To split or not to split?

[Horizon]

I'm interested to hear from other installers how they would advise a customer in the following situation:

The customer has a large roof and can accommodate all 16 panels on either the front (west) or rear (east) of his house. The front of the house is 100 degrees from south at 25 degrees inclination and would produce a 1320kWh/year output. The rear is 80 degrees from south at 25 degrees and would produce a 1418kWh/year output. There are no shading or technical issues on either roof slope and either way the system is going on a 2-string inverter with dual MPPT.

Putting all 16 panels on the east roof slope would produce around 100kWh extra per annum. However, peak production would be from sunrise until early-mid afternoon. I can't help but feel that it may be favourable to sacrifice a little overall production to gain usability with better power generation in the afternoon/evening time when the client is far more likely to be in the house.

What are your thoughts?

 

[Gavin A]

Install 3kWp on both front and back, giving a 6kWp system that will outperform either 4kWp option by 50%, and the returns will be far better than for any 4kWp option on either roof. All limited to 16amps still under G83.

At least give the customer the option.

 

[SibertSolar]

^^ ditto that, definitely a good option

 

[Horizon]

I take it by proposing the split you both agree that it's worth sacrificing a little production for a better spread of power production. For what it's worth, the rear roof would take 6kW all on its own as well.

 

[SibertSolar]

I would imagine you would have more "useable" production throughout the whole of the day, are the owners at home during the day? You might struggle to put more than 6kWp on a 16A limited G83/2 inverter though, although I could be wrong

 

[Gavin A]

depends on the angle of the roof, steeper roofs will take more than 6kWp - actually all will, it just depends on the level of losses that are deemed to be acceptable. We tend to stick to under 1% losses from limiting through the year, but there's no technical reason for it to need to be that way, we've got a 6.84kWp ENE / WNW system installed limited to 16amps generation for example.

Next week we're installing an 8.4kWp dual tracker system limited to 16amp export with 700Ah battery back up... as an example of another way of doing things.

But 6kWp is reasonably safe for all but the shallowest of east west systems.