PV Setup - success, Want to see how it fares

Nila · January 2013

Hi Everyone,

Thanks for the support I have received in this forum regarding my solar setup.

I have 4x 200AH lead acid batteries connected to a 3.5Kw inverter (I have been told this is low and want to double the bank soon )

I have 2000Watts panels (8 * 250 ) 4 parallel strings. the VMP at specs is like 30.3 and I was told this is low for charging the battery 100%.
My Inverter's built-in charger will take care of it I believe for topping of batteries.

I use a charge controller from my friend's company in China its PWM . so its not a big brand.

I am getting voltages varying from 51(rare)-55v(mostly)-63v(rare but this occurs often) during cloud changes,etc.
I am receiving amperes of 20-32 average. Mostly staying around 26A.

Are these variations normal? or should they be staying at same voltage?

Is the Voltage good enough to charge the batteries fully?

My Inverter is a domestic and it is not hybrid or latest , It will always use Utility's power whenever possible and use batteries only for backup. also It will charge the batteries whenever it finds the voltage low but it will charge it only when there is supply from utility.

So to prevent batteries from being overcharged with panels as well as inverter and also to always use batteries when it is possible, I have a cut off switch for utility and I will manually switch it off at morning and again back to ON at evening.

Is there anyway to like add a circuit to do this?.

If i can double the bank, I can get away from the double charging issue, but that wont still help me with the Inverter always using the Utility everyday issue.

Open to any ideas,etc.

I am not an Engineer or have any background on electronics,etc. I am a software person and did this all with help of my friends and research in internet and I am thankful for the support I have received in this forum

Also I will soon post all the nice photos of this setup.

I was longing for the day where I can say this , Im typing this at the moment on a computer that uses the power from my PV's

Have a nice day . Thanks for reading.

Photowhit · January 2013

Re: PV Setup - success, Want to see how it fares

Depending on the quality of your electronics, there should be no need to turn anything off, the charge controller for the PV shouldn't let things over charge, nor should the built in charge controller in the inverter.

Since your only using the batteries in a backup situation, you could just let the Solar charge them, there won't be a load to draw current from them, so you should have no worries. If you have a week or so of little sun and have had an outage during the week and have drawn down your battery bank, you could consider charging with the inverter to return the battery bank to full.

"I am getting voltages varying from 51(rare)-55v(mostly)-63v(rare but this occurs often) during cloud changes,etc" Battery voltages will change depending on where and what is happening to the battery bank, in the morning before the sun has come up you should be at the lowest, When charging you should spend time at around 56-7 before falling to around 55V. From your specs a reading of 63V is impossible unless you have a bad meter or you have disconnected your battery and are reading your VOC.

"Is the Voltage good enough to charge the batteries fully? " No, you really need close to 70 volts VMP to charge your batteries fully, with a VMP of 60.6 you have too little voltage to reach the 57 volts or so after losses in wires and charge controller.

Nila · January 2013

Re: PV Setup - success, Want to see how it fares

My Usage on the morning is like around 400w max (LCD TV + few ceiling fans ), I do want to be using the power from solar setup instead of drawing from the Utility at the morning to reduce the bills.

When i dont turn the utility power, Inverter will always take power from the Utility hence the power generated from the PV will never be used.. and since it has an inbuilt charger which I cannot set to off, it will also charge the batteries and keep it at 100% lol.

and btw,I think my specs are incorrect because when I was reading VOC with the multimeter,I received readings close to 68, and now when connected to the batteries, I seem to be doing 58 most of time and 62 occasionally, I believe they are VMP but the charge controller may be confusing that .

Measuring the voltage with the multimeter during load at the PV cable is the VMP ? and I can try to do that.

Also I am worried with the amperes/voltages varying lot like every 2 seconds, is this a misconfiguration or PWM charge controller will always do this?

BB. · January 2013

Re: PV Setup - success, Want to see how it fares

A PWM controller is nothing more than an "on/off" switch. On--current flows and the battery charges. Off, the battery stops charging (and the array voltage floats up to Voc--voltage open circuit).

With a PWM controller... The battery bank voltage sets the Varray voltage (plus wiring and controller drop). This happens during "bulk" charging mode (100% of available array energy goes to battery bank). Bulk is usually when the battery is less than ~80-90% full and takes the full available current from the array.

When the charge controller is in absorb or float, the switch is being turned on and off every several seconds to hundreds of times a second (depends on the brand/model of the charge controller). So, placing a meter on the array wiring will show something between Vbatt and Voc (and it may jump around a lot between those two voltages).

-Bill

Nila · January 2013

Re: PV Setup - success, Want to see how it fares

BB. wrote: »

A PWM controller is nothing more than an "on/off" switch. On--current flows and the battery charges. Off, the battery stops charging (and the array voltage floats up to Voc--voltage open circuit).

With a PWM controller... The battery bank voltage sets the Varray voltage (plus wiring and controller drop). This happens during "bulk" charging mode (100% of available array energy goes to battery bank). Bulk is usually when the battery is less than ~80-90% full and takes the full available current from the array.

When the charge controller is in absorb or float, the switch is being turned on and off every several seconds to hundreds of times a second (depends on the brand/model of the charge controller). So, placing a meter on the array wiring will show something between Vbatt and Voc (and it may jump around a lot between those two voltages).

-Bill

Hi Bill,

Thank you for replying,

I can now understand the PWM more.

few more questions though!;)

1. Regarding what to expect :

I am getting 25-30 amperes at sun from morning to noon and about 10-12 when its cloudy and around 3-4 amperes at late evening and there is an annoying partial shading that I have to fix ( only at late evenings )

Is it good enough to expect from the 4 strings of 2 ? I read VOC on the combiner box / panels as well as at the charge controller, I do not see any noticeable voltage drops so far and panels are near the batteries (less than 4meters and I use 16mm2 wire)

2. Regarding adding more batteries/checking the quality of existing ones:

Also I would love to check the health of my batteries to be sure it is good enough to add more battery into the pack.

What is the best way to check it ? the specific gravity stuff I assume .

These batteries were like for past 6 months were used with my Inverter's inbuilt charger and I had 0% knowledge on battery maintenance, so adding water is the only thing i have done to maintain them so far., I quickly checked voltages and they seem to be fine around 12.7 or little high i forgot.

I don't really know if my inverter would have equalized them at regular intervals, I need to find its specs/manual to find if that really does it.

Would you suggest to check the battery health and add more battery now or like any solar beginner just murder the first bank to learn then organize it properly on the second haha.

3) My entire house is using about 20 KWH a day ( 5 adults+1 kid) and from my Utility bills I am using about 20 KWH a day.
My inverter is connected to only half the appliances like Lights/Fans and 2 big computers (2 monitors and 3 monitors respectively)

Other stuff like Airconditioning/water pump and washing machine / refrigrators are all connected separately on another line.
I want to to be independent of the utility 100% for the line that I use with inverter? I dont know how much kwh that this line uses seperately but I am like sure it is 10-12KWH

so assuming it is 12KWH , How many batteries and how many panels more I would need to the current setup so I can just forget switching my Utility line on/off each day ?

P.S
My utility is like very cheap even after their recent price increase of 100% lol.. but the reliability sucks, its down like atleast 12 hours a day minimum.

BB. · January 2013

Re: PV Setup - success, Want to see how it fares

paimpozhil wrote: »

1. Regarding what to expect :

I am getting 25-30 amperes at sun from morning to noon and about 10-12 when its cloudy and around 3-4 amperes at late evening and there is an annoying partial shading that I have to fix ( only at late evenings )

What are the Vmp/Imp of the panels and how are they connected together (series, parallel, series/parallel, etc.)?

Also, what is the battery bank? (voltage, AH, flooded cell, agm, series/parallel connections, etc.)?

But yes, under light clouds, I would expect a 50% (or even more) decrease in current.

Is it good enough to expect from the 4 strings of 2 ? I read VOC on the combiner box / panels as well as at the charge controller, I do not see any noticeable voltage drops so far and panels are near the batteries (less than 4meters and I use 16mm2 wire)

16 mm^2 is close to 5 AWG wiring--That is certainly heavy enough for 30 Amperes. At 12 meters and 5 awg with 30 amps of flow--that is only ~0.3 volts drop -- Small drop and should not cause you any issues.

2. Regarding adding more batteries/checking the quality of existing ones:

Also I would love to check the health of my batteries to be sure it is good enough to add more battery into the pack.

What is the best way to check it ? the specific gravity stuff I assume .

If they are flooded cell batteries (you can open the cap and draw electrolyte out the top)--Then yes, using a (good quality) hydrometer (and thermometer if the batteries are not at ~25C) is the best way to learn the state of charge of the battery bank.

Measuring the specific gravity when the batteries are fully charged (i.e., you charge/equalize the battery bank and the SG no longer rises when measured ever 30-60 minutes)--That will tell you the health of the cell (as batteries age, the sulfur in the electrolyte is permanently bonded to the lead in the plates--reducing battery capacity).

Under charging batteries is one of the common ways that people "kill" their battery banks.

These batteries were like for past 6 months were used with my Inverter's inbuilt charger and I had 0% knowledge on battery maintenance, so adding water is the only thing i have done to maintain them so far., I quickly checked voltages and they seem to be fine around 12.7 or little high i forgot.

Lead Acid batteries are very sensitive to voltage... If you measure 12.7 volts while the battery is "resting" (no loads/charging for 3 or more hours)--That is around 100% charged. If the battery was being recharged at that moment, then that is a very discharged battery. If the battery was under any significant load for a period of time, then you probably would be reading less than 12.7 volts.

I don't really know if my inverter would have equalized them at regular intervals, I need to find its specs/manual to find if that really does it.

Would you suggest to check the battery health and add more battery now or like any solar beginner just murder the first bank to learn then organize it properly on the second haha.

Yea--That will teach your wallet/bank account a lesson it will never forget.

Read about batteries--Such as:

Battery FAQ
www.batteryfaq.org

You will see that until you know what is going on inside your batteries (voltage, current, Amp*Hours, etc.)--They probably are being abused and will not last near as long as you would like (failing to check electrolyte levels and adding distilled water when needed to prevent plates from becoming exposed is another common way of executing batteries).

3) My entire house is using about 20 KWH a day ( 5 adults+1 kid) and from my Utility bills I am using about 20 KWH a day.
My inverter is connected to only half the appliances like Lights/Fans and 2 big computers (2 monitors and 3 monitors respectively)

Guessing--But I would think that you don't have enough solar panels to supply hardly a fraction of 20 kWH per day... Say you have ~680 watt array on your controller and you get at least 5 hours of sun on a good summer day (noon time equivalent sun), I would guess your usable power at:

680 Watts * 0.52 system efficiency * 5 hours of sun = 1,768 Watt*Hours = 1.8 kWH per day

Other stuff like Air-conditioning/water pump and washing machine / refrigerators are all connected separately on another line.

I want to to be independent of the utility 100% for the line that I use with inverter? I don't know how much kwh that this line uses separately but I am like sure it is 10-12KWH

so assuming it is 12KWH , How many batteries and how many panels more I would need to the current setup so I can just forget switching my Utility line on/off each day ?

At this point, it is not worth going off grid to avoid your utility. It would probably cost way too much (you can see from my guess, you would need about 10x larger solar array, minimum, to supply 20kWH per day).

It certainly can be done, but it is not where I would start.

My utility is like very cheap even after their recent price increase of 100% lol.. but the reliability sucks, its down like at least 12 hours a day minimum.

What I would suggest... First, measure all of your loads with a Kill-a-Watt type meter. Measure the number of kWH per day for each appliance/device you currently use.

Then review the usage and, where possible, replace with a more energy efficient version of the device (it is almost always cheaper to conserve power than it is to generate power). Obviously, Air Conditioning is a huge user of energy, refrigerators may be too. And large desktop computers+monitors may use several kWH per day each, vs 1/5 to 1/10th that amount if you were to convert to laptop/more energy efficient computer systems.

Next, after all of your conservation efforts and re-measuring your energy usage--Take your daily KW usage (or at least your estimate of usage during the 12 hours you are off grid) and multiply by 1-3 days of storage and 1/50% maximum battery discharge... Say you decide you want to supply 4 kWH for those 12 hours per day of power outage:

4,000 Watt*Hours * 1/48 volt battery bank * 2 days of storage * 1/0.50 max discharge = 333 Amp*Hour @ 48 volt battery bank

Next, you need to make sure you have a large enough battery charger for that battery bank. Typically, we would recommend a 5% to 13% rate of charge (solar) and up to 25% rate of charge for an AC mains/generator powered battery charger (but you have to monitor battery bank temperature--you can over heat a batter bank with >~13% rate of charge--You should have a remote battery temperature sensor to ensure that the battery does not overheat and get into thermal run away and "boil/melt down"). High battery temperatures can really reduce battery life (for every 10C increase above 25C in battery temperature, approximately 1/2 of the life will be taken away--If you run a battery bank at ~35C average temperature, the battery will last about 1/2 as long).

So, for a 333 AH @ 48 volt battery bank, a 13% rate of charge would be:

333 AH * 0.13 = 43 amp battery charger

So, at the very least, a charger, battery bank, inverter (or inverter+charger) plus your utility mains to start.

A backup generator (if you sometimes get a few days of power outages):

43 amp charger * 59 volts charging * 1/0.80 typical charger efficiency * 1/0.67 typical charger Power Factor = 4,733 VA (volt*amps)

So a ~5kW rated (minimum) backup generator to power my mythical 43 amp "typical" 48 volt battery charger.

If you wanted to (later?) install a solar array (pick 10% rate of charge as a good balance for cost effective solar):

333 AH * 59 volts charging * 1/0.77 panel+charger controller deratings * 0.10 rate of charge = 2,552 Watt Array

And, for summer when you have 5 hours or more of sun per day:

2,552 watt array * 0.52 system efficiency * 5 hours of sun per day = 6,635 kWH per day

Note, you should only plan on using around 66% to 75% of your available solar power per day--It is very difficult to use exactly 100% of your power per day... Sometimes you have more sun, sometimes less... Some days you will use more power (washing, vacuuming, more fan use), other days less.

-Bill

Nila · January 2013

Re: PV Setup - success, Want to see how it fares

Hi Bill

Thank you for writing really long but I guess answering your questions will be easy before I can digest all the information you have put up for me.

1. IMP/VMP of panels

8.25 / 30.3 and they are 250 nominal watts

also note, I seem to be getting more VMP but I am not sure if im measuring it right or if i can measure it at all lol..

The readings on the controller LCD says I am like around 55-62 and sometimes at 51.

2. Array design

4 strings parallel and 2 in each serial line. would u say 4*2 ?..

3. I want to go off grid ONLY for my essential electronics and my crappy grid will take care of A/C/ Refrigrators/washing machines.

So I am trying to achieve the 10 KWH mark a day.

Note: I do have 2000 Watts of panel ( I know nameplate value lol..) and not 680,

Nila · January 2013

Re: PV Setup - success, Want to see how it fares

To give you some more information about the sun hours here as well as the temperatures .

We have nearly 30C average room temperature around the year.. average high being around 32-33C and average low being around 26-27C

We do get lots of sun here, there is no way we would have like even 1 or 2 continuous rainy/cloudy days.

BB. · January 2013

Re: PV Setup - success, Want to see how it fares

paimpozhil wrote: »

1. IMP/VMP of panels

8.25 / 30.3 and they are 250 nominal watts

also note, I seem to be getting more VMP but I am not sure if im measuring it right or if i can measure it at all lol..

With a PWM charge controller--you really cannot measure Vmp--Just Varray-battery-charging and Voc...

The readings on the controller LCD says I am like around 55-62 and sometimes at 51.

What voltage is your battery bank--I guessed 12 volts, but it appears 24 volts? Or is is 48 volts?

And, the LCD readings--is that Amps or Volts? I am betting confused.

2. Array design

4 strings parallel and 2 in each serial line. would u say 4*2 ?..

I would say it just as you did "4 strings parallel and 2 in each serial line." ... We do not need to shorten responses--There is just too much room for confusion.

3. I want to go off grid ONLY for my essential electronics and my crappy grid will take care of A/C/ Refrigerators/washing machines.

Yea--if you can shift your power usage to when utility power is available--that is your most cost effective energy usage.

So I am trying to achieve the 10 KWH mark a day.

For a family that has never attempted to conserve before--cutting power usage by 1/2 is certainly possible... However, to keep power usage low--you have to keep on everybody to turn stuff off when not in use, avoid getting that 2nd or 3rd refrigerator, etc.

There are some very nice new technologies out there (like heat pump based water heaters which can be 2-3x more efficient than a normal resistance heater based unit) that can help too. Note, with a kill-a-watt type meter, you may find that many entertainment devices (DVRs, A/V equipment, digital receivers, etc.) may use quite a bit of power when turned "off" (really standby).

Note: I do have 2000 Watts of panel ( I know nameplate value lol..) and not 680,

I made a guess--not knowing your battery bank voltage.

With larger panels (like the 250 Watt units you have) do not really have a good match between Vmp rating and standard 12/24/48 volt battery banks.

For optimum charging, normally, you would use a MPPT charge controller and setup the solar array to have Vmp>Vbatt...

Nominally, a Vmp~17.5 to 18.6 volts for a 12 volt bank, ~35-38 volts Vmp for 24 volt bank, and ~70-76 volts Vmp for a 48 volt battery bank when using a PWM charge controller.

Vmp~30 volts is not high enough for a 24 volt bank and not low enough for a 12 volt bank... And two in series at Vmp~60 volts will not sufficiently charge a 48 volt battery bank (Vmp falls with hot weather/solar panels).

And driving 60 volts into a 24 volt battery bank will cost you almost 1/2 of the array's capabilities vs using a MPPT charge controller.

MPPT controllers are buck mode switching power supplies (usually)... Which can take higher voltage/lower current and efficiently down convert to low voltage/high current used by a battery bank. So of like the DC version of an AC Variable Transformer can match 230 VAC to 115 VAC loads.

Obviously MPPT controllers are a bit more complex than an "AC transformer" and a whole lot more expensive than PWM controllers (5-10x the cost for "good" MPPT controllers).

-Bill

Cariboocoot · January 2013

Re: PV Setup - success, Want to see how it fares

Couple of problems I can see:

2kW of panel on a battery-based system will typically yield about 4 to 5 kW hours AC per day. Pretty far off your 10kW hour goal.

That 30C ambient temperature will decrease the Voltage output of the panels, making charging your 48 Volt system from a nominally 60 Vmp array even harder to achieve.

You should think about acquiring a 9th panel and setting the array as three parallel strings of three in series and using an MPPT controller to convert the higher array Voltage into greater charging current. You'd get almost 1 more kW hour per day that way.

Nila · January 2013

Re: PV Setup - success, Want to see how it fares

I have 48v battery bank, that is 4X 12v batteries at 200AH.

So adding 1 panel and then using the MPPT is the way to go like you said.

Since I have setup this already in the wall,etc I feel lazy to change the setup , May be in a month time I would change this back.

For now, at this setup how much of the KWH/day I can expect to use?

Nila · January 2013

Re: PV Setup - success, Want to see how it fares

Hi Bill

Sorry for confusing you,

I meant the Voltage of PV is displayed in the screen, it was between 51-62 and Amperes is around 20-32 depending on the time.

Thanks for all the information you have given me.

My one last question would be...

as-is ( for next one month) how much power should i be expecting from my current setup ? (kWh / day)

Is it good to like turn off my utility during day time since I really work at USA times, I dont use computers,etc at morning my time.

I guess only 200-300 Watts of electrical items would be running during the day time here.

So if i leave the utilty on, my inverter would always use utility and hence I would draw even lesser solar power than I would have available.

Im guess leaving the utilty OFF on day time manually will force my inverter to draw from the battery and use solar power more? or am i wrong with this assumption.

Cariboocoot · January 2013

Re: PV Setup - success, Want to see how it fares

As a rule (Panel Watts * hours of sun * 0.52 efficiency factor) you could expect 4 to 5 kW hours per day from that. Up the panels by one and you could gain another 1kW hour. If you can "load shift" you may realize better:
By the rule-of-thumb I should get only about 1.8 kW hours per day. In fact it's more like 2.5 (or even a bit better) because I can run things when the batteries are full and the panels are still producing. So instead of a 0.52 efficiency factor mine is more like 0.71 (part of which is increased panel output from high elevation).

It doesn't look like load shifting is an option for you, since you won't be there much of the day. Although you could perhaps rig things to run on timers.

Disconnecting the grid from the solar circuits is a good idea. It can be done automatically under certain circumstances. For instance using an inverter with built-in charger and programming it to 'see' the grid as a generator and connect the AC In only when the batteries are below a certain Voltage. Without the functions in the inverter you can still do it, but you have to build some external circuitry to control the AC transfer.

BB. · January 2013

Re: PV Setup - success, Want to see how it fares

paimpozhil wrote: »

Hi Bill

Sorry for confusing you,

I meant the Voltage of PV is displayed in the screen, it was between 51-62 and Amperes is around 20-32 depending on the time.

You need to really pay attention to the battery voltage over time (and current usage)...

With a battery at 25C:
12.7 volts (12 volt battery) or 50.8 volts == Battery is Full (if not current is flowing)
13.2-13.6 / 52.8-54.4 volts == Battery is being "floated" for storage/non-use (battery is getting just enough current to avoid self discharge)
13.8 to 14.4 / 55.2 to 57.6 volts == Battery is being "gently" charged
14.5 to 15.0 volts / 58-60 volts == Battery is getting a "heavy" charge
15-16.5 / 60-66 volts == Battery is being "over charged" to equalize cells (bring up low cell specific gravity)

Note that battery type matter... AGM and GEL batteries should not (typically) be charged over 14.4 (57.6) volts--It can cause them to vent gases/electrolyte.

And batteries are current sensitive too... For example, most GEL batteries should not be charged at over ~5% rate of charge (C/20) or they will develop gas pockets internally (and lose capacity/current output).

And how much current a battery will take is based on charging voltage and state of charge... For example, a very discharged battery may be taking 100% of the charger's current and only show 13.6 volts... Or it may be 100% charged and only 1-2% of rated Amp*Hour capacity.

as-is ( for next one month) how much power should i be expecting from my current setup ? (kWh / day)

Without knowing your "hours of sun per day", I would be just guessing... In cloudy/monsoon season--you may average 2 hours of sun per day, or less... If you have very dry air, high elevation, etc... you may get 5-7 hours per day of sun.

More or less, I usually use 4 hours of sun for North America as the dividing line for "good solar" power. So a well designed system, I would guess a minimum (9 months of the year) to be:

2,000 watts of panel * 0.52 typical AC system efficiency * 4 hours of noon time equivalent sun per day = 4,160 kWH per day

But, during poor weather, you could get 1/10th that amount... No Sun = No Power

Now looking at your system with the less than optimal solar array/charger configuration--The typical day to day maximum current I would expect would be around:

2,000 watts * 1/59 volts charging * 0.77 panel+controller deratings = 26 amps

So your 20-32 amps actually sees OK... However, you need to look at the battery bank voltage when that occurs. If you are getting 26 amps at 48.0 volts (battery near dead) and never see more than 10 amps when battery is closer to 57 volts (and still needing charging)--Then your low Vmp is probably hurting the array's ability to output current during hot weather.

You want the charge controller to hold ~14.5/58 volts for ~2-4+ hours per day to finish charging a battery (the last 10-20% of battery capacity). If your solar power system does not do that (holds ~58 volts for less than 1 hour per day), then they are probably being under charged.

Is it good to like turn off my utility during day time since I really work at USA times, I dont use computers,etc at morning my time.

It is tough to say--Off Grid Battery Systems have a lot of losses (you see the 52% derating I use--panel derating, battery charging losses, charge controller losses, AC inverter charges, and even AC charger losses--It really never makes "economic sense" to cycle batteries when you have AC mains power available (cycling batteries wears them out too--So you may have to replace the batteries more often to "save" utility power--And battery replacement may cost more than utility power).

A typical computer center uses batteries/generator for backup power only--Otherwise using utility power to recharge battery bank, run computers (basically your system is a big UPS, uninterruptable power supply, with solar on the battery bank).

At this point, it is really up to you. Get a kill-a-watt type meter and start monitoring your power usage and measure specific gravity of the battery bank to make sure you are keeping the battery bank healthy (a Battery Monitor is a very neat tool to help monitor your battery bank too).

I guess only 200-300 Watts of electrical items would be running during the day time here.

So if i leave the utilty on, my inverter would always use utility and hence I would draw even lesser solar power than I would have available.

Im guess leaving the utilty OFF on day time manually will force my inverter to draw from the battery and use solar power more? or am i wrong with this assumption.

It depends on how you want to use your system... More as an emergency power/backup utility power? Or do you want to "save money" with the solar array?

Gets back to using the solar array to save money while "wearing out the battery bank" "needlessly"...

If you want to save money--Then the best way would be to use appliances when the sun is up to basically use the excess power from your solar array (i.e., batteries are fully charged, and not being discharged by the load).

So, if the batteries are fully charged, using a few hundred watts, or even over 1 kW, while the sun is up (i.e., 9am-3pm during sunny weather with fully charged bank) is as close to "free power" as you will get.

If you start cycling the battery bank to save money (use power at night, charging during the day)--The wearing out of the batteries may make this a money losing operation.

In the US, I use roughly $1-$2+ per kWH as a very rough estimate of the cost of off grid (solar+battery) power (battery replacement every 3-8 years, new charge controller/inverters every ~10+ years, etc.).

If your power is, for example, costing you $0.20 per kWH and you can "save" 4 kWH per day--That is $0.80 per day of savings... How long will your batteries last? 5 years?

$0.80 per day * 300 days a year of sun * 5 years = $1,200

How much did your battery bank cost? How long do you think it will last? How much power will you "divert" to solar per day? How much work will it take you to control the power diversion, etc...?

-Bill

Nila · January 2013

Re: PV Setup - success, Want to see how it fares

BB. wrote: »

You need to really pay attention to the battery voltage over time (and current usage)...

With a battery at 25C:
12.7 volts (12 volt battery) or 50.8 volts == Battery is Full (if not current is flowing)
13.2-13.6 / 52.8-54.4 volts == Battery is being "floated" for storage/non-use (battery is getting just enough current to avoid self discharge)
13.8 to 14.4 / 55.2 to 57.6 volts == Battery is being "gently" charged
14.5 to 15.0 volts / 58-60 volts == Battery is getting a "heavy" charge
15-16.5 / 60-66 volts == Battery is being "over charged" to equalize cells (bring up low cell specific gravity)

Note that battery type matter... AGM and GEL batteries should not (typically) be charged over 14.4 (57.6) volts--It can cause them to vent gases/electrolyte.

And batteries are current sensitive too... For example, most GEL batteries should not be charged at over ~5% rate of charge (C/20) or they will develop gas pockets internally (and lose capacity/current output).

My batteries are Lead acid. and typically they are at 30'C and not 25.

They were at voltage of 57 most of the day today ( with that limited load on them ), I still believe my panels are giving me close to 61-62 volt max lol .

Looks like my panels can charge them upto 90-95 % or possibly even full, Charge controller reported them at 100% and inverter too reported them being fully charged , and voltage read 61.2V at inverter may be because of the batteries being connected to the panels .

And how much current a battery will take is based on charging voltage and state of charge... For example, a very discharged battery may be taking 100% of the charger's current and only show 13.6 volts... Or it may be 100% charged and only 1-2% of rated Amp*Hour capacity.

Without knowing your "hours of sun per day", I would be just guessing... In cloudy/monsoon season--you may average 2 hours of sun per day, or less... If you have very dry air, high elevation, etc... you may get 5-7 hours per day of sun.

More or less, I usually use 4 hours of sun for North America as the dividing line for "good solar" power. So a well designed system, I would guess a minimum (9 months of the year) to be:
2,000 watts of panel * 0.52 typical AC system efficiency * 4 hours of noon time equivalent sun per day = 4,160 kWH per day

But, during poor weather, you could get 1/10th that amount... No Sun = No Power

Now looking at your system with the less than optimal solar array/charger configuration--The typical day to day maximum current I would expect would be around:
2,000 watts * 1/59 volts charging * 0.77 panel+controller deratings = 26 amps

My sun hours MUST be over 5 or even be 6. We get clear sun of upto 12 hours a day for MOST of the months in a year.

I live at madurai where the weather is always mildly hot ( 30c is mildly hot for me but may not be for you ) and we would always have 12+ hours of sun rise to sun set time.

There is no big monsoon/rainy seasons / or chilly winters lol. winter is 25-28c/ summer is 35c and rest of months are somewhere in between.

Rain and cloudy days are rare. so I am not worried about availability of sun here . This is no fun but happy it is alteast helping with my solar power .

]

So your 20-32 amps actually sees OK... However, you need to look at the battery bank voltage when that occurs. If you are getting 26 amps at 48.0 volts (battery near dead) and never see more than 10 amps when battery is closer to 57 volts (and still needing charging)--Then your low Vmp is probably hurting the array's ability to output current during hot weather.

You want the charge controller to hold ~14.5/58 volts for ~2-4+ hours per day to finish charging a battery (the last 10-20% of battery capacity). If your solar power system does not do that (holds ~58 volts for less than 1 hour per day), then they are probably being under charged.

I need to read the system voltages bit more to see if this is adequate for me already .

My UPS charger will charge my batteries over night and batteries will be already at 100% by the time it is morning.. I switch of the utility and let sun take care of the day.

and by evening the batteries are full, I switch on the utility back.

Usually my batteries will run out if there is a power outage of 8-10 hours but last 2 days, with panels, batteries stay 100% at the evening after the 10 hours of outage deliberately caused by me.

It is tough to say--Off Grid Battery Systems have a lot of losses (you see the 52% derating I use--panel derating, battery charging losses, charge controller losses, AC inverter charges, and even AC charger losses--It really never makes "economic sense" to cycle batteries when you have AC mains power available (cycling batteries wears them out too--So you may have to replace the batteries more often to "save" utility power--And battery replacement may cost more than utility power).

A typical computer center uses batteries/generator for backup power only--Otherwise using utility power to recharge battery bank, run computers (basically your system is a big UPS, uninterruptable power supply, with solar on the battery bank).

At this point, it is really up to you. Get a kill-a-watt type meter and start monitoring your power usage and measure specific gravity of the battery bank to make sure you are keeping the battery bank healthy (a Battery Monitor is a very neat tool to help monitor your battery bank too).

It depends on how you want to use your system... More as an emergency power/backup utility power? Or do you want to "save money" with the solar array?

Gets back to using the solar array to save money while "wearing out the battery bank" "needlessly"...

If you want to save money--Then the best way would be to use appliances when the sun is up to basically use the excess power from your solar array (i.e., batteries are fully charged, and not being discharged by the load).

So, if the batteries are fully charged, using a few hundred watts, or even over 1 kW, while the sun is up (i.e., 9am-3pm during sunny weather with fully charged bank) is as close to "free power" as you will get.

If you start cycling the battery bank to save money (use power at night, charging during the day)--The wearing out of the batteries may make this a money losing operation.

In the US, I use roughly $1-$2+ per kWH as a very rough estimate of the cost of off grid (solar+battery) power (battery replacement every 3-8 years, new charge controller/inverters every ~10+ years, etc.).

If your power is, for example, costing you $0.20 per kWH and you can "save" 4 kWH per day--That is $0.80 per day of savings... How long will your batteries last? 5 years?
$0.80 per day * 300 days a year of sun * 5 years = $1,200

How much did your battery bank cost? How long do you think it will last? How much power will you "divert" to solar per day? How much work will it take you to control the power diversion, etc...?

-Bill

Regarding wearing out the batteries needlessly, You have given me a lot of information that is very helpful.

To be honest, I do not want to hurt the batteries at all.. they have costed me close to 1k$ for me. That is more than 8 months of Utility BILL in full for me.

The idea here is to only tap the solar power instead of making it go for waste. my daytime load is very low.. sub 300 watts or so.. I think even 10 amperes from the sun is enough to cover it?

My UPS will always have batteries charged, so unless I switch utility off, I cannot take full advantage of solar.

Battery bank cost: I think 900$.

How long ? : i dont know.. may be max 4 years if im being optimistic.

How much power I plan to divert to solar : I want to use it as much as realistically possible.

How much work to control the diversion : Its just a switch . we need to turn it on/off. My mom will do it.

Since my power is very cheap I would be happy to use the night loads with it.,and use the solar power for all of the daytime usage.

When batteries are full, would it still drain it and re-charge it for daytime or would it just take the electrons on the wire and not disturb batteries?

Cariboocoot · January 2013

Re: PV Setup - success, Want to see how it fares

When batteries are full, would it still drain it and re-charge it for daytime or would it just take the electrons on the wire and not disturb batteries?

Essentially, yes. If the panels are capable of producing all the power the loads require the batteries will remain fully charged and won't contribute to the power.

That 30C temp will not only decrease panel output it will also affect the batteries. A remote temperature sensor for the charge controller is a really good idea in this case, as it will adjust the charging Voltage according to the battery temp: higher temp = lower charge Voltage. Otherwise you run the risk of overcharging them.

The problem with switching loads on/off manually to make use of the otherwise wasted solar power is that there may be more/less power on any given day and the switch might not go on/off at the best time. It's better than nothing, though.

I believe MidNite Solar's Classic controller has a function for utilizing 'surplus' solar to the most exact standards of availability. Perhaps someone who has one of these can confirm this.

BB. · January 2013

Re: PV Setup - success, Want to see how it fares

paimpozhil wrote: »

How long ? : i don't know.. may be max 4 years if im being optimistic.

Wow! Realistic expectations of battery life. If they are not deep cycle but car/truck/marine batteries, the life could be as short as 2-3 years if cycled more than 10-20%.

How much power I plan to divert to solar : I want to use it as much as realistically possible.
How much work to control the diversion : Its just a switch . we need to turn it on/off. My mom will do it.

Sounds easy, until Mom forgets or has to leave the house to run an errand. I would suggest you look at timer switches. Either automatic (such as a lamp timer) or a wall switch that you twist (or punch a button) for 4-8 hours per operation. All it take is one "oops" to take out your battery bank. (think automation, goof proof to protect your investment).

Since my power is very cheap I would be happy to use the night loads with it.,and use the solar power for all of the daytime usage.

When batteries are full, would it still drain it and re-charge it for daytime or would it just take the electrons on the wire and not disturb batteries?

As long as the batteries are reasonably charged and you have a good solar charge controller--Then you can have AC loads that are roughly the amount of power available from your solar array.

You could put a voltage meter on your battery bank, and when the voltage is over ~13.2/26.4/53.2 volts--Then you know the energy is coming from the solar array and not from the battery bank (battery voltage has to be below ~12.7 volts for a 12 volt baank to be discharged).

-Bill

Nila · January 2013

Re: PV Setup - success, Want to see how it fares

My Chinese charge controller does have the temperature sensor and I have let the sensor to lay on top of one of the batteries is that correct or should i let it hang on the wall?

I dont know if it needs battery temperature or room temperature.

So this "Higher the temp/ lower the charge voltage" is helping me actually with that lower VMP panels (30.x) haha and at same time it is killing my batteries quicker ouch!.

Is there a better way than manually switching it ? like a circuitry to sense the light ? or sense the battery status and then set it on/off?

My charge controller has a nice relay feature which would ( their sales person said ) inform the inverter when to use utility . My inverter cant really use it lol as its very basic and has no extra features.

Nila · January 2013

Re: PV Setup - success, Want to see how it fares

BB. wrote: »

Wow! Realistic expectations of battery life. If they are not deep cycle but car/truck/marine batteries, the life could be as short as 2-3 years if cycled more than 10-20%.

Sounds easy, until Mom forgets or has to leave the house to run an errand. I would suggest you look at timer switches. Either automatic (such as a lamp timer) or a wall switch that you twist (or punch a button) for 4-8 hours per operation. All it take is one "oops" to take out your battery bank. (think automation, goof proof to protect your investment).

As long as the batteries are reasonably charged and you have a good solar charge controller--Then you can have AC loads that are roughly the amount of power available from your solar array.

You could put a voltage meter on your battery bank, and when the voltage is over ~13.2/26.4/53.2 volts--Then you know the energy is coming from the solar array and not from the battery bank (battery voltage has to be below ~12.7 volts for a 12 volt baank to be discharged).

-Bill

Batteries are deep cycle, and manufacturer promise 20% discharge lol.. but i am not going to test it or trust them.

Thanks for idea of timer switches / wall switch with twist, Not sure if they are available easily in my place but I can order online if needed.

There's my mom/wife/brother and dad and i have told them all to do it if other one forgets until I figureout how to automate this lol

Thank you bill and Cariboocoot (I know its not your name but is cool), Let me see how this goes.

BB. · January 2013

Re: PV Setup - success, Want to see how it fares

The temperature sensor is usually either bolted to a battery terminal (lead post takes heat from inside battery) or just take a piece of Styrofoam (insulation), carve a pocket in it to hold the sensor, and tape/glue/wedge between batteries on the side of the battery case.

You want the temperature of the inside of the battery (chemical reaction temperature)... Not the room temperature.

-Bill

PS: Anyway you want to automate the transfer is fine... Battery voltage is not a great way of estimating state of charge, but you could use a voltage controlled switch set to >13.2 volts to turn on loads, etc... Or if the charge controller has a programmable output--use it to turn on loads when the controller is in "float".

-Bill

Cariboocoot · January 2013

Re: PV Setup - success, Want to see how it fares

paimpozhil wrote: »

My Chinese charge controller does have the temperature sensor and I have let the sensor to lay on top of one of the batteries is that correct or should i let it hang on the wall?

I dont know if it needs battery temperature or room temperature.

It's for battery temp. Probably the best is to tuck it between two batteries if that's possible. Usually they adhere to the side of a battery case. You want it to detect the warmest part because you're actually trying to determine the interior temp of the battery. Some have sensors that stick on a battery post, turning the post into a thermal conductor from inside the battery.

So this "Higher the temp/ lower the charge voltage" is helping me actually with that lower VMP panels (30.x) haha and at same time it is killing my batteries quicker ouch!.

Afraid so. There's actually a "tropical mix" of electrolyte that is used sometimes to compensate for this.

Is there a better way than manually switching it ? like a circuitry to sense the light ? or sense the battery status and then set it on/off?

It is possible to use a Voltage controlled switch (one example: http://www.solar-electric.com/volconswit.html) to activate loads. Top-end charge controllers have a programmable auxiliary output that can do the same thing: battery in "Float" output "on".

My charge controller has a nice relay feature which would ( their sales person said ) inform the inverter when to use utility . My inverter cant really use it lol as its very basic and has no extra features.

This sounds similar to what I just described, only set for "low battery Voltage" or "low solar input" (perhaps permanently). It would trigger a relay to connect utility power to the inverter (if it has a built-in charger) and loads. Again, high-end charge controllers and inverters have similar functions (usually for automatic generator starting, only it can be used with the grid as "generator").

Photowhit · January 2013

Re: PV Setup - success, Want to see how it fares

paimpozhil wrote: »

My batteries are Lead acid. and typically they are at 30'C and not 25.

They were at voltage of 57 most of the day today ( with that limited load on them ), I still believe my panels are giving me close to 61-62 volt max lol .

Looks like my panels can charge them upto 90-95 % or possibly even full, Charge controller reported them at 100% and inverter too reported them being fully charged , and voltage read 61.2V at inverter may be because of the batteries being connected to the panels .

I think the greatest danger to your batteries will be under charging, I don't know if your inverter can top the batteries off properly, but at 30C temps and 30.3 VMP I doubt(Know!) your solar panels are NOT giving you high enough voltage to do more than the bulk charging. The voltage from the solar panels is reduced in hot temperature, in 30C your panels may well be 50C -60C and will produce less than the VMP. With out a load, panels will produce more voltage, so be careful how you measure the voltage.

PV Setup - success, Want to see how it fares

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