Solar collector integrated into OWB?

I am not sure if its is good fit. Flat plate exchangers only heat to about 80 degrees (at best) above the outdoor temp, thus on thirty degree day, the heated water would be 110 degrees. Putting in hotter water doesn't help what happens is the panel radiates more heat to the outside air than is received from the sun. Evacuated tubes can go about 160 degrees over ambient so they would be good fit but they are far less efficient than flat plates per square foot so you need far more square feet of evac tubes to match up with flat plates at higher cost. The other issues is that in the summer when you don't need the heat you will have too much of it and will have to cover the panels or install some way of dumping the heat.

The current thinking is take the money you would spend putting in solar hot water panels and buy gird tied PV instead. That way you are building up a credit during the summer when there is plenty of sun and use the credit when you want (of course this varies state by state).

It's a really complicated design issue, as touched on by peak bagger. evacuated tubes would be the only thing I'd consider for that installation, for the reasons stated above. they will deliver heat at much higher temps than flat plate collectors. I generally (read: always) use flat plates. the range of output, product quality and price are all over the map with evac tubes, and the 3 factors don't always correlate well.
The Ridiculous: I heated my house this winter mostly with solar generated electricity. it was cheaper than propane most of the winter.
on the other hand, you could use 2-3 flat plate collectors to maintain the temps in the OWB (prevent condensation?) and deliver DHW all summer with no fire, then drain them and let them sit idle for 5-6 months to save the complication of freeze protecting them in the winter. that would be a reasonable solution.
karl

peakbagger said:

I am not sure if its is good fit. Flat plate exchangers only heat to about 80 degrees (at best) above the outdoor temp, thus on thirty degree day, the heated water would be 110 degrees. Putting in hotter water doesn't help what happens is the panel radiates more heat to the outside air than is received from the sun. Evacuated tubes can go about 160 degrees over ambient so they would be good fit but they are far less efficient than flat plates per square foot so you need far more square feet of evac tubes to match up with flat plates at higher cost. The other issues is that in the summer when you don't need the heat you will have too much of it and will have to cover the panels or install some way of dumping the heat.

The current thinking is take the money you would spend putting in solar hot water panels and buy gird tied PV instead. That way you are building up a credit during the summer when there is plenty of sun and use the credit when you want (of course this varies state by state).

Click to expand...

BTW peakbagger, what sort of "PV powered solar hot water" do you have? we've been looking into this.

I have AET flat plates, Alt E store used to sell a DC kit that included the DC pump but I don't see one listed anymore.

I have a DC pump and 40 Watt PV panel with Art Tec Controller. When the sun is out and the controller senses that the top of the collector is warmer than the tank, the pump runs, otherwise it doesn't. The same 12 volt pump with brushes has been running for 10 years this way. I cant remember the brand of pump I have but have an Elsid sitting in a box if the original one ever dies. I had an indicator light on the system that burned out long ago from the varying voltages. The pump does hum so I know when its working. No need for AC to the system, it just runs. Guy Marston the owner of Art Tech http://www.arttec.net/ has a good website you may want to look at.

Here is a link to DC pumps http://www.altestore.com/store/Solar-Water-Heaters/Circulating-Pumps/c419/

It is important to note, this is a closed loop system on 2 story house, the pump only has to overcome friction in the piping and panels not elevation head. If someone has a drainback system, pump sizing is a lot larger.

peakbagger said:

I have AET flat plates, Alt E store used to sell a DC kit that included the DC pump but I don't see one listed anymore.

I have a DC pump and 40 Watt PV panel with Art Tec Controller. When the sun is out and the controller senses that the top of the collector is warmer than the tank, the pump runs, otherwise it doesn't. The same 12 volt pump with brushes has been running for 10 years this way. I cant remember the brand of pump I have but have an Elsid sitting in a box if the original one ever dies. I had an indicator light on the system that burned out long ago from the varying voltages. The pump does hum so I know when its working. No need for AC to the system, it just runs. Guy Marston the owner of Art Tech http://www.arttec.net/ has a good website you may want to look at.

Here is a link to DC pumps http://www.altestore.com/store/Solar-Water-Heaters/Circulating-Pumps/c419/

It is important to note, this is a closed loop system on 2 story house, the pump only has to overcome friction in the piping and panels not elevation head. If someone has a drainback system, pump sizing is a lot larger.

Click to expand...

Oh. I've built lots of those. I was thinking you had something like this:

https://www.sunbandit.us

the low prices of PV panels and lack of Overheating, lack of moving parts, chemicals, all make it very appealing.
karl

If I didn't own the SHW panels, I would just add more grid tie panels and pick up one of the nyletherms on E-bay and be done with it.

Using a 7 panel system I calculate that in the middle of summer it would displace the equivalent of 1/2 a cord a month, I located my boiler building to add panels at a later date.

Basically the cost of putting in the system vs the wood saved just was not worth it.

tuxedoblack11 said:

The panels would only be to heat the DHW in the fringe and summer months NO space heating. I calculated 1-30 tube collector that reaps 44k btus per day which is way over my DHW elements 30k output.

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What do you have for a DHW heater?

I just figured a typical 4500w hot water heater element would generate 44k btus in 2.9 hrs. of steady heating.

Or, if it ran all day, it would generate 368k btus.

Checkout my setup on YouTube...username - kntryhart I have evacuated heat pipes in parallel with my Eko. The system works very well! Enjoy.

I did it with standard solar collectors (one is homemade) I have 164 sq ft of panels and used a 200 gallon non pressurized stainless solar draindown tank. the 200 gallon tank has 3 copper coils with pumps. One to supply my h2o heater for DHW controlled by an aquastat, one to draw heat from the wood boiler and one to supply heat to boiler system. A separate 2 stage controller determines if pumps runs to supply heat to the solar tank from boiler system (periods of no sun when burning wood) or draw from the solar tank to the boiler system (periods of good sun while heating house). Contribution to my space heating varies depending on weather, but it does contibute some to boiler system space heating on good sun days. I have had to use my electric for water heater very little since this was installed. The 3 large solar panels & draindown tank were used off C/L and cost $1,000 bucks. Had I purchased the system new for lots of $, I might have been disappointed in space heating output, But saving 20 - 30 bucks a month on hot water heater electric and considering the whole solar part of my system cost around $2,000, it will pay off in a reasonable time just heating my DHW.