New to off-grid; need help to fix/upgrade existing system

raindog

Greetings from The Bahamas!

I moved to a very small, off-grid cottage on a Bahamas out island a little over a year ago. Recently I have been unable to run the 4 cu. ft. fridge (Avanti, Amps: 15, Voltage: 115 Volts) through the night. There are 2, 250 watt solar panels mounted on the roof, receiving full sun when the sun is shining. There are 2, PVX-1040T Sun Xtender batteries hooked to a 24volt MicroSolar 1000/2000 (surge) Pure Sine Wave Inverter. The fridge is plugged directly into the inverter. I have an additional load comprising a small laptop and a smartphone used to provide hot spot for internet connectivity. These are plugged in (charging, more or less) much of the day and into the night (for research).

The cottage was not used for year-round living by the previous owner, and I expected that I would need to upgrade the solar system. However, since I will be building on an addition to the cottage and will have some greater power needs at that time, I am concerned to do a minimal fix/upgrade at present, with a view toward a more robust upgrade in the future.

Since I am thinking I need batteries, I have looked at a few: Sun Xtender  PVX-1290T and the Renogy AGM 200ah.  I am unsure whether these will work? I am also considering doubling the solar array to 1000 watts, if that will help.

I am aware that the ultimate system upgrade will require more batteries/panels and a larger inverter, and that the batteries I purchase now should probably not be mixed with the future batteries. But, I have a second, small, DC system here (2 – 6 V batteries combined for 12 V; 1 – 75 W panel), which runs a couple lights and a small fan, when needed. Perhaps I could upgrade that system with the batteries I purchase now at the point that I upgrade the main system?

I am uncertain, but I think my problems with power shortage began or were greatly exacerbated by the week long spell of cloudy weather associated with Hurricane Dorian earlier this year.

Many thanks for help and suggestions!

Estragon

I'd check around locally to see if you can get GC2 or L16 size flooded batteries at anywhere near US prices (~$125 for GC2).  Sealed AGMs have advantages, but tend to be about 2x the cost of flooded, and lack the ability to monitor SG for battery health.

The small fridge is rated 228kwh/year, so I'll assume about 750wh/day in your climate.  Further assuming 50w x 12hrs for a laptop & hotspot, that'600wh + 750 = 1350wh ÷ 85% inverter efficiency = ~1600wh/day.

Using solar averages for Freeport it looks like reasonable winter average pv output for 500w rated pv might be 500w x 75% x 5hrs = ~1900wh/day.  Enough to run loads with mainly sunny days, but little reserve for runs of cloudy weather as you've recently seen.

2 x  ~125ah @12v batteries is 125ah@24v, about 3000wh total storage, of which only 50% should be used regularly for decent battery life.  1500wh might get you though one cloudy day, but any more would be drawing down to where permanent damage is possible/likely.

Adding pv would help, but another possibility worth considering is a small generator (eg ~2000w Honda or similar inverter type).  Almost everwhere gets runs of gloomy weather for which adding pv and battery capacity is prohibitive.

raindog

Thank you for your detailed answer!  I can now see more clearly why I am having difficulties

I suspect I've effectively killed the batteries, as they show fully charged on the controller (Schneider 41xm?) by about noon, but I lose power soon after dark.

I am more concerned to put the right items in place that I can live with and build a larger system on over the next year or so, than I am about the expense. I am sensitive to buying something that I find is useless before it's time.

How safe are the flooded batteries as compared to the AGMs?  The current location of the batteries is inside, on a small, screened porch. I have a dog, Rain, who can get to these if chasing some varmint whose gotten in. 

I would pay quite a lot to avoid the noise of a generator and hauling gasoline (~$5/gal.) for it over miles of very rough and rocky dirt roads to get up here.

Add to all this that I am a little (+/- 100 lbs. -- cannot lift 5 gal. container of gasoline), old, retired lady and her dog.  We are living quite simply, but still need a few things (computer for research and photo editing -- big computer/monitor still in storage in Florida -- , refrigeration (more than at present -- may go to propane), various small hand tools & clippers for Rain).

I know I can make this work, with a little help along the way.  I'm learning more every day, and am very thankful for your help.

We've got ice in the fridge for the night!

Photowhit

I would look  at your final goal  in terms of use. mismatching by adding later to batteries  or solar array  can create cost and use problems. Best to have all your batteries  the same age/size/model.  Solar panels also!

What  charge controller do  you have (I  might have missed it,  you have done much better than most at giving us info to use)

raindog

The one for the ac part of the system is a Schneider. It says "Listed 41XM" on the side (I am unsure if this is model #).  I think it's a C60, 60 amp.

Thanks! 

I am preparing a shipment of dog food and other items from the States. I would be able to ship the batteries/panels, etc. on the pallet. There is not much here on the island.

Estragon

In terms of safety, there isn't a whole lot of difference in an application like yours.  Flooded do gas in normal operation, and need to be topped up with distilled/de-ionized water occasionally.  This need not be unsafe if proper protection (eyes, rubber gloves, etc) are used.  The small bit of gassing shouldn't be an issue in a screened porch.  AGM don't gas in normal operation, but can do so in abnormal (overcharging/overheating) operation.

The main danger with any battery is electrical and fire risk.  Proper fuses/breakers are important to reduce this risk.  They should be in some sort of vented enclosure to prevent accidentally dropping a metal tool across terminals, etc., and due caution used whenever working around them.  You wouldn't want Rain putting one wet paw on one terminal and another on the opposite one!  

As photowhit said, knowing your eventual goals and expectations is important in avoiding having to buy gear that later turns out not to be useful.  Fridge/freezers and water pumping in particular tend to be common loads that move a design up a notch or two.  

Is propane easily available and reasonably priced (In my case, it's ~$5/gallon, and I'm also getting on in years and 100lb cylinders seem to get heavier every year)?  If so, a propane generator and fridge may make sense.  In most cases though, adding panels etc to run an electric fridge makes more sense.  A modern full sized AC fridge/freezer might use about 50-75% more power than the 4cu.ft for maybe 5x the space.

Is water from a rain filled cistern, pumped from a well, piped from a utility, or ??.

Marc Kurth

How old are your PVX-1040's? What is on the small round white sticker. If you cannot see that, what are the first digits on the bar code label?

Can you get a rough idea of what your battery bank voltage is, with no charging or discharging for at least an hour or so?

Marc

raindog

If I am understanding this correctly, it appears that 2 enormous 250ah AGM batteries would supply my current daily need and give approximately 3 cloudy day's worth of power. The panels I have now are sufficient to keep a charge on the batteries (? -- but will plan to upgrade with a larger array of all new panels at a future date).

It appears that most of the current ac system, batteries, etc., date back to 2015.

Perhaps replace the controller with mppt controller? Better for batteries?

I have discovered (by finding a receipt) that one of the 2 ev panels is a Trina polyvoltaic panel, but the specific model is not listed. The two panels differ visually.  Plan to replace these entirely and sell or find other uses for them (e.g., perhaps, new, more robust water pump, shifting current, Shurflo pump to garden water supply).

Switch refrigeration to propane, making way for desktop computer/monitor (-- alternatively: new laptop with robust external graphics capability to run large, 4k display). Propane is already installed for stove and on-demand hot water.

Looks OK?

raindog

@Estragon : Yes, many neighbors, also off-grid, use propane. I have 20lb. cylinders I can carry; $30-35/refill; man comes around to pick-up. Works OK, but usage would go up with propane fridge. For me, now, a cylinder lasts several months.

I have cisterns with a small Shurflo pump providing water to the house. It runs on the dc system provided by the 75 watt panel and 2 6 volt batteries. This has run without issues so far

@Marc Kurth : No dates on batteries; bar code label #s are 0140321. I found paperwork indicating they were purchased in 2015.
Not sure how to get the voltage, but I'll check to see what I can do tomorrow.

Marc Kurth

The first digits of the serial number is the year of manufacture. Your batteries were made in 2014. 

mountainman

Fwiw I run fridge hwh and stove on propane in my camper. A 20 lb tank cost 8 Dollars and last 10 days with 2 people.  $24 monthly. I Can't justify the cost of pv and battery replacement  for running electric fridge.

raindog

@Marc Kurth : So, at ~5 years old, the batteries were most likely nearing the end of their lifespan anyway, especially since it is relatively hot here, and there's no ac. Thanks!

@mountainman : If I would have to replace the tank every 10 days, I would not be a happy camper. I'll have to check around more about this.

littleharbor2

• That's some cheap propane.

Estragon

Running the fridge in your climate, my guess is it would use roughly two 20# tanks/month or maybe a bit less.  Estimate is based on what I've read from folks using propane fridges in off-grid cottages in northern US and Canada using ~1lb/day, and considering your climate is likely warmer on average.

At $30-35/20lb for propane, an AC fridge likely makes more sense.  That said, a small propane generator (or one converted from gasoline) may still make sense.  Unlike gas, propane stores pretty well.  With a pv system sized to cover the vast majority of cloudy periods in your climate the generator wouldn't be needed often, but may help keep system size reasonable by not having to cover more extreme runs of gloomy weather.

softdown

littleharbor2 said:

• That's some cheap propane.

He is paying $2/gallon while she is paying $8/gallon with pick up and delivery service included. $2/gallon is an astonishingly low price for 20 pound cylinders. 

If one has a several hundred gallon propane tank and orders in August, one pays $1.19/gallon locally. Propane isn't expensive, it is the fill up service that we pay the most for. The prices are also seasonal and varying - like gasoline. 

Back to raindogs scenario, here are my thoughts:
1) I'm impressed by her knowledge to date.
2) Battery longevity in the sunny Bahamas is likely very significantly shortened by the weather. I would imagine the Atlantic helps keep things cooler but my Bahamas memories were of very warm weather - at least at that time. The humidity always compounds the warmth of course. Though batteries care not about humidity. 
3) I would think the Bahamas would generally be a good sunny solar location. I would rely on solar vs propane for refrigeration.
4) A desktop would eat into her energy usage. An energy efficient Windows 10 laptop hooked into an led television via HDMI would lend good graphics. Mine worked well until a large dog stepped on the HDMI connection at the laptop (the dogs enjoy the run of the house), My Windows 7 laptop with oversize screen and three processors uses a surprising amount of energy. I disconnect the power cord during the last ~ hour of usage to help out. 

"20 pound cylinders" really hold 4 gallons of propane due to the safety float valve required. Maybe 16.5 pounds of propane assuming they are properly filled. 

Photowhit

littleharbor2 said:

• That's some cheap propane.

Propane fill is just under $10 here for 20 pounds. Exchange run $15-18 for 15 pounds.Central Missouri, Tractor supply filling.

Flooded batteries on a screen porch pose no problem. The main worry would be corrosion in enclosed areas, or hydrogen build up in very small areas.

Look for a balanced system rather than a larger battery. No time to do math right now.

softdown

https://www.amazon.com/CRC-05046-Battery-Terminal-Protector/dp/B000CIPUNC/ref=sr_1_4?crid=10539KK6UNMKH&dchild=1&keywords=battery+terminal+protector+spray&psc=1&qid=1572300981&sprefix=battery+terminal,aps,459&sr=8-4

raindog

@ : Estragon  Yes, I am leaning toward sticking with the electric fridge.  I think that, for the most part, if I just pay careful attention to the weather for the infrequent times when it looks as though we are going to have more than one cloudy day in succession, I can wiggle through by turning the fridge off at night and, perhaps, adding ice (I'm getting quite good at making that work by now). In general, we have a pretty dry, sunny climate.  A small, 7-10 cu. ft. fridge/freezer will be adequate for our needs (Avanti makes one at ~244 kwh/year).

I didn't know there were propane powered generators 'til now! Thanks!  We'll see ... machines of this sort don't last long here ....

@softdown : despite the remark about machines above, I've had pretty good luck with computers (~20 years in the Florida Keys before here). I'd have to guess at the wattage of the desktop, as it was custom built; the monitor is ~57 watts. This would be limited use, as I can use this little laptop (33 watts) for everything except graphics. The laptop I was considering, that would drive the monitor (since I need color calibration capability), needs 120 watts.

My questions now: (1) is it possible for me to just replace the battery bank at this point? (-- especially since there will be construction on the house in the near future and I'd rather not have a bunch of brand new solar panels around), and (2) will the 2, 250ah batteries work and give me a bit of flexibility down the road?

raindog

@photowhit : Are there benefits to going with the flooded batteries other than cost?  I don't think I quite have the concept of "balance" in this context yet. And, it's a bit difficult to balance when the living arrangement is still in flux.

@softdown : Thanks for the CRC suggestion!  When the batteries started showing signs of failure, I had the terminals cleaned. Now I see rust!  I'd forgotten about CRC.

mcgivor

Perhaps it is best to replace the batteries for now, if you have managed to get by, adding to an existing system always seems to leave something incompatible. Building a second new system from scratch would allow the older one, or vice versa, to be dedicated to a specific task such as running the refrigerator whilst providing redundancy should a component fail in either, being on an island usually means lengthy waits for replacement parts.

Flooded LA batteries are more forgiving than AGM, they can be equalized to correct imbalances in cell voltage , each cell can be checked with a hydrometer to assess state of charge or condition. The downside is they are less efficient, require regular maintenance requiring distilled water periodically which increases as they age and are somewhat messy. With either, especially in the tropics, charging temperature compensation is essential, this brings on the next contender, the drop in LiFePO4.

The LiFePo4 drop in replacement type batteries are probably the most versatile substitute for lead acid, they are self contained with internal electronics to prevent over discharge, overcharging, short circuit protection, over or under temperature protection, individual cell protection and various other parameters and no temperature compensation is required. The initial cost may seem high, but the cycle life expectancy actually makes them competitive. The downside is they don't  tolerate low temperature, which in the tropics is generally a non issue. Additionally they have a higher energy density which makes for a smaller, lighter bank, not significant in a stationary application, but transportation often considers weight. LiFePo4 also charge at maximum current until fully charged which shortens charging times both with generator or PV, unlike lead acid, which need a long absorption period.

Think long and hard about your future endeavors, keep an open mind, there are alternative solutions which may not be commonplace, for now at least, but they are real despite popular belief. 

raindog

@mcgivor : yes! I've already started looking at the LiFePO4s and pretty much decided this is the right way to go considering my circumstances (--the remoteness, the heat/salt, etc., the shipping, limited space - tiny house, how meaningless warranties are from here, and on and on). It appears to me that 2, 12 volt 100ah batteries of this sort would give me quite a lot of flexibility and a little peace of mind.

I am unclear whether the total battery amperage would be sufficient, however, as I don't understand this too well ... yet. I think the battery market people don't make this any easier either. Still working on it ...

Looking at replacement panels too: if they are on the roof when construction of house addition starts, they should be OK.

Thanks!

spacebass

You must somehow buy an 'Inverter' fridge though I understand from Bill on here such technology is scarce in th U.S. An inverter fridge uses less electricity generally and does not have the start up  constant big peak in electricity demand .
I would not believe per gospel exactly what is promoted by industry moguls as You have already noted re batteries.
I am in the process of buying 4 x 110 ah lithium battery packs , I will post my experience .I have one already , the built in BMS limits charge to. 12.6 volts , I am also using a 100 ah Hitachi sealed car battery which I can charge to. 14.3 volts.  the lithium goes down to 9.9 volts and the car battery goes down to 11.2 so I gain on downside with Lithium but also gain on the upside with lead acid, so not overjoyed with my first lithium analysis. If I had to choose which battery gives me the longest output / utility it woul be the Hitachi. Car battery.
You will know that lead acid batteries are heavy I would not think You could move this 100 ah battery, so this may be the deciding factor.
My experience as a novice is You should go for 2 x 220 ah or 4 x 110ah lithium , as I am now moving to from 2x 220 ah lead acid , which just does not do 1700 hours to 0800 hours without any solar input .(I Do have a big inverter fridge) I am moving to the lithium not because I am convinced it will deliver. on it's promise but because I am getting batteries nearly half price. 

raindog

@spacebass : Hi and thanks! I ran searches looking for an inverter compressor fridge. It seems they are only available in the USA in the very large, ~22 cu. ft. models from makers like Samsung and LG. Such a shame -- the people who would most benefit from them are denied the option. I will check in Nassau, but appliances here mostly come from the US.

I'm still trying to determine my needs re: the batteries, etc. Actually, this setup worked for a year for me without much issue, but it is not really sufficient for full-time living. The batteries are old (~ 5 years -- longer than most last in this climate according to neighbors), and, I believe, I drained the last life out of them during Hurricane Dorian, online, trying to keep tract of the storm.

I'll get help to move the batteries from the boat to the car and car to house; after that, I don't plan on moving them.

How much sun do you get in your location?

raindog

@mcgivor : can we discuss small wind turbines here? Realizing that I would need more power, I did some research on small wind turbines and hybrid systems before moving here. I am located on the edge of an ~70-80' cliff, facing the open Atlantic. Lots of breeze up there (-- house sits back from the edge and down the slope).

Prospects for this seem to be mixed among my seafaring neighbors. There's some objection to noise and maintenance difficulties; on the other hand, some feel it would be a workable solution and that the noise objection is overstated.  It's been a while since I looked at small wind turbines.

mcgivor

Personally I've no experience with wind turbines but would think as an auxillary source they may be of some use if conditions are ideal, but they will add to the complexity of the system design, they need some way to stop or dump the excess power when there is no need for charging.

When designing a system the loads will determine the battery capacity, the battery capacity will in turn determine the PV required to maintain the battery capacity,. Building a safety margin is good practice to cover periods of cloudy weather, this can be difficult to predict as well as being potentially damaging to lead acid batteries as they don't like to be drawn down to low voltage levels  without receiving an immediate recharge, LiFePo4 on the other hand tolerate partial states of charge without negative impact.
 
Starting a new thread for the design of a system may be the best place to start, collect all the information for relevant loads in watts along with projected time of useage, this will provide information to get the ball rolling, don't be conservative, be realistic and the rest will flow into a sound design. 

As previously mentioned, it may be better to replace the batteries of your current system for now and plan for the future with a new but parrallel system for redundancy purposes. There may be a need for more specialized equipment if LiFePo4 is selected, particularly regarding the charge controller, it's not particularly difficult but there needs to be a starting point.

Based on the description in the original post you have ~ 100Ah at 24V or 2.4Kwh, of which 1.2 Kwh is usable which is about what a typical refrigerator needs with very little wiggle room for more than a day.

Your thoughts on how to proceed will provide valuable information 

softdown

spacebass said:

You must somehow buy an 'Inverter' fridge though I understand from Bill on here such technology is scarce in th U.S. An inverter fridge uses less electricity generally and does not have the start up  constant big peak in electricity demand .
I would not believe per gospel exactly what is promoted by industry moguls as You have already noted re batteries.
I am in the process of buying 4 x 110 ah lithium battery packs , I will post my experience .I have one already , the built in BMS limits charge to. 12.6 volts , I am also using a 100 ah Hitachi sealed car battery which I can charge to. 14.3 volts.  the lithium goes down to 9.9 volts and the car battery goes down to 11.2 so I gain on downside with Lithium but also gain on the upside with lead acid, so not overjoyed with my first lithium analysis. If I had to choose which battery gives me the longest output / utility it woul be the Hitachi. Car battery.
You will know that lead acid batteries are heavy I would not think You could move this 100 ah battery, so this may be the deciding factor.
My experience as a novice is You should go for 2 x 220 ah or 4 x 110ah lithium , as I am now moving to from 2x 220 ah lead acid , which just does not do 1700 hours to 0800 hours without any solar input .(I Do have a big inverter fridge) I am moving to the lithium not because I am convinced it will deliver. on it's promise but because I am getting batteries nearly half price. 

Typo?

BB.

Regarding Wind Power... I, personally, are not a big fan if it. The wind turbines are relatively inexpensive and many times, unreliable. Add towers, concrete, method to service the turbine (lifts, tilting tower, crane, etc.), cabling, controller, etc... This is one area were do it yourself Wind Turbines can be better than purchased.

Here are some web forums that do have more wind discussions than we do:

www.otherpower.com (good forum for DIY Wind Power)
Hugh Piggott - Scoraig Wind Electric site for tons of info
Scoraig Wind "Recipe Book" for DYI Turbines 
www.greenpowertalk.org 

-Bill

softdown

softdown said:

spacebass said:

You must somehow buy an 'Inverter' fridge though I understand from Bill on here such technology is scarce in th U.S. An inverter fridge uses less electricity generally and does not have the start up  constant big peak in electricity demand .
I would not believe per gospel exactly what is promoted by industry moguls as You have already noted re batteries.
I am in the process of buying 4 x 110 ah lithium battery packs , I will post my experience .I have one already , the built in BMS limits charge to. 12.6 volts , I am also using a 100 ah Hitachi sealed car battery which I can charge to. 14.3 volts.  the lithium goes down to 9.9 volts and the car battery goes down to 11.2 so I gain on downside with Lithium but also gain on the upside with lead acid, so not overjoyed with my first lithium analysis. If I had to choose which battery gives me the longest output / utility it woul be the Hitachi. Car battery.
You will know that lead acid batteries are heavy I would not think You could move this 100 ah battery, so this may be the deciding factor.
My experience as a novice is You should go for 2 x 220 ah or 4 x 110ah lithium , as I am now moving to from 2x 220 ah lead acid , which just does not do 1700 hours to 0800 hours without any solar input .(I Do have a big inverter fridge) I am moving to the lithium not because I am convinced it will deliver. on it's promise but because I am getting batteries nearly half price. 

Typo?

Lithium batteries are well known for accepting higher charging voltages. It almost seems like disinformation in its current state.

raindog

I think I will take mcgivor's advice and replace the batteries for now. I think the knowledge I will gain from designing a new system from scratch will really be worth a great deal when it comes to managing the larger system in the future.

Being more self reliant is one of the reasons I moved here. I suspect I could tie in to the local grid for what it will cost to stay off of it and run all my stuff, but that would negate part of the journey.

So I am thinking of just increasing the ahs of the batteries and leaving the remainder of the system as is. Seems I'm pretty much back to where I started re: battery selection (although the size of the batteries is a bit daunting). I'm looking at the Renogy 12v/200ah. Three reasons beyond the ah boost:

• They are relatively cheap, ship "free" ~~ahem~~, and seem to have fairly good reputation/support (-- the latter being most likely imaginary in my circumstance);

• I've read that they perform well in marine use, so should do OK in my salty environment;

• I think I can make a strong case for them being "solar" batteries with the Customs office.  If I can't make this case, I will pay 30% duty, among other charges, that will significantly add to the cost of the batteries. This would probably be a less touchy issue were I shipping a whole system.

I can think of several alternative uses for these batteries, should they still be alive when I move to the new system, so that makes me happy.

Marc Kurth

Be sure to have your supplier CLEARLY indicate "Solar Batteries" on your invoice. This is standard procedure when shipping to many countries.

softdown

I keep marveling at raindog's "transformation" from poor forlorn little lady to secret agent with customized computing living on top of a 75' cliff overlooking the ocean while preparing for a substantive home addition. 

Just an idea here - there are likely many boaters that make regular trips between Miami and the Bahama's. Monohulls are capable of ferrying serious weight. You might chat them up about ferrying the needed gear. Everybody wants to help a senior lady (I think?) I hope. 

I'm sure that shipping to the Bahama's is quite expensive for several reasons.