New partial off grid system help needed

[Tobym]

Hi I'm new here great site buy the way. Im new to the world of solar and could do with some advice. I am in the process of installing an entirely off grid 12v led lighting system trough out my home as I renovate. So I have worked out ill use a max of 70 4watt mr16 down lights, 1or2 led strip lights and 20 or so mini deck lights 0.21 watt each and 3 led outside wall lights at 4.8watt each so I make that 322.6 wat or 26.88 amp so round it up to 400watt or 33.3 amp to cover any changes. I'm also going to run a couple of 12v charging sockets to charge iPads,iPhone and other small electronics. The rest of the house will be on conventional 240v grid ( at the mo).
Here's we're I want to Check on a few things I have purchased 4 x170w panels (I have attached a pic of data plate on panel to help). I am planning on running the panels in series as I believe this to be the most efficient way to go. Then I will need a 30a but will buy a 40a mppt cc and charge my batteries in
.1st option 12v configuration so I can feed my 12v system with no faffing about which makes sense to me except for....
2nd option 24v configuration as again I believe this to be the most efficient way but now I need get my voltage back down to 12v.
Is there any such thing as a mppt cc that charges at24v but supplies the load terminals with 12v or would I then need to purchase a tranny to drop back down to 12v which in itself has its own wastage.
Thanks in advance for you help any that you lovely people could offer would be greatly appreciated. Toby

[Sunking]

I make that 322.6 wat or 26.88 amp so round it up to 400watt or 33.3 amp to cover any changes.

Completely useless information. What you must know is how many watt hours you will use in a day.

Watt Hours = watts x hours. All you got is watts.

Amp Hours = Amps x Hours. All you got is amps.

Once you figure out how many watt hours you need, you are going to be extremely shoocked how much it is going to cost you. Sooner or later you will ask yourself; Why am I paying $2 Kwh going off grid instead of paying the electric company 10-cents per Kwh?

[inetdog]

Hi I'm new here great site buy the way. Im new to the world of solar and could do with some advice. ...

1st option 12v configuration so I can feed my 12v system with no faffing about which makes sense to me except for....
2nd option 24v configuration as again I believe this to be the most efficient way but now I need get my voltage back down to 12v.

Is there any such thing as a mppt cc that charges at24v but supplies the load terminals with 12v or would I then need to purchase a tranny to drop back down to 12v which in itself has its own wastage.
Thanks in advance for you help any that you lovely people could offer would be greatly appreciated. Toby

1. The economics of any even partially off-grid system when grid is available and reliable, and the cost of grid power is under $.50 per kWH are doubtful. Take a close look at the various discussions of off-grid with grid for more details.
2. You change AC to AC with a transformer. You change DC to DC with a converter or power supply. Or, if you have a 24 volt bank made up of to 12 volt batteries a battery balancer. Each of these has its different cost and features.

[Tobym]

Ok great thanks for the replies I am quite lucky I have a very light house and have brought up my children to understand that elecric cost money and we are very carful on how much power we use.
I have worked our watt/hours for the lighting in the house and believe it would be about 530 watt/hrs or 44 amp/hrs per day this I believe is a over estimation. I also believe I'm able to lower the outlay buy having already owned a great condition very few cycled 145ah 12v battery I also have the poss of getting (6x 100ah deep cycle batteries that have been maintenance charged but never had any load taken from them) for a very cheap price. This means that Im in a good position for saving my self money within a few years. Am I right or am I kidding my self and should just scrap the idea unfortunately I have already wired my new extension in 12 cable so would have to pull the ceilings back down and rerewire. Any more advice would be really helpful.

[axis11]

Do you really need to have all those lights? You might want to check actual consumption of a sample 4 watter mr16. I had a few of those which were rated at 4 watts but when I tested the actual power draw, it was just about 1 watt. You could avoid unnecessary cost if you could design the size of your system as accurate as possible.

[Tobym]

Ok I hadn't considered that I will check them and see. 70 lights is the max amount of what I'll need as I live in a 4 bed house. Does any one know If there is a cc out there that can charge at 24v and put 12vload out.

[axis11]

I have not seen the type of CC your looking for. Better keep it simple. 12v, 24v or 48 volts. Dont mix the voltages.

[Tobym]

Ok I totally get that but won't I loose the efficiency of charging at a higher voltage? I don't really know how exactly to work out the figures of what will be coming from my panels to my cc and then into my batteries. So I can't do the equations of the two options and see what better. Could anyone work those for me or better still tell me how to work it out for my self. Thanks

[axis11]

You actually reduce losses if you go for higher systems voltage, say 24 or 48 volts. The panels you have are designed for a 24v system.

Options:
1. Panels in 4s configuration to charge 12v batteries using Mppt CC, use 12v loads. (limit no. of batteries in parallel)
2. Panels in 4s configuration to charge 48v or 24v batteries using Mppt CC, use 48 or 24v loads respectively.
3. Panels in 4s configuration to charge 48v or 24v batteries using Mppt CC, add a 110 or 220v inverter. Use lights that run on 110v,220. This gives you flexibility when you need to run other devices in the house.

[Tobym]

Ok thanks again I understand all of that that's the reason y I wanted to go up in voltage. As I have a 12v lighting system installed it seems I have no choice on charging my batteries in 12v but wouldn't I be waiting a lot in wattage and amperage or is it negligible. If its going to be a big loss am I not better off charging 24v and stepping down as a lot of the converter 24>12 I have found say the are 90-95% efficient.

[daz]

Ok thanks again I understand all of that that's the reason y I wanted to go up in voltage. As I have a 12v lighting system installed it seems I have no choice on charging my batteries in 12v but wouldn't I be waiting a lot in wattage and amperage or is it negligible. If its going to be a big loss am I not better off charging 24v and stepping down as a lot of the converter 24>12 I have found say the are 90-95% efficient.

Hi there Tobym. Welcome to Solar Panel Talk.

Charging your batteries from a higher voltage source is where you make your savings in efficiency. Whether you charge your 12V batteries from a 48V array, or whether you charge your 24V batteries from a 48V array, the principle is the same. At the moment you are missing the relationship between voltage and current!

For your installation, as you already have the 12V LED lights, it wouldnt make sense to change that. And stepping down the battery bank voltage, from a higher voltage, to 12V is not a good idea. This will entail additional cost as well as more loss (due to inefficiency). What you need to do is setup a 12V system that is charged from a higher voltage solar array (ie 48V). Unfortunately 12V systems limit you when it comes to expanding.

Doing it the way you suggest, charging a 24V battery bank from a higher voltage array, and then stepping down the 24V to 12V defeats the whole purpose of going with a higher voltage array!

[axis11]

My mistake, I was thinking you dont have the lights yet. So now that you have your panels, batteries, 12v lights on hand, you will be forced to wire your battery bank for 12v. You can reduce losses at an additional by using thicker wires. Test the power draw of the lights to avoid sizing a large battery bank. If your estimated daily power draw is 44AH @12v, 200Ah x 12v battery is enough for you, or two x 100AH. It would be better if you could get a single 200AH battery to avoid a parallel connection.

So your sytem would be 2 panels in series----MPPT CC----12v battery @ 200AH----12v loads.

You may use your 145 AH battery since its already there but be reminded that the battery will be subjected to about 30% DOD. Not very bad but not very good either. You need only 2 of the panels at the moment. Installing all 4 would subject the battery to excessively high charge rates which shorten the life of the batt significantly.

[Tobym]

So do u not thinks I should install a 4 panels then with 400ah of batteries so as to be able to harvest and store enough power during the winter or do u think that 200ah will be with my panels that only say 4.85a will be enough for the winter

[axis11]

Unless your location cant get at least 2 sunhours a day during winter, you dont need more panels. Keep it as a reserve. Use the battery you have now until dies so it doesnt get wasted.If you have calculated your loads correctly, I would say you can get at least 3 years for the 145 AH battery. When the time comes to replace the battery, then size it up to match the panels and loads.

[Tobym]

Ok great two panels then is it worth getting a 40a cc then or uprate that in a few years as well