New to solar need a LOT of advice...

[TheLastFreeRadical]

Good evening ladies and gents! 

I need some advice and a whole lot of no BS as I have been fed this in spades...

A little background...

I am not completely ignorant as to electrical issues, I can install lights, plugs and pull wires to a db board, more by experience than knowledge.

My wife and I live on a farm in the Parys Fochville area, the house has an existing off grid system, specifically a "quarter" system as referred to by the sparky that installed it... (more on this later) I am not completely ignorant, as in, I know when I am out of my depth and need advice. 

The sparky that installed the system, is a car battery salesman (should have been the first clue) and could not give me any specific info or detail about my system, this made me nervous...Next he suggested that panels be wired in series... All of them... Which led me to this forum. 

So get ready for some stupid (probably) questions. 

My current system consists of 3x250w panels, a Sunniva 5kva inverter and 4x12v 180ah (48v) batteries. 

(I am thinking this is an Axpert inverter)

Currently we are running gas stove and geyser, most days the power goes out at 9pm ish, we basically run a 32" tv and dvd player at night 3-4 hours, and a "energy efficient" refrigerator-freezer combo.

My father in law gifted me 3 panels, 310w and now we get to my questions. 

1. The 3x250w (114.3Voc added up) panels I currently have are run in series, to add the 3x310w (136Voc) panels to the system they will also be run in series and added in parallel to the existing panels to stay under the 145Voc of the inverter. Their V isn't the same as the existing 250w panels, will this cause damage? I know it will not be as efficient as running the same V strings, but will it cause damage if they are still under the overall Voc of the inverter?

2. There is no tripswitch or disconnect between the panels and the inverter and it seems to me to be a good idea to have something , what will I need? 

3.We have cut back on our usage of electricity to the point where we can almost live with the system as is (coffee machine became a pour-over Hario v60 boiled on the stove, microwave, what's that? Hair dryer?  Open a window, etc... )  , but it is still a drag to start the generator 3 or 4 times a week for an hour or two,  to have a late evening, do you think I will need more batteries aswell or will my current batteries be enough? (my theory is that the batteries never get fully charged on the current 750w solar (theoretical, probably more like 400w, not even considering the constant draw of the fridge). I switch all lights and tv and dvd player off at 11pm most nights and then it is just the refrigerator and cellphones charging.

 

Thank you for all the replies and for a place where you can ask these questions and not get BS all the time (I have lurked for a bit and read through a couple of the beginner threads). More questions will follow but I thought I would start with the big ones. 

[TheLastFreeRadical]

Sorry for the bad pic, there is a db right next to the inverter. These are the current panels (x3 in series) 

[Guest]

15 minutes ago, TheLastFreeRadical said:

1. The 3x250w (114.3Voc added up) panels I currently have are run in series, to add the 3x310w (136Voc) panels to the system they will also be run in series and added in parallel to the existing panels to stay under the 145Voc of the inverter. Their V isn't the same as the existing 250w panels, will this cause damage? I know it will not be as efficient as running the same V strings, but will it cause damage if they are still under the overall Voc of the inverter?

I would not do that, mix 250w and 310w. You will end up with a 250w array and if there is a weak spot on any of the 250w panels, over time it could become a problem.

If you want to do this, consider, like I, having 200w and 310w panels, put the 310w panels on a separate controller, connected to the same battery bank.

 

18 minutes ago, TheLastFreeRadical said:

2. There is no tripswitch or disconnect between the panels

Breakers (trip switch) that are for solar DC voltages - make sure of this, and / or Anderson Connectors. 

20 minutes ago, TheLastFreeRadical said:

3.We have cut back on our usage of electricity

Aaa, the NEEDS part ... can get quite expensive to drop the needs loads as low as you have, but quite satisfying when you can use stuff and not worry about the batteries or generator.

It is a long journey, and you will get lots of ideas and advice here on PF.

24 minutes ago, TheLastFreeRadical said:

(my theory is that the batteries never get fully charged on the current 750w solar (theoretical, probably more like 400w, not even considering the constant draw of the fridge)

What batteries do you have?
What is your watts, average and peak?
How many hours do you want to power things?

[TheLastFreeRadical]

I currently have 4x180ah batteries (deep cycle although I am not sure about make /model) in series to make up 48v. My current draw is usally 150w to 250w according to the inverter in the evening. This includes the tv, dvd player,  refrigerator and two cell phone chargers)   Normally there are nothing else running, not even lights.

[___]

50 minutes ago, TheLastFreeRadical said:

Their V isn't the same as the existing 250w panels, will this cause damage?

It probably won't cause damage, but you will lose power. It's difficult to say how much.

If you look at the power vs voltage curve of a PV panel, you'll see that it peaks at a certain point and then drops off a cliff. The Vmp (Voltage, max power) is on the peak of this cliff.

Now if you run panels with different voltages in parallel, the possibility exist that the one string might pull the voltage up, operating the other one at a voltage that is too high for it to make any power. This should not be dangerous, as the kind of voltage you have to make before you push them into reverse breakdown is usually about an order higher, but still: If this happens you essentially lose the entire 250W string.

On the other hand, it is also possible that the lower-voltage string will be the dominant factor and that it will pull the voltage down. So instead of doing 8.5A at 36V (typical for a 310W panel), you'd be doing 8.5A at 30V, so you will be derating your panels to 250W panels.

In practice, the MPPT hunts up and down until it finds a point where the maximum overall power is made. I expect the dominant factor to be the 250W panels (they will drop off too sharply if you go too high), so the effect should be that the 310W panels are pulled down to a lower voltage causing them to operate like 250W panels.

However... the question remains whether you should do it. My instinct remains to put them on a separate mppt, but this is a 48V system, and the MPPT I would recommend (a BlueSolar 150/35) costs around 4.5k, around the price of two panels. So 4.5k and you have peace of mind... or not... difficult to answer.

[TheLastFreeRadical]

My long term (very long term, wife's contract just got canceled) idea is to add two banks of 4x200ah batteries (replacing the 180ah batts) and get 3 banks of 3x310w panels (9 total) which  should be overkill, but for now I have ve to make do with what I have. 

[TheLastFreeRadical]

This was my thinking too, either it will work at 250w or it will blow up 

 

 

Edit: 310w V is 36.9v vs 250w V of 30.38v, 0.3a difference

[___]

23 minutes ago, TheLastFreeRadical said:

Edit: 310w V is 36.9v vs 250w V of 30.38v, 0.3a difference

Rule of thumb. Open circuit a cell makes around 0.6V. At Vmp they make around 0.5V. Of course this isn't exact and YMMV, but its close enough when you're spitballing the numbers. The >=300 modules are usually 72-cell modules. The <265W modules are usually 60-cell modules. Current is usually around 8 amps.

You could do some other unorthodox things too. Because the current is within 0.3A, you could put a 250W module in series with a 310W module to form a larger combination of similar cells. You could futher mix them up, 2 x 250W in series with a 310W module (making a larger 192 cell string) and for the other side, 2 x 310W module win series with a 250W module (a 204-cell string). Now there's a mere 12 cells disparity between the strings, or 6V at max power. Compared to 18V the other way. The total loss is now around 50W instead of 150W.

Of course, I used the word unorthodox for a reason... :-)

[Guest]

14 hours ago, TheLastFreeRadical said:

... 4x200ah batteries (replacing the 180ah batts) ...

Let us know what makes and model batteries you have.

Before you plan to buy more, ask here, most of use have been a around the block on batteries, and what not to buy. 

[DeepBass9]

Have a look here, this is my experience : 

 

[TheLastFreeRadical]

I will probably have some time this weekend to get my new panels up, and then it will be seen if it will work like this, thanks for the replies guys! 

[DeepBass9]

On 1/30/2018 at 10:03 PM, TheLastFreeRadical said:

Currently we are running gas stove and geyser, most days the power goes out at 9pm ish, we basically run a 32" tv and dvd player at night 3-4 hours, and a "energy efficient" refrigerator-freezer combo.

I run my fridge and freezer on a timer so they are off overnight when they are not opened. I try to keep them full (even if it is just waterbottles) to give a bit more thermal mass to prevent the temperature from rising too much

[___]

20 hours ago, The Terrible Triplett said:

Let us know what makes and model batteries you have.

Before you plan to buy more, ask here, most of use have been a around the block on batteries, and what not to buy. 

What TTT says here is important. To my mind there is very little sense in upgrading from 180ah to 200ah. A lot of money for just 10% more. The only reason to do it would be if you had particularly crappy batteries and you were moving to something better, and even then I'd rather run the crappy ones into the ground first and get at least some value from them.

We've had this discussion before. A decent set of 400Ah batteries (or thereabouts), which is where you want to go if 200Ah isn't enough, will set you back 50k. You can get Pylontech lithiums for that price now, so for just about anyone who needs more than 200Ah nowadays the answer is to go Lithium.

[TheLastFreeRadical]

5 hours ago, plonkster said:

... To my mind there is very little sense in upgrading from 180ah to 200ah. A lot of money for just 10% more.... 

The battery upgrade will probably be 5 or 8 years down the line when the 180ah's get old. The 180's has no names or ratings on them, I am not expecting them to be good quality or to last very long, hopefully by then the prices on batts/technology will be better. 

[Chris Hobson]

33 minutes ago, TheLastFreeRadical said:

The battery upgrade will probably be 5 or 8 years down the line when the 180ah's get old. 

With no name or ratings on them 5-8 years is going to concertina into 1 year. Start budgeting for it now.

[TheLastFreeRadical]

That is very true. My next step will be a wind generator (we are in a little valley where 9/10 it is very windy, and then after that will be new batteries. If these ones go out before then, I guess we'll be having early evening, every evening. 

[Chris Hobson]

22 minutes ago, TheLastFreeRadical said:

My next step will be a wind generator (we are in a little valley where 9/10 it is very windy, 

I am not saying you will not benefit from a wind turbine but make sure you research it thoroughly. I live in a narrow valley and every evening we get a katabatic winds but so far my wind turbine project has stalled due to there being two problems with most commercial wind turbines

1.  They only start producing any real power once the wind is strong enough to blow the washing over the fence into the neighbour's yard. 
2. You can install a sizeable solar farm for the cost of a wind turbine. There are some cheap ones and they may be good I just don't know.

If you decide to go DIY I have a myriad of plans and video etc.

 

[TheLastFreeRadical]

I've just seen the prices on decent ones, wow . 

 

Thats 4 new batteries right there. Add a separate controller and its 6 more panels. 

[Chris Hobson]

8 minutes ago, TheLastFreeRadical said:

Thats 4 new batteries right there. Add a separate controller and its 6 more panels. 

That's the problem. You can import N48 neodymium magnets for under R2k and the rest is fibreglass and enameled wire and bearings etc. I think one could build something decent in the R7-10k range.

[___]

20 hours ago, TheLastFreeRadical said:

The 180's has no names or ratings on them

That sounds to me like the kind of batteries we commonly use for backup at telecoms stations. Looks like this:

They are usually better than the 105Ah rubbish used by 4x4/caravan weekenders :-)

 

[TheLastFreeRadical]

I'll see if I can upload a pic this evening, mine looks more like a really big car battery (black with a yellow top if i am not mistaken)