DarthPuppy
Posts: 685
Joined: Sun Aug 11, 2013 8:45 pm
Delivery Date: 11 Aug 2013

Re: Solar capacity needed for my Leaf?

Mon Sep 16, 2013 7:44 pm

At what point does it make economic sense to skip the micro-inverters and do a second inverter? I was originally thinking 4-6 panels, but am now thinking 10 panels. Would I be better off with 10 panels and 1 inverter or going with 10 of the AC units with the micro-inverters?

Also, I'm guessing that 1 inverter has more risk as it could be a single point of failure that knocks 10 panels out. While if a micro-inverter dies, I still have 90% of the panels producing. So that might shift the point at which it makes sense to switch from micro-inverters to a single inverter.

Of course, I'm an accountant, not an engineer, so I could really use some insight on that. :?

Thanks!
'13 Leaf SL
'18 Honda Clarity Touring PHEV

swaltner
Posts: 114
Joined: Fri May 24, 2013 10:05 pm
Delivery Date: 27 Jul 2013
Location: Wichita, KS

Re: Solar capacity needed for my Leaf?

Mon Sep 16, 2013 8:49 pm

Two advantages of micro-inverters over string inverters.

- Micro-inverters allow each panel to generate their max power when one or more panels are being shaded. In a string-config with large inverter, if you have a string of ten 240 watt panels with nine generating 200 watts and one being shaded by a chimney and only generating 100 watts, the power output of the string would be 1,000 watts. For micro-inverters, you get would be generating 1,900 watts from that array.

- Micro-inverters allow per-panel diagnostics. Since you are collecting per-panel production data, you can easily spot any panels/inverters that are underperforming and investigate.
2013 Leaf SV

DarthPuppy
Posts: 685
Joined: Sun Aug 11, 2013 8:45 pm
Delivery Date: 11 Aug 2013

Re: Solar capacity needed for my Leaf?

Mon Sep 16, 2013 9:01 pm

Thanks swaltner! Those are good points to consider.
'13 Leaf SL
'18 Honda Clarity Touring PHEV

pchilds
Posts: 418
Joined: Sun Jun 17, 2012 12:14 am
Delivery Date: 31 Jul 2011
Leaf Number: 006141
Location: SoCal

Re: Solar capacity needed for my Leaf?

Mon Sep 16, 2013 9:10 pm

swaltner wrote:Two advantages of micro-inverters over string inverters.

- Micro-inverters allow each panel to generate their max power when one or more panels are being shaded. In a string-config with large inverter, if you have a string of ten 240 watt panels with nine generating 200 watts and one being shaded by a chimney and only generating 100 watts, the power output of the string would be 1,000 watts. For micro-inverters, you get would be generating 1,900 watts from that array.

This is not correct, if one panel is shaded, a diode across the panel shunts the current and you will get 1,800 watt minus the loss in the diode.
2011 LEAF, gone,
2012 RAV4 EV,
2015 Model S 85D,
Solar PV 5.25 kW system.

User avatar
drees
Moderator
Posts: 6221
Joined: Fri Apr 23, 2010 3:51 pm
Location: San Diego

Re: Solar capacity needed for my Leaf?

Tue Sep 17, 2013 12:47 am

pchilds wrote:This is not correct, if one panel is shaded, a diode across the panel shunts the current and you will get 1,800 watt minus the loss in the diode.

It really depends on the type of shade, but typically with the sort of soft shade you get the diodes don't have that sort of effect.

There's a good reason why the string-inverter guys are selling "optimizers" to compete with micro-inverters.

If a couple simple bypass diodes would take care of the issue, there'd be no reason to sell an "optimizer".
'11 LEAF SL Powered By 3.24 kW Enphase Solar PV

ERG4ALL
Posts: 603
Joined: Thu Sep 23, 2010 11:17 am
Delivery Date: 10 Mar 2011
Leaf Number: 000404
Location: Phoenix/Show Low AZ

Re: Solar capacity needed for my Leaf?

Tue Sep 17, 2013 8:49 am

Unless I missed it, what is the total output of your existing system annually? Because there are various things that affect output (e.g. number of sunny days per year, air quality, temperatures, etc.) taking the total output would let you know on average what each existing panel is generating. From that you have already done the math on how much extra power you think you need. Just working with rated panel output ignores the real-world factors.
Reserved 4/20/10, Ocean Blue Ordered SL 9/30/10, ESVE Installed 11/22/10, Delivered March 8th, 2011.

DarthPuppy
Posts: 685
Joined: Sun Aug 11, 2013 8:45 pm
Delivery Date: 11 Aug 2013

Re: Solar capacity needed for my Leaf?

Tue Sep 17, 2013 10:45 am

Good point. When I'm back at home, I will take a look to see what total production was for the past year.
'13 Leaf SL
'18 Honda Clarity Touring PHEV

AndyH
Posts: 6384
Joined: Fri Apr 23, 2010 3:43 pm
Location: San Antonio

Re: Solar capacity needed for my Leaf?

Tue Sep 17, 2013 12:51 pm

Darth,



What you'll find here are primarily on-grid folks. Also you'll find folks that primarily are retrofitting a PV system to an existing roof . That requires adjusting for less than optimal panel siting. And that's where the conversations normally start to look like spaghetti. ;)

A properly sited system has no shading and therefore doesn't need work-arounds to minimize the damage shading causes.

Another argument you'll find from the micro-inverter crowd is that micros allow each panel to work independently and provide max energy harvest. Except that most of the microinverters are installed on oversized panels - so the max collection days are limited by the smaller inverter, not the capability of the panel.

One cool thing about microinverters is the per-panel monitoring that gives the instant-gratification smart phone crowd pretty pictures to look at. Yes, there are per-panel MPPT devices like the Tigo maximizers that provide panel-level data and panel-specific energy harvesting should one be forced to work around shading. But that's market driven, not because of some failure of central or string inverters. Put another way, a PV system is a marathon, not a sprint. Annual inspection and preventive maintenance is normally sufficient.

Nothing made by man is perfect, and hot electronics are not happy electronics. At some point inverters will fail. My personal choice is a central inverter that's mounted at chest-height. It can be gutted and completely rebuilt in less than one hour if necessary. Because the devices are normally placed in better environments than rooftops, they normally don't require rebuilding very often.


http://www.mynissanleaf.com/viewtopic.php?f=45&t=10736
http://www.mynissanleaf.com/viewtopic.php?f=45&t=11807
http://www.mynissanleaf.com/viewtopic.php?f=45&t=12282
http://www.mynissanleaf.com/viewtopic.php?f=45&t=11966

You can use microinverters, a central inverter, or a hybrid system with individual MPPT units and a central inverter. They'll likely give similar service in both harvest and lifespan. It'll most likely come down to what your local installers are used to working with and what they charge for labor. Installers generally like micros because they can do the job faster yet get the same income from the installation - they generally push them because it's better for them, not necessarily better for you.
Last edited by AndyH on Tue Sep 17, 2013 1:41 pm, edited 1 time in total.
"The stupid become extinct."-Bill Mollison
2018 Outlander PHEV
2015 smart Electric Drive (lease ended Feb, 2018)
OpenEVSE Plus DIY

User avatar
wsbca
Posts: 505
Joined: Tue Aug 03, 2010 4:33 pm
Delivery Date: 0- 0-2011
Location: SL-E powered by 3KW AC Solar in SoCal

Re: Solar capacity needed for my Leaf?

Tue Sep 17, 2013 1:21 pm

I have NFI, just passing it on - you might want to check out this post - all parts for a microinverter based PV system of about the size you need, for what seems to me a very good price per watt, and maybe very near you.


viewtopic.php?f=17&t=14367
I was promised a jet pack!

DarthPuppy
Posts: 685
Joined: Sun Aug 11, 2013 8:45 pm
Delivery Date: 11 Aug 2013

Re: Solar capacity needed for my Leaf?

Thu Sep 19, 2013 10:28 am

Ok, I checked the SCE meter and it appears that over the past year, my 5.8kW (DC) system produced 7400 kWh AC, which exceeded what was used by the house by a little over 1,400 kWh.

Using the same factors would suggest an additional 2.5kW (DC) system (10 panels) would produce just under 3200 kWh AC over the course of a year. That should pretty nearly cover my Leaf even if the next summer is hotter and I don't have the 1,400 kWh of over-production from my existing system due to using the air condition more.

Thank you all for your wonderful counsel. I'm now collecting proposals for an appropriate size system. :D
'13 Leaf SL
'18 Honda Clarity Touring PHEV

Return to “Solar”