Free, More Hot Water? - Part 1

A solar water heater for an RV? Is it possible? Wouldn't it be cool to unroll a small rubber collector on the roof of your RV, adhere it to the roof, plumb it into your small-ish water heater and have LOTS more hot water, while using less propane and/or electric to heat it? Sounds like a Free Lunch, doesn't it?

Nope. Not this time.

Here's the scoop. For years folks have been using Solar Thermal hot water systems. In fact, Passenger Pete has two solar collectors on his roof that feed a heat exchanger mounted on the top of his electric hot water heater. This system is filled with anti-freeze and circulates through a coil that exchanges heat with water circulating around in another coil. This is a good working system, but a bit too complex for what I'd use in an RV. It needs thermostats and pumps to maximize it's use and the heat exchanger system itself would have to fit someplace.

In a simpler system we have a collector of some kind (more on that later) on the roof and it feeds the hot water heater/tank directly. So there's no anti-freeze in the system, just water. Of course you'd have to make sure that it is drained in the winter (if you actually HAVE winters!) or have some way of draining water back into your water system and out of the collector if there was a danger of freezing. So far, so good. Since this project is really in the planning stages, I am not sure what temperatures the water will get to from the collector, so I will have to test some different configurations. I'm hoping I can set up a simple recirculating system that feeds my little Atwood 6 Gallon water heater.


I'll put bypass valves on both sides, so I can disconnect the collector from the hot water system. I mean, if it's cold, why heat all that extra water! That brings up another good point, since the collector has to have water in it to heat, then it stands to reason that you could have more gallons of hot water to use. I'm looking at adding a 6-10 gallon collection system so I should be able to have that much more hot water.

How do you get the water up to the collector? Good question....yes, I know I'm talking to myself, but that's okay. I figured a small 12v water pump near the inlet of the hot water heater running from power I get from my solar panels (or you could install a small one amp solar panel) with a manual switch or perhaps a flow switch or temperature switch or even a pressure switch wired in for automatic operation. Since the system only needs to pump water up to the collector and that will only happen when the sun is up, it won't really affect my solar charging or power consumption. I'll have to make sure the pump will lift water to the height of the roof. The one pictured will lift water 2.5 meters or 8.2 feet and will pump 350L/hr or 92.5 gallons/hr of water. It uses 450mA of current. Gravity will be used to get the newly heated water back down to the hot water heater.

Now, on to the roof! I'm looking at a flat, tubular style of rubber or polypropylene collector. These get connected to "manifolds" that if needed can be daisy chained together to form the basic collector. From the manifolds they will be connected to flexible hoses leading down into the coach, probably through the refrigerator roof vent opening.

I've got to figure out how much square footage of collector we'll need to feed the water heater. Since it's flat and will be a few square feet in size the weight of the water will be spread out. that's a good thing because it weighs 8.4 lbs/gallon. I try to be as nice to my roof as possible. Roof leaks kill so many RV's.

I am waiting for several manufacturers to get back to me with some real technical specs of the collector material. Mainly, I'll need the amount of liquid they hold per square foot and how much they will heat water at a given sun level. Then I'll be able to calculate how much area the collector will have to cover to make this work.

Of course, since it's WINTER here, I can't really do any heavy, "real world" testing, but I will assemble the test system now and plan on writing a second article as more information is available.

Be seeing you...Down the Road,

Rich "The Wanderman"
http://www.thewanderman.com

Why Winters Are No Fun (For Me.)

Aero Cruiser Left Side

    Here in the Northeastern United States we have this thing called Winter. For you folks in regions that don't have it, it's the time when RV enthusiasts dream of being back on the road. Unless, of course, they are die-hard winter campers that enjoy the "roughing it" aspect of camping without. Personally, I LIKE a hot shower now and again. To each his own! There are RVs available that can be used in winter, are well insulated and set up well. I don't have one of those. Ah well, maybe there's a way to retrofit the one I have.....

For me, Winter is more about planning and researching improvements for the RV and plotting trips to far away (OK not THAT far) places in my RV. If you've read my Introduction:

  http://wandermanblog.blogspot.com/2011/11/welcome-to-my-little-corner-of-internet.html

you'll know I wanted my motorhome to have the ability to let me escape on a moments notice. I keep the RV stocked with most everything I'll need for a week or two away.The freedom from reservations and the increased spontaneity really are great. I couldn't tell you any other mode of travel would allow for this kind of flexibility. Besides, I can rarely stitch a few days together from my wacko schedule.

Aero Cruiser In The Distance

I sit here today, looking out the window at the light snow flurries slowly wafting down, my RV covered and nicely framed in the window. It's pretty, but a bit depressing. I'd rather be working on it or driving it someplace or setting up camp...or any number of things rather than looking at it covered, shivering in the cold. OK, I KNOW it doesn't actually shiver, but you get the idea. So here I sit, researching, writing, and plotting. I'm very glad I was given the opportunity to have an audience for my rather convoluted thought processes.

EPDM Solar Water Heater Roll

I'm looking forward to a beautiful Spring season so I can start putting some of the cabin fever fueled, R&D to good use. Over the Winter you'll see articles on everything ranging from better battery technology to electric fireplaces. From Solar water heating to the latest and greatest gadgets to make RV'ing better. I'm researching a particularly cool technology to use LCD to eliminate shades, drapes and tint!

My free time and nervous energy turned into useful information, not a bad thing. Most of the time!

If anyone wants to suggest a topic for an article, please don't hesitate to post a comment. I have the time, and I'm willing to use it! It truly makes the time go by faster, at least subjectively. And I learn a great deal in the process.

Sounds like a great deal to me!

Be seeing you...down the road,

Rich "The Wanderman"
http://www.thewanderman.com

How Much Do You Have In The Bank? - Part 1

Batteries. We all need them. We all want more capacity. I mean, the whole idea of RVing is to take the luxuries and necessities of home on the road with us. Comfort is a GOOD thing. So is convenience.

Lithium Ion Latop Battery, Cooking

Batteries have been around a LONG time.The technology hasn't changed all that much in hundreds of years. A bit of lead, a bit of acid and behold, a battery. Yes, they've gotten marginally better in the intervening years, but there hasn't been a great leap in that technology for quite a while. We did have Ni-Cd's then NiMh, both had their advantages and disadvantages. (Anyone remember battery "memory?") Well, there is something relatively new afoot in the battery industry. Lithium Ion chemistry has taken most other types out of the mix when it comes to small electronics (cell phones, laptops, etc.) The problem is the basic Lithium Ion chemistry can go into something called "thermal runaway" it doesn't happen often, but when it does it can be catastrophic.

Imagine having that happen near you propane tank!

3.2V LiFeP03 Cell

There is a fix. A new chemistry. Still based on Lithium Ion technology, but MUCH more stable. Lithium Phosphate (LiFePO4). These have all the advantages of Lithium Ion technology, but won't meltdown like a bad nuclear reactor. (Two and Three Quarter Mile Island, anyone?) They can store a lot more power than typical lead acid batteries, they weigh less, and can be discharged further than the typical 50 percent of lead acid without damage. They can be charged using existing technology and can be retrofitted pretty easily to any RV.

Sounds Great Right???!?

There Ain't No Such Thing As A Free Lunch. (TANSTAAFL)

They cost. They cost big. But wait! The prices are slowly coming down. A couple of years ago they were $3,000 (2009) now you can get a 200Amp/Hr setup for around $1,500. Now that electric vehicles are becoming more common place (let me tell you about my GM EV1 someday...) the batteries that drive (yes, pun intended) are dropping in price due to increased demand. With more factories expanding all the time it won't be too long before you can get these for $500/200Ah!

Typical Lead Acid Battery

Let's do some basic economics math. The typical RV has two lead acid batteries that provide around 200A hours total. You can discharge them safely to 50 percent so you have 100Ahrs to play with. They can usually be charged/discharged (a "cycle") around 500 times or so. The average cost for these are around $150, perhaps you have to have them shipped. They weigh around 80 pounds each so figure some money for that as well. If you take $150 times two batteries that's $300 and then divide it by 500 cycles you get  about 60 cents a cycle.

4 cell 12.8V nominal LiFePO4 Pack

Now look at lithium phosphate batteries. Today, the cost of one 200Ah battery would be around $1500 but that's where we have to take another path. You can discharge these to 80 percent so from 200Ahrs you get 160Ahrs to play with. You can do this for 3000-5000 cycles! So if you look at the cost $1,500 divided by 3000 cycles = 50 cents a cycle! At 5,000 cycles it's only 30 cents a cycle! This does NOT take into consideration that you are getting 60 percent more amp hours per cycle to play with. If you figure that in, it's even less expensive since you could go with a smaller battery.

Did I mention they weigh 30 percent less that a lead acid battery!

Do you remember when I mentioned TANSTAAFL?

There are differing opinions on charging these beasties. Surely, a quality charge controller that can be programmed what the voltages should be at the various stages (Bulk, Absorb, Float) will work fine. The problem is that sometimes the cells themselves can vary in voltage and not charge fully. If you have four cells per battery pack, it's important to make sure each one is close to the other to make sure the battery lasts. They also do not like being overcharged (Who does?) and REALLY do not like being discharged below around 10.8 volts. Shouldn't be a problem as long as you monitor them and/or get a low voltage cut-off...I will be getting one and setting it at around 85 percent discharge. This way I can't destroy my expensive battery pack!

Typical Cell Mounted BMS

There are electronics that can manage all this for you. Available as a separate device or even pre-built into (onto?) your battery back. These will fix that problem right up at a bit of added cost. They are called Battery Management Systems (BMS) and can range from under $100 to multi-thousand sophisticated versions with LCD displays and lots of bells and whistles.

While I believe it is important to monitor your batteries (any kind) I believe the best monitoring software is in you own brain! Keep an eye on you voltages and you'll be OK. Check the individual cells once in a while and see if there any variance, If so, charge the low cell, or drain the high one :)  I oversimplify, but these batteries are pretty robust.

Conclusions?


I'm not ready to make any set conclusion on a direct swap for lead acid at this time. I will be testing a 400Ah pack(s) in the coming weeks and will keep everyone posted on the results. It SEEMS like a great advance for RVers (What's not to love?) However, I'll be the guinea pig and experiment with them. Likely, something will fry, explode, melt down, or not be as advertised. Let the manufacturers put their product where there mouths are!

Various sizes of LiFePO4 cells

Stay Tuned to this space in the coming months for some real world testing data from yours truly. Everyone could use more in the battery bank, couldn't they?

Be Seeing you, down the road.

Rich "The Wanderman"
http://www.thewanderman.com