FW: Solar panels

12 posts / 0 new
Last post

I would think it's a shade. Where do I put that in?

Alan Crittendon, PE, LEED AP

Alan Crittendon's picture
Offline
Joined: 2011-09-30
Reputation: 0

Is there a way to put power generation into equest? I was really just
thinking about the shade portion but this would be great too!

Alan Crittendon, PE, LEED AP

Alan Crittendon's picture
Offline
Joined: 2011-09-30
Reputation: 0

Alan,

I have no idea how to do that in eQuest. I never tried. The last time I
attempted PV in eQuest was doing it with Photovoltaic modules and
electricity generator. I'll get back to you once I test it. I have some PV
cells that I use with their info so let me fill it in and see how accurate
it compares to the data I use from PV Watts.

I'll use a 230W polycrystalline cell to check it because that's what we
specify.

Thanks,

PETER HILLERMANN

Peter Hillermann2's picture
Joined: 2011-09-30
Reputation: 0

Alan,

I would stick to PV Watts calculator with filling out the LEED form. eQuest
is complicated and you need to know exactly what panel you are using with
which type of inverter etc. It gets into the weeds quick. I would only model
this if you are doing a large power facility or large amounts of power
generation. Our company has started adding PV to its bag of tricks and just
looking at the way eQuest does it you would need time to analyze your
system. Remember each PV system is different depending on what you are
trying to achieve. I have found out it is almost as complex as knowing which
HVAC system to select for a building.

Thanks,

PETER HILLERMANN

Peter Hillermann2's picture
Joined: 2011-09-30
Reputation: 0

Alan,

You got me off on a tangent because I do love solar panels. Remember that
your panels are connected in series and that if one gets shaded your entire
row goes out, unless you are using micro inverters. You really need to do a
shading study and if you use REVIT this can be done easily. When using a PV
panel as a canopy or shading device you need to watch the summer time
shading on your wall. Typically a long shadow on the wall by parapet or
cornice might shade the panel, which is created by the noon day sun. Just
push the panel a little further off the wall.

Best of luck to you and I hope it all works out.

PETER HILLERMANN

Peter Hillermann2's picture
Joined: 2011-09-30
Reputation: 0

It has been awhile since my last PV studies (they were for fixed units,
not tracking), but I did manage to account for everything within
eQuest... maybe what I can recall will help:

Specific to the "how" to account for PV arrays' effects on a roof or
other building surface's envelope loads, you really can learn it all by
just exploring the required inputs in detailed mode. Create a 'dummy'
PV module with made up values under the utility tab, then create an
electric generator of the type photovoltaic array. When you do this you
can explore all the variables regarding how they're mounted
(coverage/standoff/surface/tilted/etc). In doing so you can select the
roof surface which is being shaded. Parametric runs for each variable
can help you find a "sweet spot" specific to your site for each of those
variables.

Alternatively, I just popped in and it looks like you could also define
all the geometries by first making building shades of the appropriate
geometry/orientation/etc. and then assigning those within the electric
generator window tabs.... Seems like extra work but then you could have
them in your 3D view if that matters to you.

Alan's right to think of them first as a shade, but fixed panels can be
a little trickier when it comes to the building envelope loads. I can't
speak for other programs (and I don't doubt there are simpler options
from a UI perspective), but I know eQuest does go so far as to account
for the degree of convection between your roof surface and panels
(working from weather data wind speed) and the rate of transfer through
the panels, beyond just accounting for direct solar loads. For any
faults with complexity it does seem to do a sophisticated job of
modeling PV generation.

On a related note, I'd be somewhat surprised if any alternative programs
don't allow you to define properties of the inverter equipment... those
losses can be a pretty big deal for any ROI study, iirc. In any case,
Peter's suggestion to use an outside program to work out the power
generation is not something I disagree with, but I just wanted to be
suggest if you go that route to consider what's possible within eQuest
to accurately account for the arrays' envelope effects.

NICK CATON, E.I.T.

Nick-Caton's picture
Offline
Joined: 2011-09-30
Reputation: 805

Alan,

eQUEST can model the power generation as well as the roof shading. You need to create (1) an electric generator, which is the inverter, and (2) the PV array. Go to the Utility & Economics tab, right click on the project name, and ?create photovoltaic module? to define the array. Do the same to create the inverter, but choose ?create electric generator? and specify the type as ?photovoltaic array?. I would recommend getting the data sheets for the inverter and panels before starting; eQUEST requires specifics. However, most of the info should be readily available on the product data sheets.

You link the array to the inverter(s) through the electric generator properties window, an example of which I have attached. On the same tab you can define the mounting conditions to take shading credit. If your array spans multiple roof surfaces, you?ll want to create a building shade representing the array?s footprint, and then mount the array on that building shade. You can tweak the shade?s transmittance, if desired.

I?ve never done a direct comparison to PV Watts, but both use TMY2 weather data for radiation input. eQUEST only models fixed arrays, but it provides much more control over the array?s metrics compared to PV Watts. The added control can be overkill if a quick estimate is sufficient for the project?s needs, but for a PV system that has been fully designed, I would prefer to model it in eQUEST. Check the PS-C report to get the array?s annual output.

Thanks,

DAKOTA KELLEY

Dakota Kelley's picture
Offline
Joined: 2011-09-30
Reputation: 1

Alternately you could do your PV calcs in RETscreen ? its really easy to use and quick. You need Microsoft XL to run it though.
Regarding modeling the roof reflective ? just create an external building shade to sit over the area you need.

Vikram Sami, LEED AP

Sami, Vikram's picture
Offline
Joined: 2011-09-30
Reputation: -1

I sent this yesterday but have a couple more things to add:

1) how does LEED deal with solar power and does Section G2.4 ASHRAE
90.1-2007 just mean that you can't take credit for the utility buying back
the extra energy or cant model at all?

2) Has there been any CIRs that discuss solar PV from LEED?

Alan Crittendon, PE, LEED AP

Alan Crittendon's picture
Offline
Joined: 2011-09-30
Reputation: 0

My LEED-NC v2.2 Reference Guide p188 says ?On-Site Renewable Energy and
Site-Recovered Energy costs are not included in the Proposed Building
Performance (this is a LEED for New Construction exception to ASHRAE
Standard 90.1 G2.4); therefore, these systems receive full credit using the
PRM??examples include PV?

p264 of the BD+C 2009 Reference Guide has a similar note about using
harvested free energy for EAC1 performance.

As far as CIRs I?m not sure, but LEED has always been pretty clear that you
count on-site renewable energy production for both EAC1 and EAC2.

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, HBDP

*From:* equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Alan Crittendon
*Sent:* Wednesday, November 24, 2010 12:07 PM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] FW: Solar panels

I sent this yesterday but have a couple more things to add:

1) how does LEED deal with solar power and does Section G2.4 ASHRAE
90.1-2007 just mean that you can't take credit for the utility buying back
the extra energy or cant model at all?

2) Has there been any CIRs that discuss solar PV from LEED?

Alan Crittendon, PE, LEED AP

*From:* Alan Crittendon [mailto:alanc at dwcei.com]
*Sent:* Tuesday, November 23, 2010 1:28 PM
*To:* 'equest-users at lists.onebuilding.org'
*Subject:* Solar panels

Does ASHRAE 90.1 allow the use of solar panels when calculating the proposed
bldg? if so how do you model them?

Alan Crittendon, PE, LEED AP

David S Eldridge's picture
Joined: 2011-09-30
Reputation: 2000

Hi Alan,

Your questions appear broad enough to suggest the following:

- The LEED reference guide addresses G2.4 specifically under
EAc1 - better check that out, as the guide take precedence over 90.1
where they conflict when LEED modeling.

- It also details two approaches to either include your PV in
the proposed model or to use the exceptional calculation method to find
those savings outside of the model. You get to choose.

- You might also want to review EAc2.

- "How do you model solar panels:" First you need to select
your weapon-of-choice. You can use eQuest, or a multitude of other
programs (RETscreen and PV Watts have been mentioned in a positive light
on this list... see archives for discussions). What you choose depends
on your approach per above. I'd suggest getting that far and then first
giving it a try so you can phrase more specific questions if you have
any issues come up.

- Remember inquiries not specific to eQuest may be more quickly
answered on the [bldg-sim] list.

While I haven't submitted a project with utility buy-back, I'm unaware
of anything disallowing purchased energy to be included in the
calculation of the achieved cost savings. I'd caution however to be
prepared to document thoroughly how that calculation is made. To put
myself in a reviewer's shoes, I'd personally think a visual would be in
order to demonstrate when and to what magnitude the energy production
exceeds consumption through the year.

I have my own general LEED question for everyone:

I thought a fundamental change in LEED v3 is that they no longer
consider precedent (CIR's) a justification for anything... Any
project's LEED review team is fully permitted to completely change their
stances between projects as they deem fit to make their case-by-case
re-interpretations. Is my world-view overly bleak, or is it advisable
to caution others to take any CIR's with a grain block of salt these
days?

NICK CATON, E.I.T.

Nick-Caton's picture
Offline
Joined: 2011-09-30
Reputation: 805

Page 274 of BD+C 2009 Reference Guide directly answers the question: 2.1
model the systems directly in the proposed design energy model.

Now all I have to do is figure out how to do it!!!

Alan Crittendon, PE, LEED AP

Alan Crittendon's picture
Offline
Joined: 2011-09-30
Reputation: 0