SunPower SPR-E20-327-C-AC Power Testing

[ajonestx]

Not really. It was built in 1980 and is reasonably tight by construction/building codes of that time, but nothing too off the wall. However, probably about half of a low electric bill is lifestyle choices and common sense energy conservation measures. For example, extensive use of nighttime ventilation during cooling season allows limiting annual A/C air handler run time to an average of ~ 120 - 150 hrs./yr. depending on weather (BTW, I'm inland, not coastal so summers get quite toasty here relative to downtown/coastal San Diego as well as about 20 % sunnier. But then, I set the summer thermostat at 80 F and shut the A/C off when we're not home. I've also got a solar thermal water heater that provides ~ 90-95 % of my annual DHW load. That alone replaces ~ 1,900 kWh/yr. of the annual electrical usage.

My overpriced, oversized, non cost effective but otherwise well designed Sunpower system (with 327 STC W panels same as yours) provides the rest of the much reduced electrical load. Why I got the overpriced, oversized S.P. system is a long, boring story, but I knew it wasn't going to be cost effective from the beginning and economics had nothing to do with it.

If one goal of the exercise is a lower electric bill in the most cost effective way(s), the key is to first reduce the load as much as possible through lifestyle adjustments, then conservation measures, and only after all that is done to the greatest extent possible within lifestyle choices and lifecycle costing methods, see if/what kind of alternate energy devices (if any) make economic sense.

Then, of course, all that needs to be balanced against other priorities, but that's another topic altogether.

ok wait. I read some of the details in your last post... 120-150 hours of annual HVAC run time? I just looked into our usage (ecobee) and it tells me we ran the air handler 641 hours last year! I thought we were being aggressive with our cooling settings at 78 degrees in the morning and evening, 82 degrees while away (during the day), and 79 degrees while sleeping. Heating settings are at 71 degrees in the morning and evening, 64 degrees while away (during the day), and 64 degrees while sleeping. What tools are you using to identify individual loads in your house? Are you running a separate whole house fan tied to a thermostat that automatically allows you to use the "nighttime ventilator" in lieu of the conventional HVAC system?

Yes, we too investing in PV (not purely because of economics), but had hoped to get our investment back some day. We also put in a little extra infrastructure to accommodate some expansion for that future EV, but that has not happened yet.

Well, I have made it through PV Dummies chapters 1 through 3 and admit I was going to originally skip the chapters on household energy use and improving efficiency, but with your little nudge, I went for it. I also admit that there were some friendly reminders about things we can do better. Some of the underfloor batt insulation has fallen down (partly due to little critters who enjoy playing in it) and we have been thinking about spray foam, but have not found the right contractor yet - will probably push this topic more. Also, read the section about cleaning the coils on the frig - funny, we had a little leak the other day and cleaned them for the first time in 10 years as part of the repair - might need to do this more often (not sure if I can clean them twice annually as the book suggests). The book also reminded me about conducting an energy audit - we loaned our Kill-a-watt meter to someone years ago (forgot who) and we actually just put it in the Amazon cart the other day. The book also reminded me about efficient appliances - most of our appliance are about 10 years old and starting to fail - energy star upgrades are in the near future. What I cannot figure out is how our tankless water heater has lasted for 20 years (it might be that I flush the inside coils with vinegar every couple of years) - that thing needs to go soon!

Oh, and it appears that my version of PV Dummies is 2010 with lots of references to fluorescent only one very small reference to LED - I guess a few things have changed in 12 years, but not much.

Curious... is your solar water heater 100% domestic water (open loop) or does it have anti-freeze (closed loop). I might be using the wrong terms.

Once the kill-a-watt meters comes in the mail, I hope to find a nice quiet electrical day to turn the house off and itemize the loads better. I was hoping that Sense could pull some of the data out, but there are too many loads that it just could not isolate to be a dependable load analysis tool.

[J.P.M.]

ok wait. I read some of the details in your last post... 120-150 hours of annual HVAC run time? I just looked into our usage (ecobee) and it tells me we ran the air handler 641 hours last year! I thought we were being aggressive with our cooling settings at 78 degrees in the morning and evening, 82 degrees while away (during the day), and 79 degrees while sleeping. Heating settings are at 71 degrees in the morning and evening, 64 degrees while away (during the day), and 64 degrees while sleeping. What tools are you using to identify individual loads in your house? Are you running a separate whole house fan tied to a thermostat that automatically allows you to use the "nighttime ventilator" in lieu of the conventional HVAC system?

Yes, we too investing in PV (not purely because of economics), but had hoped to get our investment back some day. We also put in a little extra infrastructure to accommodate some expansion for that future EV, but that has not happened yet.

Well, I have made it through PV Dummies chapters 1 through 3 and admit I was going to originally skip the chapters on household energy use and improving efficiency, but with your little nudge, I went for it. I also admit that there were some friendly reminders about things we can do better. Some of the underfloor batt insulation has fallen down (partly due to little critters who enjoy playing in it) and we have been thinking about spray foam, but have not found the right contractor yet - will probably push this topic more. Also, read the section about cleaning the coils on the frig - funny, we had a little leak the other day and cleaned them for the first time in 10 years as part of the repair - might need to do this more often (not sure if I can clean them twice annually as the book suggests). The book also reminded me about conducting an energy audit - we loaned our Kill-a-watt meter to someone years ago (forgot who) and we actually just put it in the Amazon cart the other day. The book also reminded me about efficient appliances - most of our appliance are about 10 years old and starting to fail - energy star upgrades are in the near future. What I cannot figure out is how our tankless water heater has lasted for 20 years (it might be that I flush the inside coils with vinegar every couple of years) - that thing needs to go soon!

Oh, and it appears that my version of PV Dummies is 2010 with lots of references to fluorescent only one very small reference to LED - I guess a few things have changed in 12 years, but not much.

Curious... is your solar water heater 100% domestic water (open loop) or does it have anti-freeze (closed loop). I might be using the wrong terms.

Once the kill-a-watt meters comes in the mail, I hope to find a nice quiet electrical day to turn the house off and itemize the loads better. I was hoping that Sense could pull some of the data out, but there are too many loads that it just could not isolate to be a dependable load analysis tool.

Replies in approx. order of your questions:

1.) That's ~ 135 hrs./yr. of air handler run time when during the cooling season - not for all HVAC loads - that is, just A/C. I'm not at my primary home just now so the numbers are not in front of me, but the propane furnace runs about 90 - 100 hrs./yr.
Air cond. size is 5 ton (60,000 BTU/hr.).
The propane fired air heater is 120,000 BTU/hr.
Summer temp. interior air set temp. is 80 F, A/C is OFF when not home.
Winter is temp. set 68 F. when home. Off when not home.

2.) Some tools I have used for analysis of my dwellings, their heat transfer characteristics and the HVAC equipment they use:
- 4 Kil-A-Watt meters.
- 2 Fluke multimeters.
- Several calibrated (by me) thermomerters.
- 3 or 4 stopwatches.
- 1 ea, 500 ml graduated glass cylinder.
- 1 strobe light.
- Several tape measurers.
- Several levels.
- 1 hand held pyranometer about the size of a pack of cigarettes I've had since 1976.
- 1 Davis Instruments Pro II plus without the IR sensor.
- 1 Davis Envoy 8X data logger.

3.) No whole house fan. I had one in Buffalo and it was cost effective. now, my CA home size and whole house fan mat. and labor as well as the greater cost effectiveness of other methods made whole out fan not as cost effective here as other methods and anyway,> cost than life cycle savings as calculated when CA house was purchased. Several box window fans and a good eyeball ability to sense climate conditions do the trick for the cooling season now. In cooling season, A/C - if it comes on at all - only does so after usually about1600 hrs P.D.T. and cycles until thre outside temp. cools to 82 F outside, usually by 2100 - 2200 hrs, or so at the latest. Then, the fans usually come on. "Sailing" a house in that fashion is not an exact science.

On the fridge coils, if you can get at them, washing with a damp cloth is a superior method to simple dusting or vacuuming. A long as someone is taking the time, removing the last few micrometers of what's a pretty good insulator (a dust layer) seems like a no brainer. I did some before/after trials on my fridge and as I seem to recall (~ 15 yrs. ago or so), the damp cloth seemed to improve (lower) the 30 day fridge usage by maybe 10-20 % over simple vac or dusting. As long as you're going to take the time to do it...?

Your terms are fine. My solar DHW is a direct device, that is, the potable H2O circulates directly through the collectors. There is no secondary heat transfer loop. Much simpler, and much more cost effective. Besides, most of the required heat exchanger products foisted on the unaware public are junk and a built in future failure. With respect to my system, because of the (mostly) non freezing climate here, the differential controller provides freeze protection by circulating (heated) potable H2O through the collectors whenever the collector sensor temp. drops to +42 F. or so. The annual penalty of that method is maybe 2- 3% of annual hot water output/yr, vs, maybe 7 -12 %/yr for the heat exchanger penalty alone - and that's before any fouling penalty for the heat exachanger. See D & B. for a brief discussion on heat exchanger design penalties.

On insulation, foam vs. batts: If cost effectiveness is a consideration, I'd be careful about spray foam, I'd also be careful about shrinkage.
Fiberglass batts may settle a bit under gravity but they don't shrink much and so don't have much of anything in the way of leakage paths that foam cracks can create. Think of a well insulated door that's always open about 0.5 cm or so and what that can do to the door opening (hole) heat transfer rate.

Low energy appliances are great - I'm a big fan if the life cycle savings are > the cost differential for sllghtly less efficient equipment - but only after sensible and thoughtful life style changes have been put in place.

I believe the 2010 ed. of the Dummies book is the latest ed. but don't worry, the info. is still good. all the laws of physics are still in force.

[bcroe]

. Once the kill-a-watt meters comes in the mail, I hope to find a nice quiet electrical day to turn the house off and itemize the loads better. I was hoping that Sense could pull some of the data out, but there are too many loads that it just could not isolate to be a dependable load analysis tool.

Adding to the above, the kill-a-watt meter is likely not a one day project.

The basic energy theme here for half a century, is start by identifying
exactly where the energy is going, and how much. Then eliminate as
much WASTE as possible. Finally cover remaining usage with solar. It
has never been sacrifice comfort to reduce essential usage.

When I got settled in here in 2004, I turned everything off, fridge, freezer,
HVAC not running. To my horror the disc was spinning merrily along at
300W (it had been stationary before the move). That is 2630 KWH a
year somehow being wasted. I spent over a year tracking down every
standby drain on 60 circuits. After dealing with the locked attic fan and
the heat pump sump heater, there were still 100 tiny loads that all added
up. TVs, wall warts, clocks, door opener, on and on.

I eliminated most of this waste, by a variety of means. Example, the door
bell trans was burning 3.5 standby watts, use duty cycle as close to zero
as you can get. I took it out and connected to the furnace transformer.

In the end I was left with about 60W, from GFIs, and security devices like
my 10 motion detector lights. Bruce Roe

[ajonestx]

Adding to the above, the kill-a-watt meter is likely not a one day project.

The basic energy theme here for half a century, is start by identifying
exactly where the energy is going, and how much. Then eliminate as
much WASTE as possible. Finally cover remaining usage with solar. It
has never been sacrifice comfort to reduce essential usage.

When I got settled in here in 2004, I turned everything off, fridge, freezer,
HVAC not running. To my horror the disc was spinning merrily along at
300W (it had been stationary before the move). That is 2630 KWH a
year somehow being wasted. I spent over a year tracking down every
standby drain on 60 circuits. After dealing with the locked attic fan and
the heat pump sump heater, there were still 100 tiny loads that all added
up. TVs, wall warts, clocks, door opener, on and on.

I eliminated most of this waste, by a variety of means. Example, the door
bell trans was burning 3.5 standby watts, use duty cycle as close to zero
as you can get. I took it out and connected to the furnace transformer.

In the end I was left with about 60W, from GFIs, and security devices like
my 10 motion detector lights. Bruce Roe

Too funny! Oh my... 300 watts of standby. Yes, the kill-a-watt meter arrived in the mail yesterday and we got started. Already identified problems with incandescent Christmas tree lights at 80 watts (we have already replaced them with LED), coffee maker at 0.7 watts continuous (just to run the clock that I do not need), and one 300 watt floor lamp that needs to be replaced. This will take some time - agreed, this will not happen in one day. To your and J.P.M.'s point, essential usage, comfort, sensible and thoughtful lifestyle changes are all relative to each individual, but by looking at each one with decent data, a proposed adjustment can (or not) be made. But without the data, you will never know if you have the opportunity to reduce energy usage.

[J.P.M.]

Adding to the above, the kill-a-watt meter is likely not a one day project.

The basic energy theme here for half a century, is start by identifying
exactly where the energy is going, and how much. Then eliminate as
much WASTE as possible. Finally cover remaining usage with solar. It
has never been sacrifice comfort to reduce essential usage.

When I got settled in here in 2004, I turned everything off, fridge, freezer,
HVAC not running. To my horror the disc was spinning merrily along at
300W (it had been stationary before the move). That is 2630 KWH a
year somehow being wasted. I spent over a year tracking down every
standby drain on 60 circuits. After dealing with the locked attic fan and
the heat pump sump heater, there were still 100 tiny loads that all added
up. TVs, wall warts, clocks, door opener, on and on.

I eliminated most of this waste, by a variety of means. Example, the door
bell trans was burning 3.5 standby watts, use duty cycle as close to zero
as you can get. I took it out and connected to the furnace transformer.

In the end I was left with about 60W, from GFIs, and security devices like
my 10 motion detector lights. Bruce Roe

I did the same before my first Kill-a-Watt meter back in the day. Then, like you I turned everything off, went circuit by circuit and timed the electric meter going around with a stopwatch for each and every circuit- a real PITA - looking for devices that came on and learning as I went, chasing leaks and learning. There were a couple of detective stories along the way similar to yours like the garage door opener sensor at ~ 7W and the air handler motor replacement that leaks about 4 - 5 W. A few loads I keep like the 12 W on the cable box for the TV my wife watches and some ~2 W nite lights on in halls where my bride and I have hall sex when we pass each other at around 3 A.M. going to/from the john. Between what I know about, what I indulge myself in as slothful waster too lazy to look for but still wonder about, I'm down to somewhere between 80 and 100 W "idling" load.

Like you, I live quite comfortably and don't practice hair shirt level sacrifice of creature comfort on the altar of the more ignorant side of energy conservation, but also like you I try not to waste energy due to hubristic ignorance.

As for security, I'm not paranoid in the same ways or at what I consider some others' levels or concern, but what security measures I do have don't require electricity.

[bcroe]

Nothing can be done about standby current of dozens of GFIs, pretty small total,
not really waste. The motion det lights have demonstrated much better security
than my neighbors have. The energy mostly goes to the 24/7 standby drain, the
lights are so seldom on they fall into the noise level. They really are a pleasant
luxury, looking out you know nothing is out there because they are all off. Then
as you carry the garbage to the next building, you are never in the dark. Nice to
have the place light up when you arrive at night. Far more efficient and effective
than the all night pole lights the previous owner left me. Bruce Roe

[SunEagle]

Nothing can be done about standby current of dozens of GFIs, pretty small total,
not really waste. The motion det lights have demonstrated much better security
than my neighbors have. The energy mostly goes to the 24/7 standby drain, the
lights are so seldom on they fall into the noise level. They really are a pleasant
luxury, looking out you know nothing is out there because they are all off. Then
as you carry the garbage to the next building, you are never in the dark. Nice to
have the place light up when you arrive at night. Far more efficient and effective
than the all night pole lights the previous owner left me. Bruce Roe

I think the problem with motion detect lights is that in some neighborhoods thieves just stay away from lit areas. And while they may get surprised by the lights coming on they may also understand that they are not being looked at so they proceed with their mayhem anyway.

I have CCTV cameras that consume some amount of power but I do feel safer knowing they are watching and recording anyone that comes to my remote located home. I also have some solar powered motion detect lights which is handy to have by not needing my flashlite.

Each person has to determine what works for their home and how much power they don't care about using to keep it safe.

[J.P.M.]

Nothing can be done about standby current of dozens of GFIs, pretty small total,
not really waste. The motion det lights have demonstrated much better security
than my neighbors have. The energy mostly goes to the 24/7 standby drain, the
lights are so seldom on they fall into the noise level. They really are a pleasant
luxury, looking out you know nothing is out there because they are all off. Then
as you carry the garbage to the next building, you are never in the dark. Nice to
have the place light up when you arrive at night. Far more efficient and effective
than the all night pole lights the previous owner left me. Bruce Roe

All/Most of my paranoid neighbors have motion detector lights on their property. Problem is, we've got a fair amount of nocturnal animal activity around here so the neighborhood is a constant light show going on/off at night.

[sonoran]

keep it safe

SE, would you kindly private message me ...thanks

[SunEagle]

SE, would you kindly private message me ...thanks

Sorry. The PM option has been disabled due to too many people trying to spam the forum.

You can ask me for information just by posting a question

[ajonestx]

Replies in approx. order of your questions:

1.) That's ~ 135 hrs./yr. of air handler run time when during the cooling season - not for all HVAC loads - that is, just A/C. I'm not at my primary home just now so the numbers are not in front of me, but the propane furnace runs about 90 - 100 hrs./yr.
Air cond. size is 5 ton (60,000 BTU/hr.).
The propane fired air heater is 120,000 BTU/hr.
Summer temp. interior air set temp. is 80 F, A/C is OFF when not home.
Winter is temp. set 68 F. when home. Off when not home.

2.) Some tools I have used for analysis of my dwellings, their heat transfer characteristics and the HVAC equipment they use:
- 4 Kil-A-Watt meters.
- 2 Fluke multimeters.
- Several calibrated (by me) thermomerters.
- 3 or 4 stopwatches.
- 1 ea, 500 ml graduated glass cylinder.
- 1 strobe light.
- Several tape measurers.
- Several levels.
- 1 hand held pyranometer about the size of a pack of cigarettes I've had since 1976.
- 1 Davis Instruments Pro II plus without the IR sensor.
- 1 Davis Envoy 8X data logger.

3.) No whole house fan. I had one in Buffalo and it was cost effective. now, my CA home size and whole house fan mat. and labor as well as the greater cost effectiveness of other methods made whole out fan not as cost effective here as other methods and anyway,> cost than life cycle savings as calculated when CA house was purchased. Several box window fans and a good eyeball ability to sense climate conditions do the trick for the cooling season now. In cooling season, A/C - if it comes on at all - only does so after usually about1600 hrs P.D.T. and cycles until thre outside temp. cools to 82 F outside, usually by 2100 - 2200 hrs, or so at the latest. Then, the fans usually come on. "Sailing" a house in that fashion is not an exact science.

On the fridge coils, if you can get at them, washing with a damp cloth is a superior method to simple dusting or vacuuming. A long as someone is taking the time, removing the last few micrometers of what's a pretty good insulator (a dust layer) seems like a no brainer. I did some before/after trials on my fridge and as I seem to recall (~ 15 yrs. ago or so), the damp cloth seemed to improve (lower) the 30 day fridge usage by maybe 10-20 % over simple vac or dusting. As long as you're going to take the time to do it...?

Your terms are fine. My solar DHW is a direct device, that is, the potable H2O circulates directly through the collectors. There is no secondary heat transfer loop. Much simpler, and much more cost effective. Besides, most of the required heat exchanger products foisted on the unaware public are junk and a built in future failure. With respect to my system, because of the (mostly) non freezing climate here, the differential controller provides freeze protection by circulating (heated) potable H2O through the collectors whenever the collector sensor temp. drops to +42 F. or so. The annual penalty of that method is maybe 2- 3% of annual hot water output/yr, vs, maybe 7 -12 %/yr for the heat exchanger penalty alone - and that's before any fouling penalty for the heat exachanger. See D & B. for a brief discussion on heat exchanger design penalties.

On insulation, foam vs. batts: If cost effectiveness is a consideration, I'd be careful about spray foam, I'd also be careful about shrinkage.
Fiberglass batts may settle a bit under gravity but they don't shrink much and so don't have much of anything in the way of leakage paths that foam cracks can create. Think of a well insulated door that's always open about 0.5 cm or so and what that can do to the door opening (hole) heat transfer rate.

Low energy appliances are great - I'm a big fan if the life cycle savings are > the cost differential for sllghtly less efficient equipment - but only after sensible and thoughtful life style changes have been put in place.

I believe the 2010 ed. of the Dummies book is the latest ed. but don't worry, the info. is still good. all the laws of physics are still in force.

Running down the list of your replies to my questions...

ok, your run time hours are still VERY low for the size systems you are running and obviously the reasonable lifestyle choices you have made, the window fans and the "OFF" function is working while you are away must be working very well. Just adding up my May through September hours (assumed AC and no heat), I am still coming up with about 300 run time hours (per Ecobee). I had the fan running 5 minutes per hour some time back, but turned that off. I might look into my settings again.

We also like the summer temp a couple of degrees cooler and the winter temp a couple of degrees warmer - this could impact things too.

Good advice on the frig coils - we need to pull it out later this week to get at the extension cord that I think is blocking one of the wheels and I'll see about getting the coils damp wiped. I have to admit that I do think the frig runs a lot less after vacuuming them. Hard to believe.

Cost effective solution a few years ago was the batt insulation under the house. With the amount of critter activity and the amount of insulation that is now sitting on the ground, we are no longer considering a cost effective solution - we are looking for the right solution that critters do not like, stays in place and keeps the cold out of the floor. We have considered batt, rigid polyiso, Styrofoam, and spray. Not sure where this is going to land, but the critters have made into through the floor, up the walls and are now in the attic. But this little tangent is not the purpose of this discussion - it is noted that insulation is important for reducing load. But, if you have ideas for under floor insulation that is critter resistant, stays in place, and will not shrink, I would love to hear your ideas.

Not sure if I am up to the challenge of solar DHW, but I like the sound of your set up. I was never a fan of secondary transfer loops, glycol and anti-freeze - just sounded like it was too many additional points of failure, but could not find an open loop system (did not look hard) that had the right freeze protection. I had given up looking after getting hung up on having to drain the system every time it got cold outside. But if you have a differential controller to push hot water through the outside coils, that sounds simple enough to work very well. Would you recommend the manufacturer to me? Oh, and what is, "D&B"?

Fair enough on appliance efficiencies - we usually do not just replace our appliances just to get better efficiency, but we absolutely do consider efficiencies when we have to. I am still kicking myself for not getting the higher efficiency air conditioner when we replaced it last time - the renovation cost was so far over budget, we accepted the lower cost option.

Well, I have made it through PV Dummies chapter 4 (and yes the physics has not changed, only some of the tools). Continues to be a good read so far - more interesting information... enough sunlight hits the surface of the earth to provide 35,000 times the energy that humans use - WOW. Refreshers on photo transformation into electricity and heat. So if PV is only about 15 to 20 % efficient, that would suggest that 80 to 85% of the solar energy is going to heat, right? Do you know if they have considered heat dissipating fins on the back of PV (like transformers)?

[J.P.M.]

Running down the list of your replies to my questions...

ok, your run time hours are still VERY low for the size systems you are running and obviously the reasonable lifestyle choices you have made, the window fans and the "OFF" function is working while you are away must be working very well. Just adding up my May through September hours (assumed AC and no heat), I am still coming up with about 300 run time hours (per Ecobee). I had the fan running 5 minutes per hour some time back, but turned that off. I might look into my settings again.

We also like the summer temp a couple of degrees cooler and the winter temp a couple of degrees warmer - this could impact things too.

Good advice on the frig coils - we need to pull it out later this week to get at the extension cord that I think is blocking one of the wheels and I'll see about getting the coils damp wiped. I have to admit that I do think the frig runs a lot less after vacuuming them. Hard to believe.

Cost effective solution a few years ago was the batt insulation under the house. With the amount of critter activity and the amount of insulation that is now sitting on the ground, we are no longer considering a cost effective solution - we are looking for the right solution that critters do not like, stays in place and keeps the cold out of the floor. We have considered batt, rigid polyiso, Styrofoam, and spray. Not sure where this is going to land, but the critters have made into through the floor, up the walls and are now in the attic. But this little tangent is not the purpose of this discussion - it is noted that insulation is important for reducing load. But, if you have ideas for under floor insulation that is critter resistant, stays in place, and will not shrink, I would love to hear your ideas.

Not sure if I am up to the challenge of solar DHW, but I like the sound of your set up. I was never a fan of secondary transfer loops, glycol and anti-freeze - just sounded like it was too many additional points of failure, but could not find an open loop system (did not look hard) that had the right freeze protection. I had given up looking after getting hung up on having to drain the system every time it got cold outside. But if you have a differential controller to push hot water through the outside coils, that sounds simple enough to work very well. Would you recommend the manufacturer to me? Oh, and what is, "D&B"?

Fair enough on appliance efficiencies - we usually do not just replace our appliances just to get better efficiency, but we absolutely do consider efficiencies when we have to. I am still kicking myself for not getting the higher efficiency air conditioner when we replaced it last time - the renovation cost was so far over budget, we accepted the lower cost option.

Well, I have made it through PV Dummies chapter 4 (and yes the physics has not changed, only some of the tools). Continues to be a good read so far - more interesting information... enough sunlight hits the surface of the earth to provide 35,000 times the energy that humans use - WOW. Refreshers on photo transformation into electricity and heat. So if PV is only about 15 to 20 % efficient, that would suggest that 80 to 85% of the solar energy is going to heat, right? Do you know if they have considered heat dissipating fins on the back of PV (like transformers)?

I've seen 1/4" semi rigid wire mesh work to keep most bats/mice out of insulated spaces of any orientation. Anyway, many critters don't seem to like fiberglass insulation any more than most humans like contact with the stuff. For my $$ and for the most trouble-free use, fiberglass batts are hard to beat. Just provide lots of ventilation to insulated spaces and keep liquid water away from the batts or loose fill. Rigid stuff shrinks, sad often smells after a time.

For lots of reasons, I'm not a big fan of rigid insulation, although it does have its uses and applications. The rigid polyiso you mention may be dangerous. When it burns, depending on excess (or actually the lack of sufficient excess) theoretical combustion air, it can liberate a bunch of nasty stuff, hydrogen cyanide being one of them. Just sayin'.

I designed my solar DHW and it was/is pretty standard with a few applicable design tricks I picked up from my real job of engineering and designing power boilers, heat transfer and other process equipment for refineries, chemical plants and the process industries in general. For a very thorough discussion of solar water heating, see D & B (that's Duffie and Beckman BTW). Differential controllers are plentiful and easy to come by.

However, as well running and trouble free as my DHW system is and has been, if I was starting from scratch again, and still heating water with resistance electricity, I'd seriously consider using a combination of PV and a heat pump water heater (HPWH), particularly in a moderate (i.e. mostly nonfreezing) climate. Reason: The annual overall thermal efficiency of my system is ~ 35%-40% after piping and standby losses which is pretty good. However, a decent PVsystem operating at, say, 18 % overall output/input efficiency coupled to a HPWH operating with an annual C.O.P. of something > 2.0 gets me as much or maybe even more in the way of production efficiency for a lot less maint. than most any well designed and well running solar domestic flat plate water heaters require. The freezing problems avoided alone make it worth considering.

On harvesting excess heat from PV devices, the 1st law of Thermodynamics does indeed dictate that if/when a PV device is operating at quasi-steady state, the power output plus any irradiance that's reflected off the device plus any heat rejected to the surroundings by the device will == the irradiance the device is subjected to. For many years now, and about 2-3 times/yr. around here, the subject comes up about how easy it would be to harvest all that excess rejected heat by various and what I call "You Could Just (do this and it would work)" schemes.

Well, the idea is straight forward and it can be done. However, in the past, at this time, and probably for some time into the future, it's not a practical or cost effective idea for most applications. If it was, you'd see it being done on an industrial scale at this time. Q.E.D. Heat scavenging and heat recovery schemes have been around longer than Sadie Carnot. The principles are well known.

I'm in a somewhat unique union of knowledge sets with respect to this situation. I know a fair amount about solar energy and its applications, and a lot more about process engineering, equipment design, heat transfer, fluid mechanics and Thermodynamics, including heat recovery methods for equipment. As a practical matter, such schemes are not cost effective for most all photovoltaic devices at this time. Central concentrating systems need them for cooling the central receivers, but that's not what we're talking about here.

Right now, and because they are not (for many reasons) cost effective, for non concentrating (i.e. flat plate) PV genertors heat recovery devices and schemes remain the province of redneck engineering practitioners, conmen and well-meaning but blissfully ignorant and so, perhaps dangerous tree hugging solar simpletons.

For a primer on sunlight and how solar cells work (transforming sunlight into electricity) see chap. 23 of D & B, it's the best primer on photovoltaic system theory and design I've seen.

Also, and more BTW, I just downloaded the 4th ed. (2013) as a free PDF. Root around and you'll find it.

[ajonestx]

I've seen 1/4" semi rigid wire mesh work to keep most bats/mice out of insulated spaces of any orientation. Anyway, many critters don't seem to like fiberglass insulation any more than most humans like contact with the stuff. For my $$ and for the most trouble-free use, fiberglass batts are hard to beat. Just provide lots of ventilation to insulated spaces and keep liquid water away from the batts or loose fill. Rigid stuff shrinks, sad often smells after a time.

For lots of reasons, I'm not a big fan of rigid insulation, although it does have its uses and applications. The rigid polyiso you mention may be dangerous. When it burns, depending on excess (or actually the lack of sufficient excess) theoretical combustion air, it can liberate a bunch of nasty stuff, hydrogen cyanide being one of them. Just sayin'.

I designed my solar DHW and it was/is pretty standard with a few applicable design tricks I picked up from my real job of engineering and designing power boilers, heat transfer and other process equipment for refineries, chemical plants and the process industries in general. For a very thorough discussion of solar water heating, see D & B (that's Duffie and Beckman BTW). Differential controllers are plentiful and easy to come by.

However, as well running and trouble free as my DHW system is and has been, if I was starting from scratch again, and still heating water with resistance electricity, I'd seriously consider using a combination of PV and a heat pump water heater (HPWH), particularly in a moderate (i.e. mostly nonfreezing) climate. Reason: The annual overall thermal efficiency of my system is ~ 35%-40% after piping and standby losses which is pretty good. However, a decent PVsystem operating at, say, 18 % overall output/input efficiency coupled to a HPWH operating with an annual C.O.P. of something > 2.0 gets me as much or maybe even more in the way of production efficiency for a lot less maint. than most any well designed and well running solar domestic flat plate water heaters require. The freezing problems avoided alone make it worth considering.

On harvesting excess heat from PV devices, the 1st law of Thermodynamics does indeed dictate that if/when a PV device is operating at quasi-steady state, the power output plus any irradiance that's reflected off the device plus any heat rejected to the surroundings by the device will == the irradiance the device is subjected to. For many years now, and about 2-3 times/yr. around here, the subject comes up about how easy it would be to harvest all that excess rejected heat by various and what I call "You Could Just (do this and it would work)" schemes.

Well, the idea is straight forward and it can be done. However, in the past, at this time, and probably for some time into the future, it's not a practical or cost effective idea for most applications. If it was, you'd see it being done on an industrial scale at this time. Q.E.D. Heat scavenging and heat recovery schemes have been around longer than Sadie Carnot. The principles are well known.

I'm in a somewhat unique union of knowledge sets with respect to this situation. I know a fair amount about solar energy and its applications, and a lot more about process engineering, equipment design, heat transfer, fluid mechanics and Thermodynamics, including heat recovery methods for equipment. As a practical matter, such schemes are not cost effective for most all photovoltaic devices at this time. Central concentrating systems need them for cooling the central receivers, but that's not what we're talking about here.

Right now, and because they are not (for many reasons) cost effective, for non concentrating (i.e. flat plate) PV genertors heat recovery devices and schemes remain the province of redneck engineering practitioners, conmen and well-meaning but blissfully ignorant and so, perhaps dangerous tree hugging solar simpletons.

For a primer on sunlight and how solar cells work (transforming sunlight into electricity) see chap. 23 of D & B, it's the best primer on photovoltaic system theory and design I've seen.

Also, and more BTW, I just downloaded the 4th ed. (2013) as a free PDF. Root around and you'll find it.

Fair points on the insulation - I started the insulation experimentation using chicken wire under the batts and that held very well, but the openings were not small enough. I'll look into the option of 1/4-inch to 1/2-inch hardware cloth.

D&B - ha! I just figured out that you were referring to the college engineering book (Solar Engineering of Thermal Processes, Photovoltaics and Wind: Photovoltaics and Wind 5th Edition). I have this one on order and it should arrive in a couple of weeks.

DHW (solar, HP or other) is pretty far down on my list, but it is interesting to think about the options. I appreciate your ideas and the idea about using PV to power a HP to heat water.

Since you brought heat pumps up, do you know of any tools that I can use to evaluate the cost difference between using propane (at $2.16 per gallon) for space heating vs. heat pump (at $0.08 per kWh)? Note: this nonfunctional dual fuel set up is not here in 77008. The programming is messed up and defaults to propane 100%. It should run heat pump as primary with propane as back up - hope to get this fixed in a couple weeks and wonder what it will do to my electrical bill.

on heat recovery, I did not mean to go down that rabbit hole... I was mostly just wondering if fins or heat sinks of some sort have ever been used to reduce the temperature on PV to make them more efficient. I'll look at D&B and see what kind of data they have in there and even with my limited engineering background, my eyes gloss over when I hear people talk about heat recovery - I just can't make the math work in my head. I know they can prove it works sometimes with math - and I know (as you do at refineries), when you have a large process that generates large amounts of heat, it can be cost effective to capture that heat and use it for other purposes. For PV? maybe not.

D&B... free? Ugh... I'll look for it, but admit that I will probably actually read pricey the 5th edition paper book rather than the online version. Online is good for specific topic searches, but not so good for reading (IMO). OK. back to my homework - PV Dummies Chapter 5.

PS: I worked on many building projects "inside the fence" and amazed at the network of piping and systems that you guys put together. I also got to build a couple of labs that housed 12-foot-tall walk in hoods where they assembled little pilot plants. All very impressive stuff!

[bcroe]

. Since you brought heat pumps up, do you know of any tools that I can use to evaluate the cost difference between using propane (at $2.16 per gallon) for space heating vs. heat pump (at $0.08 per kWh)? Note: this nonfunctional dual fuel set up is not here in 77008. The programming is messed up and defaults to propane 100%. It should run heat pump as primary with propane as back up - hope to get this fixed in a couple weeks and wonder what it will do to my electrical bill.

The energy comparison used here, is 1 gallon propane = 27KWh. Crank in the efficiency
of the furnace, the heat pump COP over your temp range, and some prices.

I have seen the price of propane rise from $1 in the summer, to $5.40 in Feb. The electric
eqiivalent (at $0.11/KWh) and a COP of 1 is only $2.80. Bruce Roe

[ajonestx]

The energy comparison used here, is 1 gallon propane = 27KWh. Crank in the efficiency
of the furnace, the heat pump COP over your temp range, and some prices.
0I have seen the price of propane rise from $1 in the summer, to $5.40 in Feb. The electric
eqiivalent (at $0.11/KWh) and a COP of 1 is only $2.80. Bruce Roe

Thank you for this. Are you saying that the electric equivalent of $1.00 per gallon of propane OR $5.40 per gallon of propane is $2.80 per kWh?

Or, to complicate things, does this rough calculation change as the average outdoor temperature (53581) ranges between 70F and 13F.