Solar pv install

DrChatNuff · October 2007

Hi guys
Calling from Lagos Nigeria/Africa] where i need advice on how to install a 2kw pv system, materials ive acquired are [10] 200watt kyocera panels, an outback power panel system vfx3048e inverter[2], an mx60 c/controller and [16] 12v 258amp concorde sealed batteries, i have minimal knowledge, but feel with advice from this forum i'll be just ok.It is a 48volt system although i'm a bit worried considering books say 2000watt systems should be 24volts, are there any downsights, plus my largest hope is someone advising me the best way to wire up the panels, and b/4 you ask , the products were bought on Ebay ,thats why i havent the necessary Advice. Diagrams will be appreciated
Thanks guys

nigtomdaw · October 2007

Re: Solar pv install

Hi You can download the manuals for your outback equipment from this link.http://http://www.outbackpower.com/manuals.htm

There are no problems using 48 volt base voltage with 2000 watts of PV. The higher 48 volts system voltage will save you money on wiring costs by allowing thinner connecting cables in the system. Simply put your 48 volt systems has to push half the amps around that a 24volt system does. You still need to spec all cabling properly though to avoid voltage drops and safety issues .

The manuals will help with this as well as 2 simple equations I use regulary which are
V=IR (Volts=Amps x Resistance) and
P=VI (Power "watts" = Volts x Amps)

With a little simple math you can always find the unknown if you have 2 out of three bits of data.

The batteries need to be wired to match the inverter voltage of 48 volts so wire 4 together in series positive to negative to provide one 48 volt string.
Make up 4 identical strings this way and then connect each string together in parrallel ie positive to positive. When you connect your main inverter wires male sure they are at opposite ends on the strings ie Positive from string one and negative from string 4. This will give you a 48 volt 1032 amp/hr bbank.

You do not say whether your panels are 12 or 24 volt but they can be wired to a higher voltage than your main system voltage of 48 volts say 60v or 72 volts to feed in to the MX60 charge controller which will then convert the voltage back to the 48 volt range to achieve optimum charging. You still need to install the proper ac and dc fuses or disconnects but you should find the majority of your answers inside the VFX inverter and MX60 charge controller manuals on the link I have provided.

Ive always been a supporter of RTFM (Read the Flippin Manual) and then if you get stuck this is the place to come with your questions and or the Outback Forum from the same link in this thread.

I have Xantrex equipment and there manuals with there equipment are very good with wiring diagrams for batteries and equipment and I suspect Outbacks will be just as good, so start downloading and reading it will be an excellent starting point for you. HTH

crewzer · October 2007

Re: Solar pv install

A bit more info:

Here’s a link to OutBack wiring diagrams: http://www.outbackpower.com/wiringdiag.htm

For a system with a 48 V battery bank, your PV array of ten 200 W Kyocera modules will be difficult to configure. Here are the module specs: http://www.kyocerasolar.com/pdf/specsheets/KC200GT.pdf

The basic challenge is that the array’s operating voltage must be high enough to deliver sufficient charging voltage to the batteries. For your AGM batteries, the target voltage is ~57 V, so the array’s temperature-derated operating voltage must be at least 60 V.

Considering Nigeria’s warm climate and other operating efficiencies, the nominal (STC) array voltage will probably have to be at least 75 V. The STC Vmp of each module is 26.3 V. Three wired in series will make for 26.3 V x 3 = 78.9 V, so that’s good enough.

However, with three modules per series string, the largest array you can build from 10 modules is a nine-module array configured as three modules per series string and three strings in parallel (“3 x 3”).

Finally, note that the bulk stage charge current from a 1,800 W array will be ~27 A, or ~2.6% of the battery bank capacity. This array will struggle to charge the battery bank and supply power to daytime loads.

HTH,
Jim / crewzer

DrChatNuff · October 2007

Re: Solar pv install

appreciate your help guys, but JIM considering you saying i'll have trouble charging the battery bank what is the best way to go, is it best going for a different kind of battery or wht would you consider the best option. and since you suggested it best wiring the panels in series of three pairs then parallel them up do you think i should have gone for lower watt panels.

BB. · October 2007

Re: Solar pv install

Doctor,

What Jim is saying is that you need three (to four) panels in series to generate enough voltage to charge your 48 VDC battery bank in all conditions.

With 10 panels, it only divides by 2 or by 5 evenly... 2 panels is only 2x20.8=41.6 volts at 35 degrees C... Not near high enough to charge your battery bank (you need 57 volts + 2 volts controller drop = 59 VDC minimum).

Three panels will give you ~62 volts dc, 4 panels =~83 volts (this is Vmax-power under load at high temperature)...

Looking at 5 panels in series will give you ~104 VDC at 35 Centigrade, but, then you have to look at the cold temperatures for your area (bright cool morning, no load on panels)...

Assuming that you may get a rare frost (0 Centigrade), the maximum panel voltage would be ~36 VDC (Vopen circuit, minimum temperature day):

3x36v=108 VDC (Vmax open circuit OK for controller)
4x36v=148 VDC (Vmax is too high for operational controller, very close to Vnever exceed of 150 VDC)
5x36v=180 VDC (Vmax will damage MX-60 controller).

A 3x3 panel (series/parallel) array will use 9 of your ten panels.

A 2x4 setup will use only 8 of your panels and 3x4 would may also work OK --but is more panels than you have (but is very close to damaging the MX 60 controller on a cold day--if you have any frost days).

A 2x5 panel system (5 in series, two parallel strings) will not be safe for your system. Remember that the MX 60 will not start unless the voltage is below 140 VDC, and can be ruined by anything at 150 VDC or greater...

-Bill

PS: I use the Xantrex array sizing calculator for their Grid Tie systems as a quick lookup tool for any brand Solar Panels and for its Vmax open circuit /Vmin temperature under load calculations. As with anything, you still need a margin of safety with the numbers supplied.

crewzer · October 2007

Re: Solar pv install

...JIM considering you saying i'll have trouble charging the battery bank what is the best way to go, is it best going for a different kind of battery or wht would you consider the best option. and since you suggested it best wiring the panels in series of three pairs then parallel them up do you think i should have gone for lower watt panels.

DrChatNuff,

My concerns about adequately charging your battery bank are two-fold. One is making sure that there’s a high enough charging voltage available, as Bill described. I covered that issue in my previous post. The three-modules per series string solution was selected because it would deliver a high enough array voltage and make the maximum use (nine modules) of your inventory. Four modules per series string should also work, but then you’d only be able to use eight modules, so you’d end up with a smaller array.

My real concern at this point is having sufficient charge current to recharge the battery bank. I typically suggest a mathematically derived charge current specification of at least 5% of battery bank capacity. Allowing for environmental issues such as array misalignment, less than optimal insolation, and other factors, only ~80% of the current spec is typically available, so a 5% design results in a typical maximum charge current of ~4%.

For your 1,032 Ah battery bank, 4% net charge current would be ~42 A. The maximum power specification for the suggested 1,800 W PV array is ~31 A, but, allowing for environmental issues, the typical maximum late morning charge current will be ~25 A. Depending on daytime loads, average daily energy requirements, and actual insolation in your area (i.e., shading is a bad thing), I fear that a maximum charge current of 25 A will not be able to recharge the battery bank. The result is that the batteries will slowly die.

Assuming your local temperatures don’t fall below 10C, the best technical solution may be to buy more six PV modules, for a total of sixteen, and wire them up into a 4 x 4 array. The resulting 3,200 W array can be handled by the MX60 charge controller and should be able to reliably deliver ~44 A to the batteries and daytime loads.

Then, all you have to do is make sure that you don’t use more energy than the system can generate.

Hope This Helps,
Jim / crewzer

DrChatNuff · October 2007

Re: Solar pv install

Hi Bill
thanks for taking an interest , i really appreciate what Jim adviced, my concern was when at the bottom he said i'd have problems charging the batteries, i'm not sure if he meant if i didnt take his advice or with his advice, so if you can explain more and ease my anxiety and explain the battery situation. If i wire up the adviced way will my battery bank be adequlately charged
Thanks

DrChatNuff · October 2007

Re: Solar pv install

Sir
the system will be installed in Nigeria where at worst temp are 17degree, i wont be able to increase the number of panels due to roof or ground space, but i really do appreciate this advice and realise i still have work to do.

BB. · October 2007

Re: Solar pv install

Doctor,

Jim has explained it better than I--There is a "standard" formula for optimal battery to panel ratio... Generally it is 3% to 10% (sometimes 15%--especially with AGM batteries which can take higher charge currents--but as always, read the manuals for your batteries/equipment to make sure that you are within guidlines).

So:

Ratio=Solar panel watts / battery storage in watts (really both are watt*hour ratings)

= 9battsx200 watt / (16batts*12v*258amp*hours) = 3.6%

It is certainly on the small side of charging... You probably don't need to reduce the number of batteries--but this not the only question relating to sizing your system.

What is also important is how much power per day you are planning on taking out of your solar system...

Kyocera's online catalog (the industrial catalog is written for world-wide use, the Solar Electric Catalog is written towards a US audience) has more information than you can possibly use--but it does a pretty good job of presenting world wide information (amount of sun, magnetic north, many possible pieces of equipment, etc.) and you can use the worksheets to calculate how big your solar panels should be for your region (or in your case, how much power you can get from your 1,800-2,000 watt array).

It appears that you are good for 4-5 or 5-6 sun hours per day (depending if you are near the coast of further inland)...

So, just as a rough start, an 1,800 watt panel with good equipment designed for off-grid use will give you (very roughly) ~60% efficiency from the solar panel (STC rating) through the charge controller, to charging the batteries, to running the inverter to the outlet):

Energy=Solar Panel Rating * Hours of sun * efficiency = power available
=1,800 watts * 5 hours * 60% = 5,400 watt*hours per day (5.4 kWhrs per day)

The above is a very rough estimate, but will give you an idea of the average amount of electricity you can pull from your array...

This is equivalent to about 5x 100 watt light bulbs running 10 hours per day (5,000 watt*hours).

How much power do you need?

-Bill

DrChatNuff · October 2007

Re: Solar pv install

Sir
we normally get at least on normal days 8hrs sunshine although it normally gets as hot as 30'c, but during the 'rainy season maybe 3, i'm normally back in Africa six months a year, three times for two months each, so the only appliances operating at other times would be low energy light bulbs[4] about 4hrs daily and a plasma 400w tv and a 300watt fridge . While i'm there i use about 6kwh daily

crewzer · October 2007

Re: Solar pv install

OK. A compromise of sorts might be to use the 1,800 W system to charge a bank of just 12 batteries wired for 48 V and rated at ~37 kWh, or six days of energy at 6 Kwh/day. Allowing for three days of autonomy and limited dischrge to 50% of capacity, this would be a appropriate sized bank.

The 1,800 W array may have trouble keeping up with energy demand when you're "there", but it should catch up when you're not. It'll also have an easier time of recharging a 774 Ah battery bank instead of the 1.032 Ah bank.

Can you sell four of the batteries?

HTH,
Jim / crewzer

BB. · October 2007

Re: Solar pv install

Doctor,

The 4-6 hours per day of sun--is really defined as 4-6 hours of "noon-time" sunlight (average power of sun over the 12 hours it is up). Also depends on having the array installed at the proper angle (either fixed or tracking type array) and no shading (by trees, buildings, electrical lines, etc).

An 1,800 watt array is close to matching your needs--Obviously, in the winter you would have to supplement with a generator or cut back on your energy usage.

You might also wish to keep the "extra batteries" and just fire up the generator/alternate energy source to change once a week or so (with more batteries you can go a bit longer between generator recharging). The AGM batteries you have are more efficient than normal "wet or flooded cell" lead acid batteries. Generally running a generator at 50-80% capacity (to charge the battery bank) is more efficient that running a generator all of the time to power random loads (few lights, tv, fridge on/off cycling, etc.) at 10-20% of generator capacity.

One item you did not mention is if you got the battery temperature probe for the MX 60 charge controller... AGM batteries (and any sealed type lead acid battery) is very sensitive overcharging and accurately monitoring the battery temperature and adjusting the charging voltage by the charge controller (battery voltage changes with battery temperatures) is very important to make sure you have long battery life.

-Bill

DrChatNuff · October 2007

Re: Solar pv install

Sir
i've got a 14kw generator, and i'm well glad you feel the concord batteries are well suitable, i have got a tri-meter 2020 and with the pre-wired powwer panel came the temp. sensor, i also have more batteries but didnt feel i should use them as i thought 16 was enough. with regards to shading the only obstacle might be dust , but with regular sprinkling that should be ok as there arent any trees or power cables in the way, would definitly appreciate any more advice from the forum and cant t-h-a-n-k you all enough

BB. · October 2007

Re: Solar pv install

Doctor,

The biggest issue is that old and new batteries typically don't play well together in one battery bank... The newer batteries will typically take more of the current/load than the older batteries--and hence will quickly degrade until the old and the new batteries will have the same end of life as the original old batteries. Replacing one or two batteries (that died early in life) in a 16 battery bank is probably worth the money--but as more begin to fail of old age (or bad maintenance)--then it is usually time to replace the entire bank.

Also, mixing battery types (AGM/Flooded Cell) or sizes in one battery bank is even a worst practice.

To a degree, you can use switches (or battery isolators for caravans or marine) and flip between an old and a new bank (example; for charging and use), but this depends on how much you want to get into the day to day management of your power system (and how much things cost to obtain and manage locally)...

DrChatNuff · October 2007

Re: Solar pv install

Sir
considering i havent installed the system yet, would you then suggest i use all 20 batteries at once, as thats the number i have,, i initailly wanted to but thought the number would be too many. I never would have joined batteries 12 months after install as i kindda figured it wasnt wise.

BB. · October 2007

Re: Solar pv install

Jim is one of the people here who has batteries and solar... Mine is a Grid Tied solar system (no batteries, just spins my meter backwards). I am approaching it from my engineering background (which was around electronics/computer system design--not batteries).

It would unwise to ignore his suggestions--If you can find a good home for the batteries--it probably would not be a bad idea to cut back on the bank size... Excessively large battery banks require more work to keep up (cabling clean, more space). You are going to need the generator for 1/2 of the year (but maybe only an hour or two per week) to make up for the small(er) solar array.

By the way, usually the best way to use your generator is to run it in the morning to bring the battery bank back up to 90% or so of capacity (bulk charging) and let the solar array recharge the last 5-10% during the sunny part of the day... Saves fuel and keeps your home quieter.

On the other hand, if you already have a generator and all of the cabling with the solar array (and the space to install the batteries)--you can use the generator to charge when you have insufficient sun to power your loads and keep your batteries charged. You don't know the health of these batteries and may find you have some "fallout" anyway--and your battery bank may reduce in size as you weed out any failing batteries. If the batteries are relatively cheap (compared to new batteries in your location), keeping them around (and charged once in a while) as spares (or for other uses) is not a bad idea.

-Bill

DrChatNuff · October 2007

Re: Solar pv install

Apologies for not replying promtly, 'time difference', i wouldn't think of ignoring the advice given, what i thought was that maybe i was using too few batteries, just now i read Sir Jim 's advice about using less batteries and i will 'certainly' take that on board. I came to this forum for advice and that's what i've been given gracefully and for the upt time i cant express my 'gratitude.
Sir Jim i didnt ignore you ,i just didnt see your last statement but thanks again 'Sir'

crewzer · October 2007

Re: Solar pv install

DrChatNuff,

Having a generator changes the equation. The VFX3048 includes a built-in charger rated at 42 ADC max. This will require ~2.8 kW from the generator, so the 14 kW unit will have an easy go.

Added to the array's 25 A, the total charge current available will be ~65 A. This will be comfortably sufficient to charge the 1,032 Ah battery bank while the generator powers the downstream loads separately by sending 230 VAC power through the VFX3048.

The generator and array together should even be able to charge a 20 battery bank (1,290 Ah). However, the array alone won't be able to fully recharge this bank and power day-time loads, so the generator would be required on a regular basis

I still think the 744 Ah (12 batteries) battery bank will offer better overall system balance, but the combination of the PV array and the generator offers a new range of options.

No slight was assumed. Instead, I'm still amazed that we can communicate so easily across oceans, continents, and cultures.

HTH,
Jim / crewzer

DrChatNuff · October 2007

Re: Solar pv install

Hi Sir
i fully understand and will go along with your Advice and funny enough it's more clearer and understanding than when i went on a pv course. Hope fully once my project is up and running it might be the start of a business in Africa, i hope you guys will still be around to help when i fall off course.
Once again Sir thank you and every one else

DrChatNuff · October 2007

Re: Solar pv install

Hi everyone or anyone, its been a while but can anyone advice me whether you can have the grid, battery storage and a generator connected off a two stacked outback power inverter panel [vfx3048/d], so when the grid goes off,battery comes on auto, and you can switch to Gen if/when necessary
Stupid question maybe, but i propbably am.

BB. · October 2007

Re: Solar pv install

Doctor,

I can't answer the Outback question specifically--But, that is not a dumb question at all--that is an ideal setup for people that have utility power that is unreliable and/or have a backup generator but need stable AC power for there home... There are a few different ways of achieving what you want...

However, it is pretty complex and would require you (or your installer) to read and understand the Outback product manuals in detail. The inverter/chargers that support this function have lots of programmable settings you have to scroll through (and probably some optional equipment required too--such as an Outback Hub, or is that a Mate?) that let you program how to use Grid Power, Generator Power, and battery power to achieve what you want. Your solar panels/charger would just connect to your battery bank separately to supply current when the sun is available and based on battery/inverter needs.

From a quick browse of the vFX manual (PDF file), it appears that it should be able to do what you want (connection Utility power to VFX, Connect batteries to VFX, connect AC out to your load, and connect a Generator Start switch)... The VFX has the ability to charge your batteries directly from AC input (programmable settings).

Here is a simplified wiring diagram (PDF file) for a system that might meet your basic requirements. This is the web page with a bunch of different wiring diagrams that you can look through for help too..

You can install a switch in front of the Inverter to allow you to use either Utility Power of Generator power as the AC source (I think--some inverters may not work correctly with Generators that don't have very stable power frequency and voltage).

I will bow out here--I am not an Outback expert--but I am sure others here can tell you what equipment you will need.

-Bill

crewzer · October 2007

Re: Solar pv install

can anyone advice me whether you can have the grid, battery storage and a generator connected off a two stacked outback power inverter panel [vfx3048/d], so when the grid goes off,battery comes on auto, and you can switch to Gen if/when necessary

Yes, this can be done. You'll need to buy a Mate and a Hub. The Hub-4 will accommodate the Mate, both inverters, and the MX controller. As Bill indicated, you'll also need a switch to select between the grid and the generator for 230 VAC in.

Most of the technical and operational information you need is covered in the various manuals. Let us know if you need any specific information.

Regards,
Jim / crewzer

DrChatNuff · October 2007

Re: Solar pv install

Hi sirs
you've come to my rescue again, sorry for the late reply it was 'time difference', i do have both a hub and mate,the downloads were very useful, i'm and encouraged knowing it being possible, i'll read through the manual and probably contact 'outback' , Thanks immensely once again and will continue getting in touch for any assistance. Thank you once more.

crewzer · October 2007

Re: Solar pv install

You can also try the OutBack forum: www.outbackpower.com/forum

See you there!
Jim / crewzer

DrChatNuff · October 2007

Re: Solar pv install

Thank you Sir, i will do that

Solar pv install

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