Going over to solar for lighting/security

[supersunbird]

Planning for an apocalypse/revolution by chance?

Can't you plan for 75% of the lights being on? Dunno about your place but generally I've got <25% of the lights on even when on the grid. At my parents place (big house) its likely closer to 10%. Outside obviously needs to be on yes.

No, just don't want to be dependent of Eskom for my security.

I have stated a few times, there is no way all will be on. I was just trying to know the theoretical system I'd need (which I still don't know because people don't read and see that AT MOST 50% will be on for about 3 hours only, so they don't need to worry about the batteries draining more than 50%), especially the total Ah of battery power required.

 

[supersunbird]

18 Rooms??? Good god you must live in a mansion.

Its big yes, but the hallway is a room for example, and the entrance roompie (portaal in afr) and the toilet.

House (3 bedrooms, dining room, sitting room, 2 x smallish general purpose rooms, kitchen, 2 bathrooms, toilet, hallway and portaal) with "flat" attached (2 bedrooms, big general purpose room, bathroom, kitchen).

 

[maumau]

Its big yes, but the hallway is a room for example, and the entrance roompie (portaal in afr) and the toilet.

House (3 bedrooms, dining room, sitting room, 2 x smallish general purpose rooms, kitchen, 2 bathrooms, toilet, hallway and portaal) with "flat" attached (2 bedrooms, big general purpose room, bathroom, kitchen).

Yep, big

 

[supersunbird]

Flat roofed house but there a big ass pecan nut tree on the northern side throwing shade over it in the summer, so solar geyser is out for saving power but we don't need an aircon, house stays nice and cool in summer, gets proper sun in winter.

The double garage though is ideal for solar panels, 7m by 5.6m. Battery bank can also go in there and its close to the DB,

 

[Gaz{M}]

I have another suggestion.

Forget the solar panels - too expensive and not reliable power.

Just get enough batteries to last 2 or 3 days with your revised power needs, then buy a cheap 1kw generator and use the to recharge the batteries if and only if you power is out for more than 2 or 3 days? You would only need to run the generator for a couple of hours. You could even run the generator while you are awake to save battery power.

Or is there a reason you simply cannot use a generator?

 

[richjdavies]

Or is there a reason you simply cannot use a generator?

I agree with the sentiment -- i.e. why use a solar panel at all if you've got the grid --> if you're storing for a few hours, why not just storage electricity from the grid.
Then as a worst case, you can always use a generator.

Problem with generators are that unused, they die -- i.e. don't use one for 6 months, and you'll probably not be able to rely on it when you need it. Thus, I think your 'spec batteries' for a few days, forget panel... and then just use your car and a lighter socket to charge those batteries if all hell breaks loose and you don't have power for those days.

 

[supersunbird]

Its already happening, power in neighbourhood off since midnight and was still off when i left at 6am.

Since the batteries are the expensive part, i do not see the point of panels being removed. Generator seems lots of work, how do i run it to charge the batteries when I am away from home for 11 hours a day.

Thats besides the point, what i’d like is the formula to see how many Ah of 12V batteries I require to run a 1000W 220V load for 12 hours. Theoretically the batteries can be empty at the end of the 12 hours.

 

[supersunbird]

Just more fuel to the fire.

12.2% average tariff increase proposed for municipal customers.
http://www.moneyweb.co.za/moneyweb-eskom-crisis/eskom-finalising-new-tariff-applications

We already use about pay R1400 to R1500pm for electricity. The same as back in 2008 despite all the increases. One can only cut so far though, so 12% plus whatever the municipality adds on means an extra R180pm next year and they say they want another 12% the following year too.

 

[HavocXphere]

Its already happening, power in neighbourhood off since midnight and was still off when i left at 6am.

Since the batteries are the expensive part, i do not see the point of panels being removed. Generator seems lots of work, how do i run it to charge the batteries when I am away from home for 11 hours a day.

Thats besides the point, what i’d like is the formula to see how many Ah of 12V batteries I require to run a 1000W 220V load for 12 hours. Theoretically the batteries can be empty at the end of the 12 hours.

Not if you want them to last.

As for your formula...I'd imagine its like this:

1kW for 12 hours >> 12kWh

12kWh / 12V = 1 000 ah

..excluding losses and assuming you run the batteries flat which I gather is a terrible idea.

 

[richjdavies]

Ball park figures are
12 kWh used = c. 14kWh needed from batteries (80-98% efficiency depending on inverter - 85% for small?)*
Maximum drain depends on your batteries - but let's say 40% drain -- so the total battery has to be:
14kWh / 40% = 35kWh
35,000 Wh / 12 V = 2,916Ah

If you want 12 hours overnight, then that number is probably right. If you wanted say, 24 hours, then you should factor in the fact that the solar will 'recharge' a certain amount every day --> meaning you won't drain so much / won't use as much energy.

Most people 'get over' this analysis just by buying too much -- and then replacing it well before it reaches the end of life --> engineering through excess

If you want to read more - this looks very good:
http://batteryuniversity.com/learn/article/bu_503_determining_power_deliver_by_the_ragone_plot

There's some simplified calculators here too:
http://rimstar.org/renewnrg/sizing_select_batteries_for_off_grid_solar_system.htm

To do a FULL off-grid analysis you need to consider:
1. Inverter will always draw a little bit of power from the batteries -- around 10-20W - 24 hours a day, even when you aren't using power.
2. How long you expect to be without generation -- e.g. for solar, that's about the 'probability' that it will be really cloudy for days and days at a time, or, if not well maintained your power-controller could die... That's why lots of people just chuck in a manual petrol generator, just in case... It's cheaper to design in a bit of fuel, than design-out very low probability sequences of cloudy days
3. Your inverter WILL break, after a certain amount of time... so that might be more-likely than the probability you're go for in 2 above
4. The Ragone / discharge plots above - for YOUR specific battery: http://batteryuniversity.com/learn/article/bu_503_determining_power_deliver_by_the_ragone_plot
e.g: http://www.sinetech.co.za/ops_batteries/ops_batteries.pdf
20% drain will mean 4200 cycles (= 11 years a 1-cycle per day),
40% drain will mean 2100 cycles (6 years)
60% drain will mean 1400 cycles (4 years?)
80% drain will mean 800 cycles (2 years)
>80% -- all bets are off!
5. Power Factor - e.g. if you're driving pumps, this can be an issue
6. How exactly you're discharging - and the related battery issues -> see battery university. Batteries 'like' certain types of loads depending on their chemistry.

* -example, this http://e-systems.co.za/System/FabSheets/0FBI3000P.pdf is 85% efficient