We have a 3 year old 2 IBA and 5 SS and I have been thinking since we got it that the roof (flat roof with a 3 foot mansard) is about 20'x120' of USABLE space that we could mount solar panels on. Has anyone ever tried that? Was there a payback? I think I can get an small business USDA grant for about 25% of the cost but not sure if I want to sink it in. Thoughts....actual experience? Any help appreciated.
Solar on the flat roof
- Thread starter trentu
- Start date
bigleo48
Active member
- Joined
- Sep 6, 2007
- Messages
- 1,887
- Reaction score
- 0
- Points
- 36
Trentu,
I had read a very basic article of a carwash owner who had installed a solar panel on the roof. It didn't get into to many details, but said he got some grants and the payback was 7 to 10 years. It sounded like he also did it for the publicity and the "green" perception.
Now I think what he was doing is generating electricity to preheat the water. Since he was up north, he could not just circulate the water through a panel like a pool (or it would freeze in the winter).
This is something I would like to look into as well...BigLeo
I had read a very basic article of a carwash owner who had installed a solar panel on the roof. It didn't get into to many details, but said he got some grants and the payback was 7 to 10 years. It sounded like he also did it for the publicity and the "green" perception.
Now I think what he was doing is generating electricity to preheat the water. Since he was up north, he could not just circulate the water through a panel like a pool (or it would freeze in the winter).
This is something I would like to look into as well...BigLeo
PaulLovesJamie
rural 5 bay SS
I checked into it recently at the PA Renewable Energy Festival http://paenergyfest.com/
Specifically I was going to do a small project at home, then if it worked out put in a larger system at the CW.
For home water heating, I was finally able to get a manufacturer to tell me the btu rating. It bothered me that nobody would answer that question - now I know why. The systems for heating water for home use only produce 35,000 btus per day. Thats "enough" for a family of 4's hot water usage... supposedly. For comparison purposes, my woodburning stove produces 60,000 btus. Per HOUR. Here in PA the installed price for a solar domestic water system is about $6k, which runs to about an 8 - 10 yer payback at todays electricity rates. Not a good business decision. Unless you can get mileage out of the "green" image.
Photovoltaics -- nobody would talk about payback periods, they avoided it like I was asking about their vd problem in front of the wife. Finally one guy got ticked off at me and said "yes the payback is 15-20 years, thats not why you do solar you $%!!@"
Nuff said, I'm not doing solar in the short term.
Now, dont get me wrong - I want to. Badly. Just not a good business decision unless there are other measurable benes.
Specifically I was going to do a small project at home, then if it worked out put in a larger system at the CW.
For home water heating, I was finally able to get a manufacturer to tell me the btu rating. It bothered me that nobody would answer that question - now I know why. The systems for heating water for home use only produce 35,000 btus per day. Thats "enough" for a family of 4's hot water usage... supposedly. For comparison purposes, my woodburning stove produces 60,000 btus. Per HOUR. Here in PA the installed price for a solar domestic water system is about $6k, which runs to about an 8 - 10 yer payback at todays electricity rates. Not a good business decision. Unless you can get mileage out of the "green" image.
Photovoltaics -- nobody would talk about payback periods, they avoided it like I was asking about their vd problem in front of the wife. Finally one guy got ticked off at me and said "yes the payback is 15-20 years, thats not why you do solar you $%!!@"
Nuff said, I'm not doing solar in the short term.
Now, dont get me wrong - I want to. Badly. Just not a good business decision unless there are other measurable benes.
washnvac
Well-known member
I just got done my second PV project, in Delaware. I put on a 9kW system on a 6/12 pitch metal roof facing at 180 degress and no shading. (perfect conditions). Total system cost was $75,400. My state rebate was $37,700 (50%). I did not have to pay this up front, as my installer will wait for the rebate. So I only had the $37,700 to pay. System pay back is exactly 10 years based on current electric rates at my location
($.144 per kW). Then I get a 30% fed tax credit and 5 year accelerated depreciation on my remainder cost of $26,390. Warranty is 25 years on panels, 10 years on inverter, 5 years on labor. Expected panel life is 35-40 years. Bonus pay-- the electric utility will have to pay me for each megawatt I generate yearly (renewable energy credits.) These are anticipated to be $100-250 per credit. I will have 10-12 per year with this system. So that will be an extra $1200-3000 depending on price, once they are determined. I also did a 40 square foot solar hot water system at a location in Maryland (9 bay s/s). I removed a 690,000 btu propane boiler. I installed the solar with one 199,000 btu Rinnai natural gas. This is doing the same job the big boiler did. (amazing, huh?) Total system cost was $10,000, the rebate from Maryland was $2000; so my net was $8000. Monthly fuel bill dropped $400-550. (installed in February '08.) That pay back will be less than 2 years with the fed tax credit. I also did a 6kW PV system at this location, but the payback will be a bit longer because the rebates were not as good in Maryland. The rebates are key for making any project work. I would highly recommend solar for a car wash. The hot water is the easiest and cheapest to start with. I think you need at least a 35% rebate to do PV.
($.144 per kW). Then I get a 30% fed tax credit and 5 year accelerated depreciation on my remainder cost of $26,390. Warranty is 25 years on panels, 10 years on inverter, 5 years on labor. Expected panel life is 35-40 years. Bonus pay-- the electric utility will have to pay me for each megawatt I generate yearly (renewable energy credits.) These are anticipated to be $100-250 per credit. I will have 10-12 per year with this system. So that will be an extra $1200-3000 depending on price, once they are determined. I also did a 40 square foot solar hot water system at a location in Maryland (9 bay s/s). I removed a 690,000 btu propane boiler. I installed the solar with one 199,000 btu Rinnai natural gas. This is doing the same job the big boiler did. (amazing, huh?) Total system cost was $10,000, the rebate from Maryland was $2000; so my net was $8000. Monthly fuel bill dropped $400-550. (installed in February '08.) That pay back will be less than 2 years with the fed tax credit. I also did a 6kW PV system at this location, but the payback will be a bit longer because the rebates were not as good in Maryland. The rebates are key for making any project work. I would highly recommend solar for a car wash. The hot water is the easiest and cheapest to start with. I think you need at least a 35% rebate to do PV.
PaulLovesJamie
rural 5 bay SS
Agreed - if I could get the kind of rebates you're talking about, I would probably do it.
The solar HW systems I looked at were also approx 40 sq ft, & the best only produced 35,000 btu per day - I think the 200,000 rinnai is per hour. I hate to say this, but I suspect that your old boiler was way oversized, & simply replacing it accounts for your savings.
Anyway - any chance you could get the btu ratings on your solar hot water system? What is the brand & model? Maybe I just didnt talk to the right manufacturers yet.
PaulLovesJamie
rural 5 bay SS
Yes. ........
(That 10 character minimum is a pain sometimes - hence the ".........." after the "yes.")
washnvac
Well-known member
MEP...the hot water system is separate from the PV. It is four 2' X 5' solar hot water panels. (40 sq. ft. was needed to get the rebate.) It is a closed loop system, so I can use it year round. The solution is heated at the panels, then circulates down to a 120 gallon solar thermal storage tank. This solar heated solution circulates as long as there is a 5 degree differential between tank and panel. (adjustable) My fill water to my hot water reserve tank (40 gallons) is filled from the 120 gallon tank. So basically this water is pre-heated. Then I have a coil in the 40 gallon tank that runs to the Rinnai; this will bring the temp up to 110-120F for use out to the bays. My average "free" increase in water temp is 33 degrees, with a high of 45. (In other words the 57 F incoming water is heated to around 85-95, then the Rinnai picks up the rest) . Paul, I will get the actual specs/ratings on a later post. I am actually going to add two more panels to this system within the next two weeks. This should afford mostly free hot water in the Summer days, except for the cost of running the 90 watt circulator. I will try to grab some pictures later this week to post, also.
washnvac
Well-known member
Oh, I'm sorry MEP. I read right by that post. At least that explains it for others.
bigleo48
Active member
- Joined
- Sep 6, 2007
- Messages
- 1,887
- Reaction score
- 0
- Points
- 36
Why invert the DC to AC...the loss would be about 30% I believe.
washnvac
Well-known member
Paul: you are correct in your ratings. My panels are rated at 8000 btu per day. I have four, so that is 32000 btu per day. So that basically means I could raise the temp of 4000 gallons of water 1 degree. Or in my case, I seem to be getting a 30 degree or so rise. That would mean I am only heating 133 gallons at that temp. That just does not seem correct. I wish I had the Rinnai only for a month or two before solar went online. I am really not interested in installing gadgets to monitor water usage at certain times to determine exact savings. I know I am saving when it is 40 degrees outside, the roof read on the solar panels is 105, and the solar storage tank is running 75-80, with bays being used. In the Summer the circulator is running 9-10 hours, costing me only 11-13 cents per day. Like I said previously, I am going to add two more panels. So I will update how that works out. I will still post pics later.
PaulLovesJamie
rural 5 bay SS
Honestly, in this case I'd prefer to have been wrong.
Thank you very much for the follow-up info, I appreciate it.
Looking forward to pics too - I'm interested in this kind of stuff, please do show it off!
Last edited:
