Different Solar Water Heater Options

[utexas2001nc]

Hi!

I'm not a plumber, just a consumer, trying to weigh the best options for a new solar water heater for my home. We have 4 people in the house (2 bathrooms) and currently a 50 gallon electric tank. I do not run my clothes in hot water. We run the dishwasher about once per day, and could do this in the afternoon to catch the most energy-efficiency. We are in Texas, so the weather is hot and sunny and we don't freeze very often.

I have talked to multiple installers about their different products, and frankly it's a little bit overwhelming because they all recommend different set-ups.

One recommends an 80 gallon solar tank (which gives about 35 gallons of electric-heated water) but they say that even on the cloudiest of days we could expect to get 10 gallons from the solar panels, giving 45 gallons of hot water (almost what we have now with our 50 gallon tank.) They put this tank with 2 4x8 glass collectors (not sure of the brand) and a drainback system.

One person said that 80 gallons is definitely not enough, and we would have to get a 120 gallon tank. This is going to be difficult to fit into my water heater closet. This quote was going to include 1 4x10 Chromagen collector on a closed loop with heat exchanger to the 120 gallon solar tank, no drainback system.

2 other companies sell the "Sungrabber" system by FAFCO, which has 2 2x12 polymer collectors with a drainback system. This gets hooked up to a standard electric tank (80 gallons).

My questions are: is there a specific type/brand/system that works best for energy efficiency/maximum hot water? Has anyone had experience with Sungrabber? Any other general thoughts on the subject?

Thanks so much for any input you may have! I really appreciate it.

 

[Master Plumber Mark]

cost vs saveings....

did any of them tell you how much money or how long
it will take before you reach payback......???

Did they try to dazzel you with a bunch of big numbers??
Showing you with the tax incentives you would break even in no-time????




I think you are in texas and probably do not need
to worry too much about heating the home.... correct???



remember that a lot of these companies are basically "fly by night"
and will not be in business in 5 years to service what they are selling you today...
(I know cause I worked for a bunch of them a long time ago)


and I have torn out a lot of old solar systems that have been abandoned after the tanks failed....no one knew how to revive them after they failed so they sat dormant for a decade
in the garage...
..


their are a lot of differnt drain down systems and they
usually waste a lot of water and can also freeze in colder
climates when something malfunctions... I personally dont like any of them...



If all you are planning to do is heat your water, not heat the home,
I would like to know how much they claim that you are going to save over 5 years....

 

[Sponsor]

 

[99k]

I think Mark makes a very good point about payback. When I lived in Texas, natural gas was widely used to heat the home and hot water. Is natural gas available where you are or strictly electric? Take the total cost of this installation and divide it by the monthly savings you expect ... I suspect the break even will be at least 10 years or more ...

 

[utexas2001nc]

Thanks for the information!

We will be paying from $0-$1000 depending on which system we go with because of the multitude of rebates that are available (from our energy company, our local city council, and the federal tax credit.) (They are quoting me from $4000-$7000 total on the various systems.)
And they have told me that we could expect to save about 50-70% of the energy used to power the water heater. (Which I think would be $200-$300/yr.?)

(We were very surprised to hear that switching to solar could cost us LESS from the outset than going to the local box store and getting a standard water heater. Given the financial incentives, the cost is not a drawback. Really I just want to make sure I don't end up with something that is difficult to maintain or not as advertised in some other manner.)

Unfortunately we only have electric, no gas or propane available.

Thanks again for your help!

 

[Master Plumber Mark]

they are all difficult to maintain

I used to be a NOVAN solar dealer....they were the best
you could install.... they are out of business cause the tax incentives went away back in the late 80s...

It is all smoke and mirrors..... fuzzey numbers.....

fuzzy math on saveings.....


an electric water heater will use about 500 a year to heat the water, and is very very easy to service by any moron
that claims to be a plumber....

a soalr system is a totally different beast....it does not take much to screw one up ...... from a hail storm to whatever else you can think of...

the oil type or glycol systems are better than the drain down kind...caus eof calcium build up in the panels, and other freeze issues...

all soalr systems are hell to service and you will be at the mercy of anyone who claims that they can fix it 5 years from now...


you are trying to squeeze blood from a turnip and their are a lot of turnip salesman out there that tell you it can be done... ( for a very short time I was one)

honestly , you could run 2,000 feet of pex pipe on your roof and tie it into your water heater with a recirualtion pump and accomplish about the same thing for pratically nothing... for at least for the summer months...

you could put in a normal electric water heater and double wrap the heater with two blankets and almost accomplish the same thing


if all you are attempting to save is 250 per year you got to be nuts to fool with one....

for that matter,
why not put up a windmill and power your whole house???

doesent texas have some windy days???

 

[Chris8796]

If you have rebates over 75% I would go for it. I think you can recoup your costs. Since these are basically an electric heater with a heat exchanger with a closed loop, you can always remove the solar system. If the rebates are this high I would imagine alot of systems will be installed, so you may have a better chance at future service. I would agree with the others if you were in an area with very few solar systems.

 

[hj]

solar

Removing the solar is not a good idea unless you also replace the water heater. A solar water heater has the element in the location where the upper element is located, so it NEVER heats the water in the lower two thirds of the tank. This is why they specify that you will only get 30 gallons of hot water from an 80 gallon tank while using electricity. Solar tanks have specific openings and locations for the sensing thermistors, which a conventional tank does not have, so using one of those with a solar panel might not be the most efficient system. I would question the longevity of plastic heat collectors on a full pressure system. They have a tendency to fail, because of exposure, even on low pressure swimming pool systems. unless you are in an area subject to hard freezes a drain down system can be more expensive, and less efficient, than a conventional one. Less efficient because the extra step of going through a heat exchanger will lose some energy.

 

[Mikey]

A comment on payback

I installed a solar system in December of 2005, anticipating savings which would achieve payback in about 5 years. By mistake, we left the WH electricity turned off after the installation, and had plenty of hot water for about 3 weeks, until we had a long cloudy spell and the water started to cool off. So I know it works, and the water is typically around 150 degrees, so it works reaallly good. Single 4x10 panel, 80gal tank, central FL.

Unfortunately, there has been no discernible difference in our electricity consumption, so it's not obviously paying for itself.

In defense of the solar system, I have also installed a high-efficiency airconditioner, triple-pane high-E windows, and R-30 insulation throughout over the last 5 years. I have never seen any significant reduction in kWH consumed as a result of any of this. On a 12-month moving average basis, my daily kWH consumption is 35.1, with a standard deviation of 2.7 over the last 13 years.

I'm puzzled. I feel good about doing all this, but I'd feel better if my electric bill were decreasing dramatically.

 

[Dana]

I installed a solar system in December of 2005, anticipating savings which would achieve payback in about 5 years. By mistake, we left the WH electricity turned off after the installation, and had plenty of hot water for about 3 weeks, until we had a long cloudy spell and the water started to cool off. So I know it works, and the water is typically around 150 degrees, so it works reaallly good. Single 4x10 panel, 80gal tank, central FL.

Unfortunately, there has been no discernible difference in our electricity consumption, so it's not obviously paying for itself.

In defense of the solar system, I have also installed a high-efficiency airconditioner, triple-pane high-E windows, and R-30 insulation throughout over the last 5 years. I have never seen any significant reduction in kWH consumed as a result of any of this. On a 12-month moving average basis, my daily kWH consumption is 35.1, with a standard deviation of 2.7 over the last 13 years.

I'm puzzled. I feel good about doing all this, but I'd feel better if my electric bill were decreasing dramatically.

If your bill isn't going down with all of that, it just means that HVAC and hot water weren't you're biggest energy draws- time to figure out what IS!

In the same period did you get a plasma TV and a TIVO?

Do you dry your clothes with an electric dryer?

Is all of your lighting high-efficiency fluorescent or LED?

1000kwh/month is close to the national average, but it's a pretty low-efficiency average- something has to be using that power...

In FL it's unlikely that hot water was ever anything like 10% of your bill unless you have a large family with a huge laundry load. The temperature of the water coming in from the street is typically 20-30F higher than what you'd find in the cooler parts of the US. I live in MA, heat my HW with gas, but I do dry my clothes with electricity, and average about 17-18kwh/day for a family of 3. We don't live in the dark by any means, but at $0.18/kwh most appliances are now Energy Star, and all lighting is high-efficiency. We have central AC, but it isn't used NEARLY as much as a typical (even well-insulated) FL duty-cycle.

FWIW: R30 doesn't always mean much in AC dominated climates- actual performance can depend on insulation type & method of installation. The ubiquitous fiberglass batting may be great at blocking conducted heat transfer, but is somewhat translucent to radiated heat. (More is always better, but R30 doesn't always perform at R-30.) Not sayin' that's the problem, but I'm just sayin'...

As for which solar installation to go for in Texas, the BIGGEST one of course! With subsidies that high even the cost of the most expensive would have reasonable payback, and is more likely to support the load than lesser unit. 120gallons is not oversized for 4 adults. You may need more than a single 40sq.ft. of panel, but maybe not. 20-30 gallons of storage, 10-15sq.ft. of glazed flat plate per person, is the rule of thumb, which puts you at the low end of the range, which may be fine where you are- depends a lot on the location. Two 4x8s with the 80 gallon tanke would surely be enough glazing, but it's on the low end for storage- the opposite end. Eitehr may be find. But if 64sq. ft too much glazing for your location you may run into high tank-temps and need heat-dumping for part of the season (often achieved by re-radiating the excess heat back to the sky by running the panel pumps at night to cool the tank back down.)

When in doubt, go larger- particularly on storage. With an oversized tank the panels can run cooler longer, at higher efficiency, and a bigger volume of lower temp water holds as much heat as lesser volumes of higher temp water, but the higher-temp water kills the operating efficiency. If it's A,B, or C, go with the 4x10 panel with the 120gallon tank- it's probably the most-efficient. With the cooler operating temps the 40' of glazed area may in fact outperform the 64 square feet (2- 4x8s) feeding the 80gallon tank, much of the time, and will be less likely to need summertime heat-dumping. (Heat dumping adds to the electric bill, since the duty cycle of the pumps goes way up.)

Using an electric HW tank for solar storage isn't great except as a low-budget retrofit. They're not purpose-designed for solar which means they, don't have the same insulation levels which leads to higher standby losses, and without designed-in tank stratification the collectors run hotter/less-efficiently. If with subsidy they're cost-negative or zero-cost, fine, but what you get out of it will be a lot less over time.

 

[Thatguy]

The average insolation for San Antonio is 5.3 kwh per sq. meter per day, so a one square meter panel at 80% eff. would give you 160w all the time, on average.
http://www.builditsolar.com/References/Calculators/Collector/ColEfic.htm

You'd also need to know some kind of percentile figure for cloud cover to decide the size of the storage tank. 120 gallons (1100# of water) raised 90°F stores ~1 therm = ~30 kWH of energy. Your incoming water temp in summer might be 70°F.

Two of us use 35 therms/mon of NG for heating water. With a 75% efficient heater this is 1100w all the time.

This helps to keep all the units straight.
http://www.onlineconversion.com/



Mr. Mikey, if this
http://en.wikipedia.org/wiki/Analysis_of_variance
can't tell a difference between your old and new setups to some reasonable confidence level, I'd have to wonder what's going on.
I have also heard that people who changed to high eff. furnaces (let's say 80% to 95%) didn't notice anything, either.
It's strange.

 

[Mikey]

Thanks for the comments, all. I'm now trying to find what my greatest electrical load is, but still assume it's the heat pump. A friend and I are thinking about getting into the energy-audit business, and boy, have I got a test case for us!

I haven't done any ANOVA work in 40 years, but have to collect some data first anyway, so I'll have time to refresh my memory.

 

[Mikey]

Forget the big loads...

look at the little things. So far, I've used a Kill-a-Watt device (about $25) to measure a few small loads -- two computers, two refrigerators, and the plasma TV that Dana wondered about. Other than the TV, which is little-used, these account for most of what I call the "idle current" of the house. I've got to refine the numbers, but the first cut shows these items account for about half the total annual consumption. I'd really like to monitor the load at every circuit breaker in the main panel, but so far haven't found a cheap way to do that. Maybe I'll take a Kill-a-Watt apart and see if it can be adapted to do that.

 

[NHmaster]

www.caleffi.com download idronics3 Read it thouroughly.

www.buderus.com Very good solar equipment

Don't argue with me JUST DO IT!

 

[Bill Arden]

I'd really like to monitor the load at every circuit breaker in the main panel, but so far haven't found a cheap way to do that. Maybe I'll take a Kill-a-Watt apart and see if it can be adapted to do that.

They make clamp on Kwh Meters.

I worked with the Emetcon units awhile ago, but I don't have any left. I do have a palette of 2S meters and have thought about wiring up a base to the Hot water heater...

But then I just added a 8 inch thick blanket and turned the breaker off.
I can go days before it cools off and then I can use my amp meter to see how long it runs before it's hot again.

In the end I decided that I don't use very much hot water. Of course that could be a personal hygiene problem.

You should also look into other options like off-peak. Switching my house to off-peak hot water only requires me to add a second 50 gal hot water heater so that I have the required 100 gallons.

edit:
Here is an interesting link.
http://www.aceee.org/consumerguide/waterheating.htm
Interestingly they don't list 6 Hr off-peak.
Normal Electric rate .10
off-peak .06
Doubling the number of tanks to get to 100 gallons would increase my standby heat loss, but the lower rate would more than make up for it.

 

[Thatguy]

They make clamp on Kwh Meters.

I worked with the Emetcon units awhile ago, but I don't have any left. I do have a palette of 2S meters and have thought about wiring up a base to the Hot water heater...

But then I just added a 8 inch thick blanket and turned the breaker off.
I can go days before it cools off and then I can use my amp meter to see how long it runs before it's hot again.

I wired a 120v 4w analog electric clock to my 240v water heater element through a dropping resistor.
Before insulating the tank it ran 5 min out of 5 hrs. After, 5 min out of 7 hrs.

 

[Dana]

The average insolation for San Antonio is 5.3 kwh per sq. meter per day, so a one square meter panel at 80% eff. would give you 160w all the time, on average.
http://www.builditsolar.com/References/Calculators/Collector/ColEfic.htm

You'd also need to know some kind of percentile figure for cloud cover to decide the size of the storage tank. 120 gallons (1100# of water) raised 90°F stores ~1 therm = ~30 kWH of energy. Your incoming water temp in summer might be 70°F.

Only unglazed collectors at VERY low delta-T between the water and ambient air temp come anywhere near 80%. I wouldn't use that in any kind of calc. Assume 50% for an annualized average for a single-glazed panel & reasonable DHW temps. It'll be somewhat higher efficiency with a bigger storage/collector-area ratio (the 120gallons/40sf panel) somewhat lower for the lower ratio unit (80gallons/64sf), but probably no higher than 60% or lower than 40% for either.

Two of us use 35 therms/mon of NG for heating water. With a 75% efficient heater this is 1100w all the time.

This helps to keep all the units straight.
http://www.onlineconversion.com/

That seems unusually high monthly-average NG usage for simply DHW for two people. What are you using for a hot water heater, and is 75% your presumed efficiency, or the presumed efficiency of the solar/electric water heater?

Actual use patterns make a HUGE difference in actual efficiency. The EF number doesn't mean squat with NG fired tank heaters- it's all about total volume uses, but tankless on-demands tend to come in no worse than 10-15% below their EF in worst-case real-world patterns. Worst case patterns for tankless is draws of 2 gallons or less, with very few draws of over 10 gallons. For NG tanks, it's primarily total volume that counts- EF tests are run at ~60gallons/day- if you use more than that the efficiency goes up assymtotically to a hard maximum of ~79-80% efficiency @ 100% burner duty-cycle. But at 28 gallons/day NG tanks drop below 50% efficiency.

In short, a tankless with an EF of 0.82 can run anywhere from 0.67-0.82 under any real world conditions, but a "high efficiency" NG tank heater with a 0.68EF could run anywhere from 0.40-0.75 in the real world, depending on volume of load. (Used in a combi space-heating/DHW load situation it might go as high as 0.78.)

Mr. Mikey, if this
http://en.wikipedia.org/wiki/Analysis_of_variance
can't tell a difference between your old and new setups to some reasonable confidence level, I'd have to wonder what's going on.
I have also heard that people who changed to high eff. furnaces (let's say 80% to 95%) didn't notice anything, either.
It's strange.

With heating equipment the largest immediate factor in getting anything like the rated AFUE-type efficiency out of it is having the burner properly sized to the actual peak "design day" load. It's common to find furnaces 100-300% oversized, especially in older housing that has seen a number of upgrades to the building envelope (better insulation, better windows & doors, etc.). An 80% AFUE type furnace that is 300% oversized doesn't dramatically underperform a 90% furnace that's 300% oversized- they both SUCK compared to what they would do if better matched to the load. A properly sized or undersized 80%AFUE furnace can/will outperform a 300% oversized 90%AFUE furnace.

To optimize the efficiency of whatever you're installing, any time you're replacing a furnace or hydronic boiler, insist on a careful whole house heat-loss calculation (ACCA Manual-J method or similar), and don't oversize the unit by more than 10% (in fact, undersizing it by 15% is usually "safe", in terms of actually ever feeling cold.) AFUE numbers are based on about a 33% average duty cycle, which means on the coldest days of the year the thing will run almost constantly. If that's not happening, odds are it's significantly oversized, and you can subtract 10-15% (or more) off the rated efficiency, eaten up in cycling losses.

The majority of replacement furnaces that get installed are either the same or one size larger in output (to be on the "safe" side, as in, "The customer will never call the installer screaming that they're too cold 'cuz it's not keeping up.") This is the WRONG thing to do, 100% of the time. Most of the time that "safe" factor was budgeted in by the original contractor, who only ball-parked it in the first place, and in the intervening decades the building envelope has been improved, lowering the heat load.

There are similar cycling loss issues related to oversized AC equipment too- Manual-J or similar load calculations need to be applied here as well.

 

[Thatguy]

Assume 50% for an annualized average for a single-glazed panel & reasonable DHW temps.

That seems unusually high monthly-average NG usage for simply DHW for two people. What are you using for a hot water heater, and is 75% your presumed efficiency, or the presumed efficiency of the solar/electric water heater?
Presumed; we use a total of 160 gal/day.


Actual use patterns make a HUGE difference in actual efficiency.
Didn't know that.

It's common to find furnaces 100-300% oversized, especially in older housing that has seen a number of upgrades to the building envelope (better insulation, better windows & doors, etc.).
Our 83% furnace runs 1/4th of the time in winter.
We did get better windows, but I should scrounge up the NG bills from before the windows were put in.

A properly sized or undersized 80%AFUE furnace can/will outperform a 300% oversized 90%AFUE furnace.
Maybe that's why people who switch to high eff. don't see it on their bill.

don't oversize the unit by more than 10% (in fact, undersizing it by 15% is usually "safe", in terms of actually ever feeling cold.)
I've heard -10%

AFUE numbers are based on about a 33% average duty cycle, which means on the coldest days of the year the thing will run almost constantly. If that's not happening, odds are it's significantly oversized, and you can subtract 10-15% (or more) off the rated efficiency, eaten up in cycling losses.
Good. That means my house is not as leaky as I thought, based on HDD and input BTU/hr.

The majority of replacement furnaces that get installed are either the same or one size larger in output (to be on the "safe" side, as in, "The customer will never call the installer screaming that they're too cold 'cuz it's not keeping up.") This is the WRONG thing to do, 100% of the time. Most of the time that "safe" factor was budgeted in by the original contractor, who only ball-parked it in the first place, and in the intervening decades the building envelope has been improved, lowering the heat load.

Thanks for the benchmarks.

 

[Bill Arden]

I wired a 120v 4w analog electric clock to my 240v water heater element through a dropping resistor.
Before insulating the tank it ran 5 min out of 5 hrs. After, 5 min out of 7 hrs.

You can use that to calculate the standby power needed per month.
Overtime you can also measure your average power usage.

Assuming it's a 4500watt element you have to multiply the time(in hours) by 4500.

so 5 min every 5 hours would be...
(5 / 60) * (24/5) = .4 hours per day.
.4 * 31 days = 12.4 hours per month
12.4 hours * 4500 watts = 55.8Kwh per month.
at $0.10 per Kwh that's $5.58 per month.

so 5 min every 7 hours would be...
(5 / 60) * (24/7) = .28 hours per day.
.28 * 31 days = 8.85 hours per month
8.85 hours * 4500 watts = 39.8Kwh per month.
at $0.10 per Kwh that's $4 per month.

For the ROI calculations you can use the difference since only the standby power is reduced.
$5.58 - $4 = $1.58 per month savings or $18.96 per year.

if I remember right... a blanket costs about $20 so the ROI would be.
$20 / $18.96 = ~1 year

 

[protech]

First let me say that Fafco's system is trash. Stay away if you know what's good for ya.

As far as the estimates you received, I'm going to assume that they were drain back systems and not direct(open loop) systems. If that’s the case I would recommend a 120gallon tank with 2 4x8(32 square foot) collectors for a decent solar fraction. You should get 85-90% with that setup for your area.

Hi!

I'm not a plumber, just a consumer, trying to weigh the best options for a new solar water heater for my home. We have 4 people in the house (2 bathrooms) and currently a 50 gallon electric tank. I do not run my clothes in hot water. We run the dishwasher about once per day, and could do this in the afternoon to catch the most energy-efficiency. We are in Texas, so the weather is hot and sunny and we don't freeze very often.

I have talked to multiple installers about their different products, and frankly it's a little bit overwhelming because they all recommend different set-ups.

One recommends an 80 gallon solar tank (which gives about 35 gallons of electric-heated water) but they say that even on the cloudiest of days we could expect to get 10 gallons from the solar panels, giving 45 gallons of hot water (almost what we have now with our 50 gallon tank.) They put this tank with 2 4x8 glass collectors (not sure of the brand) and a drainback system.

One person said that 80 gallons is definitely not enough, and we would have to get a 120 gallon tank. This is going to be difficult to fit into my water heater closet. This quote was going to include 1 4x10 Chromagen collector on a closed loop with heat exchanger to the 120 gallon solar tank, no drainback system.

2 other companies sell the "Sungrabber" system by FAFCO, which has 2 2x12 polymer collectors with a drainback system. This gets hooked up to a standard electric tank (80 gallons).

My questions are: is there a specific type/brand/system that works best for energy efficiency/maximum hot water? Has anyone had experience with Sungrabber? Any other general thoughts on the subject?

Thanks so much for any input you may have! I really appreciate it.

 

[ARSolar]

Having researched solar hot water for quite some time, I've found that www.heliodyne.com and www.aetsolar.com are two of the best systems out there. Heliodyne has the best solar panel as far as ratings but AET supposibly has a very good panel as well.

Both drainback systems and glycol systems are used very sucessfully in this country for closed loop systems.

If I were installing a new system in my home, I would demand the best such as Heliodyne in either a drainback or glycol configuration. With your incentives get the best!!!

Have you settled on a system?

Good Luck,
AR