Intoduction and queries

Re: Intoduction and queries

Welcome to the forum Newl.

A few comments:

newl wrote: »

My current primary setup is a 12V system (I also have other smaller solar configurations around the property for dog collar radio fencing, electric horse fencing, lighting):

* 2 x 200W panels

Interesting, you have found one of the few large (high wattage) solar panels that outputs Vmp~18 volts--Which is good for 12 volt battery bank with PWM controller. Will help to keep your system costs lower.

* 1 x 30A 12V/24V PWM charge controller

If you need to add panels (now or later), this controller is only good for ~2x of your 200 watt panels. So, no room to expand without paralleling charge controllers (not usually a problem) or installing your larger controller.

* 4 x (PDF spec sheet) PDC-121000 100AH batteries currently wired in parallel. Charge controller and inverter are connected at opposite polls.

Personally, I am not a fan of lots of batteries in parallel. I like to see larger AH batteries/Cells to give you one too a maximum of two to three strings in parallel.

You have AGM (Sealed) batteries, and this might be a better idea for a remote installation. Having to buy/make distilled (or de-ionized) water for filling batteries in remote/dry region may have its own difficulties (capturing and storing clean/filtered rainwater is an option too).

A rule of thumb I like to use for sizing the batter bank to solar array size i the 5% to 13% rule of thumb:

• 14.2 volts charging * 400 AH capacity * 1/0.77 panel+controller derating * 0.05 rate of charge = 369 watt array minimum
• 14.2 volts charging * 400 AH capacity * 1/0.77 panel+controller derating * 0.10 rate of charge = 738 watt array nominal
• 14.2 volts charging * 400 AH capacity * 1/0.77 panel+controller derating * 0.13 rate of charge = 959 watt array "cost effective maximum"

AGM batteries are a better choice for a smaller array (lower self discharge rate, no equalization/mixing of electrolyte required by higher current). But that 400 watt array is still a bit on the small size for that size battery bank. It would be nice to get closer to the 10% rate of charge if this is your only power and you need the electricity.

I would suggest Battery Monitor (Victron is another very good brand) for your system. While you can use a volt meter to get a good idea of how your system is running--You cannot measure specific gravity of your bank, so you have to be very diligent/careful and understand what your volt meter is telling you. A battery monitor (while not perfect) will help you both measure/monitor your loads and help you keep the batteries happy.

Almost everyone "murders" their first set or two of batteries--Usually from under charging/over discharging/too large of loads (another reason to suggest "cheaper" flooded cell "golf cart" batteries for your first try vs the more expensive AGM). A battery monitor will help you understand your loads/battery state of charge better.

* 1 x 12V 300W pure sine wave inverter that will surge to 450W

GREAT! Somebody with a reasonable size of inverter on their battery bank. Do you have a switch to turn it off when not in use (may still use ~6-10 watts just being "on"--a significant power hit for a small power system).

My usage currently is (sans refrigerators):

* 12V LED strip lighting - 5 hours 60W = 300WH/25AH ...)

60 watts is a lot of LED... Are you planning on us 12 volt LED or 120/230 VAC lighting?

* 240V Laptop - 5 hours 25W = 125WH/.52AH (again, aiming a bit high time wise, real usage is typically 3-4 hours, W is pretty accurate even with elcheap-o plug in power measurement device)

Probably a typo/calculation error here--The way I do the sizing including inverter losses:

• 25 watts * 5 hours * 1/0.85 inverter losses * 1/12 volt battery bank = 12.3 AH @ 12 volt bank
• 25 watts * 5 hours * 1/0.85 inverter losses = 147 Watt*Hours

Your total load is ~447 WH per day or 37 AH @ 12 volts per day... The battery sizing of 1-3 days "no sun" and 50% maximum discharge (longer battery life), picking 2 days and 50% max discharge"

• 37 AH per day * 2 days * 1/0.50 max discharge = 148 AH @ 12 volt battery bank "nominal"

Your bank is a bit on the "large size" for such a system (pushes up the solar array sizing to keep "battery bank happy"). Does give you some room to grow/miss your numbers.

I assume you are in a sunny/dry area of Australia--so lets assume that you get a good 4 hours of sun for 9+ months of the year (you might do better):

• 400 watt solar array * 0.52 system derating * 4 hours of sun per day = 832 WH per day

You currently have only 447 WH of usage planned per day--So your array seems to output plenty of power for your needs (solar and loads do vary--You should never plan on using 100% of your predicted capacity every day--Monitor your battery bank and ensure that you do not "stress" your battery--cut power usage/fire up backup generator when needed).

Eventually, I'll want to add a 12V extractor fan once my gear goes into a small 3m x 3m garden shed and more than likely a pedestal for my usage being as I am currently coming into the summer months. These are the only immediate additions that I can think of apart from 12V LED lighting in the loo/shower block that I have not yet build.

If you can--use a chimney/optimize for natural circulation (inlet low, large outlet high). Fans (and any mechanical devices) tend to use a relatively large amount of energy per day to operate. If you can avoid using the power in the first place--You are better off (smaller solar powered fans do not move that much air--You can use a fan+direct connect solar panel instead--Saves the whole battery issue as you only need the fan to run when the sun is up--I would guess).

Everything else that I use runs LPG (stove, hot water system) or is rechargeable (flashlights, hot water system). Water is collected by a car port, 16M^2 which gives me 1L per 1mm of rain fall, and stored in two 5000L water tanks. This too is an area in which I need to improve, not enough surface area for catchment; working on that.

Use a 12 volt water pump to pressurize some indoor plumbing?

... I also realize that 800W of panels will be overkill for the current battery configuration. Being as the system is only a couple months old, could I get away with getting four more without too much disruption between what has been used for two months and what has been sitting on a shelf (I know that mixing batteries in terms of their life isn't a good idea yet these would be fairly close)?

For the size battery bank you have--800 Watts would not be a waste--I would hook them up (all things being equal). Good charge controllers will keep the battery voltage appropriate for the batteries. And AGMs, while they do not like high charging voltages, can take pretty much any current you throw at them. Put two controllers in parallel (run wire from each controller back to the battery bank--short/heavy wire to keep voltage drops low--should have a fuse/breaker per controller/load branch circuit for safety).

My reason for wanting to make the switch to 24V is two fold. First, I can switch the Tristar in and run all 800W (all four panels in series, single string) in an optimum configuration and gain the added obvious benefits of an MPPT controller that I can grow with as my needs grow.

Keeping the DC current down (I suggest switching to the next higher battery bank voltage if your DC current goes over ~100 amps--i.e., ~1,2 watts for 12 volt max; 2,400 watt for 24 volt bank, etc.). However, trying to find power appropriate 24 and 48 volt inverters for smaller systems can be difficult--and larger inverters use more power when idling).

Secondly, I have two refrigerators at the moment, neither of them is in use, that I would now like to start using at least one of them. I have a Waeco (Dometic) RC1180 50L and an NEC 80L bar fridge. Of the two, the Waeco draws the most power at 119W +/-10% (cheap $20 plug in digital power meter) while the NEC draws ~560W start up surge and settles to 75-80W. Consumption and space consideration wise, the NEC wins the draw. Flexibility wise, the Waeco wins because it is 240V/12V/LPG so I'll probably keep it for a backup.

If you can, get a Kill-a-Watt type meter (link to 120 VAC version) and measure their daily load (over 1-7 days or so). Small bar fridges tend to use almost as much power as a full size/very efficient home refrigerators these days (~300 WH per day for a bar fridge; around 370-400 WH per day for a full size fridge). One option would be to convert a chest freezer for fridge use (may use as little as 250 WH per day at 77F/25C).

Either way, you will proably need a minimun of 1,200 to 1,500 inverter to start a full sized fridge.

Ideally, I would prefer to go 48V and then get a 48V inverter and 48VDC->12VDC converter to be able to run all of my existing 12V gear. A bit out of my price range at the moment so I am making the (albeit costly for when I do go 48V) decision to use 24V as the stepping stone and continue to learn about the system, the technology, my usage and habits, all of which come into play.

As you have seen--It is difficult to "cost effectively" grow a solar power system... New inverters for each voltage change, perhaps a new charge controller to 48 volts, solar panels change (you may not find Vmp matching panels 2-4 years down the road) and such... If you will be going to a larger system eventually, you may just want to save some money and "skip" the 24 volt verson unless you can use it elsewhere (guest cabin, remote camp site, etc.).

Now, the part that I am not specifically clear on is the difference is between 12V@400AH and 24V@200AH (two parallel strings of two in series). I know that the power capability remains the same (Ohms Law) but does the drop in AH have an impact as such? Related to this, in reference to 48V system, would running the four batteries in a single string 48V series configuration at 100Ah also have an impact? I realize that using larger voltages means my cabling (naturally depending on distances and losses) doesn't need to be as beefy and that is an advantage in terms of cost.

I, personally, do not like to parallel batteries--So I would be better with 2 parrallel strings at 24 volts or one series string at 48 volts. The big issue is finding an AC inverter that matches your power needs/bank balance. The 48 volt inverters are going to be in the 2-4kW+ range--Great if you need that level of power and have teh battery bank+solar array to support it... But can be "over kill" for people with smaller power needs.

And, I would suggest avoiding oversizing the battery bank if you don't need the power. Batteries age faster (sulfate) if they are not quickly and fully recharged a cuople times a week (recharged to over 90% state of charge). A large bank takes a good sized array to quickly recharge--and when the batteries fail, you have to spend more money to replace the bank.

Your comments?

-Bill

Re: Intoduction and queries

Thank you Newl for finding the typos around Rate of Charge equations... I have fixed them.

So you're suggesting the following for 24V. If so, this was my intended configuration. Yes, the 48V inverters aren't cheap either.

12V Parallel 12V = 12V@200AH + 12V Parallel 12V = 12V@200AH = series for 24V@200AH

Not quite sure what you are asking... If you have 4x 12 volt @ 100 AH batteries, your options would be:

• 4x in series... You would get a 12 volt @ 400 AH battery bank
• 2x in series, then those two in parallel... gives you 24 volts @ 200 AH battery bank
• 4x in series... gives you a 48 volt @ 100 AH battery bank

All would store the same amount of energy (voltage*AH=storage energy in Watt*Hours):

• 4x 12 volts * 100 AH = 4,800 Watt*Hours = 4.8 kWH

If you have the 4x 12 volt @ 100 AH batteries, and a 12 volt inverter that currently meets your needs--Use them all. Wire them up per this website to help ensure the batteries share the load properly.

If you will be paralleling battery banks for the long term... I would suggest getting a DC Current Clamp Meter. They will allow you to monitor the DC current in each string to ensure that all are (roughly) carrying the same loads (charging and discharging--no bad connections, no shorted/open cells that can damage the other batteries over time). This meter is only $60 USD in US (Sears.com) and it is "good enough" for our basic needs (you can spend $400 USD or more for a "good one" from Fluke/etc.). I don't have any suggestions for your region.

My thought when saying that is that I could easily run the 12V off of the load connection of the charge controller. Fan and a direct connect panel is another option and probably cheaper. Another option is one of the spinning vents (we normally have a steady breeze/wind at this location).

Apparently the "wind turbine" type spinning vents are not really any better at enhancing air flow when the weather is windy. Just lots of area (sq. meters) for natural circulation (both inlets and outlets) is the best thing.

Reducing loads on the battery bank is always a good idea--especially automatic loads (i.e., fan runs during the week and you get bad weather---and can't get back in time to kill the loads--which kills the battery bank). Small loads (fans, computers, TV, etc.) that run for 8-24 hours per day can easily be more power hogs than a microwave that only runs 20 minutes a day.

Your thought appeared to get cut off?

I suppose that one of my fears is not using the bank to its potential. As examples of patterns, I don't always run lighting at night and I'll only leave the power point for the laptop switched on long enough to charge it and repeat again in a few hours when it needs it. What I do not want to do as expressed before is
(???)

Basically, if you have a good ratio of Solar Array Wattage to Battery Bank Storage (i.e., the 5%-13% rate of charge)--and you have panels available for the 10+% rate of charge--Go for it.

The batteries will be happier with more charging current available. And if there is nothing you can do with 1 or 2 batteries pulled from the bank (i.e., take two extra panels+batteries for another guest tent/work area???)--Just add the panels and see how the system performs.

In any case, you will be learning from this bank/system--See how everything works. If you add/install a larger inverter (the AGM batteries are real good at surge current)--And keep the DC power leads short and heavy (between battery and inverter)--You might be quite happy with the existing bank and a 12 volt 1,200-2,000 watt inverter to run the bar fridge.

Note, while MSW inverters are much less expensive--MSW may be hard on the refrigerator (cause it to fail an early death--it very hard to predict if the fridge will last 10+ years or only 1-2 years on an MSW inverter--Just do not know). Induction motors generate more waste heat because of the non-sine wave form from MSW (modified square wave) and can age the pump faster.

-Bill

Re: Intoduction and queries

newl wrote: »

I am currently wired up with the second method; charging on opposite corners +/- and pulling from the opposite +/- corners to those two. The last method is simple enough to implement with a couple extra cables that I'd be prepared to shell out for to have them made up to length. Would I still need to charge and use from opposite ends though?

As long as you don't do #1 (feeding a "ladder network" from one end)--You are fine. The idea is that to any battery in the string, you have equal length (resistance) wire paths. + and - lengths do not need to be identical--just the total + and - path lengths.

I've been having a circuit breaker trip intermittently the past week. I'm fairly certain it is because of the way I wired it and it is probably undersized.

I'm using a double pole 20A 500VDC breaker primarily for isolation. One one pole, I have the positive of the panels come in and then out to the PWM charge controller. The PWM charge controller output then goes through the other pole of the same breaker and then out to the positive side of the battery bank.

I then have a second identical breaker fed off of the opposite positive lead of the battery bank into that breaker, bonded both poles and then out to the inverter.

I guess this does not make sense too me... How large is your inverter? 20 Amps on the 24 VDC battery bus is only good for ~400 watt of continuous AC output (power=voltage*current*inverter-efficiency).

Being as the two existing panels are wired in series, the Imp is 11A, Isc is 11.5A which is well below the rating of the breaker, though it probably isn't if both poles need to be utilized to get the 20A capacity.

Paralleling beakers/fuses is not usually a great idea (minor resistance variations can steer the shared current away from one breaker and into another).

I feel that I've probably confirmed the cause (someone is welcome to chime in with wisdom ), not specifically 100% sure what sized breakers that I should be running. While on the topic, fuse size suggestions would be very helpful too. I'm about to build up a power board and redo things so they'll sit nicely on the shed wall. With this redo, I found a 600W/1000W TSW inverter for a decent price and that covers my existing requirements and meets surge requirements as well.

For example, a 24 volt DC input to a 1,000 AC inverter should have a branch circuit/wiring rated to a minimum of:

• 1,000 watts inverter output * 1/0.85 inverter eff * 1/21 volts batt cutoff * 1.25 NEC derating = 70 amp minimum wiring/fusing/breaker rating

So, round up to the next standard (like 80 amps). And ensure you don't have much more than 1 volt wiring drop (24 volt bus) from battery to inverter (short/heavy cabling).

-Bill