Solar Panels added to OWB

[Mac B.]

I have 2 solar water panels that came off of my parents house. I want to adapt them to my OWB, has anyone done this before? I will only use them in the summer so I won't have to burn wood to heat my DHW. The panels are 4' X 10' and in good shape. Also what angle do the panels have to be?

Mac

 

[pook]

I'd figure what the first & last day the panels would be in use then figure the day in the middle & angle the panels so its perpendicular to the sun on that day at high noon. better would be if the panels could be angle adjusted

 

[Mac B.]

Thanks for the replies, as far as the angle goes the roof I am going to put them on is a lean to so it is basicly flat. I forgot to add that in my earlier post. So do I need more angle than this.

Mac

 

[Dustyw]

I took some off my grandparents house and they were on a 45 degree angle. They used air instead of water, but I wouldn't think it would make much difference.

 

[atlarge54]

Helluva difference between winter and summer sun. You might be in decent shape on a flat roof. I'm in northern Indiana and I swear if I had some collectors pointed NW they'd boil water. I have windows that face both N and W and the afternoon sun seems to shine in FOREVER.

Keep in mind approx 200BTU/sq ft/hr so you're looking at 16,000 BTU/hr. Don't know what you water usage is but that's a starting point.

 

[Mac B.]

NW will be good since that is the way my roof i tilted to. The roof has only 15-20 degrees of slope max.

Mac

 

[mbergeon]

I've heard the ideal angle is your lattitude. IE if you are at 40 degrees that should be the angle of your panel. If you are at the equator it would be 0 degrees or flat.

 

[pook]

the flatter it is, the more apt it is to collect debris [dust, leaves,etc] which block the sunlight

 

[ks_osage_orange]

If you really are going to only use them in the summer, when the sun is at a high angle in the sky. Then they should be layed flatter, but not flat. My guess is about 20 degrees above horizontal facing south. The sun probably reaches around +80 degrees up from the horizon at midday on the summer solstice at your latititude.

 

[sesmith]

You'll find all the answers to you're questions (and more) here:

http://www.builditsolar.com/

 

[pdhowell]

Angle of solar collector

I have installed solar collectors, in addition to my wood stove to heat our home. The answer to the angle issue depends on what you want to do with the collector, heat, hot water, winter, summer.

In general collectors for year round use, typically hot water, would use your latitude. Just checking, for central North Carolina, that would be about 36 degrees from horizontal. If you want to optimize the collector for winter use, say space heat, you can drop this by up to 10 degrees, but usually not less than 30 degrees. Collectors need some vertical for the hot air/water to rise, they don't do well when lying flat and horizontal.

The collector can be mounted in the vertical angle, latitude plus or minus 10 degrees. The the direction angle, (aspect) is plus or minus five degrees.

The biggest problem is often dumping heat off them in the summer. The collectors need to be covered, or have a pump pushing fluid through them at all times into a heat dump, basically a finned radiator outside of the dwelling. Evacuated tube collectors are safer in this situation than flat panel, are slightly more efficient but more expensive.

I have an Apricus system (apricus.com). From our limited experience, I anticipate that it will my house during the day for half the year, during the day, late September through middle November, and February through May. It heats hot water year round. Only in December and January, when the solar energy is low, do I have to use some oil (backup) during the day when I am not home to keep a wood stove going.

The drawback is the high initial cost and the need of a clear southern exposure. The cost is presently partially offset by the 30 percent tax credit. My system was planned to have a 8 year payback, but is more effective than anticipated. (It was planned as a domestic hot water system, but when the demand for hot water is satisfied (110 gallons (storage) of 130 degree water per day), it puts the rest of the heat into my heating ducts through a hot water coil, direct from the collectors. Basically, it heats hot water in the morning and the house in the afternoon. In the evening, we use the wood stove. Wood of course, is another variant of solar heat.

Hope this helps,I have discovered that every install is different.

 

[Junkfxr]

You beat me to it pdhowell. That's basicly what I was planning to reply as I was reading through the thread. We've been off grid since 1999 and use solar as our only electricity, with diesel generator back up. Use it for some heat also so I have fooled around with all kinds of angles for maximum output and always find that the angle equal to your latitude is the best for year round performance if you have stationary panels.

 

[pdhowell]

Solar panel angles

Junkfixr, you are right. Thanks for reminding me, others, that photovoltaic panels are almost placed at the latitude, thermal collector plates have a couple more variables. but are also usually placed at the latitude too.

For what is worth, as a quick and dirty approximation, aiming collectors at the sun at noon at about this time of year (halfway between the summer and winter solstices, June 21, December 21) is the proper angle. Dave

 

[Mac B.]

OK that is what I was looking for as far as angle goes. If i am only heating water in the summer months what am I going to need to control the pump to the collectors with? I was thinking of puting it on a timer to come on around 9:00am - 5:00pm or is there more to it than that just to heat water? I am going to use my 500 gallon OWB that is very well insulated as my holding tank.

Mac

 

[Junkfxr]

OK that is what I was looking for as far as angle goes. If i am only heating water in the summer months what am I going to need to control the pump to the collectors with? I was thinking of puting it on a timer to come on around 9:00am - 5:00pm or is there more to it than that just to heat water? I am going to use my 500 gallon OWB that is very well insulated as my holding tank.

Mac

Yep, it's a little more complicated than that. There is a temperature differential pump controller that needs to be used. It senses the difference in temperature between the collectors and the liquid in the holding tank and turns the pump(s) on as long as the temperature in the panels is higher than the temperature in the tank. If the pump is wired up to just a timer, when the temperature in the panels gets lower than the tank temperature, say, like on an overcast or rainy day, it'll cool the water in the tank as it's being pumped through the panels. You'll also want someway to keep it from freezing in the winter. Personally, I'm real fond of drain back systems. Solar heating isn't rocket science but it does take a little thought but once you start understanding thermal dynamics some, it becomes real easy. The worst part is trying to prevent freezing in the winter. PM me, I've got a realy good artical that I can pass along to you that will make the whole process a lot easier..... if I can find it.

 

[Mac B.]

Junkfxr, the panels I have are drain back type. I would be intrested in the article you have if you will post it or send it to me.

Mac

 

[Junkfxr]

I just thought of something else that might interest you. If you ever get up around Mount Airy, stop in at Hicks Waterstoves, www.HicksWaterStoves.com
They've got the one in their building plumbed up with solar collectors and sell all of the stuff to do it with too.

It'll Tuesday before I can look for the article that I was talking about earlier but when I find it, I'll let you know.

 

[pook]

might be simpler, cheaper & not as efficient to locate a temp sensor on the coldest part of the panels so that when it gets hot the coldest water from the tank gets pumped.........i'm not familiar with the cost of a differential sensor system

 

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