# Need help - New here.....

Solar Expert Posts: 28
Hi All,

I am planning a backup system for when there is a power cut.

Latitude/Longitude: 24.54541, 91.759905 (from google map)
Grid: 120-220V AC (its in a village, voltage drops for periods of times)

My estimated power consumption is approximately 1000 watts for about 2 hours. The load shedding can last anything from 45mins-90mins and sometimes longer 3-4 hours.

Some times lost of short ones, like 10-15mins several times, mostly after sunset.

I am thinking of using a 12V or 24v 2000VA inverter ( ideally pure sine wave)

1000watt for 2hours = 2kWh + 20% extra.

2200/(24x.8) = 114.5Ah

DoD=60%
114.5/0.6 = 190.8Ah

So 2x100Ah Deep cycle wet cell in series for a 24v system?

Are my calculation correct?...and am I going the right way of estimating? etc.

The house (2 floors, flat concrete roof and floors) is wired with extra Live cable running to appliances that will run from the AC out of the inverter. Using the existing distribution boards ( 1 on each floor) and the Neutral cable.

The Batteries and the inverter and charge controller will be located in a room on the roof, all close together, short cables will be used. PV panels will be on the flat roof, no more than 10-15ft max. The AC line from the inverter will run back to ground floor, before Mains Breaker and after the Meter, about 30-40ft. max.

My questions and are as follows.

1. How many panels (only can get 75watts ATM) will I need.

2. The inverter will have a built in charger but no facility to connect solar panels. Can I somehow use Mains supply (Grid) to charge on a cloudy day and solar panels for all other times? Can that be automated?

3. I am aware of voltage drop and current loss in the cables on the DC side of the inverter. Should I also be worried about the AC side cabling?

4. Which is better interims of longer runtime on the batteries, 12V or a 24V system? Advantages/Disadvantages?

Thanks,

• Solar Expert Posts: 8,207 ✭✭✭✭✭
Re: Need help - New here.....

If your local power utility does not allow "Grid-Tie or Net-Metering" where, surplus power you generate, gets fed back into the grid, and deducted from your bill, I would forget the solar, unless you need it for longer than 6 hour outages.

Instead, I would look a creating a large UPS (Un-interruptible Power Supply) and have it run off of 48V (instead of 12 or 24). This uses thinner copper wires, and easier to wire the bank, if you can purchase 48V inverter/charger in your area. Use the largest DC voltage you can buy parts for, 12V being the least favorable, and 48V being desirable. This should switch very quickly when the power fails, and recharge batteries when the power comes back on. It may even help eliminate power quality problems too.

60% DoD for the batteries is a bit too much - the deeper the discharge, the shorter the battery lifetime. If it only happens once or twice a year, not a problem, but weekly, you will see shorter battery life, and needing to replace in 5 years instead of 7.

The batteries will weigh an awful lot, are you sure your roof can support the weight ?

If after a year, you find your batteries drain too fast, you can start adding the expensive solar panels, or maybe a small generator to recharge the batteries after dark. You can buy a lot of generators for what a small solar array would cost.
3KW generator = \$400
3KW solar = \$20,000
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Solar Expert Posts: 28
Re: Need help - New here.....

Your the second person that mentioned generators, they can be bought for the price of a battry+inverter system.

1. How noisey are they?
2. Do they produce sine wave or do you need a inverter?
3. Anyway to auto start and auto transfer between ac and gen?

Thanks again.
• Solar Expert Posts: 8,207 ✭✭✭✭✭
Re: Need help - New here.....

1. How noisey are they?

Varys, little Honda inverter units are hardly audible

2. Do they produce sine wave or do you need a inverter?

Nearly always a sine wave, but you are running off your batteries and inverter,
so the generator only gets fired up when your battery bank gets low, and then to
recharge the batteries

3. Anyway to auto start and auto transfer between ac and gen?

Yes, but you loose power for about a minute or so, while the gen decides if it's a power outage, or just a 20 second glitch.

I like the inverter/charger, and a battery bank. No fuel to purchase/store/go stale,
and quick switchover if power fails.

What, specifically, are the loads you are trying to power ?
Computers? Drug refrigerators? water pumps, lights, air conditioners ??
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Solar Expert Posts: 705 ✭✭
Re: Need help - New here.....

A \$600 Kipor inverter style manual start genny at 2kw using a gallon of gas every 3 to 4 hours on eco throttle maybe a simlper solution 2 your problem \$ wise . Ive got one and its my back up back up if im in the poo poo stroke generator mode ,, ps needs u there when the power puffs out.

KIS. HTH Nigel
• Solar Expert Posts: 28
Re: Need help - New here.....
mike90045 wrote: »
1
Nearly always a sine wave, but you are running off your batteries and inverter,
At the moment I am on the grid, for backup, we have 2ft rechargeable tube lights, they cost \$30, life of about a year. Not very bright and they don’t last very long.
What, specifically, are the loads you are trying to power ?
Computers? Drug refrigerators? water pumps, lights, air conditioners ??
Summer time:
5x Ceiling fans - 80-100 watts each
6x 4ft tube ligts - 60watts each
10x Enegry saving lights 11watts each
1x fridge freezer (about 5ft tall and 2ft wide) not sure of the watts
1x LCD TV - ~100watts (maybe)
All lights may not be ON at the same fime

Winter:
6x 4ft tube ligts - 60watts
10x Enegry saving lights 11watts
1x LCD TV - ~100watts (maybe)
All lights may not be ON at the same fime

There is also a water pump, 750watts, but that wont be connected to batteries. There is huge tank on the roof that lasts a while, but if on geny then I might connect it in a really bad day if the water runs out. Even then there is man power to carry water from large pond.

Spoke to someone who has a geny, he said it has 1700watts printed on it and to start it he pulls a cable. I think its one of those small ones you are refering to, cost about \$400.