Info on panels wanted

[The master plan]

These are for sale locally, but I can't find any info on them. Btu per day would be what I am looking for....




No pipes, just 2 sheets of copper with water running in between the dimples on the sheets. They measure 3 foot by 8 foot.

I can get six for $1700...may be able to go to $1500 for 6...

[jfweaver]

It looks like the company dropped off the planet around 1985 when the solar tax credits ended (they may have lasted until 1988?). I don't think I'd spend that much on them all things considered.

For what its worth, a quick internet search shows you can get 1 or two evacuated tube collector systems for about the same price. They will be more efficient, weigh less and
come with a warranty.

[Exeric]

I think you answered your own question about paying that price for 30 year old panels. But that's far from the end of the story. You need to do your homework before deciding between solar hot water and solar PV. A lot of us (well... me) think your best bet is PV since you live in cold Minnesota. Even if you are snowed in on a cold winter day and are getting zero solar energy to speak of, you can still use the banked credits from the PV power from spring, summer, and fall to subsidize the shortfalls in solar energy you will experience in winter. That's a big deal.

The alternative is to get an enormous solar hot water system that still might not meet all your heating needs in winter. Then you would have this similarly enormous supplus of hot water in spring, summer, and fall that you couldn't use and would just be throwing away. Not very economic compared to a correctly oriented and sized solar PV system. I'm speaking just for a primarlily heating climate like you live in. This wouldn't necessarily be true for a mixed climate.

[MN Renovator]

$1500 of solar PV will pay off quicker than $1500 of hot water. Grid-tied PV is nice because you aren't going to run out of capacity to store the hot water and then be stuck and you lose a bunch of efficiency in the winter when they are surrounded by snow. I think even though $1500 doesn't get you too far into the PV game but $1500 of the contribution to the solar would make a good match for a heat pump water heater and/or one of the super efficient inverter mini-splits used heating and cooling. With natural gas being super cheap(relative to electric resistance heating) and the lack of gas water heaters that tie into solar hot water, the amount of resistance heat you need to use in the winter makes for a payoff period that is extremely long. The solar PV installer that lives down the street from me says it takes about 30 years to pay off even a 2 panel water heating setup and the plumbing isn't easy or cheap and there is more maintenance than PV. He showed me his eGauge power usage and in the summer and some of the swing seasons it keeps up with the usage but in the winter, when you need it more, you get less.

[jeff5may]

The master plan,

What type of heating were you planning on providing with these panels? Being 1980's-era tech, they might be rather low in efficiency. Considering your Northern latitude, you would need more than 6 to provide lots of useful hot water, especially in winter.

Solar PV, heat pumps, budget billing and net-metering go hand in hand. Before this decade, thermal solar combined with a massive heat store made better economic sense. But hardware prices have been falling fast, and continue to fall as we speak. With small-scale systems, the installation price is now more of a factor than the hardware. If you can DIY, the savings will allow you to add more panels.

[Ryland]

Are those aluminum framed panels? if not I can get you a much better deal on the wood framed panels, even if they are aluminum framed panels $1,500 seems rather high!

How to use SRCC solar collector ratings

It has been years sense I worked with solar hot water in MN, but I helped put a system on in St Cloud MN, near where I assume you are, it has about the same SF as 8 to 10 of those panels and was designed to heat 100% of the domestic hot water and keep a 1,800sf house at around 50 to 55F on it's own in the dead of winter, additional heat was with a masonry mass wood stove and of course insulation!
Now I know everyone on here who is from California says that 6 panels will not heat your shower water in the winter, but they also figure out excuses to bust out the winter coats when it gets down to 65F

These panels are 1980's tec, but what you can buy today for flat panel solar collectors are pretty much exactly the same! low iron dimpled glass, aluminum frames, tiny bit of insulation in the back... not much has changed.

Also, a BTU is the energy it takes to raise one pound (8 pounds to a gallon) of water one degree.

[Exeric]

Ryland,
Yes it's very fashionable to lump all Californian's together, and easy too. Go for it and see where it gets you. As for getting enough heat out of any solar system in the far north climates in the dead of winter - it seems to me I remember hearing Randen, someone who I very much respect, saying that in the month of December there was hardly any heat generated from his system to heat his shop. And from what I recall it was a very well engineered system that worked on most of the same principles as the system we are talking about here.

But I won't bring up the exact quote so as not to embarrass your weak ego. If you've figured out a way to store November's heat to replace all of the dearth of heat in December for Randen, and do it cheaply and without a lot of work... well then please tell us all.

[stevehull]

Great discussion! I had not thought about the implications for low cost PV competing with solar hot water collectors.

In a home renovation I am planning, am strongly considering the use of a geothermal heat pump for both domestic hot water and for radiant heat. Also incorporating about 10 kW of PV with grid tie. The high COP of the water heater makes sense.

I had not fully recognized the implications of the long term storage of watts "on the grid" but it just makes sense now that I think of it.

Steve

[Ryland]

Originally Posted by Exeric

As for getting enough heat out of any solar system in the far north climates in the dead of winter - it seems to me I remember hearing Randen, someone who I very much respect, saying that in the month of December there was hardly any heat generated from his system to heat his shop. And from what I recall it was a very well engineered system that worked on most of the same principles as the system we are talking about here.

What I am saying is that it's working for many people who live in this area, so while I don't know Randen or why their system failed to perform.

Here is one project that I worked on about 10 years ago and every time I see the home owner he's still thrilled with his house and that it's heated with the sun, http://strawbalefarms.com/active.html I worked on 4 other houses in Wisconsin and 1 in central Minnesota that have near identical solar hot water systems as their main source of heat and they all work in December.

[Exeric]

Ryland, I'm glad this is moving away from such a p***ing match!. I have never disputed that you can design any solar heat system to match the average BTU requirements for a specific location and size of structure. But the point of this whole thing is the word AVERAGE. We don't live in an average world. When there is high moisture content in the air there is very little heat getting through, sometimes almost none. That is because that moisture, whether it is fog, rain, sleet, or snow, will absorb most of the infrared rays from the sun. That shouldn't be a revelation. There's anecdotal evidence all the time from members on this thread that this happens.

Sometimes there can be long stretches of stormy or foggy weather. The longer the stretch of this weather the more you are screwed with a solar thermal system. You will get almost no heat out of that system for that long stretch. Even if you then get a similarly long stretch of clear blue skies and completely make up for that BTU shortfall you are still screwed. To make things simpler I'll convert a long stretch of BTU representations into unit values of 0 or 1. Not very accurate but you will get the idea. Plus I'm make the similar assumption that you can't store the heat. Again, not that accurate but for month long stretch of similar weather it approximates the truth. Even a thermos bottle will only retain heat or cold for a day or two.

In your location you average 1 BTU each month in December, January, and February. December was a stormy month. In December let's say your BTUs coming in was 0. January was a great month and you got 2 BTUs. February you got the average, 1 BTU. Because a thermal system does not really story heat very well December was a total loss. January had an abundance of BTUs, (2!) but you wasted 1 BTU because it was more than you needed. February came right in on the design spec for the system for the month. Your system worked to specification using the AVERAGE BTUs required for your location. You got 3 BTUs out of your solar thermal system, and averaged 1 BTU for each month. What is there to complain about? Well you might complain that you froze your butt off in December. I would.

On the other hand in a net metered solar PV system, which for simplification I'll assume the same equivalent BTUs in watts, you didn't freeze in December. That's because you designed the size of the array for the whole year's electrical requirements. The grid stored your excess energy when you generated it and returned it when you needed it. It functioned just like a huge perfect battery.