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vawtwindy

Newbie

Joined: 23/10/2010
Location: India
Posts: 31

Posted: 11:13am 04 Jan 2012

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Hi
I am pretty new to this solar topic.

Planning to use 60watt worth of LED's totally on battery and planning to charge those battery on solar pv. And this is a kind of garage (rented place) even in day hours i will not have light ray's. So it would be utilised around 16hrs a day.

60*16=960Wh, average sun light per day will be around min 5 to max 7 hrs.

Can anyone help me in identifying the battery size and the size of solar panel required for this?

vw

vawtwindy

Newbie

Joined: 23/10/2010
Location: India
Posts: 31

Posted: 12:50pm 04 Jan 2012

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when i was checking freesunpower, it shows me 450Ah battery size and 2 x 80w panels are required,

they are calculating for 3 days work hour, i guess they are giving it by calculating inverter loss also, if i use directly 12v dc system, do i still need to use the same size?

yahoo2

Guru

Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 01:33pm 04 Jan 2012

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Hi vw,
I would be happy to give you a few pointers on how to work this out, in the end local conditions and your long term plans will help decide what you install.

The size of your system is decided by what you will do during the months that the solar panels produce the lowest daily power.
1 fit as many panels as it takes to keep the batteries charged
2 run a generator for a short time once or twice a week in the mornings during these months (with a suitable charger).
3 undercharge the batteries and replace them after 2-5 years instead of 7-10 years.

For my area this is may june and july (winter)

these are some figures for sunny south Australia

solar generated (calculated at the panel, no losses factored in)

PV panel 190 Watt rated
June ------390 watt/day
Sept-Oct---935 watt/day
Dec-Jan--- 1480 watt/day
Mar-Apr----840 watt/day
dark clouds in the afternoon are a real power killer!
probably subtract 10% to 30% for inefficiency in the system (charging, wiring, heat, etc)

As the graph shows not only is there less power in winter, there are less hours in the day to fully charge a battery. to get from 90% to full charge you should factor in an hour in the afternoon to "top them up". wont need a lot of amps for this last bit, just time.

Deep cycle batteries are usually rated in amp hours, totally discharged over 100 hours. the quicker the discharge time the less power can be removed and the deeper and longer the discharge the less times it can be recharged before failing.

Have a look at a few spec sheets for batteries on the internet and take notice of the 10 and 20 hour discharge rate (C10 and C20). The total amps removed from the battery per night should be less than 50% of this figure at a minimum, 30% in an ideal world.

That's pretty much it, size the panels to supply power for the lights and charge the batteries during good sunlight hours, then calculate the batteries size to cope with the load for the rest of the day.

need to decide on a battery bank voltage to calculate battery size.

regards yahoo

I'm confused, no wait... maybe I'm not...

yahoo2

Guru

Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 12:11pm 05 Jan 2012

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Here's a few calculations if the system was at my location, assuming lights are on 7 days a week.

960 wh plus 20% margin
1150 Wh /16 = 72watts/hour

BATTERY SIZE
discharge time
16 hours power drain -5 hours sunlight = 11hours 792 watts

12 volt system 792/12 = 66 Ah

66 Ah / 30% = 220 at C10 rate

240 to 320 Ah battery @ C100 rate (depends on battery quality)

PANEL ARRAY SIZE
fully charged by panels in winter
390 watt per day/190 watt panel = 2.052W generated/day per rated watt (see first post for seasonal watts per day generated from a typical panel)

1150/2.052 = 560 watts of panels (7x 80 watt panels)

power surplus
spring 1350 watts
autumn 1350 watts
summer 3200 watts

option of using generator twice a week for 10 weeks in winter
600w per day/190 watt panel = 3.15W/rated watt/day (this would leave us 210 watts/day short for two and a half months)

1150/3.15 = 365 watts of panels (5 x 80 watt panels)

power surplus
spring 480 watts
autumn 480 watts
summer 1700 watts

70 Ah of charging needed every 4 days over winter (before midday so the panels can finish the charge)

VW, you can adjust the figures for your latitude and weather ( I am below 30 degrees south)
I find the biggest factor in how many panels to install is the amp rating of the charge controllers I choose.

regards yahooEdited by yahoo2 2012-01-06

I'm confused, no wait... maybe I'm not...

Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 04:14am 30 Jan 2012

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This is very difficult.

Although you may be able to get some long term insolation figures from your local meteorological office for your particular location, local cloud and weather conditions can vary hugely.

For instance, living on one side of a high mountain range to the other, can have a dramatic difference in rainfall and cloud cover, as well as usable direct solar, even though the locations may geographically be fairly close.

Do some research, a nearby university, or major large solar project, may have several years of accumulated data that you can use. A good architect should also be able to get you some relevant local data if you know one.

Once you know the average number of hours per day of direct sunshine per month,and the number of cloudy days per month, you can then start doing some calculations.

As you will know, India is a very big country, and the climate down near the coast is very different to way up in the northern highlands. And the days of direct sunshine will be much higher at the higher northern altitudes than down near the southern coast.

Cheers, �Tony.

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