14 hours ago, Bush Man said:

Would it then make sense to add additional panels if the batteries can only use 900W of the existing 1500W panels?

Probably not, if you base everything on a random reading you got one morning a few months ago and totally disregard all the posts above. Who knows, you probably had 3 days of full sun prior to that the pump never ran during that time. Your batteries might have been close to fully charged at that time? 

We are all shooting from the hip here, because we don't have a load graph showing your load requirements over a few days. You don't have a BMV to get accurate State of Charge data and also probably no battery balancers either. Everything is based on assumptions that could be totally out of line. My calculations show, you do not have enough panels to charge your batteries, based on a few assumptions (once again), not facts or data. 

You cannot manage what you don't measure. Looking at what your load is for 10 minutes during a sunny morning 2-3 months ago is not measuring. Install WatchPower on a laptop and plug your inverter into the laptop and let it run for 3 days. Then post all the graphs. Based on the graphs we can then help you and give you advice. 

2 hours ago, Bush Man said:

 

On a typical sunny day last year while charging the batteries mid morning I almost never saw the Axpert PV Input reading exceed 900 Watts, despite the 1500 odd watt panel array.  

Having looked at my own data for a year there are 20 days where we exceeded 95% of capacity. A quick look at PV Ouput show that getting close to 100% production off your panels is the exception rather than the rule. Mid morning I would not expect more than about 70% of production but that would translate to nearly 1100W on your system. So we are still 200W short.

1 hour ago, Bush Man said:

Would it then make sense to add additional panels if the batteries can only use 900W of the existing 1500W panels?

Your batteries whilst in bulk phase of charging could take 100% of your panel's production.

What is program 31 set to? It should be enabled. That may account for your limited PV production.

You mention that the 800W pump is only used when another solar pump does not supply sufficient water. 800W is a doddle for a 5kVA Axpert but I am wondering whether use during cloudy weather and then insufficient charge to replenish your batteries has not compromised your battery bank.

Having looked at Omnipower datasheets it would appear your bulk charge should be between 57.6V and 58.8V at 25^oC and float at 54.0V. Changing your bulk setting may solve your problem. I would charge at the lower end (i.e. 57.6V) as this is over gassing voltage and  although VRLA batteries generally can tolerate 1psi ~ 6.8 kPa  before they vent one does not want to lose electrolyte unnecessarily. 

Before we add a string - charge your batteries with a gennie and check them with a voltmeter to see that they are still performing well. Your local battery supplier should have a  battery tester you could borrow.

 

20 minutes ago, The Terrible Triplett said:

The 5.5 is the average good sunlight hours in South Africa over 1 year. 

"Good sunlight hours" do you multiply that with 100% of array capacity?  80% 75%? 

 

Of the 72 South African PV systems reporting to PV Output only one has an efficiency over 5.5kWh/kW and the average is somewhere between 3 and 3.5 kWh/kW. 

 

Addition: text in bold

Concur. On my 1800W array I was getting 7 or 8kWh in summer, and sometimes 9, and 6 or 7 kWh in winter.

7 hours ago, Bush Man said:

Before I go there, however, I would like to see if I can't remove the potential culprit from the equation, i.e the pressure pump

I use a pressure pump permanently here as I don't have a tank high enough , yet , and the one I use is a 360 w pump works perfectly the only thing is you must make sure you don't have any leaks on it. 

Have a look at this thread:

Regards  

Paul

5 hours ago, plonkster said:

I stand to be corrected, but given our long conversation about balance in battery banks, I suspect that even a smallish load could be detrimental to the battery it is connected to. During charging it acts as a bypass shunt, and during discharge it means your one battery is always a couple of watt-hour lower than the other one in the morning. I don't know, this might be nothing to worry about, but I would be concerned about how it adds up over time. If you have a balancer on there as well it might not matter, the balancer should cancel out some of that during the day, but my gut feeling is still that it would be better to use a DC-DC buck converter to step it down to 12V. Once you have that it also opens up other avenues for low-power devices, such as 12V 5W LED downlights :-)

I can concur. My dad used todo this one is one 24V system and one of the batteries failed, prematurely last year. Since then I put a 24V-12V buck booster in to run his LED lights from a balanced battery bank. Simple rule: don't do it. Rather balance your load, as well as your charge across the batteries as evenly as possible. 

1 hour ago, Chris Hobson said:

Of the 72 South African PV systems reporting to PV Output only one has an efficiency over 5.5kWh/kW and the average is somewhere between 3 and 3.5 kWh/kW. 

I agree @Chris Hobson. I have a dual axis tracker and on a good day I can hammer the PV to an efficiency of 6.89 kWh/kW, but on average for a month, I can only achieve 3.95 kWh/kW. On a bad day like today, starting off with overcast weather and rain late afternoon, I can only achieve 2.46 kWh/kW. I ended up at 90% SOC when the sun set, constantly draining my batteries throughout the day. I am in the fortunate position that I can go back to grid to charge my batteries. With no grid, I would probably end up at about 70% SOC tomorrow morning and if we have another day like today, would end up tomorrow evening with a SOC between 50 and 60%.  

1 hour ago, Chris Hobson said:

Of the 72 South African PV systems reporting to PV Output only one has an efficiency over 5.5kWh/kW and the average is somewhere between 3 and 3.5 kWh/kW. 

I did a quick calculation on mine: 3.5kwh/kwp installed over the last 366 days. BUT... and I have to stress this, most of this was running the inverter in what I sometimes call "axpert mode", that is either full on- or off-grid. Just looking at February, month-on-month, I see almost a 20% improvement since reconfiguring the inverter in ESS aka hybrid mode, so that's 4.2 vs 3.5 for last year. So I'd say that the rather low 3-3.5 might be related to the popularity of the cheaper hardware.

Still, you guys have a point. 5.5 is somewhat on the high side. I get up to 5.8 in summer, but on average over the whole year it is definitely lower.

1 hour ago, plonkster said:

So I'd say that the rather low 3-3.5 might be related to the popularity of the cheaper hardware.

I don't think it has got anything to do with what you paid for the inverter, but rather what type of inverter. My inverters will do whatever load I require throughout the day. Any deficit will come from the batteries during poor/overcast conditions. Although I am able to track the sun 100% throughout the day, if my load is only 1000 watts, that is all they will do and I will end up with an efficiency of maybe 3 kWh/kW. Not because what I paid for them, but rather what my load requirements were for the day. If I installed a grid-tie inverter, I can get 4000 watts out of my 3780 watt panels, peaking at 5125 watts at times from 7h30 to 17h30, irrespective of my load and I will end up with an efficiency of 7 kWh/kW. I can achieve exacttly the same with the cheap inverters, as long as I create enough load throughout the day with aircons and heat pumps to ensure I run the panels flat out throughout the day. Once the long haired power guzzler wakes up, I pretty much run flat out in any case, . 

Don's experience and my experience is very similar. I can manipulate my loads to achieve a almost perfect bell-curve. The top 10 systems are all GTIs barring one anomalous Axpert at position 4 and one small Axpert at position 10. Position 11 is a very ordinary 4.2kWh/kW. 

3 hours ago, Chris Hobson said:

multiply that with 100% of array capacity?  80% 75%? 

Can tweak it for different hours in winter versus summer so yes, if one wants, it can go down to the closest T.

Added in the calcs are losses of wires, batt efficiency, average batt temp, DOD, batt ages etc. 

So to answer the question, if one REALLY wants to get it as close as damn, then fill in the numbers. ;-) 

Here on the forum I am giving a general ball park that gives an picture of not too many roses, taking the numbers per month will add more thorns, but not too many I hope.

38 minutes ago, Chris Hobson said:

I can manipulate my loads to achieve a almost perfect bell-curve.

I agree @Chris Hobson, I don't have the time to sit here every day doing the job of a PLC switching things on and off to keep the load at a maximum and drawing power from my batteries to a minimum. I let the system run its course. If I end up with an efficiency of 3.0 kWh/kW, tough luck, that is what it is.

2 hours ago, Don said:

I don't think it has got anything to do with what you paid for the inverter, but rather what type of inverter.

Sure. Except hybrids generally cost more than non-hybrids, which is what I was getting at. The popularity of the cheaper non-hybrid units will push this number down a bit.Of course you can force a perfect bell curve -- I used to do the same thing -- but my new results suggest that on average I was getting 20% less out of the sun even though I put some effort into it.

It's still way too early to tell though. Today I was a good 15% less than yesterday. Why? Cause we had a meeting at school early morning and the normal morning loads got pushed later in the day, so the batteries filled up earlier and since we had more PV than load some of it was lost. No when I was running non-hybrid, a lost a LOT more like this, and I had to cycle my batteries much more to "make space" for it.

Aaaanyway, my point is just I'm not really buying the low 3.5kwh/kwp number. I think it should be over 4 with better equipment. Still a far cry from 5.5 though.

38 minutes ago, plonkster said:

I'm not really buying the low 3.5kwh/kwp number. I think it should be over 4 with better equipment. Still a far cry from 5.5 though

I agree, that is why I got the Axperts  Efficiency does not come from the quality of the product, it depends on what the sky looks like on the day.  

1 hour ago, plonkster said:

... had more PV than load some of it was lost.

We should not look at it as lost, it is not lost, just not used.

If you are not there to use the power you are still saving compared to paying Eskom, not?

And if you are out till late or away on holiday, the load is powered for much later and I would hazard an assumption, comparing my setup, load also runs even later into the evening off batteries before set SOC kicks in.

So we save a bit there too.

Flip side to the more PV than load in summer, is winter. More load than PV especially in Cpt with winter AND rain.

Don't fret the small stuff say I.

5 hours ago, The Terrible Triplett said:

We should not look at it as lost, it is not lost, just not used.

If you are not there to use the power you are still saving compared to paying Eskom, not?

And if you are out till late or away on holiday, the load is powered for much later and I would hazard an assumption, comparing my setup, load also runs even later into the evening off batteries before set SOC kicks in.

So we save a bit there too.

Flip side to the more PV than load in summer, is winter. More load than PV especially in Cpt with winter AND rain.

Don't fret the small stuff say I.

It depends on how much cash you have to throw at this "money savings project".  It doesn't help much to save a couple bucks at the expense of say 1KW PV, which cost roughly R10,000! In most cases, most people won't recoup that extra R10,000 in their entire solar usage lifespan. But that also depends on the size of the system. 

Someone else, on the other hand may not see it like that and buy as much as he could + some

I don't want to take this to the fight club but if Mike can only manage 5.4 kWh/kW then us mere mortals are going to struggle. Plonky I hear you with regard to Axperts but there is a fair sprinkling of SMAs, Sunnyboys and Victrons in the lower echelons too. If you look at the data the median ( I am not going to work out the average) is about 2.5kWh/kW so I have adjusted up already to take the Axpert factor into account.  Getting your system efficient takes a bit of homework and planning and Joe average just does not do it. We tend to remember the days when we produce over 6kWh/kW and the days when we produce a whole lot less tend to get lost in the day to day routine. 

8 hours ago, The Terrible Triplett said:

We should not look at it as lost, it is not lost, just not used.

It's an opportunity lost. That load of washing could have been free, but because I didn't do it at the time, and didn't have anywhere to store it, the opportunity is now lost and it now costs me money. It's not a biggie. But we're moving the goal posts, we're not arguing that here :-)

The argument is that 1) 5.5kwh/kwp is too high, most people never make that, and my counter argument is that 2) the proposed 3.5kwh/kwp is too low again, with proper equipment and good usage patterns you should make 4 or more.

I think one thing is becoming clear though, and that is that there is a lot more to it than a simple multiplication sum. Part of the reason I get such a healthy return with my relatively small array is precisely that by all standards my array is undersized. At its peak it makes 850w most days (50w short of rating), whereas my daytime consumption is easily 400W constant because the washing machine and tumble dryer runs every day. So even with a low DoD on the battery (95%) the slight surplus I have is just enough to recharge, I have somewhere to put that energy, so my array can run flat-out almost every day with minimal battery discharge.

BUT... soon I will upgrade my array and double the size. And guess what? Then my number is going to plummet and it might well be closer to 3.5kwh/kwp. This will of course irritate me no end and all sorts of plans will be devised to make better use of the opportunity and push the number up. Point remains, that number we use is meant to help someone ESTIMATE the size of their array, and this is usually important because people are cash-strapped and don't want to oversize that thing. Using 5.5 will tend to undersize the array, and using 3.5 will tend to oversize it.

For someone in the city who doesn't have that much space/cash, you go with 5. It will likely be over-optimistic, but he has the grid to help him. For someone who is off-grid you'll go with 3, cause the consequences of getting it wrong is that much more expensive (starting the Diesel gennie).

I'm rapidly coming to the conclusion that PV is now so cheap (compared to battery storage) that multiple oversized arrays pointing in slightly different directions (for a better spread over the day) might just save so much on battery storage that it's worth it, even if your kwh/kwp number sucks.

:-)

8 hours ago, The Terrible Triplett said:

We should not look at it as lost, it is not lost, just not used.

I think its more about efficiency.  Like not servicing the old Mazda and having higher and higher fuel usage... makes me irritable  

BUT:  I plan to have more strings facing NORTH, EAST and WEST. Get as much SUN TIME and hopefully "extend" the time I don't use batteries.  

8 minutes ago, SolarNoob said:

I hear that the differences could be due to the inverters used, but is that assuming that the inverters are all using the same panels?

Any idea what I could expect from a 3KW thin film array?

As PLonky has alluded to it all about loads. So if you match your loads  I would say 16-17 kWh. If you are in the Western Cape higher in summer and lower in winter and if you are north then probably a more balanced seasonal variation. This is assuming you go with the recommended tilt for your latitude. One can change you tilt to  favour either summer of winter. I have a 4 season tilt regime (easy to implement on my ground mounted panels) and I have a fairly even seasonal solar production. This figure is a guesstimate as there are a myriad of other factors influencing solar production. Thin film has surpassed poly-crystalline in efficiency but seem to age faster.

37 minutes ago, plonkster said:

At its peak it makes 850w most days (50w short of rating) ...

Plus one on that. Max out the array. Now I want to go bigger in winter and in summer ... so each swing of season the internal argument starts. 

Conclusion I came to? It will drive you stark raving mad over time. Sort out the base load that eats at your pocket, then slowly increase for as I have made it clear in my head, things like a microwave, dishwasher, washing machine are NOT savings, they "increases" system costs ito bigger inverters. Lights, TV, computers stuff bla bla bla that runs hours on end, now that is a saving.

 

37 minutes ago, plonkster said:

This will of course irritate me no end

Jip, stark raving mad the OCD will drive us.

 

37 minutes ago, plonkster said:

... that number we use is meant to help someone ESTIMATE the size of their array

Amen, it is aimed at JUST batteries and the recharging of JUST them. Safety I add is the 1 days backup to say 20% DOD so effectively it is 10% per day over 2 full days.

Will adjust the next calcs to 4.5 hours instead of 5.5. Would that satisfy most?

 

26 minutes ago, SolarNoob said:

I hear that the differences could be due to the inverters used,

There are a host of factors affecting the results. Starts at how the panels are mounted, the wires ... the entire system and then how it is optimally used.

 

28 minutes ago, Mark said:

Like not servicing the old Mazda and having higher and higher fuel usage

So you service it regularly, fuel usage is down, so are we now going to drive more? (cwl)

Nope, we are going to use the Mazda in the most efficient way possible.

 

Don't fret the small stuff. Baseload is the one that eats your pocket. Keep that powered 24/7/365 ... that is a real challenge. 

Which by the way, I did!!! Them UPS batts I got last year for free, 4 x 100ah sealed lead acids, is running purring off-grid a few things, never going below 80% DOD. The 2 x 200w panels charge them with ease. 24v 385va inverter never straining. Set and forget ... till "someone" wants to touch things. I sit on my hands now.

On the main system, 4xT105RE's, the fridge and freezer is off-grid. SOC never goes below 80%. And it if does? Tough. System can handle it.

Daily loads on main system are set to go back to Eskom on a variable SOC setting, between summer and winter. Again, set and forget. ALL I need is the 7 day SOC. For all the panels can produce, is used in the day between load and charging.

But it took years to get MY balance.

3 minutes ago, Chris Hobson said:

One can change you tilt to  favour either summer of winter.

I tested that on my 2 x 200w panels. Manually adjustable. Makes a HUGE difference in winter.

1 hour ago, The Terrible Triplett said:

Which by the way, I did!!! Them UPS batts I got last year for free, 4 x 100ah sealed lead acids......

Heresy! TTT got something other than Trojans..... wait he got given them..... ah he is human after all - willing to subvert his principles on the odd occasion.

1 hour ago, Chris Hobson said:

... - willing to subvert his principles on the odd occasion.

With a SMILE on my face yes!

Let me tell you another secret. Lets really rock this little boat properly seeing the door was cracked open ...

Had them for a few months after they came out after years in a UPS where 2 of the 6 batts failed. So obviously they where whatever.

I hammered them for a few weeks with a equalizing charge daily. I have a real controller see. A Victron MPPT100/30 controller.

Then I got, accidentally, a new BMV balancer.

Installed it expecting the worst.

For weeks a few times a day, at certain volts from the panels, balancer clicks on, checks, goes off. To repeat again.

Never once did it do anything. So I horse traded the balancer for a tablet with Hein. 

How is that possible you may ask?

Well, easy, when I got them, as I said, I equalized them. Today it is set to auto equalise every 4 weeks ... I think. Must check again. Set and forget you see.

For what we spend on battery banks, do we really want to argue the value of a good controller? O wait, we don't, we are stuck with Chinese imports and have to make a plan hoping it is the best one in the long run. (cwl)

Drop mic (that mic that was broken the previous 2 times) ... walking away from the balancers, Victron sorts it out one time.

Hi TTT

I assume this is the bank that with the BMV 600. Do me a favour on a Sunday or on a day you not flat out busy, measure your battery voltages  at about 94-95% SOC and again at about 96% SOC. I would be very interested in the voltages.