Where is the weak link?

[zuluphil]

My load is 4 x 50 w and 3 x 8 w lights on a day/night switch: 224 w (<20a) x 13 hrs = 260 amps used

My system is 3 x 200w mono panels in parallel connected via 15 mtrs. 4mm dia cable to a 40 amp PWM controller,
controller connected to 4 x 100a/h 12v gel batteries giving 200a/h @ 24v. connected to a 600w pure sine inverter

My problem is that I only have enough power for one night and a few hours and takes over two days to charge up.

I have already bought a 30 amp MPPT controller which is rated max PV input power 390w @ 12v/780w@24v
I understand that I will need 2x100a/h 12v batteries to give me 100a/h 24v extra back-up.

My question are, do I need an extra panel to go in series to give more amps, will my new controller handle it,
I am confused by the wattage rating on the MPPT controller it seems that it will not handle 4 x 200 w panels
Any comments would be appreciated p.s. be gentle with Me... I am a newbie.

[br2an]

My load is 4 x 50 w and 3 x 8 w lights on a day/night switch: 224 w (<20a) x 13 hrs = 260 amps used

My system is 3 x 200w mono panels in parallel connected via 15 mtrs. 4mm dia cable to a 40 amp PWM controller,
controller connected to 4 x 100a/h 12v gel batteries giving 200a/h @ 24v. connected to a 600w pure sine inverter

My problem is that I only have enough power for one night and a few hours and takes over two days to charge up.

I have already bought a 30 amp MPPT controller which is rated max PV input power 390w @ 12v/780w@24v
I understand that I will need 2x100a/h 12v batteries to give me 100a/h 24v extra back-up.

My question are, do I need an extra panel to go in series to give more amps, will my new controller handle it,
I am confused by the wattage rating on the MPPT controller it seems that it will not handle 4 x 200 w panels
Any comments would be appreciated p.s. be gentle with Me... I am a newbie.

Your load appears to be a total of 224w over 13 hours = 2912 watt-hours
Your battery capacity is 4 x 12v x 100a-h = 4800 watt - hours

Percent of battery capacity used in one night is 2912/4800 = 60%

If my math is correct then your batteries would be even less than 40% (other inefiiciencies in the system) after one night, much too low.

Btw, I am new to this as well so I won't offer solutions (that's dangerous) but thought I would try to calculate your system to see if I have it right.

[zuluphil]

Tnx B2ran,
That is exactly how I see it and I hope that adding 2 x 100a/h would help as well as cutting the hrs used back a little.But if my charging is taking too long now, what happens when I add two more batteries?

[thastinger]

The stickys in the off-grid section has all the info you need plus a calc you can punch your numbers into.

How many sun hours do you have there?

[Mike90250]

Tnx B2ran,
That is exactly how I see it and I hope that adding 2 x 100a/h would help as well as cutting the hrs used back a little.But if my charging is taking too long now, what happens when I add two more batteries?

You will just need a couple more weeks to kill (destroy) all the batteries. You are using too much power for your panels and batteries. deep discharges will quickly ruin the batteries.

If you are consuming 3,000 watt hours, you need to harvest nearly 6,000 watt hours to have full recharging. In an average situation, where you have effective sun for 5 hours in summer (4 in winter), you need 6000/4 = 1500w of PV panels, properly aimed, to have a balanced system.

Ideally, you need a battery bank that is sized large enough that daily use only consumes 20% of the capacity. That gives you some reserve for a cloudy day without needing to start the generator. You could stretch it to 30%, if you don't mind reduced battery life (2 years instead of 5-10)

BatteryServiceLife.jpg

[daz]

My load is 4 x 50 w and 3 x 8 w lights on a day/night switch: 224 w (<20a) x 13 hrs = 260 amps used

It always better to work in WH (watt-hours) than AH (amp-hours), as WH is independant of battery voltage and easier to work with.
The first thing I would recommend, is checking the exact power draw of your load (aka the lights), and determine if they draw exactly as their nameplate says, or less. Remember, just because the manufacturer puts a sticker that says your light draws 3W, doesnt mean it actually draws 3W. They could mean 3W light output, with a total unit consumption of 7W.

So, let's just assume that everything runs exactly at nameplate power....
4 x 50W = 200W x 13hours = 2600WH, and
3 x 8W = 24W x 13 hours = 312WH.

2600WH and 312WH = 2912WH
This is your daily load that you have to replenish.

My system is 3 x 200w mono panels in parallel connected via 15 mtrs. 4mm dia cable to a 40 amp PWM controller

Just a quick note before I carry on....It is always better to run your panels in series to avoid unnecessary losses (plus very expensive cables!). Also, with the size array you have, you are wasting a lot of power by using a PWM controller. You should definitely change to MPPT!!

Ok...I assume you mean Northern Zululand in KZN, South Africa? If that is the case, you are better off than us chaps down here in Durban! You have, if I remember correctly, 5KWm2 solar insolation!

Right! You say you have a PWM controller and a 600W array, which means you are only getting roughly 1,500WH of power a day to use.....so you can immediately see where your problem is.....you need 2,912WH per day, but you are only putting in 1,500WH to the batteries, which is about half the power that you need

...controller connected to 4 x 100a/h 12v gel batteries giving 200a/h @ 24v.

You should not be using GEL batteries in a solar system, you are liable to cause injury to yourself! GEL batteries require a controlled charge, something which your solar system is not going to provide. Overcharging GEL batteries will cause irreversible damage to the batteries (and more than likely you!). You need to stick to the deep cycle batteries, either FLA or AGM. GEL batteries should never be used in a solar system.

Your batteries are only able to provide a total of 4,800WH, of which the maximum you can use is 2,400WH. Recommended amount would be 1,440WH on that capacity. Now remember we calculated that you require 2,912WH? Well your batteries are unable to provide that! You are currently discharging your batteries to 61%, which is way over the maximum recommended discharge for lead acid batteries. Your batteries will have a very short and expensive lifespan!

My problem is that I only have enough power for one night and a few hours and takes over two days to charge up.

Well, we have seen from the calculations above why your system can only run for 1 day, and then take 2 days to recharge. Your system is under-powered and is failing.

I have already bought a 30 amp MPPT controller which is rated max PV input power 390w @ 12v/780w@24v

The maximum current a 30A MPPT controller can handle is:
12V system : 360W
24V system : 720W
48V system : 1440W

So for your existing panels, you are forced to go 24V, or you will exceed the controllers maximum current (and damage it).

I understand that I will need 2x100a/h 12v batteries to give me 100a/h 24v extra back-up.

Before you go and buy more batteries, first design your system correctly, or you will end up wasting more money!! You currently have no-where enough solar panels (for a PWM controller), and your battery capacity is too small.

My question are, do I need an extra panel to go in series to give more amps,

Solar panels in series provide higher voltage, not higher current (current stays the same). Solar panels in parallel provide higher current (and conversely lower voltage).

will my new controller handle it,

Your new MPPT controller can handle:
12V system : 360W
24V system : 720W
48V system : 1440W

I am confused by the wattage rating on the MPPT controller it seems that it will not handle 4 x 200 w panels

Why are you confused? Your controller specifically tells you that it will not handle 800W...so no confusing necessary! If you need 800W, then you need a bigger controller....

Any comments would be appreciated p.s. be gentle with Me... I am a newbie.

I have answered all your questions, and it appears you have 'jumped the gun' so to speak. You have bought equipment that does not work together (ie GEL batteries) as well as buying to little (ie too little battery capacity and solar panels)!

You need to go have a look at the stickies in the 'off-grid' section of the forum. That is a good starting point, and it will answer a lot of your questions!

[br2an]

Tnx B2ran,
That is exactly how I see it and I hope that adding 2 x 100a/h would help as well as cutting the hrs used back a little.But if my charging is taking too long now, what happens when I add two more batteries?

Sorry I can't offer a lot of advice on how to 'fix' your system, but I can ask you a simple question that might help. Can you reduce your load? It sounds like you are just running lights. Is that correct? If not, you might want to list the actual devices you need to operate.

The reason I say this, it may well be cheaper to switch to a special device that uses your battery power more efficiently. For example, LED lights vs flourescent vs Incandescent or using dc motors directly off the batteries.

If you can reduce your load, you may be able to get your system to work for you with just a few modifications.

Good luck.

[SunEagle]

My suggestion would be that until you can expand you panel wattage, charger control capacity and battery bank the best you can do is cut you load.

Try only using half you lights and run them for only 8 hours instead of 13. This will at least give your battery system a better chance of being charged back up.

[Sunking]

Can you spell TRAIN WRECK.

[SunEagle]

Can you spell TRAIN WRECK.

Well he probably won't be able to expand his panel wattage or charge controller let alone adding more batteries so the best he can do is cut down his load so the battery system can handle it without failing by next Tuesday.

[zuluphil]

Hi Daz, thanks for taking the time to analyse my system, Yes I do mean up the road from You and I am trying to get a system installed by a "professional" company to work after giving them two chances to get it right. and paid them a lot of money. ,I think that you maybe understand that with the increasing cost and unreliability of our power system coupled with the security threat, I need some lighting around my premises . I am only calculating 5.5 hrs @ 600 watt = 3300 watts pd. Here is where I get confused. As I said I am a newbie who does not understand how it works. Where does the " 5KWm2 solar insolation!" come from?
Does the 3300 watts of 12v from the panels get halved by the controller when it converts to 24v?
Will the MPPT controller take 600 watts 12v input if it is converting to 24v to the batteries?
Thank You Mike90250 for info, thastinger, I am goggle-eyed looking for clues in the sticky's especially as I don't know what question to ask! Sunking thank you for your positive, helpful and common ground advice, OH SORRY ! I meant:-
Br2an and Suneagle thanks for your positive,helpful and common ground advice which is probably the best way to salvage something out of the system,It is a security light system around my lodge and I could possibly remove 2 x 50 w lights back onto the grid and turn the others off at maybe 2.am keeping a remote operated switch to override the timer occaisonally

[Sunking]

I am only calculating 5.5 hrs @ 600 watt = 3300 watts pd. Here is where I get confused.

Well here is one poin tof confusion on your part is not understanding the difference between power and energy

Watts is the measurement of electrical power at any given moment in time. Example a 100 watts light bulb uses 100 watts. Think of it like an engine and horse power. You kind of know how much power a 100 hp engine uses, but you do not know how much energy it uses without more information like a time element and fuel consumption.

Watt Hours is the measurement of electrical energy. The formula is very complicated and takes 16 years of US education to grasp and master. Anywhere else in the world a 5th grader knows it.

Watt Hours = Watts x Hours.

For example how many watt hours does 100 wat light bulb use in 10 hours. Simple 1000 watt hours or 1 Kwh. So when you stated 5.5 hours x 600 watts = 3300 watts pd is gibberish nonsense. 5.5 watt hours x 600 watts = 3300 watt hours or 3.3 Kwh

OK depending on the type of controller you are using to generate 3.3 Kwh of usable energy using a MPPT controller will require you to generate 4.95 Kwh, or if using PWM 6.6 Kwh. So lets assume you use your money wisely you will use a MPPT Controller. We now know you must generate 4.95 or lets just call it 5000 watt hours or 5 Kwh. All we need to know is how many sun hours you receive. For a battery system you have to use worse case which in the USA is usually December and January. You go to tables provided by Nrel or PV watts to get the Sun Hours which is Expressed as W^/M2

So you go look for your area and see the Insolation is 3 Kw/m2 which translate directly to 3 Hours. So all we have to do to find the panel wattage required is factor out the time element hours so the formula is: WATT HOURS / HOURS = WATTS. Plug in your numbers. 5000 watt hours / 3 Hours = 1666 watts required. Round that up to a nice even 1700 or even better 1800 watts so you can use cheap 200 watt panels.

For batteries is really easy. You need 5 times your daily usage in watt hours. 3300 wh x 5 = 16,500 watt hours. From there is a matter of selecting battery voltage. In this case with 1800 panel watts we must use either 24 or 48 volts. Pick one, 48 is less expensive, but you want 24. To find the Amp Hour capacity the formula is Watt Hours / Battery Voltage. So 16500 wh / 24 volts = 687 AH @ 24 volts.

Last thing is charge controller amps. For MPPT the formula is Panel Wattage / Battery Voltage. So 1800 watts / 24 volts = 75 amps.

There it is. Now you understand Train Wreck.

[daz]

Hi Daz, thanks for taking the time to analyse my system, Yes I do mean up the road from You and I am trying to get a system installed by a "professional" company to work after giving them two chances to get it right. and paid them a lot of money. ,

No problem! Although I do think that your installer may have ripped you off....

I think that you maybe understand that with the increasing cost and unreliability of our power system coupled with the security threat, I need some lighting around my premises .

Definitely! Especially you chaps up North.
Well that is the advantage to an off-grid system, you do not need to rely on the grid power, especially as we come into winter (I saw on Thursday they said Eskom only had 0.6% headroom available!).

I am only calculating 5.5 hrs @ 600 watt = 3300 watts pd. Here is where I get confused. As I said I am a newbie who does not understand how it works. Where does the " 5KWm2 solar insolation!" come from?

Where do you get the 5.5 hours from?
The 5KWm2 is the total available energy in a m2 for Northern Zululand. So that is the figure you need to use, as that is the lowest figure for winter (aways design for worst case scenarios).

So 5KWm2 x 600W solar array = 3000W total energy produced by the solar panels. Although this is not the energy that you get to use, as some is lost as inefficiency in cables, batteries, controller, etc.

Does the 3300 watts of 12v from the panels get halved by the controller when it converts to 24v? Will the MPPT controller take 600 watts 12v input if it is converting to 24v to the batteries?

The controller does not step-up voltage, it usually steps-down the voltage. Your 600W might come into the controller as 34Voc and 27Vmp, not 12V. 12V is the nominal voltage of your panels, not the actual voltage. When using an MPPT controller, always run the panels as high a voltage as you can to reduce losses.

Now when dealing with PWM controllers, you lose a lot of power, as a PWM controller is only about 65% efficient (as compared to 95% for MPPT). This is why you are getting so little power into your batteries (roughly half the total power produced by your solar panels per day).

Your load was 2912WH, so the required power per day that you need would be;
if using a PWM controller : 6000W
if using a MPPT controller : 4368W

Which means you would need a solar array size of;
for PWM : 1200W
for MPPT : 874W (round up to 900W)

So you can see from above that it is much better to use a MPPT over PWM, even though MPPT is more expensive than PWM! You save money on the amount of solar panels required!!

[zuluphil]

Sunking, thank you for your patience and explanation, the fog is slowly lifting. Daz, Thanks for that, So from my new found knowledge ( ) I think I can get using my existing installation 3 x 200w panels into a 30 amp HPPT rated at 780w @ 24v to 2 x 100a/h 24v batteries- only using 2 x 50w led and 3 x8 w led ........6 hours a night useage! Please tell me that I,m right, Would I also be correct in assuming that to add another 100a/h 24v battery would be an advantage? I will go up onto the roof now and double check all the ratings as the labels do not agree with the website info and actual readings are necessary as you said previously, before I connect the new MPPT controller.

[daz]

I think I can get using my existing installation 3 x 200w panels into a 30 amp HPPT rated at 780w @ 24v

Yes, your 30A will handle a 600W array @ 24V (assuming your controller can handle the 24V system....double check first!).

to 2 x 100a/h 24v batteries-

Should be fine, assuming they are 24V batteries and not 12V!

only using 2 x 50w led and 3 x8 w led ........6 hours a night useage!

2x50W= 100W x 6hours = 600WH, and
3x8W = 24W x 6 hours = 144WH
For a total of; 600WH + 144WH = 744WH load a day

So your system should be able to handle that (assuming the batteries have not been damaged!!).

Would I also be correct in assuming that to add another 100a/h 24v battery would be an advantage?

An advantage? Well, that depends....if you are going to start paralling batteries together...no advantage. However, if you will be increasing your system's voltage by adding more batteries (IE in series for a 48V system), then yes. Batteries in parallel do not last, so it actually costs you more. It is better to rather buy one big battery, or increase your system's voltage (by using lower voltage higher capacity batteries).

I will go up onto the roof now and double check all the ratings as the labels do not agree with the website info and actual readings are necessary as you said previously, before I connect the new MPPT controller.

Definitely! It is always better to know exactly what you are working worth, rather than relying on the salesman!