DIY Solar Options

[arngnick]

I live in northern PA and I have over 600 gals of storage for my wood boiler. I have started thinking about adding a homemade solar panel to heat the 600 gal which in-turn will heat my DHW.

So far I have looked at many solar collector options using PEX, CPVC, and copper that are encased in a simple insulated box with glazing on top. To heat the water inside I plan on putting a coil in a 30 gal propane tank with a PEX or copper coil in it. All this with a small pump to keep the water flowing. The tank will be plumbed in series with my 600gals so I will rely on stratification to get the heat where it needs to be in the tanks.

I am hoping this will reduce/eliminate the need for me to fire my boiler much in the summer. Does anyone have any suggestions as far as materials, designs, or experience with such systems?

 

[EatenByLimestone]

I don't have any suggestions, but think that's a really good idea. It should work without an issue as long as you can get that 600 gallons warm enough to heat your incoming water fast enough. It should work in winter also as long as the sun continues to hit the collector.

There are plenty of solar collector build videos on youtube.

Matt

 

[arngnick]

I am hoping to gain whatever I can...In the winter it will not be an issue as I will be heating the tanks with my boiler daily. I haven't been able to find a video that has given me quite the info I am looking for but there is alot of good information out there.

One more question...what is the max water temp I could expect from this type of system?

 

[bmblank]

Check out the evacuated tube collectors on this site. (broken link removed)
The evacuated tubes should be much more efficient. They have allot of other stuff for solar and other ways of heating.

 

[EatenByLimestone]

I think the max temp would depend on the type and size of collector that you fabricate and be limited by the high temperature that the components can handle. If you built a collector large enough to raise the water temperature 80 degrees, but the components could only handle a 60 degree rise you might run into a problem.

Matt

 

[EatenByLimestone]

You might want to find out if the incoming temperature of your water varies in the summer vs the winter. While water lines should be below the frost line so they do not freeze, the ground may be 50 in the summer and 35 in the winter. This would radically change the amount of btus needed to heat it to the temperature you want.

Matt

 

[begreen]

Moved to the green room so that you get some experienced options mentioned.

 

[WES999]

Have you looked at this website? http://builditsolar.com/
Lots of good ideas for DIY solar water heaters.

I built this version: http://builditsolar.com/Projects/WaterHeating/Metal1K/Metal1K.htm
For 600 gl you would probably need 6 or 8 4' x8' collectors.
I would go with copper tubing.

My system with 2 4' x 8' collectors will heat 100 gl to 120-130 during the summer.

BTW do not use anything steel or cast iron, it will rust and it will leak.
I had to replace the pump with a stainless model, and replace flanges with bronze.
I also had to add high temp poly barrel liners to the tanks.

 

[arngnick]

DIY is a must for me for cost reasons. Found some good info on the BuilditSolar site! Found alot of the answers I am looking for. I am leaning toward a copper tube collector with aluminum fins. I am running a closed loop system so I should not have to worry about parts rusting. I am not nessasarily looking to heat the whole 600 gals but to have enough BTU's stored in the tank to heat my DHW. So if the top 100 gal get to 130-140 degrees I will be good to go plus I will have added storage for the really hot days.

What do you guys thing about using windshield washer fluid or the pink RV antifreze in the loop as opposed to glycol?

 

[DBoon]

If you just plan on using this for summer heating, then a home-built collector would seem to make a lot of sense. For winter heating, a purchased collector would probably provide better cold weather performance.

I've been modeling a scenario of 2 to 4 collectors with 200 to 400 gallons of storage for summer/winter DHW and heating needs. Without getting into the details of my model, for 30 gallons of DHW usage/day a two collector system with a 100-120 gallon tank is probably going to be sufficient for your DHW needs. Realistically, you would need a large amount of solar panels (the 6 to 8 as previously mentioned) to heat 600 gallons in the summer- and I think you would still find that it didn't meet all your needs (i.e. lots of water at 100-110 degrees, just a little too cool for everyday usage). It might be better to go with a smaller dedicated DHW tank and fewer panels.

If you use more hot water per day that what I modeled, and the use is consistent throughout the day while the sun shone, then you might be able to get by with an 80 gallon tank.

In either case, you would still need some sort of backup heat source, just in case the weather didn't cooperate. I would simply suggest that your DHW storage tank be an electric hot water heater and just keep the top element turned "on" and set at 120 degrees F. That would give you 20-25 gallons guaranteed to always be at 120 degrees F and a reasonable heating time for additional water. It also wouldn't require that you heat the entire tank to 120 degrees. Then, if the occupants of your home are cooperative, scheduling laundry on days when the sun is shining is a good way to keep the usage consistent with the availability of hot water.

I think you will find that trying to get 70-80% of your DHW heating needs from solar in the summer is not too hard. Going to a full 100% can be a lot more costly and likely just not worth it unless you are dedicated and have money to burn.

 

[arngnick]

I not sure if I was clear in the description of my setup...I have a 620 gallon battery that is currently heated by my wood boiler. My home is heated from this battery as well as my DHW. If I do not use solar I will be batch burning the boiler through the summer. I am trying to reduce/eliminate my firings by adding a solar heat exchanger in the system to add extra BTU in my storage when the sun is availible mainly for DHW. If I get enough heat to use for heating then GREAT but this is not my intent. I am not trying to heat the whole 620 gallons just enough to make 30-40 gallons of hot water per day. Meaning the 50-100 gallons in the top of the tank will need to reach 140 degrees.

The way that I heat my DHW from the battery is through a plate exchanger and 2 circulator setup this maintains a consistant temperature in my electric hot water tank.

Hope this helps and thanks for the info so far!

 

[Circus]

I understand your desire to utilize your existing water storage but the fact is it's too large and the heat will be deluded throughout. A completely separate, correctly sized thermal siphon water heater would be the simplest, cheapest and most reliable. Your flat plate collectors, RV antifreeze (propylene glycol) and heat exchanger is on the right track. My thermal siphon water heater holds 35 gallons and when the temperature reaches an upper limit a thermal switch, stolen from a Lasko box fan running a 25 watt instant hot water pump, pumps the hot water into a second and then third 35 gallon tank. In the winter only the siphon tank is hot, in the summer all tanks are hot. A ball valve mounted on the basement ceiling has a modified handle that reaches to the bathroom floor so I can choose between the tanks by turning the valve with my foot.
PS The second tank is really an electric water heater so when the weather sucks you just flick on the fuses. If the November clouds last for weeks the SHW can act as a preheat for the electric water heater. Costs only pennies daily to heat 90 degree water to 120.

 

[Seasoned Oak]

You might want to find out if the incoming temperature of your water varies in the summer vs the winter. While water lines should be below the frost line so they do not freeze, the ground may be 50 in the summer and 35 in the winter. This would radically change the amount of btus needed to heat it to the temperature you want.
Matt

The water temp varies but not because of the ground temp,but because of the water temp at the source.Ground temp stays around 50 all year long.

 

[pdf27]

Might be worth thinking about knocking up your own version of one of these:
(broken link removed to http://www.willis-renewables.com/how-it-works.htm)

Basically it's a tiny cylinder in parallel to your existing hot water cylinder (battery in your case). As it heats up, it rises up and siphons hot water into the top of your tank/battery while drawing in cold water from the bottom of it. They do need a lot of attention to detail (extra insulation around them and a flap valve to stop back-siphoning at the very least), and I suspect if you're doing DIY will take a LOT of trial and error on your part. However, if you can get a small hot water cylinder and plumb it up in parallel to your existing battery then it might end up working quite well.

 

[arngnick]

Might be worth thinking about knocking up your own version of one of these:
(broken link removed to http://www.willis-renewables.com/how-it-works.htm)

Basically it's a tiny cylinder in parallel to your existing hot water cylinder (battery in your case). As it heats up, it rises up and siphons hot water into the top of your tank/battery while drawing in cold water from the bottom of it. They do need a lot of attention to detail (extra insulation around them and a flap valve to stop back-siphoning at the very least), and I suspect if you're doing DIY will take a LOT of trial and error on your part. However, if you can get a small hot water cylinder and plumb it up in parallel to your existing battery then it might end up working quite well.

This is almost exactly what kind of system I was thinking except I will have a small pump to circulate from the collector and depend on stratification to work in the storage battery.
Thank you!

 

[pdf27]

I was on a solar installation course last week (potentially quite a bit subsidy available for solar hot water from this summer in the UK, but you have to have an installer's ticket for your system to count, and the subsidy is only big enough for DIY to be worth it) and this came up. If you notice on that diagram it has "hot fluid pumped from solar panel" - you could have it totally convection-based, but only if the pipe runs are quite short and the panel is below the hot water cylinder.

If you've got any questions let me know and I'll see if I can answer.

 

[arngnick]

Thank you so much! I will try to keep you posted on my progress. This is going to be a longer project for me I am in no hurry.