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Solar System for farm.


Chris Hobson
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Hi I am in the process of installing a smaller PV system on the farm and would like to bounce ideas/problems off the members of this forum.

 

Previously I have looked at complete systems that would give me complete autonomy for 3 to 4 days and the quotes run into several 100k and are basically unaffordable. Currently I do have a 10 KVA diesel generator which supplies the farm. It is 3 phase which is problematic in that you are limited to 15A per phase. I have tried to reconfigure it as a single phase as per wiring diagram on the inside of the cover but the engine cannot cope with the load. 

 

I have revisited the problem and changed my approach. Most of the heavy domestic consumption is during the day (washing, ironing dishwasher etc.) What if I installed a fairly large PV system to power this domestic consumption during the day and still run the generator at night for a couple of hours providing my home and my staff with light etc. This saves on batteries as there is almost no consumption overnight.

 

My current thinking is 2KW of panels (another 1KW to be added later) - 4 x 12V 260Ah batteries and an Imeon 3.6 inverter. The Imeon is expensive but makes absolute sense in my situation. Occasionally we entertain and now you would like to use lots of domestic appliances. The Imeon can give you up to 6KW by combining PV,  battery and generator output. There are other inverters that can do the same thing for less money but I worry about build quality.

 

The initial installation should be fine with 8 panels connected in series. However when I add the extra 1 KW I might run into problems. The Imeon has a 510V upper limit and with our lowest temperatures going down to about -8 degrees C in winter and using VOC and temperature coefficient variation I come to a limit of 11.97 panels - not quite the 12 panels I was hoping for. If I split the 12 panels into 2 strings in summer we again run into minimum V problems. Any ideas?

 

The batteries are perhaps a bit light for the system but there is no real load overnight baring a Freezer that draws 66W and a fridge that I hope will have similar  consumption. If I find that the batteries fail after a couple of years perhaps Musk's offering will have hit our shores by then and I would invest in them. The price of batteries kill PV systems.

 

Any input from members is welcome.

 

Chris

 

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Hi Chris

 

Everything sounds do-able.  Just one suggestion from my side: Rather start with 3KW instead of starting with 2KW and adding 1KW later. Keep in mind that even with 3KW panels you would not neccessarily get 3KW unless the irradiance is 1000W/m2 and the sunlight is hitting the panels directly (not at an angle) - most of the time you will get much less than 3KW from panels totalling 3KW.

 

Working on 3KW (12 x 250W panels) all connected in series (1 string), their MPP voltage is around 30V per panel x 12 which gives you 360V. The MPPT voltage range on the Imeon is between 120V and 450V. The MPP amps is around 8 amps which would is also lower than the Imeon's 18A limit. Open circuit voltage for the string would be about 12 x 38V => 456V which is also below the limit of 510V - thus according to me it should work perfectly.

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Hi Superdiy

 

The start of 2KW is definitely budget constrained the extra 1KW should be up before Xmas. I am designing a frame for 12 panels and will add as soon as there is R10 000 without a creditor's name on it.

 

VoC for the panels is 38.4 V. This is measured at 20 oC. Solar panels become more efficient the cooler they are. There is a 0.148 V increase per degree. So now your VOC at -10 oC is 42.84.V  multiplied by 12 gives you 514V. You chaps along the coast do not really have to worry too much but inland we do as this scenario demonstrates.

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Hi Superdiy

 

Thank-you - that is the information I was needing. I did not know how much of a safety margin there is in these calculations. I am putting in a Santon 1000V DC Isolator and could just switch the PV's off at night if I think we are going to have a very cold night and measure the DCV in the morning. From experience in the ratings of various other components I realise there is some leeway. However with a R30 000 inverter I just wanted to be sure.

 

I am going to mount the PVs on a steel frame on the southern edge of a old cement tennis court facing north. Plan to build the frame so that I can alter the angle summer/ winter/ equinox seasons.  The internal angle I get from various solar calculators is 8o, 56-58o and 29.5-32respectively. Our farm is at 32oS What is the general increase in power by doing this over a fixed installation at 30o for instance?

 

I have been supplied 6 A Solar fuses. I have 8 (12 by Xmas) Yingli 250W panels with a Current at PMax of 8.24 A and a short circuit current of 8.79 A. Plan to connect the panels in series. Are the 6A fuses correct or should I be getting fuses of a higher rating?

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Visit www.solarpaneltilt.com to get the formulas to calculate the optimum tilts for each season.

 

6A fuses will not work - they will blow all the time. I would suggest at least 12A fuses - from the "Littlefuse Fuse Selection Guide": NORMAL OPERATING CURRENT: The current rating of a fuse is typically derated 25% for operation at 25

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Normal crimping tool works just fine - it might take you a few seconds longer per crimp, but for a once-off DIY job I guess a minute or two on the total job is not too bad.  I crimped and then soldered mine for better reliability.

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  • 2 weeks later...

I have been advised that an Axpert 5kVA would better suit my needs so now my system would be Axpert inverter, 12 250W Yingli panels in 4 strings of 3 panels each and 4 12V 260Ah batteries. Just one question if the V exceeds the max MPPT voltage of 115V but is less than the Max VOC of the inverter (145V) how does the system behave?

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I am travelling to Port Elizabeth (3 hours away) on Monday to collect an Axpert 5kVA inverter and 4 12V 260Ah batteries and the last of the panels.I have had to change my design to accommodate the Axpert's lower maximum for the PV Array. I would like to ask experienced solar techs to check my planned installation and see if there are any errors or omissions.

 

I will now have 12 Yingli 250W panels in 4 strings of 3 connected with 4mm solar cable and fused with 8 x12A solar fuses. This will run to a combiner box and a 16mm cable will run from the box into the dwelling (17m away)  connected to  PV Lightening protector and 2x 40A solar fuses. Finally a DC Isolator and on into the inverter.

 

The batteries will be less than 2m from the inverter and 25mm cabling used 2 pole battery disconnect with 100A fuses. this is a little less than the 120A maximum but I will only be able to charge up to 10A with my current generator. The cabling will handle 120A but the max A is probably closer 80A hence the fuse at 100A. if my generator is upgraded I just need to increase the size of the fuses.

 

On the AC input lightening protectors and 16A breaker and power on lamp?.  On the AC output 25A breaker power on lamp? and on to DB. The generator will be permanently connected to the inverter input. So inverter output replaces generator output on the DB board.

 

Thank-you

Chris

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Hi Chris,

 

Have a fuse for each PV string in the solar combiner. This makes it easy in the field to see if each string is performing or not.

You can install the lightening surge arrestors in the combiner as well, if you have space.

 

I see the 5kva Axpert can manage 3000w of PV, so you doing very well there.

As PV efficiency is very poor, perhaps look at adding a 5th or perhaps 6th string to you system. Only do this if you find yourself running out of battery power early in the day.

Yes, it will be a bit larger than what the Axpert can handle, but at least you then know you will get more power out on bad solar days.

 

Everything else sounds fine. Good luck!!!

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Hi Chris

 

I think you're doing extremely well. Congratulations on your planning, and strongs with our build.

 

Wetkit, what will the practical implication be of using more PV with the Axpert 5kVA than the prescribed 3000W? (Eg. Chris's anticipated 15 x 250W panels).

 

One tends to think that the inverter will not "know" it's more than 3000W, but that could be a risky asumption.

 

My plan is to do something similar.

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Lets say you have installed 3000W of PV. That 3000W is rated at 1000W/m2 sun shine and at 25C.

Now say it is a bit cloudy, you will be looking at 500W/m2, thus only 1500W.

 

Now say you installed 4000W PV. During that cloud you will now be looking at 2000W.

With full sun you might have 4000W available, but only 3000W can be used.

Yes, it is a bit of an overkill, but if you running completely off-grid that extra 500W during cloudy periods can make a huge diffrence.

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Hi DB9

 

I have a Lorenz pump with 1.2 kW of panels that delivers roughly 2500l an hour and we have a Southern Cross windmill that pumps a head of 180m and about 2km which delivers stock water on top of the mountain. Plan to run normal household appliances. We have a gas electric stove which draws 2000w. If in summer we generate enough PV power I will bake bread in it. Generator to power two backup pumps.

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Chris, rather lose the electric oven and get a gas one. The costs of the panels to drive the oven will be way more than the cost of a gas oven. The wife says gas bakes better than electric in any case.

 

How much did your pump cost you? I have a borehole I would like to irrigate from and I am torn between buying a second hand wind pump and reconditioning it, or buying a bigger solar pump. I have about 1.5Ha of (currently) dryland lucerne that could do with some help!

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Windmills are expensive. A new mill (8ft) is just under R30 000. You can pick up second one for under R10k but the re-conditioning and erection is going to cost about another R10k. Then you sit with 19th century technology and if something goes wrong (depending on the depth you need a team (3-4 strong guys) to raise the piping. 

 

The Lorenz installation cost R60k at the time but panels are considerably cheaper now. Several chaps are using PVs to irrigate now.

 

In summer we are going to be producing far more energy than we need (perhaps 3 times) and my wife says electric bakes better than gas (my wife says your wife says.....). You don't have to put up with my grumpy wife so the electric stove stays to be run on gennie most of the time. They say 1st step reduce you consumption but my wife put a line through Step 1  :P .

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I was hoping to buy a wind pump really cheap, or 2 even to make one that works. I have one already (8ft Climax) which is not too difficult to pull the rods on and the hole I want to irrigate from has shallow water.

 

If I leave my place, before I have driven to the nearest shop I can count 5 wind pumps doing nothing in various states or repair (or disrepair). I'm sure pick those up for cheap and get one working for much less than the 30-40K+ a new solar pump would cost?

 

Don't knock the old tech too much, The stuff was designed to work off grid and last for years. Another big selling point for the wind pump is that they don't get stolen, unlike pumps, cables and solar panels which are in great demand.

 

Have a look at my thread under Installations, I am recently off grid and surviving (this is a solar powered post....  :D )

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Windmills are elegant machines but they do have some drawbacks.

 

1)The number of people who can cast a good white metal bearing are becoming fewer and fewer. 

2) You turn rotary motion into linear motion (albeit in a very innnovative way) this tend to put pressure on certain parts.

3) They tend to fail mechanically in a howling gale (even with the brake on) rather than in a light breeze and under those circumstances they tend to self- destruct with bits of Pitman arms or crosshead rollers getting between the gears. The only mill I know of whose brake works properly is a Beatty Pumper imported from Canada in the 1930s. The rest of the mill is so poorly designed that I would not want one even as a gift.

4) You have a rod passing through a pipe and the associated wear and tear is something that you have to avoid at all costs. Pipe protectors or the Supermax cylinder where the water comes up in a separate pipe is what I use. We have 12 mills on the farm and at the moment there is only 1 out of order.

 

In terms of irrigation any modern system is going to need pressure so you going to need a pump anyway. There is a farm neighbouring my brother's farm that has about 2 ha of irrigation that is flood irrigated but there are I think 13 windmills dedicated to that patch of lucerne and invariably there are 1 or 2 mills out of order.

 

Theft is not something I even considered (I am 10 km from my nearest neighbour) and yes I have never heard of a mill been stolen so that would be an advantage. My neighbour has lost some panels near roads etc. 

 

An option would be to get another 8/1 or  6/1 and drive a mono (I don't really like them).That would pressurise your system and you could use drag lines or permaset or in fact anything you chose.

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