Author Topic: Comments on my off grid solar (Read 1991 times)

RIjake · « **on:** March 26, 2012, 03:54:22 PM »

I'm putting together a small system on the cheap.

Here's a preliminary layout of my 12V solar setup for my off-grid cabin. The loads for this system are minimal as we have a VC Vigilant wood stove for heat, Servel LP for fridge, on demand hot water and range. The AC loads are the 115VAC Grundfos soft start well pump (1280W max), LED bulbs in lamps (6 watts each) and maybe a laptop (?W). Also the ignition for the on demand water heater (48W max). DC loads are a 12V CD player from a car, a power port panel for cigarette lighter chargers for ipods and cell phones and a couple CFL lights for the basement. Less than 1400W plus a fudge factor.

I have a 5500W gasoline generator to power my battery charger to top off the batteries for days with no sun and large AC loads like power tools.

The components that I currently have are as follows;
- (3) 15W solar panels = 45 W total that will be mounted south on a 40' tower below my ham antenna. $145
- (3) Deka Marine Master Deep Cycle batteries in parallel at 715amps each. $300
- Xantrex C40 40 amp charge controller. $65
- Xantrex CM/R 40 remote display. $45
- Xantrex SW2000 pure sine wave 2000W inverter. $280
So far I'm into it for $835. I've still got to buy all the cable, wiring, breakers, box and fuses. So maybe a $1000 total.
I'm planning on using a Midnight Solar Baby Box with DIN breakers and a bus bar for PV and battery disconnects. Also an AC panel with circuits for wall receptacles will be wired off the inverter for lamps using LED lights and the ignition for the on demand hot water heater.

In the future I'd like to add another PV panel, maybe 125W, Xantrex battery temperature sensor, another charge controller for a home built wind generator project that I'm working on.

The batteries will be housed in an insulated and vented plywood enclosure with the fuse inside. All other items will be mounted on a wall in a small utility closet close by.

I went with the Xantrex brand simply because I have a good friend who works for Schneider Electric which owns Xantrex and he got me a 50% discount on all the components.

Any input from others with more experience than me would be appreciated. Especially the disconnects. I'm not sure that I have those right.

NM_Shooter · « **Reply #1 on:** March 26, 2012, 05:06:14 PM »

I'm thinking that the 45W panel is a little bit on the light side for your system. I'd want to shoot for a little better panel, especially if it is fixed and not tracking at all.

Affordable solar has a 260W panel for ~$350. I don't know how bad the shipping might be.

When your budget allows, upgrade to a MPPT controller as it will further optimize the power you have available.

RIjake · « **Reply #2 on:** March 26, 2012, 05:32:04 PM »

I agree, I would like to go bigger on the panel but I just wanted to get my foot in the door so to speak.

If I understand the difference between MPPT and PWM, I am maximizing the output of the panel with the MPPT right? So the PWM is less efficient?

What do you think of the way I have the disconnects wired in the box?

I though for the money it was hard to beat the Xantrex, this particular unit has three modes
PV charge control, the one I'll be using
Diversion
Load control

It also has a three stage battery charger (bulk, absorption and float)

I can connect an optional battery temperature compensator and do a manual or auto equalization too.

MountainDon · « **Reply #3 on:** March 26, 2012, 06:57:07 PM »

My first thought was that the 3 x 15 watt modules were too small; a near waste of money/time. Adding more modules later may bring matching problems. Modules mixed together through one charge controller work best when fairly closely matched in Vmp and Imp.

Second thought was the fuse. I have no idea what your level of knowledge is so if this is "old hat" to you, it's meant also for other readers.
1. AC fuses (and breakers) are different from DC units. Do not substitute.
2. There are two categories of fuses; overcurrent protection and short circuit protection. The difference is that overcurrent protection fuses are slow to blow. It can take several seconds before one blows. This will not properly protect against a short circuit. A short circuit protection fuse will blow faster than you can think "oh crap" while an overcurrent protection fuse will let you get in a whole long string of expletives before it blows; even if you have a slow southern drawl. Lead acid batteries can supply a boat load of current, right now, in a big rush if there is a short circuit and the wire size is substantial.
3. A fuse located in the same place/container as the batteries must be designed to contain the arc that occurs when the fuse blows.

With all that in mind you should have a type "T" fuse; they are short circuit protection. One source I have used is solarseller.com

They also sell DC rated circuit breakers. Their stock varies over time. I bought several assorted sizes from them. One is large enough to act as an overcurrent protection fuse for my 3500 watt inverter.

Third thought: I believe Deka are good batteries, but marine batteries are not true deep cycle batteries; at least not as good a deep cycle battery as a golf cart type of battery. They are better than automotive cranking batteries. Also check on that amp rating. 715 sounds like CCA, Cold Cranking Amps. That is the normal rating system for a battery that is used for cranking an internal combustion engine to life, and is not a reliable figure to use for use as a typical off grid battery. You want to know what the "20 hour rating" is for off grid usefulness. That Deka probably has more like 100 to 120 amp hours at the 20 hour rate. BIG difference.

The better batteries will NOT come in 12 volt versions; 6 volt is more the norm. The best batteries will be also available as individual 2 volt cells of high amp-hour capacity. Again FYI.

Yes, having a breaker/disconnect both before and after the charge controller is a good idea. I'm not real familiar with the C40, but FYI, with the Outback a disconnect is pretty much required before and after the charge controller as it makes setup/programming much easier.

I like having a disconnect or breaker that is suitable for disconnect use at the inverter. I like one as it makes it simple to totally disconnect/shutdown the inverter. Some inverters with on-off switches may still have a small drain on the batteries when off, especially if it has a remote on-off switch.

Battery temperature sensors are very goof to have. They can prevent problems, shortening the battery life, by reducing the charge rate if the temperature gets too high. That feature does not always work when equalizing though.

MPPT controllers make better use of the power from the modules than a PWM controller. They also cost more so that is a personal choice / trade off. The C40 has multi modes but only works one at a time. Nice if you have need to move it from PV module use to a wind generator.

Squirl · « **Reply #4 on:** March 26, 2012, 07:30:59 PM »

I was reading that thinking to myself, wow great prices on everything.

Since you said your panels are at the top of tower, don't forget about wire sizing and line loss. The higher wattage, the more the amps, the larger the wire needed.

PWM is less efficient, but you need a few more watts to make up for the difference in price. Your panels probably actually run at about 18 volts, the three volts over the charging voltage of around 15 are usually lost. It is not a big deal on small systems. It also has the advantage of being able to use a higher voltage panel array and converting it to match your battery, letting you run less amps and smaller wire. MPPT also lose efficiency the more they have to convert. So they are less efficient converting 120vdc to 12vdc than converting 18vdc to 12vdc.

The shipping is killer on larger panels too. It is better to buy them in bulk. I called and asked what the shipping would be on 1kw of panels, $300. I asked what the shipping was on 2kw of panels $300. A pallet is a pallet, and they are to large to ship UPS. I think the largest panel that can be shipped UPS is a Kyrocea 125w.

I would be expecting mostly weekend usage from the batteries and recharging over the week when you aren't there. 55w won't keep up with your usage over the weekend. 3 batteries will probably be enough. 715 amp hours X 12 volts = 8.5 kwh with a 50% discharge allowance 4.25kwhs.

Now I'm not an electrician, so take this for what it is worth.

You don't need to have both a fuse and a breaker between the C40 and the battery bank. From my Solar installation books, there must be a disconnect for each component. A breaker can serve that under NEC rules. You need a disconnect between the batteries and the inverter. I would connect the pump through the AC panel instead of directly to the inverter. It saves you from adding an extra disconnect.

Good start.

I also like homepower. You can find many free articles with diagrams to other solar setups.
http://homepower.com/basics/solar/

MountainDon · « **Reply #5 on:** March 26, 2012, 07:57:56 PM »

Quote

715 amp hours X 12 volts = 8.5 kwh with a 50% discharge allowance 4.25kwhs.

Don't want to beat a dead horse but I feel I must...

That info is wrong for those batteries. As I stated in the previous reply that 715 must be CCA; totally useless figure for off grid.

RIjake · « **Reply #6 on:** March 27, 2012, 03:02:10 AM »

I appreciate all the comments! The disconnects are the problem that I'm having. I'm not sure the exact type I want to use. Of course the breakers will be DC rated and the fuses T rated. If anyone can show me pics of their disconnects or specs of them I'd appreciate it.

Don as far as the batteries. You are right about the amps that I listed. Those are the "marine cranking amps" @ 30deg. The only other specs that I can find is "minutes at 25 amps" which is 175. I did a rough calculation in my mind when I was looking at these and figured for a hundred bucks each, how can I go wrong? I have bought one of these batteries locally and was planning on buying two more. I don't mind going in a different direction but as I stated in my OP, I'm looking to do this on the cheap. Let me know what you think of the battery now that you know more.
Here's the product brochure on the battery and FWIW they do market this battery for "home backup" use as printed on the battery itself. I know that may not mean much

http://www.easternmarineoutlet.com/media/downloads/5232/deep1.pdf

Squirl, yea, good prices huh? It's nice to catch a break every once in a while with a friend in the business. No discounts on batteries though $:-\$

MountainDon · « **Reply #7 on:** March 27, 2012, 06:19:40 AM »

DC disconnects are not cheap. solarseller has some Airpax breakers that are approved for disconnects. I have used them screwed to a piece of plywood. The CC mounts to the same plywood. Then I used one of the high amp models at the inverter feed. Solrseller does not always have the size you want but the prices are good.

MountainDon · « **Reply #8 on:** March 27, 2012, 06:36:54 AM »

The batteries: I find it very annoying when a seller/mfg sells a battery and states it's good for alternative energy (home backup) but then does not publish the "20 hour rate". Most likely you would be safe calling the 20 hour rate amp-hours to be about 100; 110, 120 if you prefer optimistic estimates. The CCA number just means you can draw up to that many amps for a short time without killing the battery. Means nothing to our off grid uses.

I used to use RV/Marine batteries that were very similar to those. There's only so much a mfg can do with the confines of a group 24 o whatever case. This was in an RV. It came with one battery in '83. The first battery lasted 2 years. I replaced it with 2 of a different RV/Marine brand. I think we got three years. The next set struggled to get three years. I was told to get golf cart batteries by the guy who ran the auto electric shop I used. I squeezed in four 6 volt GC's. The amp capacity only went up slightly but they lasted a full 5 years. In later years I got 7 years service by babying them; limiting their discharge to 30% for the most part.

So, I guess I'm saying that if you have one of those 12 volt batteries already, and no other use for it, add a couple more. I don't think it would be wise going to any greater number on a 12 volt system. I would also make a buss for them to connect to rather than have cables run between them as you illustrated. They will draw down more evenly with a good buss bar set. And be prepared to buy better batteries in a few years.

You should also have a ground rod in there, even though according to NEC a ground is not needed in a 12 volt DC system. One ground rod. One wire from it to a buss bar or connection plate. Ground all components to that ground buss. Then a single point connection from the negative battery buss bar to the ground buss.

Squirl · « **Reply #9 on:** March 27, 2012, 07:42:07 AM »

For a breaker between the inverter and batteries you would calculate the amp draw at 12v. So 2000/12 = 166 amps. I can’t remember if there is a 25% margin requirement, but always round up to the next size of available breaker. So a 175 amp will probably do it. http://www.solar-electric.com/mnedc175.html
I don’t know the Xantrex equivalent. I believe Schneider also makes square D.

I’m a little familiar with the kind of battery you have. They market them as dual use cranking/deep cycle batteries. They are usually sold for sail boats who use running lights more than engine starting, but require both. They will not last as long a true deep cycle marine batteries. I would not buy anything that advertises the cold cranking amps. I would take them to your local dock or marina and sell them to a sailor that will get better use out of them. You could probably get most of your money for them. I believe west marine sells them for $150.

Due to the fact that you are new to this and this will be a learning curve to battery discharge and maintenance, I don’t think that three true 12v deep cycle or cheaper 6v golf car batteries would be a bad thing off the bat. As the years go by and you may adjust your needs and learn your system, then I would upgrade to the more expensive longer term solution.

More reading if you are interested.
http://homepower.com/view/?file=HP99_pg14_Marue
http://homepower.com/view/?file=HP94_pg86_WTH
http://homepower.com/view/?file=HP119_pg104_CodeCorner

RIjake · « **Reply #10 on:** March 27, 2012, 07:54:07 AM »

Don,
I forgot about the ground rod. That was in my plan, I just forgot to draw it.

gringo · « **Reply #11 on:** March 27, 2012, 05:43:42 PM »

There is a lot of info on the Deka battery. Just go to the manufacterer's site and look for the model. Get past the one page promo fact sheet, that has about all the info most people need or want. The site and the info has all you need to make you comfortable or uncomfortable....20 hour rate and all. Not sure where the 715 Amps came from, but better to try to find out if that is a typo/error than base all the scorn on the mfg. Looks like his battery is 92 AH at the 20 hour rate and at 100 bucks that is a GOOD deal...short term and long term. You want to spend 3 or 4 times that for batteries that last (might) twice as long, better do the math.

They look pretty good and with the price they are a real find (especially for someone who said they want a basic (I think you said cheap) system. For your use, there is nothing at all wrong with marine batteries. If you do the math, you will likely see that they pay off. You wont have bragging rights on big high powered batteries that may (or may not) outlast you, but you will have a good system.

The objective is to get power and a nice simple system not buy stuff you do not need because it is there. Spend your money on a Corvette.

Sorry, power guys, but for many this is a good solution, stop beating up the ways that work simply.

Squirl · « **Reply #12 on:** March 27, 2012, 07:35:30 PM »

The purpose of the post is value for the money. He can go to wally world and get two 6v deep cycle batteries not designed for cold cranking amps for around $100 each and they would last twice as long in his application. Same money, longer lasting. Batteries advertised with cold cranking amps ability usually have more, but thinner plates. This allows them to have the greater surface area to give the juice needed for starting applications, but not the longevity of recharge cycles. That being said, I looked up the manufacturers site. The 715 is as you stated marine cranking amps, not the cold cranking amps, which is around 575 on these. That puts them into the true deep cycle area and not a dual purpose battery. These should be fine to learn on and last a few years with occasional use. Some info I saw lead me to believe they have a 90 amp hour rating.
http://www.dekabatteries.com/assets/base/0194.pdf

It’s like metric vs. standard tools. Same price, different applications. I advocate getting the right tool for the job.

MountainDon · « **Reply #13 on:** March 27, 2012, 08:03:26 PM »

Let's say they are $100 and 90 amp-hour rated. I would look around locally at what the best price on golf cart batteries is. It doesn'y pay to get into shipping costs on simple batteries. Not all Costco's and/or Sam;s Club sell batteries and they do not list wet cell batteries on their websites the last time I checked. My Sam's Club has 6 volt 210 amp-hour GC2's at $78 plus $9 core charge. Anyhow two of the GC2's give a slightly higher amp-hour rating than two of the 12 volt Deka's and at a lower price. ....... Jus my way of looking at my local options.

RIjake · « **Reply #14 on:** March 28, 2012, 09:31:28 AM »

Thanks for the help and input here guys.

Squirl, you are right on with the specs for my battery. According to Deka's specs, it's a 90 amp hour rating. So I've got to decide if I'm going to go in another direction with the batteries.

I am not going to use the panels I have shown on the diagram for the cabin. I've got a 20' shipping container that I use for storage/work shop. I'm going to use the three 15W panels and possibly that battery for a couple CFLs and/or a radio in there.

I found what I believe to be a great deal for Evergreen PV panels. As you may know Evergreen is out of business and he is trying to unload them. The seller has 110W, 180W, 185W and 190W panels for sale. These are brand new and undamaged. They are local so there is no shipping concerns. Oddly enough he is asking more per watt for the 110W panels than the others. $2.00/W for the 110, $1.50 for the other three. Normally larger panels are more per watt but he claims the 110s are more popular so he's trying to make a little more for those.

My question is, does it matter if I purchase two 110W panels or one 190W panel? Is there a loss in efficiency in going with two panels versus one? I don't mind spending $440 for two 110W panels versus $292 for one 190W if there is an advantage in multiple panels other than the additional 30W.

What do you all think?

MountainDon · « **Reply #15 on:** March 28, 2012, 10:32:34 AM »

What are the specs on both of those? Can you point/link to their specs. The specs can dictate what charge controller is best suited.

Squirl · « **Reply #16 on:** March 28, 2012, 11:36:32 AM »

It really comes down to the model and voltage. With your current charge controller you would need an 18v panel. Most of the evergreen panels were 30v, which would be completely wasted on a 12v battery bank without an MPPT charge controller.

I believe with MPPT chargers you have to match the voltages of the panels coming in if they are wired in parallel. You would probably have to get rid of the 45 watt panels.
http://homepower.com/article/?file=HP108_pg120_QandA_4

RIjake · « **Reply #17 on:** March 28, 2012, 01:08:41 PM »

Here's the specs for the 195, 190 and 180

http://www.sustainabilityninja.com/downloads/pdf/evergreen-es-190-rl-190-watt-solar-specs.pdf

If I understand you correctly these won't work with my charge controller because they are 32 Voc and 25 Vmp.

The specs for 110 panels are here

http://www.solarhub.com/pv-modules/2039-ES-C-110-fa2--Evergreen-Solar

These should work right?

RIjake · « **Reply #18 on:** March 28, 2012, 01:11:40 PM »

Quote from: Squirl on March 28, 2012, 11:36:32 AM

You would probably have to get rid of the 45 watt panels.
http://homepower.com/article/?file=HP108_pg120_QandA_4

Yes,
I'm going to use them in my connex for lights.

MountainDon · « **Reply #19 on:** March 28, 2012, 02:19:40 PM »

Quote

The specs for 110 panels are here
These should work right?

The problem with the 190 series and the C40 charge controller would be the wasted power. A waste of about 40% or so as a rough mental calculation. The C40 controller would operate safely with one of those connected to it, as it can handle up to 125 volts maximum input. but it doesn't make a lot of sense, IMO.

Those 110's are a better match to the controller and the plan to run a 12 volt battery bank. The 190's would be a good choice with an MPPT controller on a 12 volt battery system, or 2 in series for a 24 volt battery system.

The C40 would handle two of the 110's with the 110's connected in parallel to the controller.

MountainDon · « **Reply #20 on:** March 28, 2012, 02:23:10 PM »

I don't blame the vendor for asking more per watt for the 110's. Smaller panels always have been more per watt. Plus it seems that modules that will work most efficiently with a 12 volt system without going to an MPPT controller are becoming less common as module sizes in general increase.

RIjake · « **Reply #21 on:** March 28, 2012, 03:13:12 PM »

OK, I did some calculations based on information found in my Home Power archive DVD based on the Ackerman-Leist load analysis.

First the batteries

Since my loads are minimal as previously described and I am not there full time I am using 684 Wh/day AC and DC. Here's how the math plays out.

Batteries

500 AC Wh/day / 85% inverter efficiency (C40) + 96 DC Wh/day = 684 Wh/day

684 Wh/day / 12 VDC = 57 avg Ah/day

57 x 1.2 battery temp multiplier x 2 days autonomy / 50% depth of discharge = 273.6 total Ah

273.6 / 90 Ah for the Deka batteries(just to use those as an example) = 3.04 strings of parallel battery strings

Now for the Panels

684 Wh/day / 4.5 peak sun hours / 75% battery efficiency / 80% temp. loss / 90% shading / .85 derate factor = 331W peak array

So, in order to do this on the cheap, I think 3 or 4 of those batteries and two 110W panels (which is less than optimum, but I do have a gas generator and am planning on a wind generator in the future as we have about 8 mph avg at my location) would get me started. I plan to closely monitor both the batteries and amps incoming from the array.

MountainDon · « **Reply #22 on:** March 28, 2012, 03:57:45 PM »

When I run the numbers 3 batteries look okay and 2 of those modules should work too. An extra battery could be added safely within a few months of getting everything up and running, if it appears that 4 would be better. Three modules would be nice, but if the use is not full time you're likely okay with two.

Not sure how practical a wind speed of 8 mph is for wind power? Some won't even start to turn at that. But I stopped looking at wind as an option for our place after doing a wind study for a few months. So I don't claim to know very much about wind power.

RIjake · « **Reply #23 on:** March 28, 2012, 04:12:25 PM »

Don,
From everything that I've read anything over 6mph is worth looking into. Since I'm looking at building a homebrew windmill I figure I've got very little to lose. When designing your own the thing to look for is a DC motor that makes its power at around 1800 or less rpm. We'll see, I've got a lot to do before I get to that point.

Thanks for all the help on this thread. I'm learning a ton about solar. Fortunately there's quite a bit of info out there from both vendors and other resources on the web. Home Power is a great publication. I've got a pretty good handle on the basics of electricity so it seems to be coming to me pretty easily.

Thanks again

RIjake · « **Reply #24 on:** March 29, 2012, 12:28:06 PM »

Did some shopping and found Interstate 6V 330 Ah golf cart batteries for $115 each. 180Ah for $200 vs 330 for $230. I'm going with those. I also picked up two 110W Evergreen panels today for $220 a piece. Unused, leftover stock. They checked out ok.