Image Credit: Martin Holladay
More Musings of an Energy Nerd
I installed my solar hot water system about six years ago. It’s a good system. I have two 4’x8’ AE-32 flat-plate collectors (manufactured by Alternate Energy Technologies), a Superstor Ultra stainless-steel tank (at 80 gallons, it’s a little small, but it’s what I could afford), and an El Sid DC pump from Ivan Labs. Since I installed the equipment myself, it cost significantly less than a professionally installed system.
This year I had my first maintenance issue with my solar thermal system. In March, the snow covering my solar collectors finally began to melt. Unfortunately, the solar collectors were bare of snow for several sunny days, while the small PV modules that provide power for the PV-direct pump were still snow-covered. Since the sun was shining on the solar thermal collectors but the pump wasn’t circulating the glycol solution, the fluid overheated. A significant amount of fluid was released through the system’s pressure/temperature relief valve before I realized what was going on.
The solution was fairly simple, but it was a pain. I bought a couple of gallons of glycol. I drained the old fluid from the system, and introduced a new antifreeze solution into the system, the same way I did when I commissioned the system a few years ago. The whole process took a few hours.
In the future, I’ll need to move the PV modules that are wired to the DC pump to a different location, so the snow will melt from the modules at about the same time that the snow melts from the collectors. That work will also take me a few more hours.
If I had had to hire a solar thermal contractor to perform this maintenance work, the work would have cost hundreds of dollars, eating into…
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43 Comments
An expansion tank, something
An expansion tank, something a regular plumber could handle. Since it is not on the potable side a plumber is not even required, any heating guy could do it. Start dialing for plumbers, if everyone refuses, stop telling them it is solar.
What is the payback on the expansion tank on a regular system?
gas hot water tanks last around 12-15 years, yeah they only cost a few hundred, but professionally installed? By a Boston plumber? Betcha that's a grand too.
SO if they had a regular gas hot water heater, they would no doubt be a few years away from installing their second one right now.
High end stainless water heaters are also pricey, and not without maintenance. I just had the thermowell replaced in my superstore. Twasn't free.
Sometimes you get lucky and systems outlive their design life, sometimes you do not. I don't think your brother is outside the norm in maintenance costs for a standard system, considering what city plumbers cost.
Response to Keith Gustafson
Keith,
You wrote, "I don't think your brother is outside the norm in maintenance costs for a standard system."
That was precisely my point.
I agree that any plumber could replace the expansion tank. But could any plumber:
(a) specify the proper antifreeze,
(b) correctly choose the ratio of antifreeze to water,
(c) know the best pressure to use when charging the closed loop system with antifreeze,
(d) know how to purge air leaks from the system, and
(e) be able to verify that the solar hot water system was operating properly once it was repaired?
Perhaps. But perhaps not.
Another response to Keith Gustafson
Keith,
I agree that ordinary water heaters also require maintenance, and also require regular replacement. But homes with solar hot water systems almost always have an ordinary water heater in addition to their solar thermal equipment.
Since homes with solar hot water systems have additional components -- collectors, a pump, an additional storage tank, and additional expansion tank, a heat exchanger, additional tubing, and in some cases a control -- compared to homes that have only a conventional water heater, homeowners with these systems take on additional maintenance duties (and incur additional repair costs) compared to homeowners who only have a conventional water heater.
And even if the homeowner can afford to write the checks to pay the plumber, these maintenance hassles require time from the homeowner -- calling contractors, meeting contractors, and in some cases arranging for time off work to make sure the work happens.
>>>>>(a) specify the proper
>>>>>(a) specify the proper antifreeze,
(b) correctly choose the ratio of antifreeze to water,
(c) know the best pressure to use when charging the closed loop system with antifreeze,
(d) know how to purge air leaks from the system, and
(e) be able to verify that the solar hot water system was operating properly once it was repaired?<<<
One would hope there was documentation for the majority of these issues. IF not, then actually a good heating guy does this sort of thing all the time. A bad heating guy will make a mess of it.
If you have ever had an old oil fired fhw system in a multi story house, a good heating guy is indispensable
And the computer that runs my hot water system will die one day and I hope it is included in the fine print of my maintenance contract..............
Response to Keith Gustafson
Keith,
It sounds like we are in agreement. A contractor familiar with hydronic systems could probably do a good job -- but he still might not want the liability associated with fixing a solar thermal system, and he might not want to climb a ladder to check the top of the loop to verify that all of the air had been purged from the system.
"One would hope there was documentation"
Keith,
You wrote, "One would hope there was documentation for the majority of these issues." One would hope that, wouldn't one? But there wasn't any documentation at all for the system when Peter and Elana bought the house, as far as I know -- and the lack of documentation is fairly typical, I'm afraid.
There are two problems here:
1. Most contractors are lax about paperwork, and fail to provide homeowners with a good three-ring binder that documents everything the homeowner needs to do to maintain their equipment.
2. When a house is sold, the transfer of this kind of any paperwork often gets lost in the shuffle -- especially if the house is being sold due to a divorce or mortgage default. (But we all know that divorce and mortgage default are rare in the U.S., right?)
Response to AJ Builder
AJ,
Thanks for the offer. (I know it wouldn't take very long for someone to suggest that I should be the one to replace Peter's expansion tank...)
Rare bird some of us apparently
I should post some pictures... have handed over the three ring binder for two decades now. Climb on a roof, purge, change expansion tanks, install the right tank to start with... yup just changed two tanks, and and FYI...
There are better expansion tanks than the least expensive. For not much more a tank will come with a plastic liner. About 2 twenty dollar bills to cover the upgrade
Martin, you and or I need to go change the tank for your bro. I'm in.
What size tank, have tank will travel... here's an on line source for a small tank. 2.5 twenty dolla bills...plus shipping. http://www.supplyhouse.com/Amtrol-140-705-RX-15-Radiant-Extrol-Expansion-Tank-2-Gallon-Volume-7362000-p
aj
Raining today... address and
Raining today... address and I'm on the road....
:)
Rube Goldberg vs. K.I.S.S.
The underlying problem with active solar thermal is the complexity (=vulnerability) of the systems. The complexity also adds cost, in hardware, installation, and maintenance/repair.
Evacuated tube batch water heaters (the most common type of home solar heater in India, China and Latin America, and the middle east. eg: http://hainingjinhong.en.alibaba.com/product/254651229-209471028/batch_solar_water_heater.html http://energysavingtrust.files.wordpress.com/2011/07/solarmed2.jpg ) have far fewer issues- no pumps, no glycol, no controls. But they have climate limitations due to freeze potential of the plumbing to/from the (insulated) rooftop tank. In US climate zones 3 and lower this is easily managed, in zones 6 & 7 it's a bit harder.
Still, the glycol loop & flat panel approach is probably more common in the US for aesthetic rather than functional reasons.
In cold climates dumb- control drain-back systems using flat panels tend to be less problematic than glycol loop systems. A primer on the principle:
http://www.builditsolar.com/Projects/WaterHeating/DBAirLine/DBAirLine.htm
It's still a Rube Goldberg contraption, but with fewer parts, as well as fewer vulnerabilities when things like pumps or controls fail.
drainback
I'm surprised you're not using a drainback system. Aren't they much more reliable than glycol? PV powered pumps paired with a drainback system makes the most sense to me.
Martin did an article on the
Martin did an article on the boys in Maine that do it right
Response to AJ Builder
AJ,
That wasn't me -- that was Chris and Phil, the Green Architects. Here is the link:
Solar Thermal: Types, Cost, and Investment.
Complicated?
Funny, I've always thought of PV systems being more complicated and more of a maintenance challenge...
I suppose it depends on perspective.
I'll bet Martin's solar thermal system doesn't use any controllers and possibly he could have put off having to do the maintenance he described if, in the first place, he had positioned his PV panels wherever he ends up moving them.
Reply to Lucas Durand
Lucas,
I've had PV panels on my roof for 34 years, and I have never performed any maintenance on my PV panels. I've never even washed them.
I have replaced my inverter once. My charge controller was also replaced after a lightning strike.
My solar thermal system is fairly simple, as you correctly guessed. It has no controller -- just a PV-direct DC pump.
You are correct to point out that if I had put my PV modules in a better spot, my system might not have needed any maintenance. But hindsight doesn't prevent maintenance problems. Every time something breaks, it's usually possible to say, "This never would have broken if only I had [fill in the blank]."
I'm glad I installed my solar thermal system. But I also think that (a) the system is unlikely to ever save enough energy to justify its cost, and (b) the system will probably require more maintenance than my PV system.
Reply to Martin
Martin,
You're right of course.
But foresight sometimes does ;-)
Hindsight and foresight
Lucas,
Unfortunately, none us gets smart enough to have perfect foresight until we have made enough errors to gain insight -- through hindsight, of course.
The only reason ....
we are still discussing solar thermal is because none of the large brands
have come out with their air water heat pump, which are already going on in several euro and asian countries.
I still don't understand why neither Fuji or Mitsu adapted their newer cold climate optomised exterior units to provide with hot water ... beats me
Then we all know that a air heat pump water heater in 1 piece is a gogo in any of the south usa climates , and probably will have less complex issues and less maintenance.
( replacement cost is lower also )
Response to Terry Lee
Terry,
Q. "If you were designing a cost effective system today that would supply heating and cooling and DHW to a tight energy-efficient building, how would do it?"
A. This is a huge topic, and a high percentage of the articles on the GBA site are devoted to answering it. The answer depends on the type of house under discussion, the climate, site-specific issues, homeowner expectations, and the homeowner's budget, among many factors. If these issues are new to you, I suggest that you start with these articles:
Heating a Tight, Well-Insulated House
Choosing HVAC Equipment for an Energy-Efficient Home
All About Water Heaters
Q. "Does PV make sense it climate zones where the sun only shines say 50% of the time yet?"
A. The answer depends on several factors, including the cost of PV system installation and the local cost of grid-supplied electricity. PV systems make more sense in areas of the country where electricity is expensive. Insolation is only one aspect of the calculation.
Here is a link to an insolation map of the U.S.: Insolation map. Many PV arrays have been installed in areas of the country (including Vermont) with relatively low insolation levels.
Here is a link to a free online calculator that will tell you how many kWh per year you will get from your PV system in a variety of U.S. locations: PV Watts.
Hail damage to PV arrays is rare, as far as I know, but anyone concerned about this issue should talk to their insurance company.
Lessons Learned
So Martin(or anyone), if you were designing a cost effective system today that would supply heating and cooling and DHW to a tight energy efficient building how would do it?
Martin, to clarify....your pump/collector is packing snow since they are too close to one another?
Does PV make sense yet in climate zones where the sun only shines say 50% of the time yet? I read some are saying PV is down to $ .4 KWH is some locations and will be @ $.2 KWH by 2007, not sure that includes maintenance? Grid is $.10 here in midwest.
We replace ALOT of hail and wind damaged roofs in tornado alley every year, we do not have a lot of roof mounts yet, but if we did the bid would go up. What do they drill the mounts into the rafters through the cladding and seal them? We see roofs blown off every year from high wnds/tornado's, I can see flying PV debris causing more damage than 2 x 4's.
We have more wind than sun in the plains or as much for hybrid but, I read turbines are less efficient and more maintenance.
Practical Design-Builds
Martin: A. The answer depends on several factors, including the cost of PV system installation and the local cost of grid-supplied electricity. PV systems make more sense in areas of the country where electricity is expensive. Insolation is only one aspect of the calculation.
You right, it does depend on A LOT of factors… You know I read ALOT of articles out here and on other sites on the subjects. It can make one’s head swim, and that is coming from someone with ALOT of design and hot box testing experience in a different industry, but related.
I read ALOT of thermodynamic, aerodynamic, fluid dynamic, heat transfer, HVAC theory on the "Building Science" sites and you are right, there are MANY variables for one trying to put the 'puzzle' together, especially readers with a limited tech background.
IMHO, it would beneficial coming from experts such as yourself that spend a lot of time researching all of it to put it all together for us. Pick a climate zone, choose some building materials and how they behave to that climate zone and site, put all the thermo, aero, etc, theory to practical use in a building design. Integrate an HVAC, electrical, plumbing, designs to the building materials and envelope, etc….That process would demonstrate a design-build process for any climate zone.
In my many years of designing for big corporations, we don’t design the structural and mechanical systems in a vacuum. They have to integrate to the climate and service conditions we put them in, which includes the HVAC system and environment, the build process, budget, schedule, client demands, etc……
I remember back in the day when there was no integration or when the design did not care as much about cost, reliability, maintenance, manufacturing, etc, and was thrown over the fence from design engineers that had no clue. Later, oh about 15 years ago, the “Integrated Product Team” IPT was born, today known as “Design Build Team” DBT by big corporations being used in this industry now. Having the experience with those design-build practices I can see disconnect here with HVAC-DHW, building materials that are affected by them depending on drying direction, electrical and HVAC loads and consumption, etc…..
So what I am saying in a nut shell is, it would be interesting to see someone design from a clean sheet of paper explaining their choices, to watching the build and seeing if it performed to the design.
Design tools – caution, modeling like WUFI, lab testing, etc……would be interesting to calibrate the model in the process. I have two hot box test now where we are getting different results from what was designed and tested by much better software than WUFI. We have no idea why an air seal is leaking, so we are changing the test and instrument thermocouples, psig, set ups). You can’t always rely on hot box test either.
Anyway, I’m getting ready to finalize a design and build it soon, start the model as soon as I integrate the HVAC to the wall and roof system I chose, see what happens. I’ll probably take it in steps if I can, for example several blower door test and HVAC load test, start figuring the real HVAC load once the envelope is built, not rely on thermo-mass or solar calculators or the MANY theories I find out there with no little data (EG: maintenance and reliability) to back them, put it up for viewing starting with the 3d model. I’d like to see more of that on sites like this rather than theory that goes off in different directions, or a bunch of different articles that could be pulled together in a design-build blog or thread to integrate into practical use.
Terry Lee
"it would beneficial coming from experts such as yourself that spend a lot of time researching all of it to put it all together for us."
You know it's funny, but that is the one thing that the proponents of the various approaches consistently avoid doing and publishing the results. Try and pry real numbers out of the Passive House crew, or more recently here the radiant heating proponents, and see how far you get. Lots of "you just have to work smarter" or "add it to your mortgage", but real apples to apples comparisons are thin on the ground. It would be a really valuable (and a very time consuming) resource to see some modelling of all the various new approaches with real numbers attached.
Poor Solar Thermal Performance is the Other Problem
Disappointing field results from well-designed solar DHW systems are all too common.
This one is from the Net Zero Habitat House in Arvada, CO
http://www.nrel.gov/docs/fy08osti/43188.pdf
"We calculated a simple overall system efficiency for the solar water heater by dividing the thermal energy delivered from the solar tank to the backup water heater by the total solar radiation on the plane of the collectors times the area of the collectors. The monthly average efficiency varied from 2.8% in August to 7.4% in December. The annual average efficiency was 4.8%.
The low delivered energy of the solar thermal system begs the question of whether the investment is justified. The installed cost of the solar thermal system was $7,068."
And the answer is.....NO
If you can put it in yourself for $3k and do all the maintenance yourself, then the answer is maybe.
PV yearly average efficiency is typically more like 12% or so, and much less maintenance.
Malcolm
"Try and pry real numbers out of the Passive House crew, or more recently here the radiant heating proponents, and see how far you get.."
Big corporations with deep pockets have the same disconnect. I came in late as a sub-contractor on the seal leakage I mentioned above. The Engineer that is assigned to it and retiring end of the month added the seal to a design he found in service that was doing fine, to keep crude out. Although it is a new design he reverts back to it having all kinds of maintenance and reliability history and swears it is a good design choice. I disagree but since I am a sub I don’t argue, after he retires I will be redesigning it mark my words, it will fail test. Since the seal is failing he is changing the test fixture to try his hardest to get it to pass spec (picture blower door test here and passive rating’s) get the certification and make the customer happy even though it could still fail in the next few years since it was not really tested to the environment it will see. Sound familiar? Even if the data is captured by such a team or spec no one really knows if it is accurate. Most specs (ASHREA, ASTM) are put together by committee vote. Most builders, architects, PEs, walk away after the warrantee period is over, they are not around to sustain the design or learn from it more less collect data for the next design. Same thing happens in big corporations, when the design is done the designers go to the next clean sheet design. The designer don’t have the maintenance and reliability to help make good design choices, just a bunch of Engineers with opinions and no real data a lot of times, especially if there is little to no history and it’s new.
Response to Terry Lee (Comment #19)
Terry,
Q. "Your pump/collector is packing snow since they are too close to one another?"
A. My solar collectors are snow-covered from mid-November to mid-March. In mid-March, the melting begins. The solar collectors melt on the upper half of the collectors first (because the sun is so low in the sky). The lower sections of my roof are shadier and colder. The two small PV modules stay snow-covered longer (because they are near the eaves rather than near the ridge) than the upper 2/3 of the solar thermal collectors.
Response to Terry Lee (Comment #21)
Terry,
You wrote, "It would beneficial coming from experts such as yourself that spend a lot of time researching all of it to put it all together for us. Pick a climate zone, choose some building materials and how they behave to that climate zone and site, put all the thermo, aero, etc, theory to practical use in a building design. Integrate an HVAC, electrical, plumbing, designs to the building materials and envelope, etc….That process would demonstrate a design-build process for any climate zone."
Many GBA articles do exactly that -- especially the case studies we publish in our Green Homes section. These articles are usually written by a designer, a builder, or a homeowner, and they explain how the team arrived at specifications to meet the requirements of the homeowner for a specific site, at a specific budget. Some of these homes cost $120,000, and some cost $800,000.
The Pretty Good House discussions in Maine -- there have been 8 or 10 articles on the topic on GBA -- also delve into these issues.
These discussions are necessarily site-specific, climate-specific, and owner-specific. By reading how other design teams have addressed these issues, we all learn more.
Response to Malcolm Taylor (Comment #22)
Malcolm,
"That is the one thing ["putting it all together"] that the proponents of the various approaches consistently avoid doing and publishing the results. Try and pry real numbers out of the Passive House crew, or more recently here the radiant heating proponents, and see how far you get."
GBA does its best to report actual specifications and, were available, cost numbers for projects we report on. If you read GBA regularly, you'll find more cost information on a variety of projects than you will at almost any other website.
We don't try to gloss over issues of cost when it comes to ground-source heat pumps, radiant floor heating systems, or solar thermal systems. If anything, GBA is criticized by hardware sellers for repeatedly reminding our readers that some touted technologies don't make economic sense.
We have definitely reported construction cost information on Passivhaus projects, on GSHP systems, and on radiant floor heating systems -- not for every project, but for a great many. (In some cases, the numbers are simply unavailable.) We use those numbers when discussing cost-effectiveness questions.
Martin
I wasn't commenting on the lack of numbers in GBA articles. On the contrary, the numbers provided are extremely valuable given the complain I was making that the proponents of various approaches seem reticent to provide the numbers themselves.
Much as Building Science and GBA have cut through a lot of the technical claims of various methods and materials, I wish there was a resource that could attach real numbers to many of these things. I know it isn't easy to do given the variables, including local conditions, but it is very hard to make informed decisions as to, sa, how much sub-slab insulation to use when proponents of extreme amounts brush off the financial implications or tell fairy stories about the price.
Response to Malcolm Taylor
Malcolm,
You wrote, "It is very hard to make informed decisions as to, say, how much sub-slab insulation to use."
There are three approaches you can take:
(1) Install the minimum level of insulation required by your local building code. (I don't recommend this approach).
(2) Follow one of the rules of thumb established by the Building Science Corp. or GBA (for example, in this article: Can Foam Insulation Be Too Thick?).
(3) Find out how much the various insulation options will cost, and compare the energy performance of the different options using energy modeling software.
Run from solar thermal
With the low cost of PV today and into the future, I am now designing homes that use PV to heat the water with an tanked electric water heater. A LOT less maintenance and cheaper in the long run. I used to design my small homes with a small gas space heater, but now, with a tight, well insulated envelope, we can use electric HVAC systems that also work off the PV.
Note that Flagstaff is ideal for solar and requires no cooling in the summer.
I just got a call, yesterday, from someone who would like to remove their 1980 solar thermal system because they need to re-roof and they don't think it is worth it to re-install it. I have talked with 3 people in the last 5 years who have wanted to do the same thing.
Maintenance cost >= Savings? Such a deal!
If it costs $200-300 / year to properly maintain a solar thermal system, and it saves the typical owner less than that...why bother?
Solar thermal might make sense for high demand situations such as swimming pools, laundromats, restaurants, hotels, multi-family dwellings, dorms, group homes, etc, but not for single family dwellings.
A different style...
We used to live in Houston, and purchased a 'solar pre-heat' system. It was much less expensive than the drainback or other active systems. After our calculations, it seemed to do a full payback in 5 years, about the time it started leaking and the roof needed to be replaced. Economics said that if we were not an 'all electric home' and no gas available, it didn't make monetary sense. But it was in the Carter solar support years. ... It cost us about $2K, where active at the time cost about $10K (I think that was because the most the installers could charge and get rebates from the feds!).
Installing more insulation and reducing the desired level of temp on the hot water heater went a long way to reducing our energy consumption. The next big item was moving from resistance only to heat pump!
This was in the mid-late '80s, in the 'Sun Belt'. And 3 houses ago.
Thermal savings undetectable
I've got a single-panel 10x4 PV-powered pump system, installed November 2006, in central Florida. No snow problems, but a good hurricane will make me antsy. Only maintenance so far has been to replace the original pump with a Laing brushless ($185), which is almost too good. Works great, producing 160° water, but we see no reduction in electricity consumption, based on close monitoring of utility bills. Looks like our DHW energy use was minimal to begin with, and continues to be a small fraction of the total. But nevertheless, I get some small pleasure from having the WH circuit breaker in the OFF position most of the time.
Solar HW costs
Martin, We always mount the pv panel to the top of the collector. That way the conditions are the same for both. Drainback systems are much better than pressurized glycol systems because they can't freeze or boil. If your brother closed valves then he is boiling the htf turning it acidic which is eating away at the copper. If he wants to shut it down it needs to be drained and flushed to avoid further damage.
Response to Kurt Johnsen
Kurt,
Thanks for the advice. I appreciate it.
Why the hate?
Hi Martin,
Sorry you've had issues with your SHW system and same with your brother - but man! I can't understand all the hate on SHW.
It's worth pointing out that SHW is an extremely more efficient use of solar technology than PV, for a homeowner with a tiny solar window on their roof, 4x10 or 8x10 of PV is not going to make much of an impact, but if you can meet all the DHW needs of that home with SHW you are doing something meaningful. This is especially true in New England where you have hundreds of thousands of homes heating water in the middle of August with a monstrosity of an oil boiler burning at 60% (or worse) efficiency. Some of our clients have reported savings in the hundreds of gallons of oil per year. We have plenty of data to support this.
Also consider the use case of light-commercial or multi-unit buildings, and solar thermal blows PV out of the water. i.e. breweries, restaurants, assisted living homes, apartment buildings, dormitories, etc...
There is no reason to propagate the mythology that solar thermal is a science project technology. Yes, it is a piece of plumbing and there are things that need maintenance or break, and it sounds like your brother was a bit unlucky. We also recommend variable speed AC pumps over DC pumps for precisely the issue you mention (solar thermal gain to be had in overcast/cloudy conditions when there is not enough sun to run a small DC pump) plus overall efficiency. We have some engineers who have written extensively on European best practices we employ for overheating, e.g. steamback. Solar thermal takes a lot more knowledge and expertise to work well, and it really does take professionals to install it right, which is why you see so many systems that are nightmares out in the field. We know, because we end up cleaning up the mess for a lot of contractors who are no longer around. That doesn't mean the stuff doesn't work. We have over 1,000 happy solar thermal customers in Northern New England.
Is solar thermal the best solution for an air-tight passive house or for a retired couple who travels a lot? No. But I don't think beating up on the technology just because it fails on occasion or wasn't a good choice for an application is the first place is fair.
Best,
Fred from ReVision Energy - and disclosure I am marketing guy and not an engineer, so if I get some of the deeply nerdy tech stuff wrong that is why
Reply to Fred Greenhalgh
Fred,
Q. "Why the hate?"
A. I didn't express any hate. In my article, I said this about my solar thermal system: "It's a good system." And in Comment #15, I wrote, "I'm glad I installed my solar thermal system."
You wrote, "If you can meet all the domestic hot water needs of that home with solar hot water you are doing something meaningful."
What you would be doing wouldn't be just meaningful -- it would be miraculous. Research has shown that a well-designed solar thermal system can meet about 50% of a family's domestic hot water needs in in New England. If you wait for sunny days before you take a shower, you might hit 60%.
You wrote, "Solar thermal takes a lot more knowledge and expertise to work well, and it really does take professionals to install it right, which is why you see so many systems that are nightmares out in the field."
That was one of the points I was trying to make in the article. The factor you mention adds to the cost of these systems, and also adds to their maintenance costs -- in stark contract to PV systems, which are much simpler, less prone to maintenance problems, and less likely to show examples of what you call "nightmares in the field."
Solar thermal systems made a lot of sense in the 1980s. They don't make much sense now. Anyone who wants to install solar panels on their roof should talk to a PV installer.
If you've maxed out your grid-tie, then PV or solar thermal?
This may be a rare case, but suppose that a home owner has a grid-tied PV system that is at the practical or regulatory maximum. They want to replace a gas-fired domestic hot water heater, in order to decrease use of fossil fuels. An electric water heater could be connected to some additional PV panels, that are not connected to the grid nor to batteries. I don't know if any professional installer would want to try that. Or the new electric water heater would be connected via some sort of heat exchanger to a solar thermal collector.
In both cases, the collector would likely be a supplement, rather than completely eliminating the main AC power to the water heater. Which of these approaches would you recommend? Or do you dislike both of them?
Response to Derek Roff
Derek,
You wrote, "An electric water heater could be connected to some additional PV panels, that are not connected to the grid nor to batteries."
I don't recommend that approach, since it only works when the sun shines. Arguably, however, it's no worse that a solar thermal system.
Of course it's always possible to install a solar thermal system if you want one -- especially if you are an environmentalist who has already installed the maximum possible number of PV modules. Just remember that the cost of a solar thermal system, including maintenance, may be about the same or only slightly less than your cost savings from energy use reduction.
Thank you, Martin.
I appreciate your taking the time to answer my question. The irony of my situation is that I already own the additional solar panels and inverter, a thirty-tube evacuated tube solar thermal collector, and a 120-gallon electric water heater. All of these are hand-me-downs from other owners and other projects, acquired at bargain basement prices. That still doesn't make these items intelligent purchases. They are currently collecting only dust. I'd like to come up with a way to have them collect the solar energy for which they were designed.
Response to Derek Roff
Derek,
Your situation is unique. Clearly, if you already own all of the solar equipment you describe, traditional economic analyses don't apply to your case.
I'll give you the same advice I gave my neighbor, who has been gradually adding PV modules to his rooftop PV array over the years. He bought a nice new PV module, which was delivered by UPS. Six months later, the module was still leaning against a wall, inside his garage. I told him, "PV modules want to be in the sun! Get that thing on your roof already!"
Round 2
Hi Mark,
You're right, "Hate" is a bit of hyperbole and I misspoke when I suggested SHW might meet 100% of a home's needs, that's obviously not possible. I think we can predict upwards of 80% or so but I am not confident standing behind that fraction without one of our engineers chiming in, but I think we can argue for better than 50%.
I don't disagree that PV is fantastic, we were doing 50/50 PV / Solar Thermal in 2008 and now our queue is about 90% PV / 10% thermal and we are increasingly relying on Marathon heaters and HPWH's combined with PV for most residential cases. Ease of installation, bulletproof-ness of equipment, reduced costs, etc. are all strong in PV's favor.
I guess my point is - solar thermal is harder than PV and it is not for everyone or every situation, but it still has a place especially when you have pros who understand what makes it superior to alternatives (you can have superstar ROI in 7-8 person households who are on a tankless coil, and commercial kitchens, and lodging operations, and apartment buildings...). It seems like GBA should be making an effort to explain the nuances of the DHW decision-tree, rather than trashing SHW technology outright.
- Fred
Response to Fred Greenhalgh
Fred,
You wrote, "Solar thermal ... still has a place ... (you can have superstar ROI in 7-8 person households who are on a tankless coil, and commercial kitchens, and lodging operations, and apartment buildings). It seems like GBA should be making an effort to explain the nuances of the domestic hot water decision-tree."
Thanks for your feedback. GBA is a website that focuses on residential building, not on commercial or institutional buildings. That's why our website rarely discusses the needs of commercial kitchens, lodging operations, and apartment buildings.
In my defense, I'll note that my article "Solar Thermal Is Dead" explained, "Unless you’re building a laundromat or college dorm, solar thermal is dead." While my tone may have been flippant, the advice in that sentence was similar to yours.
Concerning your suggestion that we provide a domestic hot water decision tree: I provided one in my Fine Homebuilding article, The Water Heater Payoff. You may not agree with my decision tree, but at least I took a stab at creating one. (See image below; click the image to enlarge it.)
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