Reflect sun into solar water panel?

jmbergmannjmbergmann Registered Users Posts: 6
I have a 40 sq/ft solar water panel and an 80 gallon water tank connected via an active drainback system.

I am trying to figure out how to increase my water temperature during the day, but trying to avoid adding another panel to the system. If I fabricated some stainless steel panels that would reflect more sun into my existing panel, would that increase the ability of the panel to heat water to a higher temperature?

Thank you..

Comments

  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    Depending on your latitude and the time of year,,, consider mirrors.

    I built a simple flat plate collector installed ~50degrees north. In November, December January and February, with short days and low sun angles,, I place a mirror on a hinge on the uphill side of the collector. I got some scrap mirror from the glass shop, mounted it on a piece of plywood and a hinge so that I could adjust it every couple of weeks to maximize the reflection on the collector. (Net cost,,, Zero!) The mirror is about 1/2 as tall as the collector is wide. This had the effect of adding ~30% to the daily out put. This simple collector gives ~30% of the hot water needs in mid winter,, rising to ~100% by April 1. The mirror just add during the winter,,, by the equinox, the sun is high enough that there is effectively no shade on the collector.

    Tony

    The collector is ~ 30"x 144" with a simple 1/2" copper tubing loop, on top of 3/16" scrap steel plate, in an insulated box, covered with used patio door glass. Controlled by a diferental t-stat. driving a grunfos pump (7 watts) into a 40 gal used electric water heater as a pre-heat tank for a demand water heater. Today,, with filtered sunshine it raised the entire 40gal from 67f at 11 amp, to 112f at 6pm. Outside air temp of ~50f
  • FL SUNFL SUN Solar Expert Posts: 94 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    What water temperature are you looking for at the end of a solar day?
  • peterakopeterako Solar Expert Posts: 144 ✭✭
    Re: Reflect sun into solar water panel?

    What type off controller and pump are you using also there is a possible change welcome.
    My experience is that the mirrors are big problems with high wind and storm, the noise can make you crazy.

    Greeetings from Greece
  • jmbergmannjmbergmann Registered Users Posts: 6
    Re: Reflect sun into solar water panel?

    Thanks for all of your responses...

    My main goal here is to reduce the amount of time that the pumps are running that circulate the water to the collector, then another one that circulates between the exchange tank and the 80 gallon storage / electric backup tank.

    I noticed that when these two pumps are running, it's consuming 215 watts of power, and with energy rates at approx $0.15/kwh in Phoenix, i'm paying and arm and a leg to get solar water, not to mention not helping the environment much either -- In fact, my gas bill for my old gas water heater was probably cheaper than my electric bill to run my solar collector!!

    So my goal would be to get the water to a temperature quicker, then shut it off and just turn on from time to time for maintaining that temperature.

    I use a Radco solar controller, and the system I use is from a local company called Integrated Solar that appears to have purchased Radco a couple years back (I am guessing).

    Any further advice you have is appreciated...
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    I would look at the pumps. 215 watts continuous sounds like a lot, but I would guess that would depend on a lot of things.

    In my system,, It circulates with a 15 watt Grundfos pump. I don't have a clue how many gpm/h it moves,, not very many.

    Tony
  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: Reflect sun into solar water panel?

    How are you measuring the watt draw of the pumps? ... most solar water pumps are in the 15-40 watt range ... If you just measuring amps with a DVM that won't work due to the power factor
  • FL SUNFL SUN Solar Expert Posts: 94 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    Pumps serving drainback systems are higher wattage pumps by design as they have to overcome head pressure each time they start as the collector drains completely every time the pump cycles off. It also helps to eliminate an "air lock" that could happen in some of the parallel tubing inside the collector, resulting in a loss of panel efficiency.

    A fully primed closed loop circuit does not have the head losses a drainback does, and can handle a much smaller wattage pump.

    What brand of system do you have? AET?

    If you continue to maintain your drainback system, the only way to cut your run time on your pump is to install more collector area (another 80 sq ft panel). Does your single panel get full sun all day? My 80 sq ft of panel area serving my 80 gallon tank creates 170-180 deg F water every good solar day. I initially had 40 sq ft, and it wasn't quite doing it temperaturewise. I had to get another panel as well.

    On your mirror idea, the only way concentrated solar power (CSP) works is with x and y axis tracking. A heliostat would exceed the cost of the extra panel by 3 times and be 30 times the trouble.

    What is your water temperature at the end of a solar day?
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    Fl Sun,

    Mirrors may no work very well at your latitude,, but at the higher latitudes with low sun angles it give a marked improvement. (Having said that,, it we only get ~20-30% of hot water needs in the winter,,, still better than non.

    JM,
    I would question why you installed a drain back system in Phoenix? My intuition is that the extra plumbing and parasitic energy costs are substantial. Even if you get occasional freezing, a modern controller will have an anti-free cycle to keep water flowing in the event that the collector gets cold.

    The system I mention (It not here in the Northern bush where temps get REALLY cold, but rather on the temperate west coast. This system survives 10f nights with 100km winds quite regularly. I did design in a simple drain/bleed system,, but it has only been use when the house is vacant for periods of time.


    Tony
  • FL SUNFL SUN Solar Expert Posts: 94 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    icarus, good points.

    I prefer indirect glycol solar loops using a Laing pv direct pump and small panel. Still like to use a (dc) differential controller, even with pv.

    Our area can have some nasty freezes. A direct system works OK with the freeze protection valves, and /or recirculation on freezing temps. But I've found it results in a loss of hard earned hot water.

    That way, with glycol, I don't have any losses due to cold weather recirculation or bleeding. And electric consumption is $0.00 for a tank full of hot water.:cool:

    The drainback design is an interesting way of tackling the freezing issue, but they are not the most efficient.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    FL,

    The thing about glycol, evacuated tube, closed loop systems is that they are just that much harder for a DIY person to try. In most climates, you can put up with a few days,, weeks of freezing,, giving back some hard earned hot water,, because the rest of the year it is free. Even in extreme climates, you can build an automatic drain system simply by adding a couple of solenoid valves,, or you can do a manual drain for those times when it just doesn't make any sense to keep a system going.

    My first system was a DIY thermo-siphon system that circulated into a pre-heat tank. It worked fairly well, but I got tired of going up on the roof and draining it. One night I forgot and that was the end of that system. (It also doubled with a wood stove coil nto the same tank) For me,,, as opposed to a customer or an average homeowner,, half the appeal is to figure out how to make something work. (Cheaply in my case!).

    I still question the need for an autodrain system in Phoenix however. (I may have a complete naiveté about the climate however).

    Tony
  • jmbergmannjmbergmann Registered Users Posts: 6
    Re: Reflect sun into solar water panel?

    Here I am -- Sorry...

    Why the drainback? Great question, I am asking that myself. It rarely freezes here, maybe once or twice per year, and at that, it gets down to maybe the high 20's at the lowest!

    Here's why: I went with a local company called "Integrated Solar" which had two options: This Radco drainback system (that I went with) and a passive system that just feeds the solar water into a regular water heater. I chose the drainback because the local utility company out here rebates based on the efficiency rating of the system. The drainback got me a much larger rebate from the utility company, and I was really hoping I could just rely on the solar water (which I now can, since i've replumbed my system not to feed into my old gas water heater).

    I saw systems that I liked better online that I was tempted to purchase (larger / more panels, solar PV to run the pumps, etc) that would have gotten me even a larger rebate, but I was worried about having some random company install it because it's a fairly long run between the panel and the tanks. So Integrated Solar manufacturers, installs, and warrants its products.

    I don't regret the decision whatsoever, they are a wonderful company to work with -- I am just trying to get the pumps to run less.

    They DO truly use 215 watts consistantly when they are running -- I had the KiloWatt meter hooked up to it today -- However, I have since realized that I calculed the daily cost of the pumps... I calculated it at $1.5 per day, but really that's the amount of power it uses during it's daily cycle (1.5 kilowatt/hrs). So the true cost is only $0.19 per day... So I am feeling a lot better about it.

    The temperature seems to get up to about 148 by the end of the day, but that's using my oven thermometer -- Speaking of, what are you guys using? Just a type-K thermocouple digital monitor?

    So maybe it's not worth adding another panel... So maybe I reduce the time the pumps run by a few hours, or a few cents per day... Is it really worth the expense... Probably not for me.

    Let me know if I have flawed logic anywhere above... My wife questions my logic quite often ;)

    Thanks...
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    I confess that I know nothing about a closed loop system using water for a medium. Having said that,, it seems like it is the worse of all worlds. (No offense intended) Looking at the Radco System it just seems strange to run distilled water through the collector, transfer heat to domestic water, drain the distilled out when the sun doesn't shine. You don't have the danger of the glycol system contaminating potable water, but you still have water that can freeze.

    My question is since you have to go to the trouble of all that plumbing why wouldn't you just use the potable water in the loop.

    I'm sure that my ignorance will be revealed over time.

    Tony
  • peterakopeterako Solar Expert Posts: 144 ✭✭
    Re: Reflect sun into solar water panel?

    Check out Grundfos alpha2 pump. it is automatically changing between 5 to 22 watt.
    See http://www.energyproject.com/

    it seems you have a to high capacity pump trying to build up pressure and eating your e bill and pre heating your water. :roll:

    i am not aware about your controller but if installed by the same " professional ;) " as the pump then rethink about the complete setup.

    Greetings from Greece.
  • jmbergmannjmbergmann Registered Users Posts: 6
    Re: Reflect sun into solar water panel?

    Sorry, if I called the controller a Radco controller, I meant a Goldline... The entire solar system is a Radco system from Integrated Solar, but the controller itself is Goldline.

    According to the installer, the reason potable water was not used in the loop was because it would corrode the system much faster than distilled. Guess it needs to be replaced every 2 years or so...

    I will check out those pumpers further, but they just look pretty expensive, so probably will have to wait until mine go bad...
  • FL SUNFL SUN Solar Expert Posts: 94 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    jmbergmann, what are the 2 pumps make and model#'s?
  • EcnerwalEcnerwal Solar Expert Posts: 101 ✭✭
    Re: Reflect sun into solar water panel?

    In the mirror/reflector line (which we seem to have veered off of), aluminum is a much better choice than stainless steel for reflecting IR. At the low end of that, you can put aluminum foil (builders foil is nice, kitchen foil could be made to work in a pinch) on a plywood backing with glue.

    If you'd like a simple experimental verification that aluminum reflects heat better, put two similar shiny items (likely from your kitchen) out in the sun, one stainless, one aluminum. come back in a few hours and feel which one is hotter. That one reflected less heat...
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Reflect sun into solar water panel?

    As I suggested before,, but perhaps didn't make clear,,, most local glass shops have dumpster full of broken mirrors. (way better than stainless or Alum.)

    You can always ask them to save you some and give you a shout when they get some if they don't have any today. (Take them a box of donuts!)

    Mine were cut from 1/4" commercial mirrors, 18" wide. I even got the guys in the shop to cut them clean,, and I just mounted them end to end,, making a mirror 18"X 12'.

    Tony
  • LucManLucMan Solar Expert Posts: 223 ✭✭✭
    Re: Reflect sun into solar water panel?
    jmbergmann wrote: »
    Here I am -- Sorry...

    Why the drainback? Great question, I am asking that myself. It rarely freezes here, maybe once or twice per year, and at that, it gets down to maybe the high 20's at the lowest!

    Here's why: I went with a local company called "Integrated Solar" which had two options: This Radco drainback system (that I went with) and a passive system that just feeds the solar water into a regular water heater. I chose the drainback because the local utility company out here rebates based on the efficiency rating of the system. The drainback got me a much larger rebate from the utility company, and I was really hoping I could just rely on the solar water (which I now can, since i've replumbed my system not to feed into my old gas water heater).

    I saw systems that I liked better online that I was tempted to purchase (larger / more panels, solar PV to run the pumps, etc) that would have gotten me even a larger rebate, but I was worried about having some random company install it because it's a fairly long run between the panel and the tanks. So Integrated Solar manufacturers, installs, and warrants its products.

    I don't regret the decision whatsoever, they are a wonderful company to work with -- I am just trying to get the pumps to run less.

    They DO truly use 215 watts consistantly when they are running -- I had the KiloWatt meter hooked up to it today -- However, I have since realized that I calculed the daily cost of the pumps... I calculated it at $1.5 per day, but really that's the amount of power it uses during it's daily cycle (1.5 kilowatt/hrs). So the true cost is only $0.19 per day... So I am feeling a lot better about it.

    The temperature seems to get up to about 148 by the end of the day, but that's using my oven thermometer -- Speaking of, what are you guys using? Just a type-K thermocouple digital monitor?

    So maybe it's not worth adding another panel... So maybe I reduce the time the pumps run by a few hours, or a few cents per day... Is it really worth the expense... Probably not for me.

    Let me know if I have flawed logic anywhere above... My wife questions my logic quite often ;)

    Thanks...

    You will be glad in a few years that you have a drain back system without glycol.
    The glycol breaks down after a few years especially at high temperatures. It also seeps from threaded joints, and gaskets creating a leaking mess. It also gums up the pumps & internal piping including the tubing inside the collectors decreasing efficiency. The recommendation for glycol is to check the PH yearly and replace every 3 to 4 years, it 's not cheap $60 to $80 for 5 gallons. Glycol and water mixes have a lower heat transfer coefficient than water making it less efficient.
    The 215 watts for your collector pump and your HX pump is normal for a long pipe run. 148 degree water at the end of the day is great for 1 panel on a 80 gallon tank.
    If you were to add another panel you could possibly get 180 degree water from your system, but some glass lined storage tanks are only rated to 140 degree's max. The glass and steel expand at different rates and at over 140 degrees the glass could separate from the tank, ( not covered under warranty)
    Drainback systems have less problems with overheating, and there is no need to dump excess heat if there is insufficient load for a day or 2 when you go on vacation and there is no hot water consumed. The controller will just turn off the pumps when the high limit is reached and the system will drainback until the storage tank cools enough for it to turn the pumps back on.
    Bottom line ,drain back systems are a little more complex for the installer but require less maintenance for the home owner and have a longer service life than some of the other systems. The only draw back is the large pump required to circulate the water through the collectors, 19 cents a day for 80 gallons of hotwater is a bargain.
    I use a 3/4" T in the hotout line with a thermometer installed in the T, for reading the outlet temp. But you can use any type you want.
    If you are getting 148 degree water from your faucets you may want to install a mixing valve at the tank and set that for 120 degrees. It's easy to get scalded with 130+ water.
    ;)
  • jmbergmannjmbergmann Registered Users Posts: 6
    Re: Reflect sun into solar water panel?

    Great information, LucMan! Thanks for educating me on why I chose this system! I am glad that it was the right choice...

    Yeah, no complaining here about $0.19 per day for hot water and hopefully a reduction in greenhouse gasses. Although, i'm not sure if I mentioned this in a prior post or not, but I did re-wire the backup electrical element in the tank to be 110 volt, 20 amp, and I have a timer that allows it to heat up via AC from 4 to 9 AM, the coolest point of the day for the water. So that comes out to be 2000 watts for probably 2 hours of that 5 hr window.. But irregardless... still MUCH cheaper than my gas tank was. I actually just called the gas company yesterday and asked them to disconnect my account until November/December when i'll need it again for my house heater (because there's a $10 min charge per month with Southwest Gas).

    Good point about the max temp of the storage tank, I didn't realize that could be a problem. I have my Goldline controller set at the max temp of 230. I looked at the instruction manual and all of the stickers on the tank itself just now and there are not "max temp" mentions.. It's a Rheem Solaraide.

    Anyway, all very good info, thanks again LucMan
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