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Old 03-23-2015, 06:57 AM   #21
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lion's are great battery's i plan on changing out when my fla's are dead. hope the price keeps droping it would cost over 2500.00 today. ouch

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Old 04-01-2015, 01:18 PM   #22
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30W 30 Watt Solar Panel 12V 12 Volt Battery Charger Off Grid RV Boat | eBay

I was looking at this solar panel ad on eBay thinking a few of those on the roof could supply all my electrical needs. Comments?
Is this a good set up?
http://www.costco.com/.product.10011...0_April-Mailer

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Old 04-01-2015, 02:27 PM   #23
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Actually, it's better than I expected it to be when I saw it was a kit. But like all things, you make sacrifices when you go for kits. A few comments:

* Solar panels are 100W each. They're fine... but you can get much larger sizes now for short money online. Larger panels don't just give you more juice - they also give you a lot more margin for cloudy / winter days.
* Charge controller is straight PWM rather than MPPT. It's actually a decent brand, just not the latest tech. Xantrex's C40 (next model up) is only a little more $ than the C35 and is MPPT which helps you get the most out of your batteries/system.
* Inverter is pure-sine (good) but has plugs rather than direct-wire support. It's going to be extra work to wire if you also want to be able to run your devices off shore power.
* Inverter is only 2000W. Maybe that's all you need but I'd personally go with 3000W, which again, bought separately, is only like $40 more on Amazon right now.
* If you want shore power you still need the AC->DC charging component. There are inverters that do this internally. This isn't one of them.
* It doesn't say how long those cables are... but they sure look short to me...

Your mileage may vary and only you know your requirements. But me, I'd pass. This will totally work, but you'll get more functionality and mileage out of slightly better versions of each of these components. I personally think this kit is best for somebody who just wants to switch their fridge completely to solar, and has no other plans.
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Old 04-01-2015, 04:24 PM   #24
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If you're set on electric water heating, it could help things immensely if you consider a high voltage battery bank -- to the point that the heater can be run directly from the batteries without any inverter, for example. This is very much into the realm of engineering it yourself..

As an example, consider a battery bank at 96+ V dc paired with the Eemax SP3512 point-of-use instant electric heater. It's not too far-fetched to think that heater could be modified relatively easily to run from a dc source. The Home Depot product page indicates it'll give 35F temperature rise at 0.7 gpm, which isn't much, but thought experiments have to start somewhere. Anyway, 3.5kW from 120 Vrms is 29 amps so it looks something like a 4.11 ohm resistor. Put that across a 96 V battery bank and you'll draw 23.4 amps or 2.2kW (note that already we're getting less temperature rise and/or water flow than advertised). But 23 amps from a battery bank is nothing. Losses in the batteries and wiring would be kept relatively low, and most of the power would be delivered to your (luke-warm) water. A 5 minute shower would consume 0.186 kWh, and if you add 15% for losses (probably too optimistic) that's 0.214 kWh. Rounding up a little more, that's about 1 of maybe 5 daily hours of useful sunlight falling onto a single 235 watt panel.

From my perspective that's a very meager supply of warm water, but maybe it's enough for your purposes. At this scale it seems doable.

One other note: if heating water or the interior space is a big thing for you, it might be time well spent to look at using the sun to heat the water directly. Storing energy via heated water isn't so different from storing electricity, and if ultimately heat is the energy form you want anyway, you can gain some efficiency by not converting to and from electricity.
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Old 04-01-2015, 05:26 PM   #25
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More than "some" efficiency. PV collectors are lucky to see 30% efficiency, while hot-water collectors run 60%-80%. They're also dirt cheap - you can DIY your own with some copper tubing and a plywood box, although I think it's worth the cash to buy a good collector. This doesn't count the efficiency losses from the inverters, wiring, batteries, charge controllers, etc.

Not saying solar electric doesn't have its place... But if you're serious about wanting to heat hot water from the sun, it's probably worth plumbing for that. A very simple system can be done for the same cost as a good PV panel and you're going to get more mileage out of it.

nat_ster, when are you going mass-market with your 35-heat-source stainless hot water tank beastie?
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Old 04-01-2015, 05:33 PM   #26
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More than "some" efficiency.
OK, sometimes I understate.

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nat_ster, when are you going mass-market with your 35-heat-source stainless hot water tank beastie?
Maybe we just need to set up a kickstarter campaign for him and then let him know about it after it has smashed its funding goal and the whole world is waiting to get their own? It needs a good name, but I'm terrible at names. If it had been all up to me my kids might have been named "hey you," "not you," "the other one," etc.
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Old 04-02-2015, 09:17 PM   #27
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Its interesting that we have so many opposing views each backed up by theoretical figures. We're all in the same boat. We all want the cheapest system but can't risk money on experimentation because we're all paupers.

I was just toying with the idea of a wind power system.
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Old 04-03-2015, 12:10 AM   #28
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There is no question to me that the cheaper way to heat water with solar power is directly though panels designed just for that. Let the PV panels make electricity and the hot water panels make....hot water!

I think these look interesting

http://www.amazon.com/Complete-Panel.../dp/B0041XXSJW

And probably cheaper and easier than designing your whole electric system around hot water!

Just my .02
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Old 04-03-2015, 06:47 AM   #29
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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.
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Old 04-03-2015, 06:50 AM   #30
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i dont like the hookup to the w h. should enter the bottom and exit the hot water feed. also with s h w you need a good size storage tank 40 gal. min. and a place to put the tank.with a few changes it would do. i would use a heat exchanger so i could use year round. good find charles thanks for the link. i got a gas on demand from sportsmansguide and it works great. i put it in my bath and showered for over 3 months on a single grill tank. uses 2 d batteries to ignite.
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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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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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