Which batteries for off grid domestic system

[bodgersfield]

Hello, I have 12 x 250w panels and a pip 4048ms charger/inverter. I am building a medium sized off grid home in UK and need advice about batteries. What capacity and type do people recommend? I think the panels will be connected in strings of 4, and it will be a 48volt system. Any help would be gratefully recieved.

[SunEagle]

What is your expected daily watt hour usage?

Without that information sizing your batteries is point less.

[Sunking]

Batteries, Panel Power, and Inverter Power have to be matched, and there is window of C/8 to C/12 charge and discharge rate. Looks like you will be running at 48 volt battery system at 3000 watt input

That means you must use at least a 60 amp MPPT Charge Controller because 3000 watts into 48 volt batteries generates 60 amps of charge current. The minimum size battery Amp Hour capacity = 60 amps x 8 hours = 480 AH. Largest the panels can support is 60 amps x 12 hours = 720 AH. The perfect fit is C/10 or 600 AH cells. You would need to use 6 volt Industrial batteries to obtain 600 AH capacity. Consumer grade 6 volts only go up to about 460 AH which you could use. Even better and easier is using 2 or 4 volt cells. Those go up into 1500 to 4000 AH sizes.

However everything I just said is non sense because we have no clue how much power you will use in a day.

[Logan5]

depending on the distance of your array from your batteries, 48 volts may be a bit low. with a good MPPT controller you could send as much as 150 volts DC down to CC and then a 48 volt battery bank. If you want a little power, you could go with 8X L-16 FLA 6 volt trojans or similar brand. If you already have nat gas appliances you could get by on small system. but if you use electric kettle, toaster, stove/over, hotwater you will need more power.

[bodgersfield]

Thanks for the replies. My estimated daily power use is about 15kwh. The inverter/charger is 80A mppt. I am using nat gas for cooking, hot water, etc., but was hoping to have an electric fridge, washing machine, etc.

[Logan5]

15Kwh is a lot. you need to work on reducing demand first, like 90% reduction. then find a sweet place with solar and a generator. If your on a private island w/o any access to the grid, keep throwing money into it, you'll get what you want, eventually.

[solarix]

With Lead/acid batteries, the more you pay - the more longevity you can get. I generally recommend first time off-grid solar people to start with cheap ones - cause they may well ruin them before they learn how to care for the system. When the first battery pack is failing, then buy the expensive, long-lived batteries.

[PistolPete]

The rule of thumb usually is have 3 days of battery backup for your "usual loads". Now this can be adjusted for possible solar power input (are you in the unicorn sunny part of England?) and your use of some sort of generator. You can play with very strong tools like Homer or the like to see how your distributed mix may look.

[Sunking]

The rule of thumb usually is have 3 days of battery backup for your "usual loads".

Wrong answer.

[PistolPete]

Wrong answer.

Not very helpful there but there is more to this than that. Is there going to be a generator? You gave a good answer for equipment sizing but maybe he needs to take a step back and work from how much power he is planning on using then sizing the equipment.

Here is an excerpt pointing out that this is a GENERAL rule of thumb "The general rule for days of autonomy is 2 to 3 days for non-critical loads and 5 to 7"

http://blog.gogreensolar.com/2009/01...-autonomy.html

EDIT: Link didn't display properly

[bodgersfield]

I am planning on having a large-ish generator, possibly a 10kva diesel.

[Sunking]

Here is an excerpt pointing out that this is a GENERAL rule of thumb "The general rule for days of autonomy is 2 to 3 days for non-critical loads and 5 to 7"

All true but you still gave the wrong answer. Minimum for FLA is 5 days which in practice is 2 or 3 days as you never discharge below 50%. So for 2.5 to 3 days, takes 5 day minimum. Generator is required for any off-grid system regardless of battery capacity. Generator is sized to charge batteries at an 8 hour rate, and carry the load.

[GAVAN]

I have 2 calcium batterys DELKOR 165G51L 160 amp hour 12 volt on a 300 watt panel, are these ok? through a PL20 12-48v charge controller. New batterys but one seems to be going flat. any comments please?.