due to the network in my area.  They have said that they could increase it if I had additional 'reinforcement' added, which translated to a 3phase power supply, installer said last one he saw a quote for was £15k, so not an option.  Anyone challenged their DNO on anything like this?

So that translates into approve 3 x 400 panels.  So I was thinking, ok, go for that at £250 per panel with each having a micro inverter, job done.  installer then tells me this is going to cost over £3k, I was slightly taken aback by this..... I think it is their overhead model that seems to skew it, I think they employ contractors on a fixed rate, so if they are installing 20 panels or 3 panels its the same day rate, ie the team is booked out for the day.  To make it worse in my head this would be on a single story flat roof, so no need for scaffolding....

I'm still keen to add what I can, has anyone else had a small system installed and what sort of money were we talking, appreciate any recommendations in the midlands for installers.  

Does anyone have solar installed on a flat roof, what kind of fixings were used?  Any structural calcs needed?

Thanks

94JDH

Pulpdiction said:

I was looking to add some additional panels to my existing system and got a local company to ask the DNO, they've come back with an offer of an additional 750w of inverter allowance due to the network in my area.  They have said that they could increase it if I had additional 'reinforcement' added, which translated to a 3phase power supply, installer said last one he saw a quote for was £15k, so not an option.  Anyone challenged their DNO on anything like this?

So that translates into approve 3 x 400 panels.  So I was thinking, ok, go for that at £250 per panel with each having a micro inverter, job done.  installer then tells me this is going to cost over £3k, I was slightly taken aback by this..... I think it is their overhead model that seems to skew it, I think they employ contractors on a fixed rate, so if they are installing 20 panels or 3 panels its the same day rate, ie the team is booked out for the day.  To make it worse in my head this would be on a single story flat roof, so no need for scaffolding....

I'm still keen to add what I can, has anyone else had a small system installed and what sort of money were we talking, appreciate any recommendations in the midlands for installers.  

Does anyone have solar installed on a flat roof, what kind of fixings were used?  Any structural calcs needed?

Thanks

You need to check what beam sizes, centres and distance of span to determine the loading capabilities - there are some links to the timber loadings.
I'm having both flat roof areas (EPDM) so only ballast based support.