Almost there...but need a little advice

CaribSoul · July 2009

OK, I am an electrical engineer, but my experience in designing an off-grid (waaay off-grid!) system is less than a week. I'm pretty close to placing an order for a starter system for my Canadian cabin. However, there a couple nagging questions that I haven't found answers for in the forum.

This is the system I have in mind (one each of the following):

Kyocera KD210GX-LP 210 Watt Solar Panel (24V)

Morningstar SunSaver MPPT Solar Charge Controller

Sun Xtender PVX-1040T AGM Sealed Battery (104 AH)

Samlex 600 Watt 12 Volt Sine Wave Inverter

My first question is, am I doing the right thing getting a 24V panel? The higher voltage will have less voltage drop in the cable connecting to the MPPT. Since the MPPT is a switching buck converter, it will greater range of input voltage above the 12-volt battery voltage to work with. Are there reasons to use 12V panel(s) instead?

My second question also involves the MPPT. With a 12V battery the load capability is 15 Amps, which works out to be about 200W (since the battery voltage is normally a volt or 2 above 12.) Is there a problem using the MPPT load terminals for 12-volt devices (like lights, low-power coffee maker, iPOD charger, etc.) and then connecting the inverter directly to the battery? (through a fuse, of course!)

Thanks a lot for your help!

Chris

rplarry · July 2009

Re: Almost there...but need a little advice

Caribsoul
Yes the 24v panel will work well with that morningstar controller.
As far as the load terminals on the controller, I am not familiar with that controller so you would have to check the specs, of maybe someone with experience with that controller will chime in.
Good luck.
Larry

BB. · July 2009

Re: Almost there...but need a little advice

The load output on the the controller should not be used for large loads or loads with large surges (such as inverters). Excess current can damage the controller.

The LVD (Low Voltage Disconnect) is based on battery voltage--and not really an accurate method or very good at "saving" the battery (most LVD's disconnect at well below 50% state of charge--basically the problem being that determining the battery's current state of charge is pretty much impossible to measure under load or under charge by just checking the voltage).

You talked about connecting a low voltage coffee maker--You can run heating devices from solar--but the cost to produce Solar PV electricity, and the size of the panels/batteries/etc. required to produce much heat generally make such loads a poor choice. Using a camp stove (or whatever) is a better choice.

Of course, such loads can be supported--just make sure you add up all of the loads, and compare that with the amount of energy you will collect and store with your solar array system.

A 210 watt system will gather, very roughly:

210 watts * 4 hours ave sun * 1/0.50 = 420 watt*hours per day

A 120 watt heater will run:

420 WH / 120 Watt = 3.5 hours (very roughly)

With no power left for anything else.

Lastly, if you are using the system to learn, then look at getting a Battery Monitor. The higher end units (like the Xantrex) even include a programmable digital output that can be used for an alarm, to turn of an inverter, etc. if the battery goes below XX% state of charge.

A cheaper unit--but would work for setting up and testing your system would be a Watt*Hour/Amp*Hour meter from here.

If others will be using your system (spouse, guests), a battery monitor will almost be a requirement... You tell them that if the battery is below 50% state of charge--they should cut power use and/or fire up the backup genset (for example).

Read the battery faq and get a good handle on how best to use your batteries. Your AGM is a very nice battery--but a little misuse can kill them in nothing flat (and shorten their life to months or less--AGM/Sealed batteries are very sensitive to overcharging/over voltage situations).

Lastly, make sure you get the remote battery temperature sensor for the MorningStar MPPT Charge Controller... A RBTS is virtually a requirement for the MorningStar to accurately and quickly charger your battery bank (the MS controller tends to over estimate battery temperature and undercharge if the RBTS is not installed).

-Bill

icarus · July 2009

Re: Almost there...but need a little advice

As a word from someone who has been there,, done that,, my most important piece of advice is avoid the "ready, fire, aim!" Before you buy ANYTHING consider your loads,, your charging systems in toto, including Pv gennies and chargers. Assume that your loads A: are under estimated B: ARE going to grow with time,,, and C: you will over estimate the amount of power you get out of any given Pv system.

If you PLAN carefully before you BUY anything,, you will avoid the biggest pitfalls. Also try to plan components that you can "grow into" within reason,, things like charge controllers,, battery chargers, inverters etc.

Clearly it doesn't make sense to run a 2 kw inverter to run 100 watts of load,, but by the same token it doesn't make a lot of sense to buy a 300 watt inverter and have to upgrade in a year because it it too small. Same for Charge controllers., gennies and genny controlled battery chargers.

Remember,, you can always add Pv capacity,, adding batteries to an existing string is problematic.

Good luck and welcome to the forum,

Tony

PS 104 ah of battery won't give too much capacity,, with any reserve. For example,, to 50% SOC would yield ~50 ah,, three day reserve would give ~15 ah/day, 180 wh @ 12vdc. I also don't think it a good idea for battery life to go as low as 50%,, I personally don't ever go much below 80%. A pair of T-105 golf cart batteries makes a nice ~225 ah battery bank,, or 4 of them give you ~450. These can be had pretty reasonably lots of places. Keep in mind that bigger batteries need bigger charge systems. I suggest you read some of the following links:http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries http://www.batteryfaq.org/

CaribSoul · July 2009

Re: Almost there...but need a little advice

Thanks, Guys, for all the excellent advice and suggestions! It sounds like I'm on the right track for the most part--with a couple of additions. It seems I'm ok with the 24V PV panel and Morningstar MPPT controller for a 12-volt system. I had already planned on the remote battery temperature sensor--just didn't mention it. I hadn't thought much about a battery monitor, but that's a good idea. I think though that I will initially just purchase a 100 Amp shunt and dedicate an inexpensive digital multimeter to measure voltage and current. I can easily use a calculator to determine the VA. As long as I have the shunt at the negative terminal I'll be able to determine whether I'm charging or discharging by the polarity. I'll look at something more sophisticated before next summer.

I've spent a lot of time studying the battery types and I'm really sold on the AGM type. I should be ok charging with the MPPT and they are otherwise more rugged than most other types. Icarus has a good point I hadn't considered with his comment on the "three day reserve". At this time I don't have a good handle on the actual power consumption I'll need. I think I'll stick with the single puny 104 AH Concorde, until I have a better handle on my requirements. If necessary, I should be able to add a second one next summer when the coffers are replenished! And the same for another PV panel if needed, without replacing the MPPT controller. I believe I have left enough room for expansion to cover the next few years at least.

I'll also follow BB's advice and not use the load output on the controller. I'll plan to fuse both the 12-volt direct load line and the input to the inverter.

It's a family cabin, but I'll make sure the other family members will know not to bring 110V hair dryers, hot plates, coffee makers, heaters and the like. I sized the inverter at 600W, figuring that would be about right when I add a second PV panel and battery. Thanks to the truckers and boaters, there are some coffee makers and hair dryers that will operate on 12-volts at reasonable current!

I don't (and won't) have a generator for backup. The family vetoed that option! We do have propane for the stove, refrigeratorand lights, as well as a wood-burning Franklin fireplace for heat. So we won't have our fun ruined if we have a temporary problem with the electrical system! (But I hate the percolator, so I do have my eyes on a 12V coffee maker!)

Once again, thanks for your inputs. You've given me the answers I was looking for!

Chris

BB. · July 2009

Re: Almost there...but need a little advice

A couple of comments:

Take a look at the Mr. Coffee type drip maker by Coleman (I think this is the one Tony/Icarus keeps typing about--don't trust me, I don't drink coffee :roll: ). Don't use your solar electric for making coffee/hot water if you have any better way of doing it.

Regarding adding another PV panel... You are sort of maxed out with the 200+ watt panel with a 12 volt battery bank (charger is max 15 amp output).

If you want to add one more panel--then you either need another controller or need to go to a 24 volt battery bank (15 amp * 15 volts = ~225 watt max; 15amp * 30 volts = ~450 watts maximum).

If you plan to add more panels, you may need to choose a larger controller (60 amp Xantrex or Outback type) up front (or parallel more controllers later).

Genset wise--A small Honda eu1000i or eu2000i is hard to beat. Quiet and fuel efficient... Not only for backup power but for "other jobs" such as circular saw, work lights, etc. for those "special occasions" (when a tree limb falls thru your roof).

Regarding 12 volt appliances that heat--does not matter if you take 100 amps for 5 minutes, or 10 amps for 50 minutes --- it is still the same amount of energy out of the battery/solar panel:

100a*12v*5min/60minperhr=100 Watt*Hours
10a*12v*50min/60minperhr=100 Watt*Hours

-Bill

icarus · July 2009

Re: Almost there...but need a little advice

That's the one Bill,, works great!

T

icarus · July 2009

Re: Almost there...but need a little advice

Chris,

Since I know your situation all too well,,(and as you have informed me,, we are neighbours!) I'll give you a few more bits of advice that is worth exactly what you pay for it,,,,

First,, realize that as you build this system,,and once people realize that there is electricity available at all,, the desire to have it available 24/7 comes on strong. Having 24/7 lights lead to more lights 24/7. Having electricity available will lead to "can I charge my I-pod,, can I run the boom box, can I run my lap top,, can I make coffee and on and on and on.

So,, as a recreation facility you might set strict rules as to what can and cannot be use. Guests from away WILL try to use coffee pots, hair driers, curling irons, toasters etc. If you wish to keep you system reasonably sized,, you have to be ruthless about what you allow.

Realize,, that the system will grow with time,, and as much as possible, allow for that with your hardware. I would be especially concerned about Charge controllers. I would seriously suggest that you speak to your partners about getting a genny to top the batteries off in days of no sun. A small honda eu 1000 will run a 20 amp Xantrex genny and will put into the batteries a days worth of amp hours in a couple of hours if you have no sun. They are very fuel efficient,, and very quiet,, especially if you run them during the day rather than at night. If you get a few days of poor sun (as you know we can, even in the summer!) you run the risk of destroying your batteries in short order due to over use/under charge. As configured,, your ~240 watts of panel aren't going to put out any too much power.

Just for example,, we live in very small square footage, ~600. We use ~4-600 watt hours/day for all uses including water pumping, radio, telephone, lap top/satellite modem,, and lighting in the evening. The water pumping uses ~50 wh/day, the lap tops and modem perhaps 100. We do fine on 300 watts of panels into 450 ah of batteries,, drawing them down ~10% per day,, getting back to even by about noon on a good day. Having said that,, we are VERY frugal about using power. We have only 3-4 lights on in the evening,, and they don't come on until just before sunset. (The house has great natural light so we never need lights during the day, even on the darkest days to read).

We started ~15 years ago with one 60 watt panel, and 1 12vdc reading light over the bed. From there we have added all the other stuff! Remember,, no resistance heating loads, no conventional light bulbs and people need to be taught that this is a very finite system. You can build in all the controls you wish,, but others WILL screw it up when you are not there. Few people really understand,, that the batteries are in danger even thought he lights light up just fine. A battery will energize an inverter an fire a few lights until it is almost dead, with no effect on the way the lights work. I might suggest that instead of the fancy AGM batteries, you start with either two t-105 golf cart batteries,, or a pair of simple Canadian tire deep cycle 12 volts at ~$75 @ That way you can learn how to use the system,,kill one set of batteries (because everyone does!) that are cheap(er) to replace,, and then buy good batteries after a couple of years when you can see how your system performs.

Using my rule of thumb, your 210 watt will yield ~500 watt/hours a day in your location on a perfect solar day,, net/net out of the inverter. That's roughly enough to run 5 15 watt cfls for 5 hours/day.

Good luck, Keep in touch,

Tony

CaribSoul · July 2009

Re: Almost there...but need a little advice

Bill, you're right about maxing out the Morningstar MPPT controller. I was just looking at the MPPT input power from the PV panels and neglected to consider the available charging current to the 12-volt battery. Bad mistake for an EE!

I first looked at the Outback MPPTs, but it seems the smallest they make is a 60 Amp and the price is double that of the Morningstar! Then I looked at the Blue Sky lineup (like what Tony uses). The prices are much more reasonable for a 25 or 40 Amp unit, but the sticker is that they don't like 24V PV panels into a 12V battery system. I suppose I could drop back to 12V panels, since I'll only have 10-15 ft between the panel connector and the MPPT.

Then there are the battery issues. Tony, the reason I'm not convinced yet that the T-105s are the way to go is that they aren't sealed and I'm concerned about their safety and self-discharge characteristics. The cabin will be unoccupied 7-8 months of the year, with only an occasional visit from a friendly neighbor to make sure no trees have fallen on the roof! AGM batteries with their low self-discharge rate and sealed electrolyte should be able to weather the winter on their own. I'm not so sure that a regular unsealed deep-cycle battery would do well under those conditions. What's your opinion about that?

OK, let's not forget my coffee-maker indulgence! We have a four-burner propane range & oven (at least 65 years old!) It's just that I've never been able to master a percolator. I think you guys have convinced me though, that the Coleman burner-top coffee maker is the way to go. At least I'll be able to go through the familiar motions (except for flipping the switch) and I will have a visual indication when it's ready--without percolator guesswork!

By the way, it appears we WILL have a small generator. My son bought a used one today. I don't know the make or model yet. I guess now we'll have to get a battery charger and some sort of transfer switch!

There's more to talk about--but it's getting late and my eyelids are getting heavy! I really appreciate the detailed suggestions. This is a great forum and has already been quite educational. It's become pretty clear that I have a bit more work to do before I start ordering my system--as you said, Tony!

Chris

_OS_ · July 2009

Re: Almost there...but need a little advice

Hi Chris,

I have a few comments since I also have the SunSaver MPPT controller and SunXtender batteries.

The SunSaver MPPT has a self consumption of ~35mA day and night. In my case, where we have almost no sun for three months of the year this is a big disadvantage. Many of these amps are used for logging 32 days of data (daily battery voltage, daily Ah charge and so on) so if you want to use this feature it is well worth it. Besides this the SunSaver MPPT is of a very high build quality and is highly recommended.

If you want more amps you could always wait for the Morningstar Tristar MPPT (45A or 60A) due out later this year (see: Morningstar Introduces the TriStar MPPT[TM] Controller )

I also bought the Morningstar Remote Meter but was disappointed by the lack of features (for example it does not show the PV array current and charge currents). If you are going to buy a battery monitor you are better off spending a few $$ extra to get the features you want and drop the Remote Meter. After I bought the remote meter I have made my own (wireless) remote meter so if you are going down this route please feel free to send me a message and I will send you the source code for accessing the SS MPPT (there are two software programs on the net that interfaces the SS MPPT but their authors both refused to give me any source code when contacting them).

I have also spent many hours searching the net for a battery monitor that have all the features I want but have not found it yet. Currently I have the Bogart Trimetric and the Bogart Pentametric on order. The Trimetric and Pentametric battery monitors are the only monitors I have found that can measure 10mA (requires 100A/100mV or 200A/200mV shunt). One disadvantage with these monitors is that they do not take battery temperature coefficient into account. If your battery temperature will vary over a large range you have to calculate how many amp hours you have left manually if you go for one of these monitors. One of the best battery monitors that I have found that take temperature coefficient into account is the Xantrex LinkPro but again these only show current in steps of 100mA.

Regards,
Ole

icarus · July 2009

Re: Almost there...but need a little advice

Chris,

We have used both T-105's and L-16 flooded batteries in unattended locations for years without incident. Self discharge is not a issue if you have some Pv on them all the time. As you design your system,, consider having at least one panel (in parallel) that is wall mounted so that it will produce when the others might be covered with snow. I keep 4 t-105's up with a single wall mount 63 watt panel over the winter. As long as they are topped up with water before they are left,, they should be fine for 8 months,,, especially since we are so cool (cold) much of the year. Besides,, they are pretty cheap, so that if you toast one set while you are learning the loss is not that great.

As for the coffee maker. The coleman stove top works just like you Mr Coffee at home,, except you have to remember to turn it off when it is done. Realizing it is done is easy as it makes a very distinctive gurgle. The then pour the coffee into a pre-heated insulated caraffe that keeps it hot all morning.

I would also take Ole's advice to heart. You don't (at this stage) want anything that has a parasitic load while you are not there to monitor.

Keep in touch.

Tony

Kamala · July 2009

Re: Almost there...but need a little advice

Great to see new life in this thread. I very much enjoy the remote cabin pictures. Coot, I would not be ashamed of the cabin picture! Looks like home to me 8). You guys in The Dominion are lucky to have partners that share your visions about living. Period. I am close.

Coffee making seems to have become an issue. Separate thread :roll:. Honestly, it is the simplest of procedures. Lewis & Clark did it. North American pioneers did it. I won't elaborate further, but it brings to mind a meeting that I had in 1977 with a woman, at her remote island location, who had been off grid since at least 1940. Her name was Dorothy Molter. She also made root beer and sold it to canoeists traveling through the BWCA. A link

http://librarymedia.org/aging/Titles/dorothym.htm

I've been to the museum in Ely and recommend it.

Once upon a time, I lived extremely off grid for 1 or 2 weeks a year. For 25 years. I, and my companions, ( including my one and only spouse ), carried everything that we needed to be safe, warm, fed and adequately comfortable. The environment provided the luxury!

See http://www.visi.com/~ch3dietz/dc3/index.html to learn about those times. Those experiences have helped me to plan for my solar camper.

I'm done.

Enjoy... K

dagr51 · July 2009

Re: Almost there...but need a little advice

Tony, do you use a controller with your 63 watt panel when you're gone? Do you leave your Tri-metric on or shut it down?

icarus · July 2009

Re: Almost there...but need a little advice

The 63 watt panel is controlled with a simple Morningstar 15 amp pwm controller.

The Tri-metric is on the main string, and stays on all the time. I do turn the display off just for grins however,

T

CaribSoul · July 2009

Re: Almost there...but need a little advice

Dagr51, you anticipated my next question. A constant 35ma. equates to .84 amp-hours a day (at 12 volts). If the system is unattended for 8 months, that totals over 200 amp-hours. Add in self-discharge and you have a dead (and probably ruined) battery array, if there's no PV input. Of course, that's for the Morningstar MPPT. I don't know if the Blue Sky 2512ix that Tony is using has a constant current drain, but it wouldn't matter anyway if his 63W panel is active.

As for my proposed system, I've decided to go with a pair of Trojan T-105s in series. I really like the AGM technology, but it is just too expensive for the equivalent capacity--especially if we end up frying a battery while we are gaining experience with solar power!

I think I'm going to stick with my original 210W PV panel and Morningstar SunSaver MPPT. I'm still mulling over a small additional panel for a "keep-alive" source for the winter.

Chris

CaribSoul · July 2009

Re: Almost there...but need a little advice

CaribSoul wrote: »

I've decided to go with a pair of Trojan T-105s in series. I really like the AGM technology, but it is just too expensive for the equivalent capacity--especially if we end up frying a battery while we are gaining experience with solar power!

Maybe the posts are too old, but I keep seeing references to the Trojan T-105s at a price around $100. But when I look around for suppliers, it looks more like at least $140-$150. Has anyone seen better prices lately? I'll need to have them shipped to Denver, so a closer (or local) source could easily offset the price with lower freight charges.

On a related note, I see that NAWS has a Crown 225 Amp-Hour 6 Volt deep cycle battery for $125. Any opinions on the Crown vs. the Trojan?

Chris

Almost there...but need a little advice

Comments

Categories