Sorry to quibble, but while south-facing is a good rule-of-thumb, it is not true that exactly south-facing produces the greatest power in all locations. For example in San Diego, which often has morning fog that takes a while to burn off, the default system in PVWatts predicts 6413 kWh/yr for south-facing and 6436 kWh/yr for 15 degrees west of south. 26 degrees west of south still gives more (6416 kWh/yr) than exactly south-facing. Other locations, such as the Rocky Mountains, can cloud up in the afternoon, which may make an orientation east of south better. Extreme heat, which reduces PV efficiency, can also bias the optimum away from the afternoon sun.
The difference is usually not large. The take-away from this is that you won't be far off from maximum if you build south-facing, but it is typically not the absolute maximum.
Another point is that it is true south and not compass south that should be the baseline. The difference varies by up to 30 degrees across the US, so it is important to take the magnetic declination into account.
Original Message:
Sent: 11-03-2023 04:57 PM
From: David Stout
Subject: Solar in modular building construction
Kat,
It is a fact that in the Northern Hemisphere, South facing fixed angle panels will collect more solar energy than any other compass orientation. So that is the basis of my statement.
I have no problem with your covering the Solar Facts, even as I repeat them.
Ignoring solar facts leads to excess cost and not as effective installations, but many tax credits prudently require the better orientations, like my installations did.
But to really maximize solar gain, the panel array needs to follow the SUN using a tracking system and usually on a pole, which is not the condition of your question as to how to modify a small home.
David Stout.
Original Message:
Sent: 11/3/2023 5:34:00 PM
From: M Keith Sharp
Subject: RE: Solar in modular building construction
Kat,
Feel free to quote me. Just to be clear, I largely agree with David that south-facing is best, but with low envelope losses (like Passive House), you can get enough power for net zero from PV that is not optimally oriented.
A good example is the NREL Habitat House (https://www.nrel.gov/docs/fy08osti/42591.pdf). It is south-facing, but you can see how small the PV system is (4 kW) on the roof and it is 24% net positive. (It would be net zero as is with about 3 kW). With 4 kW, it would still be net zero with orientation pretty far off from south.
Even better performance is possible. If this house had thermal mass for better passive solar heating, even less PV would be needed. This house followed design priorities (aside from the lack of thermal mass) that make sense: 1. superinsulation, 2. passive solar gains (better to match these with thermal mass), 3. solar thermal hot water, and 4. PV.
PV should be the last step, after doing everything else well.
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M Keith Sharp
Emeritus Professor
Louisville KY
Original Message:
Sent: 11-02-2023 04:43 PM
From: Kat Friedrich
Subject: Solar in modular building construction
Robert, thank you very much for these leads. I am following up with some of these organizations.
David, may I quote your comment about needing to make sure that the roof faces south?
Stu, it looks like this company's website is no longer active.
Keith, may I quote your comment?
Thank you,
Kat
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Kat Friedrich
Editor in Chief
American Solar Energy Society
Monona WI
Original Message:
Sent: 11-02-2023 09:49 AM
From: Robert Mellon
Subject: Solar in modular building construction
Kat,
Here in western Pennsylvania we have three great resources for you.
The first one is a modular construction company called Module and they are doing some amazing work with modular construction and solar etc. Contact Brian Gaudio at 412-368-3412. Or info@modulehousing.com. You won't be disappointed. They are laser focused on net zero energy modular buildings etc.
The second great modular company located here in western Pennsylvania is Ecocraft Homes. They have been building net zero modular homes for more than 10 years. Founded by Elliot Fabri senior and his son Elliot Fabri junior they have built some incredible net zero homes that incorporate solar. Contact them at: 800-274-6198.
The third resource is Structural Modular's Incorporated located in beautiful Clarion County, Pennsylvania. Recently Ecocraft whom I mentioned above took ownership of this amazing modular house manufacturing facility. Structural Modular's is known for being way ahead of the typical modular homes building process. They have been innovators in modular construction since they were founded back in 1990 by the Lewis family. They can be contacted at 814-764-5555.
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Robert Mellon
Original Message:
Sent: 11-01-2023 04:21 PM
From: Kat Friedrich
Subject: Solar in modular building construction
Outside of my work at ASES, I'm writing an article on solar power for the skeptical construction professionals who read Offsite Builder.
I would like to ask the members of this forum whether you know any companies that are making use of solar power in modular offsite construction. Any suggestions of potential interviewees would be very helpful. I believe solar power is not usually used in modular construction.
I am also looking to interview a solar professional who can comment on how modular builders would need to change their designs in order to incorporate solar power.
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Kat Friedrich
Editor in Chief
American Solar Energy Society
Monona WI
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