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Old 04-03-2015, 09:39 AM   #31
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Totally true about needing a larger tank for these to make sense. I plan to do a 30-40 gallon tank.

You get more heat out of a collector in winter than a lot of people realize. They don't collect heat from the air, they collect it from sunlight, and it's all radiant energy. It's true that in winter months they're less efficient - but not zero. I got interested in this when I first visited my wife's parents' house. They had a solar hot water system installed in like the 80s, before it was really popular in the area (they're still the only ones on their block that have one). They get enough heat out of it in winter even for two people to shower, and snow (we got 5' last year) doesn't stay there. This is also how green-houses stay warm in the winter.

Also agree about tank entry. It's important for efficiency for hot water to be put into, and taken out of, the tank from the TOP, and cold water at the bottom. But top-port water heaters aren't a complete waste - their cold water inlets are all done with dip tubes that run to the bottom of the tank. Side-ports are better but more expensive. YMMV.

Still waiting for nat_ster to mass-market a "super-tank".
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Old 04-03-2015, 09:44 AM   #32
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Also, that kit looks sort of interesting but wicked expensive for what you get. I'm evaluating one of these:

4'x10' Eco Friendly Solar Heater Heating Panel for in Ground Swimming Pools | eBay

They're flexible and although you're supposed to drain them before winter they're a LITTLE more freeze- and vibration-proof than copper. I'd put it in a glazed, black-painted plywood box to increase its efficiency. I'd also set it up as a "drain-back" system, which basically means you have a small reservoir the water drains into when the pump isn't running. That prevents the panel from freezing and also from overheating.

Add a pump, heat exchanger, and simple control system and you're still at less dollars than the other kit.
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Old 04-03-2015, 02:20 PM   #33
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Yeah I was confused by that kit's installation using only the tank drain to both send and return hot water from the panels. After further investigation, I realised they have a clever device that injects the hot water though an inner-tube in the drain plug into the middle of the tank so that the water being pulled out to be heated doesnt just suck up the hot water again. Lots of positive reviews on the kit. I wouldn't need the PV solar panel, and my water tank will only be 20 gallons, so I think it would keep me covered. The wood stove I have in mind has a boiler kit which I can always fall back on in the winter, plus the electric heating element of the water heater I will use as my storage tank can always be plugged into shore-power or whatever.
I wonder if that solar pool water heater is safe for potable water?
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Old 04-03-2015, 02:35 PM   #34
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Quote:
Originally Posted by Zephod_beeblebrox2 View Post
Problem is that while heating water directly from the sun works well during sunny afternoons, the water will be cold in winter and at night.
Well... if you wanted an instant (ie no storage tank) solar water heater then yes you'd be in trouble at night. But just as energy can be stored into a chemical reaction in batteries, it also can be stored as heat in an insulated tank. Certainly in the evening the tank could be piping hot, and with appropriate design it could still be warm enough for use first thing in the morning. And like taskswap says, there's a remarkable amount of solar heat available in the winter. I'd dare say that a solar water heater will behave from summer to winter exactly (or nearly?) the same as a photovoltaic panel does. There's a reduction in the winter certainly, but with PV and with water the system can be designed to allow for that.

You mentioned paupers not being able to experiment in another post... while perhaps that's somewhat true with PV, I would suggest that some basic small-scale water heat experiments can be done "on the cheap" with found or nearly-free stuff. A scrap of aluminum siding/soffit/facia material, some PEX or copper tube, some glass from an old window or even borrow a pane out of the bus.. One thing that might not turn up easily is a water pump, but you might be planning to buy one of those for the bus anyway and could borrow it for solar experiments from time to time. It pays to do small experiments because they breed ideas that help the real thing come together better.
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Old 04-03-2015, 02:53 PM   #35
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Some time ago I posted a link and pics of a house in Alaska that is heated by solar water collectors. No question it works in winter.

My massive mega boiler is going to have to wait till fall before I start building it. I just don't have the time right now with trying to build the rest of the bus and stay making money.

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Old 04-05-2015, 10:51 AM   #36
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http://vi.raptor.ebaydesc.com/ws/eBa...=1428242297683

This looks interesting. Question is how far will it bend, will it try to peel up if its glued down and how efficient will it be at 120f
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Old 04-05-2015, 02:14 PM   #37
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That looks interesting. About half-way down the page it says "flexible up to 3% (= 3cm over 1m) across their length." It does seem like all the pictures are showing bend only on the one axis; maybe they shouldn't be bent on any other axis? I take their flexibility spec to mean that over a 1 meter/yard surface, the panel could be bent so that the middle is raised above/below the surface by 3cm/1 inch.

It's fun to look at trade-offs. Instead of best-available power density, this model offers flexibility that others can't provide. Some applications need that.
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Old 04-05-2015, 04:03 PM   #38
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Hmm... 3% does not seem too flexible. I'm not sure what the curve of my roof is but I'm sure if I walked on it, it would flex even more than 3%.

I think this panel joins the list of interesting but impractical products.
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Old 04-05-2015, 06:37 PM   #39
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I just put a small flexible panel on my roof to keep my chassis battery charged. The panel is made by Renogy and flexes up to 30%..

http://www.skoolie.net/forums/f28/so...ied-10519.html
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Old 04-19-2015, 11:09 AM   #40
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I just saw some 30% flexible panels. Now these look interesting
http://www.amazon.com/Generic-Semi-f...le+solar+panel

I've seen some listed as 210 inches long which seems impractical.
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