Inverter - Multi string or single string on 3 separate roofs

[gringogaz]

Wonder if anyone can advise on this.

Small house, 3 roofs. All 3 Sanyo HIT 230w se10's modules.
Smallest roof faces south (200 d) has 3 panels.
East roof has 5 panels and west roof 5 panels.

Should these be in one string?

Or would it be better to add 1 more panel and have 2 strings of 7 panels.
1 on south, 6 on east and 6 on west?

I am aware of how shading works but my worry is if in the initial configuration in 1 string as the sun moves around/over the top of the house in summer the 3 panels on the south roof will lower the production on the east and west roofs.

Any advice greatly appreciated.

[vinniethePVtech]

I would do each roof partition as separate strings.
East and west strings with a dual MPPT tracking inverter.
South with its own inverter.

1 string of 3, South
2 strings of 5. 1 east and 1 west

OR 3 seperate inverters, or go micro.

That is how efficiency is optimized

You are in a situation where if you combine panels from east, south, and west your string will only promote as much power as its weakest panel in that series. Almost to the same effect as shading.

Aurora "POWER ONE" and Kaco both offer dual MPPT tracking inverters.

Aurora PVI 3.0 inverter seems right for what you want, along with a sunnyboy 700 inverter

[Naptown]

Micro's will probably cost less than 3 string inverters and produce more.

[vinniethePVtech]

Micro's will probably cost less than 3 string inverters and produce more.

This is correct.

A drop of 13 enphase micros with connectors and branch terminator for landscaping = $2420

1 aurora PVI 3.0 and 1 sunny 700U = $2755

Difference is $335

How ever efficiency is to be determined based climate temperature factors. String inverters can be installed in cooler environment, micro inverters sits out on a hot roof and do have premature failure, although offering a limited 25 year warranty.

Also the enphase 215 is limited to the sanyo hit. Roughly 15watts per panel lost.

If you want the right power for the sanyo hit then it would be more in the realm of solar bridge patheon which would cost almost break even to the string inverters. harvesting power/watt ratio is all relative to cost.

[Naptown]

This is correct.

A drop of 13 enphase micros with connectors and branch terminator for landscaping = $2420

1 aurora PVI 3.0 and 1 sunny 700U = $2755

Difference is $335

How ever efficiency is to be determined based climate temperature factors. String inverters can be installed in cooler environment, micro inverters sits out on a hot roof and do have premature failure, although offering a limited 25 year warranty.

Also the enphase 215 is limited to the sanyo hit. Roughly 15watts per panel lost.

If you want the right power for the sanyo hit then it would be more in the realm of solar bridge patheon which would cost almost break even to the string inverters. harvesting power/watt ratio is all relative to cost.

You are basing the loss on the STC rating at STC conditions which are very rarely hit, so clipping of the inverter is not a big issue. higher temps will reduce module output along with humidity soiling etc etc. Check the PTC rating on that module. A 230 W module is well within the range of the inverter as long as the voltage is compatible.

[vinniethePVtech]

You are basing the loss on the STC rating at STC conditions which are very rarely hit, so clipping of the inverter is not a big issue. higher temps will reduce module output along with humidity soiling etc etc. Check the PTC rating on that module. A 230 W module is well within the range of the inverter as long as the voltage is compatible.

That argument is just as moot as saying a enphase micro inverter no matter what the enviornmental condition will harvest 96% electricity no matter what the condition. We all know heat, shading, dust effects harvest efficiency, just as modules should be based on PTC rather than STC.

I still believe due to heat variables, installing string inverters in cooler climate conditions harvest just as much power.

I could go on and on about how micro inverters with engage cables lack wire sizing to wire run lengths for voltage drop, and a misc other deficiencies. The advertising behind micro inverters are really alot of hype and the technology isn't refined to the point to where it can exceed the warranties that manufacturers promise.

String inverters have many more installation and engineering advantages when it comes to wire sizing, climate conditions. If string inverters could run multiple MPPT inputs then it would be superior to micro inverters as strings could be reduced to fewer panels having the same advantage that micro inverters do independantly with the benefit of surpassing warranty. It really comes down to comparing small apples to one big orange.

[Naptown]

I was not arguing heat variables but the fact that you stated that you are losing 15 watts of power from each module. Based on the 230W module and the 215W of the inverter. The 215 BTW is the max output of the inverter counting all inverter losses etc. Back to my argument abut your statement I still argue that you will never see 230W from a 230W module except under very rare circumstances such as a cold day with reflected light off a snow or ice field.