I000 watt partially off-grid system

bigbrovar

Hi guys. I have been lurking around this forum for a long time now but this is my first post. Going through past threads has contributed immensely to my solar setup knowledge.

I am trying to setup a small off grid system with a 12v 200AH batteries, 1050VA Interter (With battery charging capabilities), a 30A Epsolar Mppt charge controller.

As to the panels, I have access to 2 240watt 24v poly panels and 1 220w 24v poly panel.

The panel config are:

PMAX = 240w

VMP= 30.5v

Imp= 7.78

VOC=37.7

ICS=8.42

I was initially going for a 24v system until I read here that the VMP at 30 would be inaquate for a 24v setup once heat and wiring loses are subtracted. I come from Nigeria where it can get real hot (31-38c) all year round. So decided to use a 12v system with an Mppt charger.

However my Mppt charge is 30A and has a Max. PV open circuit voltage of 150V and Max. PV input power of 520W.

Question is how best do I use my panels to get the most optimal results from the panel.

My plan initially is to connect 3 panels in parallel .. Or do I connect them in series of 2 as 3 might take it over the Max PV rating of the controller.

Also what is the expected current I could get using whatever setup is recommended.

Also my country Latitude is 10º00´ North of the Equator in this case, which direction is best to point the panel towards? I hear people in northern hemisphere generally direct towards the south. Will same apply to me.

I am a newbie never done a solar project before, however I have tried to do lots of learning and catching up. Due to the shortage of professional solar installers in my country I will be heavily involved in my setup to ensure things are done right (especially with the panel setup side of things)

I would also appreciate advise on the size of breakers both dc and AC I would need between panel and controller, controller and battery, battery and inverters, and Inverters and house, grid to

inverter.

Lastly, I read somewhere that the charge controller (the Epsolar Tracer 3215BN) has the capability to backoff once it detect the battery is being charged from another source (i.e Inverter) is this a general feature of MPPT controllers or just a feature of this particular controller.

Am sorry if my questions are stupid or I should have researched more. I have been on Google and on this portal for most of the past couple of weeks.

Also apologies for my English.

Thanks in advance

zoneblue

While you dont give the specs on the third panel, its likely and ill assume that its Vmp is similar the the other two Hence all three panels in parallel will work quite well. However you are correct that this will not work well for a 24V battery. Hence your choices are to get another panel and use 2S2P configuration for 24V, or 3P for 12V. For the array a tilt some where near the latitude is the ideal, near the equator flat will be also be fine, but will be less self cleaning.

vtmaps

bigbrovar said:

Lastly, I read somewhere that the charge controller (the Epsolar Tracer 3215BN) has the capability to backoff once it detect the battery is being charged from another source (i.e Inverter) is this a general feature of MPPT controllers or just a feature of this particular controller.

That is how all RE (renewable energy) controllers work. 

You can charge a battery by connecting it directly to a solar panel, but it is likely that you will ruin the battery by over charging it.  The primary purpose of a solar controller is to protect the battery from over charging. 

As long as all your charging sources use the same RE charging protocol they will mostly get along.  There is one exception... during bulk stage of charging it is possible for multiple charging sources to exceed safe current flow for a particular battery.  There is no problem once the batteries are in absorb stage or float.

As for your other question, zoneblue's advice to get hold of another panel and operate at 24 volts is good advice and would make the best use of the materials you already have..  How many 12 volt 200 ah batteries will you use in the system?

--vtMaps

bigbrovar

Thanks @zoneblue and @vtmaps for the replies. Much appreciated. Unfortunately I lost one of the panels (The 220W panel) had an accident while transporting to my premise so right now I have 2 240watt panels with following specifications.

PMAX = 240w

VMP= 30.5v

Imp= 7.78

VOC=37.7

ICS=8.42

I have (for now) One 12 volt battery for the setup with the hope of increasing it to 2 in the near future. I had plans of going for a 24 volt system with a larger charge controller but that would go over my finances (which is already over the budget as it is) so I intend to move slowly.

With the 2 240w panels, if I connect them in series I could expect potentially around 40amps from them for my 12v setup. (kindly correct me if am wrong) which would be over the limit of my charge controller which has the following limitations

Rated  battery current 30A
Rated  load current 20A

does this mean I can not use a setup which would potentially push out 40A?

Also if I connect this panels in parallel what would be my estimated amount of charge current all things considered.

Thanks once again

vtmaps

bigbrovar said:

I have (for now) One 12 volt battery for the setup with the hope of increasing it to 2 in the near future. I had plans of going for a 24 volt system with a larger charge controller but that would go over my finances (which is already over the budget as it is) so I intend to move slowly.

When you go from 12 to 24 volts, the same controller will handle twice the power (watts). 

When designing a system we like to start by knowing the load (kwh per day).  Next step is choosing a battery that can handle the load.  Next step is buying enough panels and controller to keep the battery happy.

If, for example, you determined that you need the capacity of two batteries, then you would have to decide whether the two batteries would be in series (24 volts) or parallel (12 volts).  Either way gives you the same storage capacity (in kwh), but the 24 volt system will be more stable and efficient.

Charge controllers are rated by their output current (amps).  A controller charging a 24 volt battery can handle twice as much power as it can handle when charging a 12 volt battery.

bigbrovar said:
With the 2 240w panels, if I connect them in series I could expect potentially around 40amps from them for my 12v setup. (kindly correct me if am wrong) which would be over the limit of my charge controller which has the following limitations

Rated  battery current 30A
Rated  load current 20A

Configuring the panels as series or parallel will have little or no effect on your ability to charge a 12 volt battery with an MPPT controller.  

The 40 amps you calculated would be correct only if the panels were at standard temperature.  When they are in the hot sun they will produce less than 480 watts.  As a general rule, after derating the panels for temperature and accounting for inefficiency in the controller, you can expect to get about 75% of your panel's rating.  Thus your 480 watts (40 amps) will typically be 360 watts (30 amps). 

You certainly have the potential to produce more than 30 amps.  Most/many MPPT controllers will not be harmed by having more panels than they can handle... they will just clip the extra power that is above their ratings, so there is unlikely to be any harm done by putting 480 watts of panels on an MPPT controller that can only handle 360 watts.

If you take those 480 watts of panel and use them to charge a 24 volt battery, the current into the battery would be 480 watts ÷ 24 volts = 20 amps (before derating for temperature).  That 20 amps is well within the 30 amp capacity of your controller.

--vtMaps

BB.

OK, going with some math to size the system... 2x 240 Watt panels. We recommend 5% to 13% typical rate of charge for lead acid batteries... 5% is for weekend/seasonal systems. 10%+ for full time off grid systems.

• 480 Watt array * 0.77 panel+array derating * 1/14.5 volts charging * 1/0.05 rate of charge = 510 AH @ 12 volt batt bank maximum
  
• 480 Watt array * 0.77 panel+array derating * 1/14.5 volts charging * 1/0.10 rate of charge = 255 AH @ 12 volt batt bank nominal
  
• 480 Watt array * 0.77 panel+array derating * 1/14.5 volts charging * 1/0.13 rate of charge = 196 AH @ 12 volt batt bank minimum

Because you have 30 Vmp panels--You really need an MPPT type charge controller (MPPT controllers are more expensive) to match the Vmp 30 volts to 12 volt battery bank (or Vmp-array 60 volts to a 24 volt battery bank). Typical MPPT controllers will work on 12 volt or 24 volt battery banks (and many will work on 48 volt too--for higher end controllers).

The maximum typical output from a 480 Watt array into a 12 volt battery bank:

• 480 Watt array * 0.77 panel+controller derating * 1/14.5 volts charging = 25.5 Amp minimum MPPT controller (12 volt battery bank)

Note that a 12/24 volt controller can manage a 2x larger solar array at 24 VDC battery bank vs a 12 VDC battery bank.

I don't know if the 6 volt @ ~220 AH "Golf Cart" type batteries are common in your region--But they would be a nice fit here (2x 6 volt batteries in series for a 12 volt @ 220 AH battery bank).

Next, how much power do you want from the battery bank. 1,050 VA is a good number to know from your AC inverter--But we also need to know the Watt rating (VA is usually equal to or larger than the Watt rating).

For a 12 volt @ 220 AH battery bank--The typical output power from such a battery bank would be:

• 12 volts * 220 AH * 1/20 hour discharge rate * 0.85 AC inverter eff = 112 Watt average power (say 5 hours per day for 2 days, 50% maximum battery discharge)
  
• 12 volts * 220 AH * 1/8 hour discharge rate * 0.85 AC inverter eff = 280 Watt maximum average continuous power
  
• 12 volts * 220 AH * 1/5 hour discharge rate * 0.85 AC inverter eff =440 Watt maximum continuous power (hour or so)
  
• 12 volts * 220 AH * 1/2.5 hour discharge rate * 0.85 AC inverter eff =898Watt max surge power (few seconds to start well pump, etc.).

So, nominally, a "good size" inverter for a 220 AH @ 12 volt battery bank would be in the 280 to 450 Watt range.

And if you get 5 hours of sun on a good minimum average day:

• 480 Watts * 0.52 off grid system eff * 5 hours of sun per day = 1,248 Watt*Hours per sunny day minimum (depends on where the system is actually installed)

Anyway--Some numbers and guesses. Your thoughts?

-Bill

bigbrovar

Wow guys.. Thanks so much for all the input. my set up is quite small actually. I intend use the solar for emergency backup power (i.e led light bulb, led tv, laptop charger, cable setup box, and sound system) my total wattage is estimated to be 550 watt, 600watt tops. I also intend to isolate the appliance to be powered by solar and terminate them directly to the inverter (which only default to battery during blackouts) I am hoping that it would at least be able to give me 4 hours of backup power if not, I might consider adding to the battery backup. Blackouts in my country is a huge problem so sometimes it is nice to have a way to have at least lightings in the house. I don't intend to have all the loads on at the same time. 

One more thing, if I connect my panels in parallel, what would be my expected output from the CC? 

BB.

The panels in series or parallel--It really does not matter from a high level point of view:

• Power = Voltage * Current
• P=V*I= 30 volts Vmp * 2x 8 amps Imp = 480 Watts parallel panels (current adds)
• P=V*I= 2x 30 volts * Vmp * 8 amps Imp = 480 Watts Series panels (Voltage adds)

So, you need to look at the hardware requirements...

To charge a 12 volt battery, you need Vmp-array~17.5 to 20 volts minimum. If you have a PWM type solar charge controller (Pulse Width Modulation)--That type of controller needs the solar panels to "exactly match" the voltage requirements of the battery bank.

However, if you have a MPPT type charge controller (Maximum Power Point Tracking), these have a "buck mode switching digital power supply" inside the MPPT controller. More or less, it is the DC power version of a transformer. An MPPT controller can take high voltage/low current and efficiently down converter it to low voltage/high current needed for a battery bank (sort of like a car with an automatic transmission for another analogy--The transmission matches the power curve/rpm of the engine to the wheels).

A higher end MPPT charge controller on a 12 volt battery bank can take Vmp-array of 17.5 volts to ~100 volts. The advantage of running a MPPT controller is you can use (usually cheaper) "GT Solar Panels" in the >>140 Watt range (Vmp typically ~30 volts for such panels). Also, if you have a long wire run from the array to the charge controller+battery bank, you can use smaller diameter copper wire (and save money) with a higher voltage array.

Now--Back to your needs... There are two major considerations... Maximum Average power to supply your loads (i.e., xyz Watts), and how long you want to power those loads (xyz Watts * abc Hours per day)...

So, do you need 600 Watts on at the same time for 4 hours per day (600W * 4Hours=2,400 WH per day), or do you only need 150 Watts average (few LED lights, LED TV, satilite TV receiver, laptop computer: 150 Watts * 4 Hours = 600 Watt*Hours per day)?

You need to understand your loads... If you are in a 230 VAC 50 Hz country, see if you can get a Watt*Hour type meter like this (many brands/models out there these days--Not suggesting to purchase this one meter):

http://www.reuk.co.uk/Kill-a-Watt.htm

Once, we understand the loads, then we can better help you to design your system. Conservation is your best starting point, it is almost always to use as little power as possible--Then your off grid/backup power system can be small (and cheaper) too.

For folks that need afternoon backup power--Start with battery bank + Inverter+charger first. Using your AC mains power to recharge the battery bank is good for a starter system. Once you get the backup power system running the way you want (like a computer UPS system)--Then you can add solar panels+solar charge controller later (as funds permit).

-Bill

zoneblue

My three keys to happiness in off grid solar are:
- getting the ratio of PV to battery and inverter right (as bill outlines above).
- buy only name brand gear
- methodical workmanship

2 parallel 12v 200Ah batteries, 1000W Inverter, 700W PV. Turns out to be a reasonable fit. Beware at 12V thats 45A of charge current, which maxes out your charge controller. Not the end of the world for a mppt controller but if you havent bought the gear yet, 24V will be better.

2 series 12V 200Ah,
But now you need one extra panel, taking PV to 920W.
Charge current is then 30A which is 0.15C rate of charge, (tad high for FLA, good for AGM).

bigbrovar

@zoneblue @BB. I owe you guys and everyone who has contributed to my thread a lot, I have gone back to the drawing board to make some adjustment to my setup. Unfortunately is is a 12V system (12v inverter has already been purchased) However I intend to use it with 2 200AH batteries connected in parallel to give a total of 400AH. The inverter I am using as a Low Voltage Disconnect of 10.5v for 12v batteries which is about 70% of discharge.. not ideal but I will do well to ensure I don't get that far.

The inverter charges at 14A while the charge controller after taking in loses should charge at 20/25A (The optimum Current from the 2 24v 280w panels is 40A, My MPPT CC has a as a charge limit of 30A.

My country is about 10 degrees above the equator hence I am suppose to place my panels facing the south. Unfortunately the south facing part of my roof is completely shaded by about 3PM.. The only part of my roof not affected is the east facing side of the roof. My plan is  to have the panels installed there but tilled towards the south. (don't know if this makes sense)

From my estimation the 480w panel used with a 12v system should generate max 40A, given that the CC can only dish out 30A max. What size of cable would you guys recommend I use? from my investigation online I think 10mm2 cables might just do the job. The distance between the panels and the cc should be about 10-15 feets. 

Also I was thinking of using 50A breakers between the CC and the PV and will this be adequate protection? The breaker am looking to get is from the chinese site aliexpress and it is rated at 10  (ms) and Instantaneous Trip type B.C.D. I don't know if this would be adequate. 

I am sorry for my constant question, this is an absolute first for me and am just trying to cover my base. Thanks.

Aguarancher

At 10.5V your battery is dead

bigbrovar

Aguarancher said:

At 10.5V your battery is dead

OK.. That is depressing I guess I will have to manually keep my eyes on things to ensure it never gets to that stage. Thanks for the chart. I mistakenly assumed 10.5 was 30% SOC due to some documentation I found online. 

bigbrovar

This is the breaker I am looking to get for my setup. I am unable to get a DC breaker from all the shops in Abuja (Nigeria) and the one I found online were of the wrong Amps rating. I found this on the chinese's amazon like site thingie http://www.aliexpress.com/item/2P-63A-DC-440V-Circuit-breaker-MCB/32267474848.html?ws_ab_test=searchweb201556_2,searchweb201644_1_79_78_77_82_80_62_81,searchweb201560_4 I don't know if it is any good for my needs.

vtmaps

bigbrovar said:
OK.. That is depressing I guess I will have to manually keep my eyes on things to ensure it never gets to that stage. Thanks for the chart. I mistakenly assumed 10.5 was 30% SOC due to some documentation I found online. 

Under some circumstances, 10.5 volts could indicate 30% SOC.

You should realize that the chart gives SOC vs Voltage when the battery is at rest.  When the battery is being discharged, the voltage sags below what the chart shows. 

Example: suppose your resting battery voltage is 12.5, indicating 80% SOC.  Then you turn on a 200 watt load and the voltage sags down to 12.24 volts.  Then you turn off the load and the voltage rebounds to 12.5 volts.  You did not go from 80% SOC to 60% and then back to 80%.  You were at 80% all along.

This has important implications for how you set your LVD (Low Voltage Disconnect).  If your goal, for example, is to never go below 50% SOC, then you can set your LVD to 12.1 volts.  If you run a very small load there will be very little voltage sag and by the time the battery voltage drops to 12.1 you really will be at 50% SOC.  On the other hand, if you are running a large load there will be voltage sag and the LVD will shut off the inverter and then the voltage will rebound to some voltage that is higher than 50% SOC.

In any case, 10.5 volts is too low to protect a battery with any load, large or small.  The default LVD voltage on most inverters is designed to protect the inverter, not the battery.  As voltage falls, your inverter will draw increasing amps in order to maintain its power output.  When the voltage falls to 10.5 the current is too great for the components in the inverter, so it shuts down.  A full featured inverter will have an adjustable LVD that can be used to protect the battery.

Some charge controllers have load terminals that have a built in LVD.  They are usually intended for small DC loads like LED lights, and are usually not suitable for large inverters.  Large inverters should connect directly to the battery and should have their own built in LVD.

--vtMaps

BB.

For the direction to face your panels... You can use this link:

http://solarelectricityhandbook.com/solar-irradiance.html

And try east/west/south west/south east, panel tilt, etc... And see which direction works best for you. Part of the issue is whether your need summer/winter or all year round power from your system... But being near the equator, which direction you face is not as important as those of us towards the poles. It looks like you have lots of sun anyway (at least 4 hours of sun minimum, excluding shading).

And with shading, obviously that kills solar power collection. Even a vent pipe or electric cable (from power pole) is enough to really hurt your collection (just a couple electric cables crossing your array can kill 50% of output pretty easily)--So, placing panels, moving vents/etc. is very important.

Get yourself a good hydrometer--That is the gold standard for ensuring your batteries are operating in the correct range. The voltage chart above is "resting" voltage at ~25C--Load/charging current, battery temperature, and even age will "play" with those numbers. This is a European hydrometer and if you can find one, it has very good reviews. Otherwise, get a good quality glass battery hydrometer (rinse any hydrometer with distilled/pure water after you are done for the day--for glass hydrometers, make sure they don't roll of the shelf and break):

http://www.solar-electric.com/midnite-solar-battery-hydrometer.html

AC inverter low voltage cutoff settings are really there to protect the inverter and loads, and normally will "kill" a lead acid battery pretty easily if you bump into the cutoff limit much. More or less, ~12.0 volts is the minimum resting voltage, and around 11.5 volts (at the battery posts) would be a good low limit if the battery bank is under a good load.

Get a Digital Volt Meter so you can quickly measure battery voltage. Personally, I would prefer you to use 6 volt @ 400 AH batteries (or 2x 5 volt @ 200 AH string, 2x strings in parallel). This lets you measure each 6 volt battery voltage accurately. Otherwise, with two 12 volt batteries in parallel, it is difficult to catch a bad battery/wiring connection (read 12 volts of two parallel batteries, cannot read one battery at a time unless you disconnect a cable to the other battery).

What can help is a DC Current Clamp DMM (digital multi-meter). We can get a pretty reasonably priced meter like this $60 USD one in the US... It is "good enough" for our needs. If you can find a DC current clamp meter for not too much money locally, it would be a big help for you (in the US, it is not hard to pay >$400 for a good Fluke meter--Very nice, but hard to justify the cost).

If you are going to be using the system daily, and want to get 100% of your energy from solar--You should be looking at 10% rate of charge--10% of 400 AH is 40 amps. Otherwise, you should look at getting an AC to DC battery charger to help--Otherwise, you really run the risk of killing the battery bank. Losing sun at 3pm due to shading hurts too (you need as many hours per day of sun as you can to have the time needed to recharge your lead acid battery bank). The AC battery charger is a crutch--But it is probably worth the cost of a charger + utility power costs, vs losing your battery bank in a year due to insufficient charging.

The breaker looks good... This breaker is a two pole breaker--Normally, we would just use a one pole breaker (just in the positive lead, we typically tie battery negative ground to safety/green wire/building ground). Of course you only have to run one cable to the two pole breaker.

Typically, the breaker size for a 30 amp MPPT controller (minimum wiring + breaker) would be:

• 30 amps * 1.25 derating = 37.5 amps and round up to next standard breaker (like 40 amp)

For the AC inverter, the math would look like (for a 600 Watt inverter/AC load):

• 600 Watts * 1/0.85 AC inverter eff * 1/10.5 volts minimum * 1.25 derating = 84 amp minimum wiring+breaker/fuse rating

-Bill

Dave Angelini

You can use the type QO breakers for DC below 60vdc.

http://www.amazon.com/s/?ie=UTF8&keywords=square+d+qo+breakers&tag=googhydr-20&index=tools&hvadid=72032671507&hvpos=1s3&hvexid=&hvnetw=g&hvrand=14904118229053676074&hvpone=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_1zxo7drvqv_b

bigbrovar

Thanks guys. I think this post on Youtube might just be the solution I need https://www.youtube.com/watch?v=J0UNfzsa3L0 I ordered for same charge controller and should be getting it tomorrow. If I get a relay I could set a safe LVD from the cc which should protect the battery. I another option is to get one of these http://www.aliexpress.com/store/product/DIN-Rail-Mount-LVD-Low-Voltage-Disconnect-Module-24V-10A-Protect-Battery/316973_32555478335.html .

Unfortunately Amazon does not ship to my country so am left with shipping via chinese online sites 

BB.

Some inverters offer adjustable LVD and remote on/off (try to avoid big relays--those waste power too).

If you average loads are small, MorningStar has a really nice 300 Watt TSW 12 VDC AC inverter (600 watts for 10 minutes). Can set LVD to 11.5 volts and has a remote on/off input. Plus a "standby" function. Available both in 120 VAC 60 Hz and a 230 VAC 50 Hz model.

http://www.solar-electric.com/inverters-controllers-accessories/inverters/moin/mosu300wasiw.html

I don't know if our host ships to Nigera or not (I do not work there, I am just a volunteer on the forum).

In the end, try to design your system to use only ~25% (to 50%) depth of discharge per day.... Usually, trying to automate a low voltage shutdown that protects your batteries takes a lot of time and money--Plus a few problems along the way. Designing your systems and loads to stay within your desired window is best.

-Bill

zoneblue

Unfortunately i[t] is a 12V system (12v inverter has already been purchased)

A lesson in planning before spending? You have to choose whether you might end up dragging along that one wrong part you started from, or alternatively, if the system makes enough sense as it is for the intended design life. aka the 'Learner system'. 12V systems are actually ok for sytems under 1kWp or so. Just remember: - watch out for any future expansion needs , and - make freinds with a good voltage drop calculator and keep those wire sizes nice and fat.

The inverter I am using [h]as a Low Voltage Disconnect of 10.5v for 12v batteries which is about 70% of discharge.. not ideal but I will do well to ensure I don't get that far.

LVD, while it sounds sensible, rarely is. For unattended systems such as those that power radio repeaters or electric fences, a LVD makes some sense. But for domestic applications, its problematic for the reasons listed above. The loads are eratic and of variable size, not the case for a repeater. Relying on voltage is a crude approximation of SOC and likely give you false trips. For a second reason, you dont want to go close to LVD for your batterys sake, hence, good design and awesome management is generally a better solution.

The inverter charges at 14A while the charge controller after taking in loses should charge at 20/25A (The optimum Current from the 2 24v 280w panels is 40A, My MPPT CC has a as a charge limit of 30A. My country is about 10 degrees above the equator hence I am suppose to place my panels facing the south. Unfortunately the south facing part of my roof is completely shaded by about 3PM.. The only part of my roof not affected is the east facing side of the roof. My plan is  to have the panels installed there but tilled towards the south. (don't know if this makes sense)

Just to reinterate the formula we use to estimate peak charge current is 480Wp / 12V x 0.77 . This is a ballpark guide to the clear day noon production. From where i sit shading is worse than angle. Take bills advice and try to model your expected production using the online tools. What that gives you is Wh/d for various months of the year allowing you to manage your loads or backup charge sources as needed. So if you get for example 4 sun hours for a march average day, then you can multiple 4 times the formula peak output from the controller (4* 480*0.77) to give you 1500Wh/d.

Or you can just suck it and see

From my estimation the 480w panel used with a 12v system should generate max 40A, given that the CC can only dish out 30A max. What size of cable would you guys recommend I use? from my investigation online I think 10mm2 cables might just do the job. The distance between the panels and the cc should be about 10-15 feets.

There are two different cable considerations. The PV homerun, and the DC bus cabling. For the PV a bit of loss is to be expected there, as the cable is long and costs more. Keep that to single digit percent and that will be fine. See what kind of cable you can get cheaply and use it. (sometimes an additional panel is cheaper than the wire). But for the inverter and charge controller thats another story, you want those losses under a half percent of so. A foot or two of cable is anyway cheap. This is because you are dealing with more current and you need the electronics to have access to the all of the battery voltage.

Also I was thinking of using 50A breakers between the CC and the PV and will this be adequate protection? The breaker am looking to get is from the chinese site aliexpress and it is rated at 10  (ms) and Instantaneous Trip type B.C.D. I don't know if this would be adequate.

Remember my second key to happiness. I beleive that NAWs ships globally. You might also see if your area is served by an intenational freight forwarder. Carling/CBi breakers are industry tested and UL certified. Its these qualitys that we look for in electrical systems where the consequence of component failure can be a house fire or electrocution. There are other brands of DC breakers, but the key there is research. The chinese sadly are not known for either specifications honesty or manufacturing quality control.

That youtube video... im not sure is a very good guide. Lots of cobbled together cheaper gear there. Be especially wary of those ebay Fotek branded SSRs. They are fakes, and fail horribly. If an SSR costs less than USD50 then its a knockoff.

I am sorry for my constant question, this is an absolute first for me and am just trying to cover my base. Thanks.

Absolutely no need to apoligise. This is what we do. Even on summer holiday while the sun is shining outside. Especially when the sun is shining outside

westbranch

Did you know that, relative to most of us,  you are 'sitting' almost on top of one of the better makers of DC breakers???  CBI in Zambia  http://cbi-lowvoltage.co.za/
There should be a way to get parts mailed to you...

bigbrovar

OK I think amnin luck. After searching Through electrical stores here finally tracked down a DC Breaker from CBI but its 50A. Would this be adequate protection for my 30A Charge controller ?

vtmaps

bigbrovar said:

OK I think am in luck. After searching Through electrical stores here finally tracked down a DC Breaker from CBI but its 50A. Would this be adequate protection for my 30A Charge controller ?

A breaker on an MPPT charger should be large enough that it doesn't trip when you are making full power.  Your 30 amp MPPT controller will never trip a 50 amp breaker... that's good.  The purpose of the breaker is to protect the controller and the wiring from the battery.  When controllers fail, they may become a short circuit across the battery.  If your controller fails, you may have 50 amps flowing through the wires and the controller before the breaker trips.  What you must do is make sure the wires can handle 50 amps.  That would be #6 gauge copper wire.

By the way, some DC breakers are polarized... that means it matters which side is pos and which is neg.   The positive (line) side of the breaker should go to the battery positive and the negative (load) side of the breaker should connect to the controller.  That is because if the breaker ever trips it will be because of battery current (flowing into the pos side of the breaker), not solar power (flowing into the neg side of the breaker).

--vtMaps

bigbrovar

Thanks to everyone who responded to my requested. I have learned a whole lot from this forum and it re-enforces my decision to DIY this project. I won't have learned half what I have learned here if I had given this to a professional.

Since the last time I posted. I have gone back to the drawing board and made lots of adjustments to my system and design. I acquired a Kill-a-watt meter which happened do a proper energy audit of all my appliances.

Below is the new plan and design for my off grid system. I would appreciate if the guys in the house can have a look.

  I have very little electrical background coming mostly from IT. The idea is to have a very small offgrid system which will power essential appliances in my house. Basically Home Entertainment system and Lights. I knew for a long time that my future would be renewable and to prepare for this, I gradually installed energy efficient 8w philips bulbs in my house. I also have a 43inch LED tv, a 1100watt 5.1 sound system, a laptop acting as a media center, and a satellite receiver. Using the kill-a-wall meter.


Setup Design:

PV

I have 2 240w polycrystalline panels with the following specs

VMP=30.1

IMP=7.78

I intend to have the panels mounted on the ground. Reason for ground mounting are as follow:

•  South facing part of my roof is completely shaded by 15:00 till sun set. (This is pretty much the main reason)
•  Since it is a rented apartment, not comfortable with tempering with the roof
• Easy access to panels to carry out cleaning (Abuja, Nigeria can be very dusty) and ease of removal in case I leave the premise
•  Phobia for height

The panels would be fixed mounted and set to about 81 degrees from a vertical point facing true south.

Wiring, Distance and Losses

The estimated length of wire which would be required to the power from PV to CC should be about 60 feet (18 meters) . Hence I intend to connect the panels in series to reduce resistance and allow me use a 6mm cable with estimated loss of 3-5% (depending on the weather, position of the sun etc). I plan to use 10mm between the controllers and the batteries, and batteries and inverter . Distance between CC and battery Bank & Inverter and Battery Bank is about less than 3 Meters each. I don't know if a 10mm2 cable would be sufficient would appreciate advise.

Charge controller 

3215RN Epsolar MPPT rated at 30A

Batteries:

2 220AH FLA Batteries.  Connected in parallel

Battery Monitoring:

I could not afford a Trimetric tool so I settled for http://www.aliexpress.com/item/PEACEFAIR-NEW-product-DC-6-5-100V-100A-4-IN1-digital-display-LCD-screen-voltage-current/32417462384.html Which comes with a shunt.

Inverter

12v Sukam 1050v falcon plus inverter: would of loved to use something more industry standard but had to keep the setup within my budget. The falcon plus seem to be the best option available to me (from all the low end inverter models out there) and here is why. It has built in temperature sensor for ATC and a SMPS for power factor correction and does the "6 stage charge" at least according to this review http://upsinverterinfo.com/su-kam-falcon-plus-inverter-unbiased-indepth-review.html It also could work in low current between 90v -240v. Anyway based on my budget it was what I could afford.

Charge current = 14A   (The inverter has an in built charger which allows it to be able to charge the battery at 14A)

Protection and Safety:

I put a 10A Cbi vdc breaker between PV and CC, a 40A Cbi vdc breaker between CC and Battery, and a 63 vdc Cbi Breaker between Inverter and Battery (Would a 63A vdc breaker be adequate between Inverter and battery for a 1000w system?).

I also intend to put a 15A AC breaker between Grid and Inverter and a 20A AC breaker between Inverter and Load. 

I also intend to ground all the equipment from the panel frames to the panel, cc and inverter.

In future and close to raining season I hope to get a thunder arrestor

I intend to have all the load the inverter would be powering to terminate to a separate Distribution Board from the main house DB. This is meant to reduce issues of overloading the Inverter since only the load to be powered by the Inverter will be terminated to the inverter nothing more.

Estimated Power consumption and runtime

43 LED Tv (In eco mode) = 35W

Home Theater 5.1 = 20W

Laptop (Media center running Kodi) = 55w

Satellite Receiver = 10w

 All the Above devices are expected to run for 8 hours (which really is over estimating it because I have a job and no way I would watch Tv for 8 hours on week days (anyway)  which means

35 + 20 + 55 + 10= 120 * 8 = 960 Watt

I also have light bulbs which use a combine 120w and will run for 6 hours 

120 * 6 = 720

Small Fridge Total energy consumption for 4 hours (using kill-a-watt)  = 400w (approximately)

720 + 960 + 400 = 208222 / 0.85 (Inverter efficiency)

= 2,447w /  12v (Since it is a 12v off grid system) 

203AH. This represent about 51% Dod of my battery bank which is 2 12v  220ah batteries connected in parallel. 

I think this should be well within the safe zone of the dept of discharge for the battery.

Inverter efficiency

 Now I was unable to get a figure on the efficiency of the inverter am using -- some Indian popular brand called Sukam. I got it because it was capable of 6 stage charge and Automatic Temperature Compensation. I was informed by their technical team that the self consumption power of the inverter is 1.2A. 

 My total load on inverter would be Max 640w. Although I do not intend to turn all my load at the same time. I plan to have the lights come on only at night 18:00 - 00:00 and the fridge would come on at noon (on weekdays when am off to work and all other appliance is off) and on weekends.

Hence estimated max load based on design is 640w (the starting current of the fridge 400w + 120w from entertainment system)

 I have 90% of the component I require for this project which I intend to DIY with an electrician friend who will assist with grounding and other areas. I would appreciate if  you guys  can look into my plan and point out areas I can make improvements etc

When am out during the day, I might consider running the fridge with a timer based plug and set it to run between 10:00-14:00 depending on the weather.

What I have:

CC, Breakers, Panels,Inverter, wire, 10 mc4 connectors, a Killawatt meter, an MC4 Crimping tool, wire strippers, lugs and MC4 disconnect wrench.

Todo: 

Construct a wooden PV mount (guess wood is safer being a non conductor of electricity and all)
Battery Bank.

I hope to start the setup and installation once the tools arrive.

There is pretty much my solar plan. I would appreciate if all the gurus look through and point out mistakes and suggestions.

I have attached a schematics of the project. 


My Questions:


Is there any tool or way of designing and getting the right tilt for my PV? in my case the optimum tilt.

Dave Angelini

An ammeter, your latitude, an adjustable panel mount. One of the best things for someone learning is to watch one of the U-tube videos on a dual axis tracker over a nice long day in time lapse.

zoneblue

bigbrovar said:

PV I have 2 240w polycrystalline panels with the following specs

VMP=30.1,IMP=7.78

We usually work out the PV as the last step. Its sized to charge the battery at 0.1C during peak times.

Wiring, Distance and Losses The estimated length of wire which would be required to the power from PV to CC should be about 60 feet (18 meters) . Hence I intend to connect the panels in series to reduce resistance and allow me use a 6mm cable with estimated loss of 3-5% (depending on the weather, position of the sun etc). I plan to use 10mm between the controllers and the batteries, and batteries and inverter . Distance between CC and battery Bank & Inverter and Battery Bank is about less than 3 Meters each. I don't know if a 10mm2 cable would be sufficient would appreciate advise.

In metric cables are (usually) mm squared. Thus 10mm2 is too small for a 1000W inverter. USE the voltage drop calculator.

Charge controller 3215RN Epsolar MPPT rated at 30A

People have had varying success with this unit. Good luck.

Batteries:2 220AH FLA Batteries.  Connected in parallel

Can you not find some 6V golf carts?

Inverter 12v Sukam 1050v falcon plus inverter: would of loved to use something more industry standard but had to keep the setup within my budget. ... Anyway based on my budget it was what I could afford.

Again, good luck. Youll get some experience if nothing else. It will be wise to mount all this stuff somewhere that isnt flamable.

Protection and Safety:I put a 10A Cbi vdc breaker between PV and CC, a 40A Cbi vdc breaker between CC and Battery, and a 63 vdc Cbi Breaker between Inverter and Battery (Would a 63A vdc breaker be adequate between Inverter and battery for a 1000w system?).

It would help both us and you if you show your working math.

Estimated Power consumption and runtime

43 LED Tv (In eco mode) = 35W

Home Theater 5.1 = 20W

Laptop (Media center running Kodi) = 55w

Satellite Receiver = 10w

 All the Above devices are expected to run for 8 hours (which really is over estimating it because I have a job and no way I would watch Tv for 8 hours on week days (anyway)

This is where you needed to start. The load budget us everything. Mind your units. Try to get a realistic estimate of Wh/d for each appliance. For instance:

TV: 35W x 2hr= 70Wh/d
Lighting: 120W * 6hr = 720Wh/d
Etc;
Contingency: add 20% (for the little things)

Small Fridge Total energy consumption for 4 hours (using kill-a-watt)  = 400w (approximately)

With two panels, you might need to reconsider the fridge.

720 + 960 + 400 = 208222 / 0.85 (Inverter efficiency)

  2080Wh/d ?

= 2,447w /  12v (Since it is a 12v off grid system) 

203AH. This represent about 51% Dod of my battery bank which is 2 12v  220ah batteries connected in parallel.

We recomend 25% daily DOD, thus:

= 2080Wh/d * 1/0.85 * 1/0.25
= 9800Wh / 12V
= 815Ah battery (so you better go back and look at the load budget closer, right?)

Inverter efficiency Now I was unable to get a figure on the efficiency of the inverter am using ... I was informed by their technical team that the self consumption power of the inverter is 1.2A.

Note: 12V * 1.2A is 14W, or 346Wh/d. You just added another 20% to your load budget!

Is there any tool or way of designing and getting the right tilt for my PV? in my case the optimum tilt.

The ideal tilt is the same as your latitude.

Also: dont forget you need a disconnect panel to house the DC breakers.
Also: suggest you go back and find some of Bills posts about system sizing, the math model is well spelled out there.

Johann

bigbrovar said:

Wow guys.. Thanks so much for all the input. my set up is quite small actually. I intend use the solar for emergency backup power (i.e led light bulb, led tv, laptop charger, cable setup box, and sound system) my total wattage is estimated to be 550 watt, 600watt tops. I also intend to isolate the appliance to be powered by solar and terminate them directly to the inverter (which only default to battery during blackouts) I am hoping that it would at least be able to give me 4 hours of backup power if not, I might consider adding to the battery backup. Blackouts in my country is a huge problem so sometimes it is nice to have a way to have at least lightings in the house. I don't intend to have all the loads on at the same time. 

One more thing, if I connect my panels in parallel, what would be my expected output from the CC? 

If this system is for black-outs, why not skip the solar panels since you have a problem with the shade and just use a battery charger to charge the batteries from the grid and when the grid goes out you use power from the batteries directly or via the inverter.
This would save money.

vtmaps

Johann said:

If this system is for black-outs, why not skip the solar panels since you have a problem with the shade and just use a battery charger to charge the batteries from the grid and when the grid goes out you use power from the batteries directly or via the inverter.
This would save money.

Maybe, maybe not.  If he installs a few solar panels, then the entire system (batteries, inverter, wiring, circuit breakers, battery monitor, etc) will be eligible for 30% federal tax credits.

--vtMaps

bigbrovar

Johann said:

bigbrovar said:

Wow guys.. Thanks so much for all the input. my set up is quite small actually. I intend use the solar for emergency backup power (i.e led light bulb, led tv, laptop charger, cable setup box, and sound system) my total wattage is estimated to be 550 watt, 600watt tops. I also intend to isolate the appliance to be powered by solar and terminate them directly to the inverter (which only default to battery during blackouts) I am hoping that it would at least be able to give me 4 hours of backup power if not, I might consider adding to the battery backup. Blackouts in my country is a huge problem so sometimes it is nice to have a way to have at least lightings in the house. I don't intend to have all the loads on at the same time. 

One more thing, if I connect my panels in parallel, what would be my expected output from the CC? 

If this system is for black-outs, why not skip the solar panels since you have a problem with the shade and just use a battery charger to charge the batteries from the grid and when the grid goes out you use power from the batteries directly or via the inverter.
This would save money.

Well the project is meant to give me some level of control outside of the grid. Electricity supply in Niger can be very limited and unpredictable. On an average we get close to 10 - 11 hours of electricity in a day (best of times)  in my small town in Nigeria (outskirt of the city center of Abuja). I got the panels for free (pretty much) hence why am even starting this project at all. I wanted a system which can guarantee at least 8 hours of electricity to power my core needs (some 8w light bulbs at night) and ability to seat relax and use my home entertainment system. The fridge can be run on the fuel generator so as to take the load of the solar setup.

bigbrovar

vtmaps said:

Johann said:

If this system is for black-outs, why not skip the solar panels since you have a problem with the shade and just use a battery charger to charge the batteries from the grid and when the grid goes out you use power from the batteries directly or via the inverter.
This would save money.

Maybe, maybe not.  If he installs a few solar panels, then the entire system (batteries, inverter, wiring, circuit breakers, battery monitor, etc) will be eligible for 30% federal tax credits.

--vtMaps

Unfortunately tax credit for renewable energy is not available in my country.

zoneblue

Well if youre starting from the PV then you can work forward to see what you can do with it as follows:

Wp= 480W.
Peak charge rate into 12V is 480/12v *0.77 = 30A. Thus 30A (mppt) charge controller.
At 0.1C thats to a lead bank of 30A * 1/0.1= 300Ah at 12V.
And will supply with 4 (guess) sun hours (average) = 30A*12V *4 = 1440Wh/d (DC) (check your sun hours).
And capable of supporting an inverter of (0.25C) 300Ah * 0.25 * 0.85 * 12V= 765W (TYPO FIXED)

So your numbers are in the ball park, maybe just your expectations of it a little on the high side is all.

bigbrovar

zoneblue said:

Well if youre starting from the PV then you can work forward to see what you can do with it as follows:

Wp= 480W.
Peak charge rate into 12V is 480/12v *0.77 = 30A. Thus 30A (mppt) charge controller.
At 0.1C thats to a lead bank of 30A * 1/0.1= 300Ah at 12V.
And will supply with 4 (guess) sun hours (average) = 30A*12V *4 = 1440Wh/d (check your sun hours).
And capable of supporting an inverter of (0.25C) 300Ah *1/0.2 *0.85 * 12V = 765W

So your numbers are in the ball park, maybe just your expectations of it a little on the high side is all.

Thanks alot for the feedback. About the cc and and inverter. The cc because it is frankly what I can afford (economy in my country is going down the drain and exchange rate keeps jumping higher and higher) same with the inverter. The sukam brand is a house hold name here in Nigeria and India and they have quite a good track record. I will make sure to ensure they are mounted on non flammable mounts just to double up.

Regarding the wiring.  I plan on making the wires between the battery and inverter to be 16mm would this be adequate? (Battery is 12v, 440AH.. Inverter is 1000w) 

Also what size of wire is recommended for connecting two 12v 220AH batteries in parallel.

Lastly could you explain the reason for the 0.77 in this calc  Peak charge rate into 12V is 480/12v *0.77 = 30A. Thus 30A (mppt) charge controller. What 0.1C stands for and also 0.25C

Thanks