When solar PV or solar heating for your next renovation - Page 2

Exeric · 12-02-13, 03:20 AM

Yeah, it's a great book. There's a very detailed appendix with one section called Monitoring Your System. It's really too complex to paraphrase all the material and equations but it tells exactly how to apply the equation I just gave. What I gave was the simplified version. Since they did the work I don't really feel right broadcasting all the little details that they worked so hard to produce. So get the book. Everything you asked about is in that one section of the appendix, on pages 330-332!

I should add that the 60% efficiency I said would be the raw efficiency of common solar air panels. Elsewhere in the book they mention that usual measured efficiency on cloudless days at noon of typical panels is 40%. But a caveat: at one place in the book they actually actually used an example that if you live in Minnesota you will have to optimize everything for maximum efficiency, including double glazing, very heavy insulation, and perhaps even a selective surface (they explain what that is in the book.) So you will be taking on an extreme task. Good Luck!

MN Renovator · 12-02-13, 10:27 AM

Thanks again Exeric, I've had a hard time with finding some good resources for envelope efficiency, solar power(of non-PV variety), and I've eventually found things as I've searched but getting my hands on a good solar heating book hasn't happened yet, so this is great.

"So you will be taking on an extreme task. Good Luck!"
Absolutely, its huge and I think I'll be staging it out instead of taking it on all at one time.
I've already got the double glazing but when I do the energy modeling for my house, after upgrading insulation, the windows turn from being 35% of the heat loss into 69% of the heat loss but upgrading them to a U .2 triple glazed brings the window loss down to 36.6% and the total loss drops to 65% of what it would be with the current windows in.

Exeric · 12-02-13, 02:56 PM

One more thing MN and anyone else out there who is thinking about this. Insulating your house applies to almost any project we take on as a first priority. You know that. But after that I think one of the most important things to consider is if you can bank any renewable resource you might have, be it solar thermal or electricity from solar PV. Generally you can't bank solar thermal energy, at least not from summer to winter. That's HUGE! It changes everything. Many places in this country and elsewhere just aren't that suitable for either solar PV or solar thermal in the heart of winter. All you have to do is look at the December or January PV solar radiation maps and the concentrating solar power radiation maps at the NREL site. It can be pretty depressing depending on where you live.

However, in the USA most states allow you to bank your PV output throughout the year if you're grid tied. You can go to that same NREL site and now you can use the PV solar radiation map that gives the average for the whole year:

This isn't nearly as depressing to those folks (unless of course you live in Seattle or anywhere in Alaska). Even Minnesota now looks promising. Yeah, PV isn't quite as efficient as solar thermal but I think it more than makes up for that in flexibility. You can use electricity for practically anything, not just heating your house. This is coming from someone who is tempermentally suited more to solar thermal.

The only reason I'm using solar thermal for my house is because my climate is suited for it in winter. Also, I'm choosing a method whereby I don't have to add anything that is outside the house envelope. It's a cleaner, simpler method that appeals to my aesthetic sense. Also it allows me the flexibility of keeping a warm house when power goes down from the grid. All I need is an UPS power supply to provide power for the bathroom fan and the 26 volt ac power supply for the motorized damper that opens the duct to the roof heat.

Exeric · 12-02-13, 03:19 PM

I should also add that I live in a mixed heating/cooling climate. So when I added an insulating blanket to preserve the heat from the roof it also provides a similar duty in summer. It was amazing how much cooler the house was this past summer just because of that thin radiation barrier I put up underneath the roof. This regime would also work in a primarily cooling climate. It's basically a 2fer when one uses a roof heating system in a mixed heating/cooling or cooling climate.

Edit: Also if you have a roof or attic air conditioner that ducting will be operating in a much cooler environment in the attic with the roof insulated. So it will also improve their efficiency with far less duct losses.

jeff5may · 12-02-13, 04:13 PM

So what do you think about the new combined PVT panels? Increased PV output due to lower panel temp, plus thermal output that uses the solar cells as a selective surface? Sounds really enticing on paper. One could also use the thermal panel as a night sky radiator.

Exeric · 12-02-13, 04:35 PM

I hadn't heard of them except in concept. I didn't know they were out. Will have to google them.

12-02-13, 03:20 AM	#11
Exeric Apprentice EcoRenovator Join Date: Aug 2012 Location: California Posts: 274 Thanks: 19 Thanked 37 Times in 28 Posts	Yeah, it's a great book. There's a very detailed appendix with one section called Monitoring Your System. It's really too complex to paraphrase all the material and equations but it tells exactly how to apply the equation I just gave. What I gave was the simplified version. Since they did the work I don't really feel right broadcasting all the little details that they worked so hard to produce. So get the book. Everything you asked about is in that one section of the appendix, on pages 330-332! I should add that the 60% efficiency I said would be the raw efficiency of common solar air panels. Elsewhere in the book they mention that usual measured efficiency on cloudless days at noon of typical panels is 40%. But a caveat: at one place in the book they actually actually used an example that if you live in Minnesota you will have to optimize everything for maximum efficiency, including double glazing, very heavy insulation, and perhaps even a selective surface (they explain what that is in the book.) So you will be taking on an extreme task. Good Luck! Last edited by Exeric; 12-02-13 at 03:29 AM..

12-02-13, 02:56 PM	#13
Exeric Apprentice EcoRenovator Join Date: Aug 2012 Location: California Posts: 274 Thanks: 19 Thanked 37 Times in 28 Posts	One more thing MN and anyone else out there who is thinking about this. Insulating your house applies to almost any project we take on as a first priority. You know that. But after that I think one of the most important things to consider is if you can bank any renewable resource you might have, be it solar thermal or electricity from solar PV. Generally you can't bank solar thermal energy, at least not from summer to winter. That's HUGE! It changes everything. Many places in this country and elsewhere just aren't that suitable for either solar PV or solar thermal in the heart of winter. All you have to do is look at the December or January PV solar radiation maps and the concentrating solar power radiation maps at the NREL site. It can be pretty depressing depending on where you live. However, in the USA most states allow you to bank your PV output throughout the year if you're grid tied. You can go to that same NREL site and now you can use the PV solar radiation map that gives the average for the whole year: This isn't nearly as depressing to those folks (unless of course you live in Seattle or anywhere in Alaska). Even Minnesota now looks promising. Yeah, PV isn't quite as efficient as solar thermal but I think it more than makes up for that in flexibility. You can use electricity for practically anything, not just heating your house. This is coming from someone who is tempermentally suited more to solar thermal. The only reason I'm using solar thermal for my house is because my climate is suited for it in winter. Also, I'm choosing a method whereby I don't have to add anything that is outside the house envelope. It's a cleaner, simpler method that appeals to my aesthetic sense. Also it allows me the flexibility of keeping a warm house when power goes down from the grid. All I need is an UPS power supply to provide power for the bathroom fan and the 26 volt ac power supply for the motorized damper that opens the duct to the roof heat. Last edited by Daox; 12-02-13 at 03:25 PM..

12-02-13, 03:19 PM	#14
Exeric Apprentice EcoRenovator Join Date: Aug 2012 Location: California Posts: 274 Thanks: 19 Thanked 37 Times in 28 Posts	I should also add that I live in a mixed heating/cooling climate. So when I added an insulating blanket to preserve the heat from the roof it also provides a similar duty in summer. It was amazing how much cooler the house was this past summer just because of that thin radiation barrier I put up underneath the roof. This regime would also work in a primarily cooling climate. It's basically a 2fer when one uses a roof heating system in a mixed heating/cooling or cooling climate. Edit: Also if you have a roof or attic air conditioner that ducting will be operating in a much cooler environment in the attic with the roof insulated. So it will also improve their efficiency with far less duct losses. Last edited by Exeric; 12-02-13 at 03:27 PM..

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12-02-13, 10:27 AM	#12
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	Thanks again Exeric, I've had a hard time with finding some good resources for envelope efficiency, solar power(of non-PV variety), and I've eventually found things as I've searched but getting my hands on a good solar heating book hasn't happened yet, so this is great. "So you will be taking on an extreme task. Good Luck!" Absolutely, its huge and I think I'll be staging it out instead of taking it on all at one time. I've already got the double glazing but when I do the energy modeling for my house, after upgrading insulation, the windows turn from being 35% of the heat loss into 69% of the heat loss but upgrading them to a U .2 triple glazed brings the window loss down to 36.6% and the total loss drops to 65% of what it would be with the current windows in.

12-02-13, 04:13 PM	#15
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	So what do you think about the new combined PVT panels? Increased PV output due to lower panel temp, plus thermal output that uses the solar cells as a selective surface? Sounds really enticing on paper. One could also use the thermal panel as a night sky radiator.

12-02-13, 04:35 PM	#16
Exeric Apprentice EcoRenovator Join Date: Aug 2012 Location: California Posts: 274 Thanks: 19 Thanked 37 Times in 28 Posts	I hadn't heard of them except in concept. I didn't know they were out. Will have to google them.