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Thanks Ampster, J.P.M., Mike90250 and others for the helpful analyses and factors to consider.
We are still weeks away from making a decision on what size HPWH to buy, the decision that is now imminent is around the solar install. This is due to the need to re-roof: many roofers in our area are booked through the winter, so we need to pull the trigger on the roof pretty much this weekend.
Thanks (very much!) to the sage advice on this thread, we learned early that it's best to re-roof before installing the panels, primary reason being the chore of dismantling all the panels and racking to re-roof in say 3 years. However it's also pretty wise to put the stanchions / standoffs for the solar down during the re-roofing process. Just knowing that has likely saved us hundreds if not thousands of dollars. It has required a bit more up-front thought...
Here's a list of our questions as of two weeks ago, and the answers we've arrived at (I've been tracking these on a Google doc):
Q: How many stanchions / standoffs will be needed? A: Each row of portrait orientation panels will require two rails. Each rail requires one standoff at either end, plus one standoff every (this varies by rail type) 5 to 6 feet. So for our current design, about 70 standoffs.
Q: What panel tilt and orientation will be used? A: Contractors have quoted 0 degrees, 8 degrees, 15 degrees, and 30 degrees. All have quoted portrait orientation, matching our rafter orientation.
Q: Roofing material: is there a particular roofing material recommended? A: (not relevant to this forum)
Q: Will we REALLY get $0.0892 from our CCA for excess power generated? A: Yes, but their portion of the bill is less than half. TOU rates play a much bigger role. PG&E requires that we switch to a TOU rate once we start using net metering.
Q: How does TOU rate effect things like panel tilt? A: Optimizing panel tilt for TOU rates is somewhat in the weeds. South, southwest or west facing installations make the most sense, but since TOU rate schedules are prone to change, there's not too much to be gained by optimizing.
Q: San Francisco is foggy -- won't this kill power output? A: We will need to see. From posts on Nextdoor, this forum, and elsewhere, San Francisco is an excellent place to install solar panels, and the PVWatts estimates are not far from what people actually get.
Q: Our existing rafters are 2x6" dimensional from 1921, spaced 32" OC, running N-S, and spanning anywhere between 11' and 15'. Will this be sufficient to handle wind uplift for the panel tilt you are recommending? A: The answer has varied from each contractor. Some say "no problem", others advise caution. Being a responsible homeowner, I will add some reinforcement as soon as practical, especially on the 15' span. There may be a way to design 4x4 posts instead of standoffs at the time of re-roofing. We are proceeding with a sensible approach here.
Q: Should we just install half the panels? A: Putting up half the free panels will cost us around $3.25 per watt all told. Putting up the remaining 25 panels (we actually have 50, not 48, sorry for the error in the post title) will cost us around an additional $1.00 per watt, bringing the total to around $2.30 per watt. This has been a HUGE question for us since putting up only half the panels makes a LOT of sense. However, with the incentives drying up, and needing to do something with these panels, we've decided to go for it. The tipping point for us is around the water heater. There's a good argument that IF we are generating excess power, that we can use much of that excess power to heat our hot water and/or home, AND that doing so will likely happen at some sort of favorable rate. Plus, there's the global warming factor -- regardless of our own opinions on this, having more of a net zero home in our region will likely increase our home's resale value. So we're very likely going to go for it.
Q: Is it ok for the panels to be attached flat? A: Yes, this will decrease annual power generation by 14% relative to a 30 degree tilt, according to PVWatts. It will also result in a simpler system design with no shadowing to be concerned with, and an increased need to go up on the roof to wash debris off the panels especially around the edges. It will result in lower risk of wind damage in a hurricane. So yes, it's ok. Is it optimal? We'll let our contractor be the final judge of that.
Q: Should we buy a heat pump? A: Let's get this beast up on the roof first and see what it can do. Let's also see how the TOU and CCA rates actually shake out on our utility bills. Thanks again Ampster and J.P.M. for the valuable opinions here. There's a bunch more research to do in the area of radiant heating, hot water, plumbing, heat pumps, BTUs vs. watts, heat loss calculators, etc. That will take time to do a proper job. (Current bookmark for my research in this area: http://www.greenbuildingtalk.com/For...c/Default.aspx )
Here's our current proposed design:
Rooftop diagram 2.png
I've heard from contractors, PG&E reps and others that I've done my homework. That's in large part thanks to the help on this forum. Please let me know if there's other information / learnings I can share. Definitely still lots to learn.
We are still weeks away from making a decision on what size HPWH to buy, the decision that is now imminent is around the solar install. This is due to the need to re-roof: many roofers in our area are booked through the winter, so we need to pull the trigger on the roof pretty much this weekend.
Thanks (very much!) to the sage advice on this thread, we learned early that it's best to re-roof before installing the panels, primary reason being the chore of dismantling all the panels and racking to re-roof in say 3 years. However it's also pretty wise to put the stanchions / standoffs for the solar down during the re-roofing process. Just knowing that has likely saved us hundreds if not thousands of dollars. It has required a bit more up-front thought...
Here's a list of our questions as of two weeks ago, and the answers we've arrived at (I've been tracking these on a Google doc):
Q: How many stanchions / standoffs will be needed? A: Each row of portrait orientation panels will require two rails. Each rail requires one standoff at either end, plus one standoff every (this varies by rail type) 5 to 6 feet. So for our current design, about 70 standoffs.
Q: What panel tilt and orientation will be used? A: Contractors have quoted 0 degrees, 8 degrees, 15 degrees, and 30 degrees. All have quoted portrait orientation, matching our rafter orientation.
Q: Roofing material: is there a particular roofing material recommended? A: (not relevant to this forum)
Q: Will we REALLY get $0.0892 from our CCA for excess power generated? A: Yes, but their portion of the bill is less than half. TOU rates play a much bigger role. PG&E requires that we switch to a TOU rate once we start using net metering.
Q: How does TOU rate effect things like panel tilt? A: Optimizing panel tilt for TOU rates is somewhat in the weeds. South, southwest or west facing installations make the most sense, but since TOU rate schedules are prone to change, there's not too much to be gained by optimizing.
Q: San Francisco is foggy -- won't this kill power output? A: We will need to see. From posts on Nextdoor, this forum, and elsewhere, San Francisco is an excellent place to install solar panels, and the PVWatts estimates are not far from what people actually get.
Q: Our existing rafters are 2x6" dimensional from 1921, spaced 32" OC, running N-S, and spanning anywhere between 11' and 15'. Will this be sufficient to handle wind uplift for the panel tilt you are recommending? A: The answer has varied from each contractor. Some say "no problem", others advise caution. Being a responsible homeowner, I will add some reinforcement as soon as practical, especially on the 15' span. There may be a way to design 4x4 posts instead of standoffs at the time of re-roofing. We are proceeding with a sensible approach here.
Q: Should we just install half the panels? A: Putting up half the free panels will cost us around $3.25 per watt all told. Putting up the remaining 25 panels (we actually have 50, not 48, sorry for the error in the post title) will cost us around an additional $1.00 per watt, bringing the total to around $2.30 per watt. This has been a HUGE question for us since putting up only half the panels makes a LOT of sense. However, with the incentives drying up, and needing to do something with these panels, we've decided to go for it. The tipping point for us is around the water heater. There's a good argument that IF we are generating excess power, that we can use much of that excess power to heat our hot water and/or home, AND that doing so will likely happen at some sort of favorable rate. Plus, there's the global warming factor -- regardless of our own opinions on this, having more of a net zero home in our region will likely increase our home's resale value. So we're very likely going to go for it.
Q: Is it ok for the panels to be attached flat? A: Yes, this will decrease annual power generation by 14% relative to a 30 degree tilt, according to PVWatts. It will also result in a simpler system design with no shadowing to be concerned with, and an increased need to go up on the roof to wash debris off the panels especially around the edges. It will result in lower risk of wind damage in a hurricane. So yes, it's ok. Is it optimal? We'll let our contractor be the final judge of that.
Q: Should we buy a heat pump? A: Let's get this beast up on the roof first and see what it can do. Let's also see how the TOU and CCA rates actually shake out on our utility bills. Thanks again Ampster and J.P.M. for the valuable opinions here. There's a bunch more research to do in the area of radiant heating, hot water, plumbing, heat pumps, BTUs vs. watts, heat loss calculators, etc. That will take time to do a proper job. (Current bookmark for my research in this area: http://www.greenbuildingtalk.com/For...c/Default.aspx )
Here's our current proposed design:
Rooftop diagram 2.png
I've heard from contractors, PG&E reps and others that I've done my homework. That's in large part thanks to the help on this forum. Please let me know if there's other information / learnings I can share. Definitely still lots to learn.
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