Mostly 12v system, but...

[Medianige]

Hi

First question, please be gentle with me! Haha I'm planning on moving off grid and have worked out my energy needs, though before my partner moves in in a year or so, I will field test and see how close I am. We will live a very simple life and cook with LPG, use it for showering etc. Electricity will be needed for:

Lights (12v, 3 or 4.5w LED)
Washing machine, coffee machine
iMac, MacBook, satellite TV
Charging iPad and iPhone for Internet

I am going with 3 x 250w solar panels and probably either 6 or 8 110ah Lucas batteries. I want to set the system up so that the lights and chargers are running from 4 batteries on a simple 12v wiring loop but the washing machine, coffee machine and TV (and box) run on 220v. There will be a total of 35 LEDs on the plan, but obviously they won't all be on at the same time (if they were, between 100w - 200w)

I guess I can have the panels wired to a junction box, then from here have two charge controllers, one to supply each of the banks. One of the banks would then need an inverter to supply the major power items (coffee only once a day, washing machine a couple of times a week). I also want to somehow set up the system so that when float is reached (in winter) the extra power would power a small 12v heater to raise the temperature a little (and therefore cut down on wood burning), and in summer it will power a small 12v fridge.

For the batteries, the 12v system will be wired in parallel to keep the volts at 12. Don't know about the other 'side'? Series?

What will the issues be? Is there a problem with my proposed system I'm not seeing?

[Naptown]

If you haven't bought anything yet don't.

For your set up I would suggest the following
Buy another 12V panel and PWM charger. Run this to the 12V bank for lights and the other 12V stuff. Only the lights run off of this. If possible use 6v batteries in series for this.

Now for the 220 side
Wire all your panels in series, Get an MPPT charger rated at 20A or above. (allow for some expansion)
Wire these to a 48V battery bank and inverter. Run the rest from this. Again 6V batteries in series is better than 12V in parallel. Check your panel ratings for voltage VOC and make sure the voltage is at least 74V and below the max voltage on the charge controller at the coldest temp it has ever gotten where you are.

Reasoning for above.
Trying to run 12V inverters for large loads will create a large amp draw on the battery bank reducing it's capacity.
(Take a look at a battery chart and see how the capacity drops with larger loads)
Also by having one bank with taps in various places will create unequal charging and discharging. Your batteries will die quickly.

[Medianige]

Hi and thanks...

I have one 250w panel, will eventually have three. I'm not in situ yet, my partner and I will buy things to be delivered where we live now, otherwise it can be delivered to the bakery, the garage or the florist!!

What do you mean by PWM? I have a diagram of what I think I was going to setup. How to attach on iPad?

Do you mean have one panel to the light circuit, with its own controller and the others panels to the 'mains' appliance batteries through another and then on through the inverter?

[Naptown]

Hi and thanks...

I have one 250w panel, will eventually have three. I'm not in situ yet, my partner and I will buy things to be delivered where we live now, otherwise it can be delivered to the bakery, the garage or the florist!!

What do you mean by PWM? I have a diagram of what I think I was going to setup. How to attach on iPad?

PWM is a type of charge controller generally used for small systems and work well with a panel voltage matched to the panel. PWM stands for pulse width modulation. Basically it is an on off switch to limit voltage and current. In the case of a 12V battery the voltage would be 18 @ Vmp. Inexpensive and work well.

Do you mean have one panel to the light circuit, with its own controller and the others panels to the 'mains' appliance batteries through another and then on through the inverter?

This is exactly what I mean keep the low power things like lights and charging the I phones and I pad via a car type charger at the 12v without an inverter and associated losses. Put the high power things on an MPPT charge controller and to a 48 Volt battery bank. Preferably either 6 or 12V batteries in series.
In the higher power array this serves a couple of purposes. The MPPT controller allows more freedom in panel choices as the voltage need not be for the particular voltage of the battery, just high enough to charge them. And a 45A MPPT CC you could have up to 2160 Watts of PV panels at 48V 1080 Watts at 24V and only 540 watts at 12V By going the higher voltage route you will reduce losses, reduce the cable size and cost to connect things.

My comments in red

[Medianige]

Thank you...

So, to confirm I understand so far...

1x 250w panel to say, 2x 6v batteries (in series so they make a 12v 'system'), through a PWM; the lights and maybe one or two car charger will run off this. We won't use the lights very often and not for very long anyway.

2x 250w panels, in series, to (how many) 6v batteries (also in series) for 48v through an MPPT (?) charge controller; the washing machine, coffee machine and TV/box plus perhaps one or two spare 220v power outlets (for occasional hair dryer) will run from this via an inverter.



My existing panel has this electrical specification:
Open circuit voltage Voc (V): 59.8
Optimum operating Voltage Vmp (V): 49
Short-Circuit current Isc (A): 5.5
Optimum operating current Imp (A): 5.10
Maximum power at STC Pmax: 250w
Cell efficiency: 17.5%
Operating temperature: -40

[Naptown]

If you buy more panels only get one more like that for the Mppt controller.
for the 12V system get one with 36 cells with an VOC of around 22V If you put that panel on a 12V system with a pwm controller you will be wasting most of the power from it.
What is the coldest record temperature outside there and what is the temp coefficient on the panel you have.

[Medianige]

The coldest record temperature? Don't know. Last year it got down to -12c and the forums were all saying the coldest for many many years. We are 800m above sea level, but my cave is reasonably sheltered, certainly better than many on the 'flatter' areas. My water pipes didn't freeze (the Spanish only put them about a foot below ground) yet all my friends' pipes did. Mean low temps are; Jan, 1c and August 34c. I have been there with the mercury at 51c, but with our levels, it may well be 2-3c lower at the bottom end of the mean scale.

The panel is a Noble NSi 250w (Noble-NSi-250-96-M). It was an end-of-stock item, so I might not get one exactly the same, but for the mains system if I get another 250w, 96 cell panel with similar VOC it will be fine, yes? Will two be enough? The coffee machine will be used first thing so enough time to recharge the batteries during the day (mean sun hours is 11.5 in summer and 6.5 in winter) which is more important to my partner!! Haha.

[Mike90250]

The record low temperature is to calculate the actual PV voltage, going to the charge controller. At low temperatures, PV panels produce slightly more voltage, and if you are close to the limit of the charge controller, one frosty morning is all it takes to fry the controller.

Running a coffee maker ? Any way you can reduce you power load by feeding the coffee machine pre-heated (propane) water, so it consumes less electricity to make coffee ? Electrical heating is a heavy load on the batteries, even though it is for a short while. that 1200w coffee maker will pull about 30 amps from your 48V battery bank.

And you need to sketch up a block diagram of your plans, just so you know how it all works together before you start buying stuff

[PV panels 6, 250w series/parallel ]
[97VCD to charge controller]
[Charge controller 48V]
[Battery bank 300AH 48V]
[inverter 3000AC, 48VDC]
and all the fuses, J-boxes, wires and such

386536_224900547583406_120212794718849_544630_1918166571_n.jpg

[Medianige]

Hi Mike90250

The coffee maker is a Nespresso thing (I hate coffee but my partner NEEEEDS it - haha). It makes a cup in about 25 seconds, then turns off. I'm happy if we have to ditch it and only have the washing machine and TV and such on 'mains', after all, the Spanish coffee is unbelievable (I'm told) and a percolator would be just as good.

I planned to put the charge controllers inside, thereby protecting them from cold (and heat). The panels will be around 15-20m from the CCs. From what Naptown has said so far, my system will be:

250w panel 50w (?) panel
| |
250w panel PWM cc
| |
MPPT cc batteries
| |
batteries lights
|
inverter
|
appliances

I have the first 250w panel...I think I need to get a handle more on what actual kit I need, technically; what size Amp CCs, what power output for the inverter...etc., etc. I used a power consumption calculator that returned me a figure of 96-110kwh/month. I am starting to think 4x 12v batteries for the 'mains' (what aH?) and 2x 6v batteries for the lights, DC fridge. Originally, my partner and I figured on

[Naptown]

As I said in a previous post buy one more panel with electrical specifications (Vmp Imp) as close as you can possibly find to the one you have. Those two will go on the MPPT controller.

For the 12V stuff buy 36 cell modules ( about 18V Vmp) and use a PWM controller.

If you can't find more panels like the one you have then us it for the 12V items with an MPPT controller which will down convert the voltage for 12V without a lot of loss. If you use the panel you have with a PWM controller you will lose about 2/3 of the rated wattage.

[Medianige]

Thank you. How helpful are the people here??? Much better than most forums!! Was a bit confused by the last reply (no offence, Mike90250).

For the lights, do you think a 50w panel will suffice? I have seen one on a site here today that is 22voc so wouldn't waste too much... I have seen several 250w with similar techspecs, so I don't see a problem with a second or the mains system.

I'll now also need to look at the controllers and an inverter. I found a site that calculates the numbers of batteries and cable size. It used the assumption that I need FOUR days autonomy... 18 6v batteries!!!!!!!

[Naptown]

Thank you. How helpful are the people here??? Much better than most forums!! Was a bit confused by the last reply (no offence, Mike90250).

For the lights, do you think a 50w panel will suffice? I have seen one on a site here today that is 22voc so wouldn't waste too much... I have seen several 250w with similar techspecs, so I don't see a problem with a second or the mains system.

I'll now also need to look at the controllers and an inverter. I found a site that calculates the numbers of batteries and cable size. It used the assumption that I need FOUR days autonomy... 18 6v batteries!!!!!!!

Typically we would recommend two days of autonomy then generator time. This limits the discharge rate to 40% of capacity.
So the formula would be Daily load in watt hours x 5= Watt hour capacity of the battery bank. Divide the watt hour figure by your voltage and you arrive at the amp hour capacity of the batteries.

[Medianige]

Typically we would recommend two days of autonomy then generator time. This limits the discharge rate to 40% of capacity.
So the formula would be Daily load in watt hours x 5= Watt hour capacity of the battery bank. Divide the watt hour figure by your voltage and you arrive at the amp hour capacity of the batteries.

So... if I have a (slightly high) daily useage of 3.5kwh (I don't think I'll use this at all)

3500 * 5 = 17500; 17500 / 48 = 360aH

If I use 4x 12v batteries, does that mean I need 4x 100aH wired in series? Parallel? If I get 6, the discharge rate will be less over the bank meaning they will last longer, yes?

[Naptown]

So... if I have a (slightly high) daily useage of 3.5kwh (I don't think I'll use this at all)

3500 * 5 = 17500; 17500 / 48 = 360aH

If I use 4x 12v batteries, does that mean I need 4x 100aH wired in series? Parallel? If I get 6, the discharge rate will be less over the bank meaning they will last longer, yes?

Batteries in series the voltage increases the amp hour remains the same
Batteries in parallel the amp hours increases the voltage stays the same.

To produce the wattage you are proposing say 3.5 KWH per day usable from the batteries and assuming a worst case insolation of 3KW per square meter per day in winter.

3500W x 1.5 (Assuming MPPT controller) / 3 = 1750W of solar panels. A bit more than the 500 watts you are proposing
The reason for the 1.5 is to account for charging inverter losses. If you use a PWM controller it gets worse.

[Medianige]

Sorry, but what is insolation?

If I assume the washing machine (1000w, 220v) runs twice a week for an hour and a half, this will give a lot more time to restore energy (and I suppose drastically reduce the KwH/day figures) - how reliable are the online calculators? I seem to have to guesstimate almost everything when using them.

I'm happy with 750w for the mains and a smaller panel/battery for the lights as from March to October/November we will rarely use lights inside (until your advice I was thinking four 250w panels).