[RE-wrenches] Multiple angle conundrum

Thu Apr 5 06:58:23 PDT 2012

They are actually releasing an AC module soon. I’m not aware of a separate
microinverter.

Jason Szumlanski

Fafco Solar

*From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Glenn Burt
*Sent:* Wednesday, April 04, 2012 7:23 PM
*To:* 'RE-wrenches'
*Subject:* Re: [RE-wrenches] Multiple angle conundrum

Sunpower is in the process of releasing their own microinverter if I recall
– maybe another option.

-Glenn

*From:* re-wrenches-bounces at lists.re-wrenches.org [
mailto:re-wrenches-bounces at lists.re-wrenches.org<re-wrenches-bounces at lists.re-wrenches.org>]
*On Behalf Of *Jason Szumlanski
*Sent:* Wednesday, April 04, 2012 2:58 PM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Multiple angle conundrum

I second the microinverter option in this scenario. Since you are up
against a SunPower dealer, use the microinverter features to your advantage
since the E20 series module is not compatible.

I probably shouldn’t be saying that as an authorized SunPower dealer, but
from a competitive standpoint, I think that’s all you’ve got. The SunPower
will take up far less roof space for a given rating and in theory deliver a
similar or greater kWh/$ output over the lifetime. At least, that’s the
sales pitch the SunPower dealer will give.

I have a couple of Enphase systems that have different tilt with the same
azimuth. The lifetime output (over one year) is nearly identical from 4:12
to virtually flat if you ignore the modules that have partial shading
issues. That’s down here in Florida, however, where the sun never gets too
low in the sky.

Jason Szumlanski

Fafco Solar

*From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Kirpal Khalsa
*Sent:* Wednesday, April 04, 2012 12:38 PM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Multiple angle conundrum

Hilton....there are a couple ways to approach this.....There are some
string inverters with multiple MPPT inputs....each different slope of roof
would be installed into its own input.....the other way is to use micro
inverters or other individual module optimizers....in which case you are
completely free from mismatched orientation and slope constraints.....
If you are looking to use a single MPPT channel string inverter you may
consider splitting the arrays and having two single string inverters one
for each tilt angle....That said the tilt angle difference feeding the same
inverter does not have as big of a negative impact as if the sub arrays are
facing different directions....
good luck,
Kirpal Khalsa

On Wed, Apr 4, 2012 at 9:14 AM, Hilton Dier III <hiltondier at gmail.com>
wrote:

Wrenches,

I am talking with a potential client about a roof mounted PV array. The
client has a reasonably large south facing roof, but it is broken up by a
large (18' W x 16' H) shed dormer. The roof is 10:12 and the dormer is
6:12. I designed a layout that gave the dormer some room to avoid shading.
The client was disappointed by how much wattage I could get on his roof. I
pointed out that installing modules in the shade of the dormer was a bad
idea.

He is also talking to another installer. The other installer proposed
installing part of the array on the 10:12 roof and part on the 6:12 dormer.
The client had already asked me about that and I gave him a rudimentary
explanation of maximum power point tracking and the inefficiency of such an
arrangement. He asked them about that and their guy said "No big deal." He
is still considering the two-angle scenario.

So, how much efficiency will he lose by going with two angles? It seems
like the ultimate MPPT design error to me, but I don't have a number for
him to make my case. I suppose it all comes down to cents per delivered kWh
in the end, but two different roof angles seems the the wrong way to go.
I'd like to be able to give him a definitive idea of what he would be
sacrificing with that scenario.

Side note: The other installer is using the new Sunpower E20 modules. They
seem to be available only from the manufacturer. Anybody have a source? Has
anybody used them yet? Do they live up to the hype?

Many thanks,

Hilton

-- 

Hilton Dier III

Renewable Energy Design

Partner, Solar Gain LLC

453 East Hill Rd.

Middlesex, VT 05602

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