Solar hot water

JetMechJetMech Posts: 71Solar Expert ✭✭✭✭
I've seen a few solar hot water kits that will let you use your existing hot water heater, but not any of the evacuated tube type. My 80 gal electric is only two years old, so I'd rather not change it out. I've also read that the evacuated tube type tend to be more efficient than the plate-type. Anyone know of a kit that is a tube type and will use my existing hot water heater?

Comments

  • System2System2 Posts: 6,290 admin
    Re: Solar hot water

    The Feb/Mar 2008 issue of Home Power magazine had an article on solar hot water collectors. Whether evacuated tube collectors will be more efficient, depends on your climate and solar access. They say: "Evacuated tube collectors . . . offer good performance in cold and cloudy climates." In some other climates, flat plate collectors may perform better.

    Mike
  • BB.BB. Posts: 27,905Super Moderators, Administrators admin
    Re: Solar hot water

    Searching for Solar Wand, came up with a couple types:

    Fits in top of hot water tank. (for closed loop?)

    Solar Guppy posted a link to this bottom installed unit (open loop collector).

    Quick Connect

    -Bill

    PS: I read another site's comments about evacuated tube collectors--in areas with snow, they are so well insulated that they don't shed snow near as well as "flat plate" (with glass cover) collectors--which tend to heat and melt the snow off quicker...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JetMechJetMech Posts: 71Solar Expert ✭✭✭✭
    Re: Solar hot water

    The quick connect sounds interesting but it sounds like it's used with a system where the water flows through the collector rather than glycol. It mentions the ability to drain the system for freezing temps and I have those temps all winter.
    I saw that issue and so I assumed the tubes would be better, but knowing now that they may not shed snow I'm thinking different. Perhaps I'll stick with the flat plate style.
  • BB.BB. Posts: 27,905Super Moderators, Administrators admin
    Re: Solar hot water

    Solar Guppy recommend this place in another post here:

    SolarRoofs.com

    Looks to be about as much home builder/kit friendly as any system I have seen out there...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: Solar hot water

    Solar roofs has both open and closed loop systems ... closed loop cost more as you have a second tank and exchanger for the glycol ... but its the most do it yourself friendly system I found when I took the plunge.
  • xiphiasxiphias Posts: 52Solar Expert ✭✭✭✭
    Re: Solar hot water

    Some thoughts.

    Flat-plate collectors are a very mature technology, there are a number of good-quality brands, they have excellent longevity, and their performance is very good for most applications, particularly DHW. Evac tubes are not nearly so mature, and there is wide variability in manufacturing technique, quality, durability, etc.

    From what I understand, unless you really need the higher-temp output of evac tubes for a particular application, flat-plate is the way to go. We have a 300-tube array at work. It is working through some non-trivial issues (header flow, tube seals) that in a residential setting would be very expensive, tedious problems to deal with. We would have gone flat plate but needed the extra output of evac tubes to keep the total arrary size manageable.

    As for integrating to an existing system, the solarroofs system is similar to a common system used here in the US NE, the essentials of which are:

    80 sf flat plate collector (2 4x10 panels)
    120 gal storage tank (Superstor SSU-119 is common)
    glycol closed system
    differential control

    The rule of thumb around here is 1-1.5 gal storage for each 1 sf of collector area.

    The way they are set up is the domestic hot out from the solar tank goes into the cold input of the existing water heater. A 3-way valve is used that allows 100% solar in summer, bypassing the existing tank. The rest of the year, the solar does pre-heat (anywhere from 65-100%) for the existing. It's a pretty good setup.

    A tempering valve is used on the existing domestic hot out, as the solar tank is typically feeding very hot water to the existing tank (up to 160F).
  • JetMechJetMech Posts: 71Solar Expert ✭✭✭✭
    Re: Solar hot water

    I saw this in Home Power, issue 114.

    5044805350f4018b.bmp

    Now if I wanted to eliminate the storage tank, couldn't I just attach the cold water feed at the bottom of the heat exchanger. The tank drain would also plumb into the bottom of the exchanger, perhaps with a check valve just in case and a drain. This way, the cold water would still pick up heat on its way through the heat exchanger and mix inside the hot water heater. I don't really need 200 gallons of hot water on the ready. I know I'd lose some efficiency if there were a string of cloudy days, or in the winter, but I could always add the storage tank at a later date. In the meantime, it would save me the cost of a tank and get me up and running in time for the summer.
  • BB.BB. Posts: 27,905Super Moderators, Administrators admin
    Re: Solar hot water

    Yes, you can dump the second tank... The first (and only tank) is presumably an electric water heater (gas will work--but probably the heat loss up the flue limits its usefulness in a solar system trying to stretch the hot water over a couple of days).

    Looking at my earlier post (basically from Solar Guppy's previous links), you have two options right off the bat..

    One option is for open loop (city water though solar panels)--just pull the hose bib (drain valve) and hook this in (takes cold water from bottom of tank, directs heated water up towards top of tank--If I understand it correctly).

    Quick Connect

    I have also seen versions of the above that fit in the hot/cold water pipes at the top of the tank too (useful if you don't have access to the front of the tank).

    Or, if you want to use antifreeze in the collectors (closed loop), then use this in the hot water tap...

    Fits in top of hot water tank. (for closed loop?)

    Generally, it was recommended that you have 1-2 gallons of hot water storage (for domestic HW use) per sq ft of solar collector... 1:1 if you are in less sunny areas. Upwards of 2:1 if you are in the sunny southwest.

    Estimate use is ~20 gallons of hot water per person per day...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JetMechJetMech Posts: 71Solar Expert ✭✭✭✭
    Re: Solar hot water

    It would have to be a closed loop (or a drain-back) because the temps go below freezing here in Connecticut in the winter. The wand seems like a good idea but it looks pretty restrictive from the picture. This is also an option. I just saw that diagram and that idea popped in my head.
  • xiphiasxiphias Posts: 52Solar Expert ✭✭✭✭
    Re: Solar hot water

    This is a very simple closed-loop system along the lines of what I described above.
  • BB.BB. Posts: 27,905Super Moderators, Administrators admin
    Re: Solar hot water

    But that would require a new electric water heater for you (I believe this is the model with a double wall heat exchanger wrapped around the outside of the water tank and you can get the tank with zero or two electric heating elements installed).

    No problem with the installation (great for an all-electric home), but earlier you commented that you would rather not replace your two year old tank...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JetMechJetMech Posts: 71Solar Expert ✭✭✭✭
    Re: Solar hot water

    xiphias - that looks like a photo of the same system that is in the diagram I posted, with two tanks.

    BB - Which one would require a new tank? If I modified the system in the diagram like I mentioned, I'd only need my existing tank. Or the drainback system in the link I had also uses my existing tank.
  • BB.BB. Posts: 27,905Super Moderators, Administrators admin
    Re: Solar hot water

    Sorry JetMech,

    I mixed Xiphias' post of the water tank with internal heating loop with your posts. Two different people.

    There are quite a few variations of open and closed loop systems out there... JetMech, the last diagram you posted implied an external heat exchanger.

    I have run across external double wall heat exchangers before (double wall exchanger required for systems that use anti-freeze to heat domestic hot water--to prevent contamination of your fresh water system). Certainly an external heat exchanger can be retrofitted to an existing (or brand new) hot water tank/heater.

    In some ways, the external heat exchanger seems nice (Also applies to the other "retrofit" type heat exchangers too). Can use regular water heaters that you can buy down at the local hardware/plumbing supply store--for all of those times when the water heater springs a leak on the weekend and you don't want to wait 3+ days for delivery for a specialized solar tank with integral heat exchanger (the one from solarroof.com has a 6 year guarantee) with no hot water at home.

    Mild drawback to the external heat exchanger is that there is the requirement for a second circulating pump to move water from the heat exchanger to the hot water heater itself.... Just another cost and maintenance item.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JetMechJetMech Posts: 71Solar Expert ✭✭✭✭
    Re: Solar hot water

    Good point. But the less initial investment I have to make, the more likely my project will be approved by the missus. :roll:
  • xiphiasxiphias Posts: 52Solar Expert ✭✭✭✭
    Re: Solar hot water

    JetMech, after looking againg at the Beeman diagram you posted, yes, it's pretty much the same setup, but as BB says there's the extra circulator.

    The Superstor in the photo is a standard, single-heat exchanger, 119 gal indirect water heater. Stainless, with a lifetime warranty. http://www.htproducts.com/superstorultra.html

    I haven't priced all the parts for this kind of system, but I think it ends up in the $4-5k range from roof to basement. Payback on that is probably 4-6 years depending on how you heat your water now.
  • BB.BB. Posts: 27,905Super Moderators, Administrators admin
    Re: Solar hot water

    The 80 Gallon SSU-80 come back around $2,000 with free shipping (out of New York? $2,700 for the 119 gallon tank)...

    May be worth it with lifetime warranty... (I hate changing water heaters--and I would be in my 60's+ the next time one fails--I am willing to spend a bit more to avoid the issue in a decade or two)...

    Looks like Double Wall heat exchanger (option "DW") is an option... So don't know the price with that included--Don't really know if "DW" is required for any/all domestic hot water applications or not...

    -Bill

    PS: (I don't know anything about the company, distributor, or the product)...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • xiphiasxiphias Posts: 52Solar Expert ✭✭✭✭
    Re: Solar hot water

    The product is good. HTP is in MA. Their indirect heaters are quite well-regarded.

    80gal would be a small system. That would support 40-60 sf of collector area, tops. 1-2 people. Not unheard of, but I don't think it's too common, either.

    Never heard of the retailer.

    Not familiar with the DW option on these tanks, but double-wall hx is not necessary.
  • BB.BB. Posts: 27,905Super Moderators, Administrators admin
    Re: Solar hot water

    I just do a search on the web to try and get an estimated price for things (is it $10, $100, $1,000, $10,000 etc.)...

    Does anyone know the details of double wall vs single wall heat exchanger construction requirements?

    Here in California, we don't have too many homes with a separate boiler and hot water/steam heating... So, I am not sure what the DW requirements really are.

    I know that people use non-toxic antifreeze in these solar systems to help prevent accidents.

    In my area, we have only had a hand full of hard freezes that actually stopped water flowing in external pipes and unheated garages over the last five decades. So, I would tend to look at open loop solar (no heat exchanger required)--also, have heard about anti-freeze failure (gunk in th lines) when panels/systems overheat... Having to drain the collectors once every decade or so for a few days does not seem too bad.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • xiphiasxiphias Posts: 52Solar Expert ✭✭✭✭
    Re: Solar hot water

    Gotcha.

    I'm guessing that double-wall is probably required for some applications, and perhaps by code in some areas. But those would likely be very limited. (Multi-family dwellings? Non-residential? Beats me.)

    Looking at the install manual, double-wall really kills the output. By half....

    If you go with a closed system, glycol (food-grade, non-toxic) is what is used. There are some potential glycol breakdown issues if the system is allowed to stagnate. That said, there are some systems around here that have been running on the same glycol for 15+ years.

    Give me a month or two and I may have first-hand info. Looking into getting one of these on the roof. Have quotes in hand and currently looking at how we can get it done.
  • BB.BB. Posts: 27,905Super Moderators, Administrators admin
    Re: Solar hot water

    I have looked around for a Solar Thermal installer here--and in a county of ~700,000 -- there are only a couple and little on-line feedback.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • xiphiasxiphias Posts: 52Solar Expert ✭✭✭✭
    Re: Solar hot water

    Asked a buddy. Double-wall hx is used only when required by code. "Then and only then" as he put it.
  • noradawn456noradawn456 Posts: 5Registered Users ✭✭
    Hi, i have been thinking of solar for years. Unfortunately, the size of the system I would need is cost-prohibitive right now. 
    I do, however, want to install something large enough to supply power to my swimming pool pump. My thought is that this runs every day, year-round and is a sizable energy user, it would help in the long term. 
    Does anyone know of a site that shows how to do do-it-yourself solar systems?
  • EstragonEstragon Posts: 2,846Registered Users ✭✭✭✭✭
    You may want to try calling our hosts, or maybe start a new thread here with your pump specs.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • terracoreterracore Posts: 2Registered Users
    Hi, i have been thinking of solar for years. Unfortunately, the size of the system I would need is cost-prohibitive right now. 
    I do, however, want to install something large enough to supply power to my swimming pool pump. My thought is that this runs every day, year-round and is a sizable energy user, it would help in the long term. 
    Does anyone know of a site that shows how to do do-it-yourself solar systems?

    I started out with a similar concept- not looking for any type of expensive fancy array for whole-house usage but just to eliminate the constant draws.  I built my solar system completely DIY over a period of time as budget allowed, and now I have about 100KWH of power each month that I don't have to give to the electric company.  I am in Hawaii and our elec is almost .42 cents per KWH so it adds up quickly.  Now my power bill is only in the double digits and I didn't have to get a second mortgage to build my system.  I just bought a panel and assorted cabling and brackets about every payday until my system was complete.

    If you are powering your pump 24/7 it makes most sense to run it off solar during the day when the sun is out, and switch to grid at night.  That is more cost effective than trying to use batteries.  Switching between solar and grid is a simple matter with an automatic transfer switch. If you only need to run the pump during the day, then you're set without a transfer switch.  I have a deep freeze that only runs 8.5 hours a day when my solar provides the necessary power.  That gets the temp down to about -8 degrees and when it kicks on again the next morning it has only warmed to about 15 (well below freezing) so the freezer is 100% "off grid" even though our house is not.

Sign In or Register to comment.