Energy Matters Forums

[solar1957]

Hi there can someone please advise my next step for closing the gap to off grid power

I currently have the following
6kw of panels , b&b 5kw inverter linked to grid.
Produce between 26 and 35 kwh per day throughout the seasons
Consume between 500 - 1000 kwh per 90 days peak and 500 kwh average off peak 3kw and 1.5kw aircons used a lot during summer no heaters during winter
I have also installed a timer on the 125l hot water system so i control timing of energy consumption

I also have a :
1kw stand alone with 1 x 160ah 12v battery , 30amp controller , operating 2 x house light circuits with 8 x 12v led bulbs and 2 x 12v ceiling fans , lights and fans never run out of power and 1 x spare wire ready for 12v upright fridge when existing fridge dies
I also have 6 x 160ah AGM batteries on float charge doing nothing.

My challenge is to be able to run at least one aircon after 6pm till midnight and my cpap machine and fridge ,ALL NIGHT AND OFF MY BATTERIES and if batteries run low, switch back to grid and recharge off my grid and solar the next day, remember i dont need lights , the stove is gas .
Is there a cost effective way to set this up

regards wolf

[Gordon-Loomberah]

Welcome to the Energy Matters Forums Wolf

It seems no one wants to touch this one, perhaps because more info is required.
It really depends on how much power it takes to run your ACs. Your 6 X 12V 160AH could supply say 3kWh of energy per night (if you want them to last any significant amount of time) if they have their full rated capacity, which might be enough to run the small AC, and perhaps a small fridge. How much power does your cpap machine consume?

What sort of batteries are they- designed for cycling use, or for emergency backup power, but meant to be kept on float most of the time?

One way would be to configure your 160AH batteries into 3 parallel strings of 2 batteries, to make a 24V system. Although 3 strings isn't ideal, it's not too bad if you connect them up correctly, since you already have them there.
You'll then need an inverter-charger able to handle the starting and running load of the AC. You can connect this to the mains to pass-though and run things from the mains, or charge the batteries. The best way would be to charge through the middle of the day when your 6kW system is producing excess power.

BTW, 1kW of PV into a 160AH 12V battery via a 30A regulator??? I'm surprised the regulator hasn't let the magic smoke out! 1000W @ 12V is 83Amps. At least it will be protecting the battery, 83A is too high a charge rate for that battery.

[solar1957]

Hi Gordon
thanks for response
I know just enough about solar to be dangerous , re stand alone , i have 4 old 250 watt panels hooked up in parallel connected to the controller. The controller shows my amps going to battery between 1 and 5 amps ?
the battery charges to 13.8 volts and my light circuits are all 12v using the standard house wiring circuit. The bulbs are 7w led , the only problem i have is that if all lights and fans in the house are on the, last furthest light from power source ends up with voltage drop to 9 volts , only just enough to run light but sometimes it turns off for a couple of minutes.Under normal household use i have no lighting or fan issues and in 2 years have never run out of power , the lowest the battery has ever discharged to is 11.8 volts and gets totally recharged to 13.8 volts on a rainy winters day by 10 am. I am thinking that this system can also handle a 12v volt 270lt upright fridge , my wiring is in place , just waiting for current fridge to die , Am i barking up the wrong tree here ?
The batteries are 2 years old , they are the computer backup batteries for Commonwealth Bank head office Brisbane.
What about the 6 batteries being recharged during daylight hours like you suggest from grid tied 6kw solar,run 12v inverter , pull some more circuits from the house to run 12v inverter 240 volt for microwave,toaster,oven,jug etc and forget the air cons they can stay as they are.If this is possible what components would i need ?
your help is really appreciated

regards wolf

[Gordon-Loomberah]

1kW of panels only putting out 1-5A ( I'm assuming you mean that 5A is the maximum charge rate you see when the battery is discharged) into a 12V battery indicates there is a serious problem somewhere.

A dim light at the end of the wire suggests the cable is too small for the amount of power being drawn on that circuit. 3V drop @ 240VAC isn't a problem, but 3V drop @12VDC is a problem. The standard house lighting circuit is most likely 1.5mm^2 cable, not enough for 12V lighting.

It really depends on how much energy per day is used by the fridge as to whether or not you can run it on that single 12V battery, but I suspect it might be ok in summer on sunny, but not too hot days, but if you get a couple of cloudy days in a row, you'll flatten the battery.

The 2yo batteries may not be designed for cyclic use if they were CBA backup power for the computers. They'll no doubt work for a while, but with deep cycling they wont last very long. 2 years seems rather soon for them to be taken out of service, that sort of battery should last ~10 years if kept on float and not discharged very often. Any idea why they removed them?

6 parallel 12V batteries is a very long way from ideal, you'll have difficulty kepping them all evenly charged and discharged without careful attention to how they are connected together. If you are thinking about running 2-3kW loads, I'd suggest 24V makes more sense, it will be more efficient and the current flows will be more reasonable. 3kW @12V is 250A, which requires very large cross-sectional area cabling.

[jules]

Hi Wolf, everything depends on whether you're very definite about going off-grid soon or if it's something you'd like to do at some time in the future.

If you do go off-grid the reliability of the equipment [inverter, solar regulator etc] you're using suddenly goes up in importance. Right now your b&b inverter can drop out and with grid back-up it makes no difference to your life. If you were to go off-grid, your panels might supply more enough power for your daily needs but you would certainly need a new, good quality inverter [or inverter charger] and your existing batteries might struggle if your air-con is used a lot. Remember, with an off-grid system there's a reasonable chance that at some point in time something will fail and you could be without power for up to a few days. I'm a bit loath to say that because I also reckon off-grid systems are extremely reliable.

Going off-grid will most probably be more expensive than keeping things the way they are at the moment, unless you scale back your power usage and try to avoid using bits of equipment that devour more than 1,000W for any significant period of time.

[davidg]

1kw stand alone with 1 x 160ah 12v battery , 30amp controller , operating 2 x house light circuits with 8 x 12v led bulbs and 2 x 12v ceiling fans , lights and fans never run out of power and 1 x spare wire ready for 12v upright fridge when existing fridge dies
I also have 6 x 160ah AGM batteries on float charge doing nothing.

In relation to the batteries
so lets look at the storage you have currently

Assuming 12V batteries = 160 x 12 = (1.920kWh's @ 100% DOD) approx

1920 watt hours x 6 = 11520watt hours (11.52kWh's) x 25% DOD = 2.88kWh's usable
or
with the existing battery approx 3.3kWh's usable, unless you want to drastically shorten the life of the batteries.

For off-grid use the AH requirements are considerably greater than one thinks, FYI look at my signature 48V x 1100ah (2.1 Tonnes approx) enough for approx one night at a consumption approx 10kWh's without causing more than roughly 20% DOD. Depth of discharge is everything when it comes to Lead Acid or really any battery type really even Lithium which while it may be able to discharged more deeply still has limits particularly in Australia where temp conditions are considerably hotter and therefore must be compensated for or suffer premature cell failure