Battery and Panel Configuration

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jacostry
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Battery and Panel Configuration

Post by jacostry »

Hi there,
I have limited knowledge on Alternative Power, and unfortunately we do not have Outback specialist available in South Africa that can assist me with my project. I will appreciate if someone can assist me with the specification of the following system if possible?

Phase 1 (Backup Power System)
I am currently investigating the use of a Flexware 500 system (See spec bellow) to supply 5KW of backup Power for approx 3 hours during Power Failures
Flexware 500 X 1
VFX3048E Inverter/Charger X 2 (batteries will be charged when Grid Power 240 VAC is restored through the VFX3048E X 2)
Questions:
1) Any suggestions on batteries configuration (Amount of Batteries per VFX3048E, Voltage, A/h, Type, Series or Parallel, etc...), I can get 12V, Delkor Calcium, 102Ah (GP31), Batteries in RSA

Phase 2 (Upgrade Phase 1 from a Backup System to a Grid Interactive system with 240 VAC if needed)
MX60 X 2 (To be added to Flexware 500 to make provision for the Panels)
I would like to add Solar Panels to enable Phase 1 to work as a Grid Interactive system and not just as a backup system only
Questions:
1) Any suggestions on Battery Bank upgrade from Phase 1 to 2 (Amount of Batteries per VFX3048E, Series or Parallel, etc...), I can get 12V, Delkor Calcium, 102Ah (GP31), Batteries in RSA
2) Any suggestions on Panels needed (Amount of Panels per MX 60, Series or Parallel, etc...), I can get Sanyo HIP-180N, Pmax 180W, Vmp 36.5V, Imp 4.93A, Voc 45.5V, Isc 5.49A, Pmin 171W Panels in RSA)
3) Can I place the Panels directly on a Flat Roof because we have security problems here (I need the Panels to be out of sight), will this be workable or will the losses be to great (what will the approx % losses be)

Regards,
Jaco Strydom
Last edited by jacostry on Thu Feb 14, 2008 9:08 pm, edited 1 time in total.
rlongdon

Post by rlongdon »

Can you tell everyone about the expected power draw during this 3 hour period? What types of loads are going to be powered? Where will the equipment be located (Environment Etc.) The more details you can give the better.

You'll find outstanding resources available through this forum, the amount and quality of knowledge of the participants is nothing short of amazing!

Welcome and Regards,
jacostry
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Post by jacostry »

Thanks for your reply Russ,

The 3 Hour draw will usually occur during the day when we have unexpected power failures and I am currently using a Briggs & Stratton 9KW Generator as backup. But because I am living in a residential area I donÔÇÖt like using the Generator. Obviously I will not have the same loads on the Backup Outback system as on the Generator but the loads will consist basically of:

A typically Home Office environment; Computer equipment, Lights, Standard Home appliances but excluding any high current items such as :( Stoves, Geysers, Kettles, Air conditioners, Pool Pumps, etc...)

Regards,
Jaco
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crewzer
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Post by crewzer »

Jacostry,
Phase 1 (Backup Power System)
I am currently investigating the use of a Flexware 500 system (See spec bellow) to supply 5KW of backup Power for approx 3 hours during Power Failures
Flexware 500 X 1
VFX3048E Inverter/Charger X 2 (batteries will be charged when Grid Power 240 VAC is restored through the VFX3048E X 2)
Questions:
1) Any suggestions on batteries configuration (Amount of Batteries per VFX3048E, Voltage, A/h, Type, Series or Parallel, etc...), I can get 12V, Delkor Calcium, 102Ah (GP31), Batteries in RSA
Your net energy requirement is 5 kW x 3 hrs = 15 kWh. Assuming 90% inverter efficiency and limiting the battery bankÔÇÖs discharge to 50% of capacity, youÔÇÖll need a bank rated at 15 kWh / (90% x 50%) = 33.33 kWh.

The energy capacity of each battery is 12 V x 102 Ah = 1.224 kWh. Your need 33.33 kWh / 1.224 kWh/battery = 27.2 batteries. To make a 48 V battery bank, youÔÇÖll need 28 batteries, wired as four batteries per series string, with seven strings in parallel. The bank's rating will be 48 V x 714 Ah.

Seven parallel strings of batteries can work, but itÔÇÖs usually an invitation for all sorts of electrical- and maintenance problems. Large battery banks usually consist of bigger batteries and fewer parallel strings. The ÔÇ£ideal", a compromise between performance, maintenance, and cost, is somewhere between one string of batteries and four strings wired in parallel.

For example, a battery bank of 16 ÔÇ£standardÔÇØ L-16 batteries, each rated at 6 V x 350 Ah, might be an efficienct solution. Wiring the 16 batteries in an 8 x 2 configuration would create a battery bank rated at 48 V x 700 Ah, or 33.6 kWh.

A pair of VFX3048E inverters can supply about 80 ADC of charge current during the bulk charge stage. ThatÔÇÖs a very good match for a 700 Ah battery bank (80 / 700 = 11.4%).

Personally, I prefer VRLA batteries (AGM or gel) over flooded-cell models. However, youÔÇÖll have to run the cost-benefit analysis for your particular situation.
Phase 2 (Upgrade Phase 1 from a Backup System to a Grid Interactive system with 240 VAC if needed)
MX60 X 2 (To be added to Flexware 500 to make provision for the Panels)
I would like to add Solar Panels to enable Phase 1 to work as a Grid Interactive system and not just as a backup system only
Questions:
1) Any suggestions on Battery Bank upgrade from Phase 1 to 2 (Amount of Batteries per VFX3048E, Series or Parallel, etc...), I can get 12V, Delkor Calcium, 102Ah (GP31), Batteries in RSA
2) Any suggestions on Panels needed (Amount of Panels per MX 60, Series or Parallel, etc...), I can get Sanyo HIP-180N, Pmax 180W, Vmp 36.5V, Imp 4.93A, Voc 45.5V, Isc 5.49A, Pmin 171W Panels in RSA)
3) Can I place the Panels directly on a Flat Roof because we have security problems here (I need the Panels to be out of sight), will this be workable or will the losses be to great (what will the approx % losses be)
NOTE: OutBackÔÇÖs export inverters (~230 VAC, 50 Hz) are not utility-interactive. The export inverters can use the grid or a generator as an AC source to power loads and/or charge the batteries. They cannot sell excess power to the grid.

(1) ItÔÇÖs generally not a good idea to ÔÇ£upgradeÔÇØ a battery bank by adding new batteries to old ones. The condition and performance of the old batteries will affect the new ones and you effectively end up with a larger bank of old batteries. YouÔÇÖd probably be battery off starting with a larger battery bank.

(2) Tell us more about your siteÔÇÖs location and climate: Lat, Long, elevation, typical summer high temp, record hi temp, typical winter low temp, record winter low temp. For example: http://en.wikipedia.org/wiki/Bloemfontein

(3) Flat (horizontal) installation is generally not a good idea. Power output from the panels is reduced by the accumulation of environmental crud, by elevated panel temperature (poor natural convection cooling), and by bad Sun angle, especially in the winter (April ÔÇô August).

More later,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
jacostry
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Post by jacostry »

Jim thanks so much for your comments!

Phase 1 Comments;
I understand this much better now, I will see if I can source (AGM or gel) 6 V x 350 Ah batteries down here and configure as per your spec.

Phase 2 Comments:
On your Note: Jim, my initial explanation were incorrect in regards to the sell back of power, we do not have this option down here from our electrical supplier and this will not change soon, so I meant still using the grid but not to sell onto the grid. (So I will use the grid as a source of power only, and reduce my grid usage by 5KW if possible through Phase 2 )

1) I agree, I was hoping that I can get close to the battery spec as per Phase 1 even if I need to start with a larger bank in Phase 1
2) Thanks for the Link, see the link to my location http://en.wikipedia.org/wiki/Pretoria
3) Will think about how I can do this without loosing the Panels to theft.

Regards,
Jaco
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Post by John B »

Jaco,

The best thing to do is look at your utility meter and write down the number and then read it again three hours later to get an accurate measure of your usage. 15KWH seems really high for what you have listed.

I would have guessed a third of that or even less. If you can get it down to 3.75kwh (or it is that already!) then you can get by with one quarter of the batteries from the previous calculation, and that would be quite a bit of savings.

John
Outback GTFX3048 in PS1 (topless!) with 8 SunExtender 108Ah 12V batteries in two PS1-BE battery enclosures and 28 Evergreen 120Watt "B" modules. PSX-240 transformer for 240V loads.
jacostry
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Post by jacostry »

John,
There is quite a bit more equipment than I mentioned, but I am going to do a proper list of all equipment (Watts and Time). But yes I suppose I can switch of Geyser and all non essentials and do the 3 hour test.

Do I have to consider any additional Watts for start-up of the equipment or will the switch over be instantaneous when there is a power failure?
Regards,
Jaco
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crewzer
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Post by crewzer »

Jaco,

Thanks for the additional info. I'll post some further analysis and suggestions tomorrow.

Regards,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Location: Austin, TX

Post by tallgirl »

Jaco,

The KWH for startup is fairly low -- for example, small home A/C (say, 3 or 4 tons) has a 80A @ 240V inrush load, after which the load drops to 30A @ 240V. If the A/C runs for 15 minutes, the startup is less than 0.5% of the total.
Julie in Texas

I ride bicycles. A lot.
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crewzer
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Post by crewzer »

Jaco,

Sorry about the delayed response. I was tending to several projects over the weekend, and one of ÔÇÿem was even solar energy related! Also, I did receive your message. But now, back to the Phase 2 questions, although in reverse order.

(3) PretoriaÔÇÖs latitude is ~25 degrees South. A typical fixed-tilt angle for a north-facing array in your location would be 25 degrees. However, 40 degree tilt angle would increase winter energy production potential. This increased angle would also improve array cooling and self-cleaning. The steeper angle would somewhat reduce summer energy production potential, but the longer days would likely compensate somewhat.

IÔÇÖm sorry to learn that theft is such a concern. Perhaps some specialized security hardware might help. See: http://www.unirac.com/solarmount/aces_pdf/ii909.pdf

(2) JohnÔÇÖs comments about improving energy efficiency have merit. In fact itÔÇÖs often cheaper to invest in new energy efficient appliances and gadgets and then deploy a smaller PV system than it is to deploy a larger system to support the legacy load. But, letÔÇÖs work with what you have for now, and then you can scale from this analysis should you decide to down-size.

We demonstrated earlier that your 15 kWh/day net energy requirement would require 16.7 kWh/day from the batteries to allow for inverter losses.
Factoring in PV module effective winter operating efficiency (~88%), wiring efficiency (97%), controller efficiency (~98%), and flooded-cell battery recharge efficiency (~80%), your PV array will need to generate (16.6 kWh /day) / (88% x 97% x 98% x 80%) = ~25 kWh/day.

Insolation data indicates that Pretoria receives a daily average of the equivalent of 3.8 hours/day of ÔÇ£fullÔÇØ Sun. I suspect this data is a horizontal flat plate collector and can be improved if the array is tilted north. For comparison purposes, see the data for Brownsville, Texas, which is located at ~26 degrees North.

http://www.gaisma.com/en/location/pretoria.html
http://rredc.nrel.gov/solar/old_data/ns ... /12919.txt

Assuming worst case conditions of 5 hours/day of ÔÇ£fullÔÇØ Sun, the PV array will need to be rated for 25 kWh/day / 5 hrs/day = 5 kWh STC.

Configuring a PV array for a 48 V battery bank and for the controllerÔÇÖs limits can be a challenge. At one end, itÔÇÖs important to deliver a high enough array voltage in the summer to be able to drive a flooded-cell battery bank to itÔÇÖs EQ target of ~62 V or so. Because PV array voltage drops when the array gets hot (up to ~35 C above ambient), and also allowing for voltage losses in the wiring and the controller, the arrayÔÇÖs STC Vmp spec should be around 83 V.

At the other end, the current crop of MPPT charge controllers generally have an absolute maximum input voltage spec of 150 VDC, and the MX60ÔÇÖs operational limit is ~141 VDC. Because winter temperatures can cause the array STC Voc to increase, a correction factor must be applied. Using the US National Electrical CodeÔÇÖs correction factor of 113% for temperatures in the range of -1C to -10C, the arrayÔÇÖs STC Voc must not exceed 141 V / 113% = 124 V

So, the challenge is to configure an array with an STC Vmp of ~83 V, and an STC Voc of ~124 V.

The Sanyo 180ÔÇÖs specs are Pmax 180W, Vmp 36.5V, Imp 4.93A, Voc 45.5V, and Isc 5.49A. Wiring just two in series will result in an STC Vmp of 36.5 V x 2 = 73 V ÔÇô too low, in my view. Wiring three in series will result in an STC Vmp of 45.5 V x 3 = 136.5 V ÔÇô too high, in my view.

I think you should scout around for other modules that will fit within the boundaries IÔÇÖve recommended. For example, this 200 W Sharp should work perfectly: http://www.mrsolar.com/pdf/sharp/Sharp200.pdf

27 of these modules would provide for a 5.4 kW array, close to the 5 kW target identified earlier. 15 modules could be configured in a 3 x 5 arrangement via one MX60, and the other 12 in a 3 x 4 arrangement via the second MX60.

(1) We previously discussed a battery bank rated at ~ 48 V x 700 Ah. As you prepare for Phase 2, a bank rated at 48 V x 1,400 Ah to 2,000 AH would be better, as daily discharges would be limited to 20% to 25% of battery capacity, and this would provide you with a significant reserve in case of a prolonged grid outage and/or poor weather.

YouÔÇÖd need to look at something like Exide GNB Absolyte batteries if you want to go with an AGM type. The bad news is that theyÔÇÖre expensive, but the good news is that their recharge efficiency is very high and you could probably cut the array size down from 5,400 W STC to 4,800 W STC.

If you decide you want to stay with flooded-cell batteries, you could build a large bank worth just one or two strings if you uses big batteries like those from Rolls / Surrette. See: http://www.rollsbattery.com/

I hope youÔÇÖll return to the forum once youÔÇÖve had a chance to mull this over. WeÔÇÖll then see what we can do be of more specific assistance.

HTH,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Post by jacostry »

Jim,
I am working through your reply, some serious information here; I am currently making sure about the loads and so far my calculations were correct and the 5KW/h during the day for Critical equipment only is still the requirement.

The current total usage during a month period including Critical on non critical is approx 2600KW (Even after Solar Geyser and energy efficient bulbs were installed)

I will forward some more questions to your PM because I do not what to flood the Forum with all sorts of stupid questions.
Regards,
Jaco
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Post by jacostry »

John B wrote:Jaco,

The best thing to do is look at your utility meter and write down the number and then read it again three hours later to get an accurate measure of your usage. 15KWH seems really high for what you have listed.

I would have guessed a third of that or even less. If you can get it down to 3.75kwh (or it is that already!) then you can get by with one quarter of the batteries from the previous calculation, and that would be quite a bit of savings.

John
John and Jim, I went back to John's comment to make sure about the KW/h usage, even though our utility meter shows KW/h on the meter it actually use a unit measurement per hour. After checking this with our supplier they confirmed that I have to use the following formula to convert my units into KW/h (Units x Voltage = KW/h/1000) 2600 X 230 = 598000/1000 = 598 KW/h per month. This now makes much more sense, so my approx backup power needed for Phase 1 is actually 2KW/h Max (3 hr's x 2KW/h = 6KW/h total).
So John your prediction were quite spot on, itÔÇÖs back to the Drawing board for me.
Jaco
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Post by tallgirl »

jacostry wrote:
John B wrote:Jaco,

The best thing to do is look at your utility meter and write down the number and then read it again three hours later to get an accurate measure of your usage. 15KWH seems really high for what you have listed.

I would have guessed a third of that or even less. If you can get it down to 3.75kwh (or it is that already!) then you can get by with one quarter of the batteries from the previous calculation, and that would be quite a bit of savings.

John
John and Jim, I went back to John's comment to make sure about the KW/h usage, even though our utility meter shows KW/h on the meter it actually use a unit measurement per hour. After checking this with our supplier they confirmed that I have to use the following formula to convert my units into KW/h (Units x Voltage = KW/h/1000) 2600 X 230 = 598000/1000 = 598 KW/h per month. This now makes much more sense, so my approx backup power needed for Phase 1 is actually 2KW/h Max (3 hr's x 2KW/h = 6KW/h total).
So John your prediction were quite spot on, itÔÇÖs back to the Drawing board for me.
Jaco
Check that math -- 598KWH/month is 598 KWH/month / 30days/month = 20KWH/day, 20KWH/day / 24 hours/day = 0.833KWH/hour, 0.833KWH/hour * 3 hours = 2.5KWH.

But that's actually a useless figure -- you have to know your PEAK hourly load and use that. And for that value, you have to TURN ON your critical loads and measure the power consumed by them over a three hour period.

The "Acceptance Testing" I conducted on my system was 4 hours of usage, including washing and dryer clothes (electric washer, gas dryer), normal home lighting, TV, etc. I forget the low battery voltage, but I re-ran the same test recently and made it down to 46VDC on a 48VDC nominal system starting from ~95% SOC.
Julie in Texas

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jacostry
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Post by jacostry »

crewzer wrote:Jaco,

We demonstrated earlier that your 15 kWh/day net energy requirement would require 16.7 kWh/day from the batteries to allow for inverter losses.
Factoring in PV module effective winter operating efficiency (~88%), wiring efficiency (97%), controller efficiency (~98%), and flooded-cell battery recharge efficiency (~80%), your PV array will need to generate (16.6 kWh /day) / (88% x 97% x 98% x 80%) = ~25 kWh/day.

HTH,
Jim / crewzer
Jim,

So with the new figures according to your formulas the new requirement for Phase 2 (Taking Phase 1 into account) should be as follows:
PV Array will need to generate 17 KWh/day (7.29 kWh /day) / (88% x 97% x 98% x 80%) = ~17.17 kWh/day.

Assuming worst case conditions of 5 hours/day of ÔÇ£fullÔÇØ Sun, the PV array will need to be rated for 17 kWh/day / 5 hrs/day = 3.4 kWh STC.

Can you possibly provide new proposed Array and Battery specification with this new information if possible.
Regards,
Jaco
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Post by jacostry »

tallgirl wrote:
jacostry wrote:
John B wrote:Jaco,

The best thing to do is look at your utility meter and write down the number and then read it again three hours later to get an accurate measure of your usage. 15KWH seems really high for what you have listed.

I would have guessed a third of that or even less. If you can get it down to 3.75kwh (or it is that already!) then you can get by with one quarter of the batteries from the previous calculation, and that would be quite a bit of savings.

John
John and Jim, I went back to John's comment to make sure about the KW/h usage, even though our utility meter shows KW/h on the meter it actually use a unit measurement per hour. After checking this with our supplier they confirmed that I have to use the following formula to convert my units into KW/h (Units x Voltage = KW/h/1000) 2600 X 230 = 598000/1000 = 598 KW/h per month. This now makes much more sense, so my approx backup power needed for Phase 1 is actually 2KW/h Max (3 hr's x 2KW/h = 6KW/h total).
So John your prediction were quite spot on, itÔÇÖs back to the Drawing board for me.
Jaco
Check that math -- 598KWH/month is 598 KWH/month / 30days/month = 20KWH/day, 20KWH/day / 24 hours/day = 0.833KWH/hour, 0.833KWH/hour * 3 hours = 2.5KWH.

But that's actually a useless figure -- you have to know your PEAK hourly load and use that. And for that value, you have to TURN ON your critical loads and measure the power consumed by them over a three hour period.

The "Acceptance Testing" I conducted on my system was 4 hours of usage, including washing and dryer clothes (electric washer, gas dryer), normal home lighting, TV, etc. I forget the low battery voltage, but I re-ran the same test recently and made it down to 46VDC on a 48VDC nominal system starting from ~95% SOC.
You are correct, but that is why I used 2KW/h x 3hr's = 6KW/h instead of 0.833KWH/hour because this is usually during a peak period.

Jaco
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Post by John B »

jacostry wrote:
So with the new figures according to your formulas the new requirement for Phase 2 (Taking Phase 1 into account) should be as follows:
PV Array will need to generate 17 KWh/day (7.29 kWh /day) / (88% x 97% x 98% x 80%) = ~17.17 kWh/day.

Assuming worst case conditions of 5 hours/day of ÔÇ£fullÔÇØ Sun, the PV array will need to be rated for 17 kWh/day / 5 hrs/day = 3.4 kWh STC.
Jaco
Be careful not to "oversize" your system if you cannot connect to the grid. I have 3200 watts of PV power and generate about 12kwh of power per day on average.

I live at 19 degrees north latitude with lots of sun, but if I don't have sufficient load on the system then the MX60 shuts down the array after the batteries are fully charged because I have no where to use the excess power. This typically happens in the morning just before my pool pump comes on and later in the afternoon after it goes off.

On weekends when I am home I have been able to tinker and get over 18kwh on some days, but quite frankly I was running things that did not need to be run just to use the excess power that was available.

Charging more batteries and running them down at night is not the most economical way to go if you have grid available, and I would think that having to dispose of batteries negates any benefit you can show from getting the energy from solar.

I've been experimenting with HBX mode recently, but that too sometimes goes haywire and I found it charging my batteries using the grid when I had lots of PV power that was available and not being used. I have since turned off the charging function in my inverter, but the best use of excess power is still to sell it back to the grid so I'm looking forward to the day when I can just turn sellRE on.
Outback GTFX3048 in PS1 (topless!) with 8 SunExtender 108Ah 12V batteries in two PS1-BE battery enclosures and 28 Evergreen 120Watt "B" modules. PSX-240 transformer for 240V loads.
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Post by crewzer »

PV Array will need to generate 17 KWh/day (7.29 kWh /day) / (88% x 97% x 98% x 80%) = ~17.17 kWh/day.

Assuming worst case conditions of 5 hours/day of ÔÇ£fullÔÇØ Sun, the PV array will need to be rated for 17 kWh/day / 5 hrs/day = 3.4 kWh STC.
Jaco,

:?: I'm sorry, but I've kind of lost track here:

1) Where did 7.29 kWh/day come from?
2) 7.29 kWh/day (winter net) = 7.29 kWh/day / (88% x 97% x 98% x 80%) = 10.9 kWh/day (winter gross).
3) 10.9 kWh/day / 5 hours/day "full" Sun = 2.18 kW STC PV array size.

HTH,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Post by jacostry »

crewzer wrote:
PV Array will need to generate 17 KWh/day (7.29 kWh /day) / (88% x 97% x 98% x 80%) = ~17.17 kWh/day.

Assuming worst case conditions of 5 hours/day of ÔÇ£fullÔÇØ Sun, the PV array will need to be rated for 17 kWh/day / 5 hrs/day = 3.4 kWh STC.
Jaco,

:?: I'm sorry, but I've kind of lost track here:

1) Where did 7.29 kWh/day come from?
2) 7.29 kWh/day (winter net) = 7.29 kWh/day / (88% x 97% x 98% x 80%) = 10.9 kWh/day (winter gross).
3) 10.9 kWh/day / 5 hours/day "full" Sun = 2.18 kW STC PV array size.

HTH,
Jim / crewzer
Jim,
I have also lost track here, but lets go back to my new basic figures:

Phase 1, I need 2KW/h backup for a period of 3 Hr's = 6KW/h Backup needed
Phase 2, Install Panels and spec batteries to produce 2KW/h during the day (The batteries is only for backup when power fails and weather, Grid power will be used at night)

Jaco
Last edited by jacostry on Mon Feb 18, 2008 11:32 pm, edited 1 time in total.
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Post by jacostry »

John B wrote:
jacostry wrote:
So with the new figures according to your formulas the new requirement for Phase 2 (Taking Phase 1 into account) should be as follows:
PV Array will need to generate 17 KWh/day (7.29 kWh /day) / (88% x 97% x 98% x 80%) = ~17.17 kWh/day.

Assuming worst case conditions of 5 hours/day of ÔÇ£fullÔÇØ Sun, the PV array will need to be rated for 17 kWh/day / 5 hrs/day = 3.4 kWh STC.
Jaco
Be careful not to "oversize" your system if you cannot connect to the grid. I have 3200 watts of PV power and generate about 12kwh of power per day on average.

I live at 19 degrees north latitude with lots of sun, but if I don't have sufficient load on the system then the MX60 shuts down the array after the batteries are fully charged because I have no where to use the excess power. This typically happens in the morning just before my pool pump comes on and later in the afternoon after it goes off.

On weekends when I am home I have been able to tinker and get over 18kwh on some days, but quite frankly I was running things that did not need to be run just to use the excess power that was available.

Charging more batteries and running them down at night is not the most economical way to go if you have grid available, and I would think that having to dispose of batteries negates any benefit you can show from getting the energy from solar.

I've been experimenting with HBX mode recently, but that too sometimes goes haywire and I found it charging my batteries using the grid when I had lots of PV power that was available and not being used. I have since turned off the charging function in my inverter, but the best use of excess power is still to sell it back to the grid so I'm looking forward to the day when I can just turn sellRE on.
Point taken John and I agree because I cannot sell back to the grid in any chase so I need to make sure about the real load requirement. As far as the batteries are concerned, I need batteries only for backup purposes and I will be using the grid for my non critical equipment during the day and for all off my needs (Critical and Non Critical) at night.
Jaco
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Post by jacostry »

crewzer wrote:
PV Array will need to generate 17 KWh/day (7.29 kWh /day) / (88% x 97% x 98% x 80%) = ~17.17 kWh/day.

Assuming worst case conditions of 5 hours/day of ÔÇ£fullÔÇØ Sun, the PV array will need to be rated for 17 kWh/day / 5 hrs/day = 3.4 kWh STC.
Jaco,

:?: I'm sorry, but I've kind of lost track here:

1) Where did 7.29 kWh/day come from?
2) 7.29 kWh/day (winter net) = 7.29 kWh/day / (88% x 97% x 98% x 80%) = 10.9 kWh/day (winter gross).
3) 10.9 kWh/day / 5 hours/day "full" Sun = 2.18 kW STC PV array size.

HTH,
Jim / crewzer
Jim,

To clarify, if you can have a look at this.(See my proposed Bill of Quantities forwarded to your pm)

Phase 1 requirement (Backup of 3 hrs only)

Net Energy requirement 2 KW x 3hrs = 6KWh
Battery bank requirement 6KWh / (90% x 50%) = 13.33 kwh
Battery Specification 48 V X 225A/h = 10.8kwh (8 x 1), Trojan T-105 (6V 225A/h) ÔÇô Not sure about this please assist if possible, but this might be irrelevant if Phase 2 battery spec is different.

Phase 2 (Including Backup of 3 hrs and constant 2kwh during the day, normal grid usage during night)
6 kWh/day net energy requirement would require 6.7 kWh/day from the batteries to allow for inverter losses. (Should this only be the Backup 6 kWh or should it be the total daytime Critical requirement?)
PV array will need to generate (6.7 kWh /day) / (88% x 97% x 98% x 80%) = ~10 kWh/day
PV array will need to be rated for 10 kWh/day / 5 hrs/day = 2 kWh STC.

Jim if you can maybe comment if this is correct and provide info on the following if possible:
Proposed battery bank and specs for Phase 2
Proposed PV spec for Phase 2

Jaco
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crewzer
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Post by crewzer »

Jaco,

OK; more later today.

Regards,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Post by crewzer »

:-k Hmmmm... is the 6 kWh/day average energy requirement based on:

(a) 7 days/week (i.e, 42 kWh/week), or
(b) Should it be 8.2 kWh/day based on 5 days/week (the same 42 kWh/week), or
(c) Should it be 6 kWh/day based on 5 days/week (30 kWh/week)?

More later,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Post by jacostry »

crewzer wrote::-k Hmmmm... is the 6 kWh/day average energy requirement based on:

(a) 7 days/week (i.e, 42 kWh/week), or
(b) Should it be 8.2 kWh/day based on 5 days/week (the same 42 kWh/week), or
(c) Should it be 6 kWh/day based on 5 days/week (30 kWh/week)?

More later,
Jim / crewzer
Jim,
The 6KW/h/day were actualy the 3hr's backup required for a power failure during the day in phase 1, but Phase 2 complicates this now because now I am trying to run the Critical load during the day on the Solar System (2KW/h x 5hr's) ( But the backup requirement should still be applied for Power failure or bad weather.

As per your question, a) 7 days/week Solar, not backup ( But I think it should be 2KW/h x 5hr's = 10KW/h/Day = 70KW/h/Week)

So maybe the best would be to ignore Phase 1 and only spec Phase 2 as long as the Backup of 6KW/h (2kw/h x 3hr's) are taken into consideration.

Jaco
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crewzer
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Post by crewzer »

Jaco,

OK here we go. The baseline net requirement is 70 kWh/week, or 10 kWh/day x 5 days/week.

Allowing for 90% inverter efficiency, the battery bank will need to supply 11.1 kWh/day, or 48 V x 231 Ah. The battery bank size could be anywhere from twice the average daily energy requirement to about six times the average daily energy requirement.

Using the former 2X model, you might have to depend on the grid to regularly top off the batteries. You could set the invertersÔÇÖ ÔÇ£Grid UseÔÇØ mode to do this overnight. Accordingly, the 48 V x ~460 Ah battery bank would still be viable, although, at the estimated equivalent of ~125 50% discharges per year, the batteries would likely have to be replaced about every three or four 4 years.

Applying the latter 6X model, there should be a balance between energy use and recharging from the Sun, and grid use for recharging should be minimal. A 48 V x ~1,400 Ah would be appropriate. Big flooded-cell batteries from Rolls/Surrette or Absolyte AGM batteries from GNB would work, and long battery life (>10 years) should be expected.

PretoriaÔÇÖs latitude is ~25 degrees South. A typical fixed-tilt angle for a north-facing array in your location would be 25 degrees. However, 40 degree tilt angle would increase winter energy production potential. This increased angle would also improve array cooling and self-cleaning. The steeper angle would somewhat reduce summer energy production potential, but the longer days would likely compensate somewhat.

Insolation data indicates that Pretoria receives a daily average of the equivalent of 3.8 hours/day of ÔÇ£fullÔÇØ Sun. This data is for a horizontal flat plate collector and can be improved if the array is tilted north, as discussed above. For comparison purposes, see the data for Brownsville, Texas, which is located at ~26 degrees North.

http://www.gaisma.com/en/location/pretoria.html
http://rredc.nrel.gov/solar/old_data/ns ... /12919.txt

A winter net of 10 kWh/day would require spec-based generation of 10 kWh/day / (88% x 97% x 98% x 80% x 90%) = 16.6 kWh/day. Assuming a winter average of 5 hours/day of ÔÇ£fullÔÇØ Sun on a north-facing array tilted up at ~40 degrees, the PV array spec would be 3,320 W STC.

Configuring a PV array for a 48 V battery bank and for the controllerÔÇÖs limits can be a challenge. At one end, itÔÇÖs important to deliver a high enough array voltage in the summer to be able to drive a flooded-cell battery bank to its EQ target of ~62 V or so. Because PV array voltage drops when the array gets hot (up to ~35 C above ambient), and also allowing for voltage losses in the wiring and the controller, the arrayÔÇÖs STC Vmp spec should be around 83 V.

At the other end, the current crop of MPPT charge controllers generally have an absolute maximum input voltage spec of 150 VDC, and the MX60ÔÇÖs operational limit is ~141 VDC. Because winter temperatures can cause the array STC Voc to increase, a correction factor must be applied. Using the US National Electrical CodeÔÇÖs correction factor of 113% for temperatures in the range of -1C to -10C, the arrayÔÇÖs STC Voc must not exceed 141 V / 113% = 124 V

So, the challenge is to configure an array with an STC Vmp of ~83 V, and an STC Voc of ~124 V. One minimum option would be 25 each Kyocera KC-130 modules wired 5 x 5 for an array rated at 3,250 W STC. A single MX60 controller could handle this array for a ÔÇ£48 V systemÔÇØ.

A more conservative option would be 18 each Sharp 200 W modules configured 3 x 6 for 3,600 W STC. Although a single MX60 controller could probably handle this array, itÔÇÖs officially limited to 3,200 W STC. Accordingly, a new FLEXmax 80 controller is probably warranted.

In summary, I recommend you adjust your system BOM and weÔÇÖll then take a fresh look at it.

HTH,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Post by tallgirl »

Jaco,

Just an observation -- you're making this overly complex. My suggestion would be to decide what your objectives are in terms of KWH available for backup purposes (phase 1), and then KWH available on an average day (phase 2).

Once you have those two figures, all the rest falls out very simply. You want to have 3 hours at 2KW/h? Simple -- you need a 12KWH battery bank to avoid a depth of discharge greater than 50%, because that can ruin your batteries. My average house load is between 450 and 600 watts, and 6 hours @ .5 KW came out to a number bigger than what I have (but there are reasons for that). That was my target and testing proved it worked.

Now, phase two is 2KW average during the day. You need to turn that into KWH, then divide by insolation and inefficiencies. That will give you your array size in WDC. From there you find panels that can produce the volts and amps needed to match to one or more charge controllers.

That's it, your done.
Julie in Texas

I ride bicycles. A lot.
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