# Help: regarding solar system installation? clear some doubts...

Status
Not open for further replies.

#### Clarkdale44

##### Member
Hello

I need to clear some doubts about solar power.. I will write down my theory please correct them if i am wrong.

I must tell you that i have absolutely no knowledge of solar power system. I have tried google but couldn't understand how solar panals are calculated and how many batteries and what volt system.

If someone has 18x 245w solar pv, then what volt system should he use, 12, 24, 48 ? and why?

If using 48v system then how the panal connection will be like?

I would connect 4x panals in series to make 48v (12x4) and 14x panals in parallel to make total of around 3600 watts, is this correct?

For 3600watts of power how many batteries would require?
4x 12v battery is must to make 48v but how many amp hours(AH rating) if i need backup of around 5-6 hours?

Also i would use an AC inverter to power my electrical appliances.
How many watts or kva of inverter one would require to handle 3600 watts?

If anything is not calculated correctly or not correct please correct them and give me your insight thoughts on it.

Regards!!

Last edited:

#### spec

##### Well-Known Member
Hi Clarkdale,

Where are you from: care to put it next to 'Location'on your user page so that your location displays in the window on the left of your posts.

SOLAR PANEL TOTAL POWER
I assume that your solar panels are 12V, 245 Watts each.

Also you say that you have 18 panels.

That means that when all the panels are in bright sunlight they will be capable of producing a total of, 18 * 245 = 4410 watts or 4.41 Kilo Watts.

BATTERY CAPACITY
You say that you want to store 3600 Watts for 5 hours to 6 hours of energy in the battery or batteries. I will take the duration to be 6 Hours

If you had a single 12V battery the Amp hour capacity would need to be, (3600 Watts/12 Volts) * 6 Hours = 1800 Amp/hours

A more practical solution, for example, would be to use 18 of 12v 100 A/H, deep discharge, lead acid batteries.

INVERTER
You say that you want a mains output of 3600 watts, but as you have not told us where you are we do not know what your mains supply is liable to be.

But, in general, an inverter will operate at around 80% efficiency at full load, so you would need an inverter of (100%/80%) * 3600 Watts = 4500 Watts capacity

SYSTEM VOLTAGE

The solar system voltage you chose is concerned with practical aspects and does not affect the above.

GENERAL
The above are just the fundamental aspects of your solar system. There is quite a lot to consider when designing an efficient solar system and Maximum Power Point (MPP) and other control will be required. The detailed design of the solar system involves many aspects which need to be discussed/investigated further.

spec

Last edited:

#### Clarkdale44

##### Member
Hi Clarkdale,

Where are you from: care to put it next to 'Location'on your user page so that your location displays in the window on the left of your posts.

SOLAR PANEL TOTAL POWER
I assume that your solar panels are 12V 245 Watts each.

Also you say that you have 18 panels.

That means that when all the panels are in bright sunlight they will be capable of producing a total of, 18 * 245 = 4410 watts or 4.41 Kilo Watts.

BATTERY CAPACITY
You say that you want to store 3600 watts for 5 hours to 6 hours of energy in the battery or batteries. I will take the duration to be 6 Hours

If you had a single 12V battery the Amp hour capacity would need to be, (3600 Watts/12 Volts) * 6 Hours = 1800 Amp/hours

A more practical solution, for example, would be to use 18 of 12v 100 A/H, deep discharge, lead acid batteries.

INVERTER
You say that you want a mains output of 3600 watts, but as you have not told us where you are we do not know what your mains supply is liable to be.

But, in general, an inverter will operate at around 80% efficiency at full load, so you would need an inverter of (100%/80%) * 3600 Watts = 4500 Watts capacity

SYSTEM VOLTAGE

The solar system voltage you chose is concerned with practical aspects and does not affect the above.

The detailed design of the solar system involves many aspects which need to be discussed/investigated further.

GENERAL
The above are just the fundamental aspects of your solar system. There is quite a lot to consider when designing an efficient solar system and Maximum Power Point (MPP) and other control will be required.

spec
Thanks for your explanation, my mains AC voltage is 230v 50Hz.
About system voltage, they say there is a thumb rule that for every 1000watt we have to switch to a higher volt system.
0-1000w - 12v
1000 - 2000w - 24v
2000- 4000w - 48v

I saw this on google, just confirming it here again. And they say higher volt system is more efficient and uses thin cables and less to no voltage drop, i have no idea what that means but it looks something i would like to be aware of.

Last edited:

#### spec

##### Well-Known Member
Thanks for your explanation, my mains AC voltage is 230v 50Hz.
No probs Clarkdale44.

spec

#### ClydeCrashKop

##### Well-Known Member
I suggest checking out sites like this for ideas.
GRID-TIE / OFF-GRID SOLAR PANEL KITS, HOME BACKUP
https://www.bluepacificsolar.com/
A couple friends installed PV solar systems on their houses in Montauk Long Island. They used professional grid-tie kits & sold power back to the electric company. Even with short winter days and gray sky all winter, it paid for their heating and they made money in the summer. The state and the electric company and one other organization gave them major rebates & incentives. One of them installed most of it himself and it was almost free! Look here to find incentives for your state.
https://www.bluepacificsolar.com/solar/states-incentives.html

I see now that you are not in the U.S. but there may be something similar in your country.

#### spec

##### Well-Known Member
Thanks for your explanation, my mains AC voltage is 230v 50Hz.
About system voltage, they say there is a thumb rule that for every 1000watt we have to switch to a higher volt system.
0-1000w - 12v
1000 - 2000w - 24v
2000- 4000w - 48v

I saw this on google, just confirming it here again. And they say higher volt system is more efficient and uses thin cables and less to no voltage drop, i have no idea what that means but it looks something i would like to be aware of.
Yes,

There are practical aspects to consider with power systems, but the power of the system is constant. Thus taking a 3,600 watt solar installation at different voltages the currents would be:
(1) 12V system, current = 3,600 Watts/12V = 300 Amps
(2) 24V system, current = 3,600 Watts/24V = 150 Amps
(3) 36V system, current = 3,600 Watts/36V = 100 Amps
(4) 48V system, current = 3,600 Watts/48V = 75 Amps
(5) 60V system, current = 3,600 Watts/60V = 60 Amps
(6) 72V system, current = 3,600 Watts/72V = 50 Amps
(7) 84V system, current = 3,600 Watts/84V = 42.86 Amps
(8) 96V system, current = 3,600 Watts/96V = 37.5 Amps

As you can see, the 12V system would be fraught with problems due to the high current involved: can you imagine how thick the cables to carry the current would be. Also controlling that much current would be very difficult, inefficient, and expensive. One of the main problems is the voltage drops caused by cable resistance and contact resistance due to such a high current.

On the other hand, the current of the 96V solar system would be quite manageable.

Incidentally, this principle of reducing the current and increasing the voltage to increase efficiency, is why national grids operate at such unbelievably high voltages of up to 400,000 Volts in the UK for example.

spec

PS: as you still have not told us where you are, note that in the UK, a comma in a number is a separator not a decimal point, as is the case in some countries.

Last edited:

#### KeepItSimpleStupid

##### Well-Known Member

That becomes your starting point. Knowing how much energy per day would impinge on your solar panel facing a given direction.

The panels are rated at 1 SUN (100 mW/sqcm) at 25 degrees C. The spectrum is AM (Air Mass) 1.5 Global and typically means noon on a clear day The cell/array operates between V (open circuit) and 0V. Jsc is the current at 0 Volts (not useful), but the inverters have to operate within those limits.

The power is given at the max power point (Jmp/Vmp) . I may be using J instead of I because I worked in the research end of it. J is current/area and I is actual current.

Maximum power tracking is a way of milking the system for all it's worth. The panels can move or the operating point changed.

Don't forget efficiency of ALL of the parts. You have the amount of sunlight, the efficiency of the panels (maybe 5-15%), the efficiency of the inverters (80-95%) etc. There's seasonal variations, snow dust etc. Some systems have a way to clean the panels automatically.

There's some things you do have to realize:
1. Stand-alone (batteries)
2. Grid-Tie (when there is no utility power, you don''t have any solar power either)
3 Combo systems are becoming available.

Micro-inverters are now being used, These are smaller inverters placed at every panel raising the voltage.

specs table was cool, but to help understand it. The current capacity of a wire is related to how thick it is (specifically the cross-sectional area) and the material (usually copper). For power distribution (AC mains) the US likes about 2-3% loss and 80% loaded for what they consider a "continuous" load. The fatter the wire the lower the resistance. The voltage drop across the wire is V=I*R thus the low I is or the lower R is the lower the loss.

So batteries are a real hassle. When you co-generate, you may use electricity at the consumer rate, but excess electricity could be sold back to the utility at the wholesale rate. So, for someone that is working during the day and not home there could be less of a benefit.

Payback may be harder to calculate, when you consider, batteries (every 5), roof replacement (15-25 years), lifetime (25 years is a good number).

#### Clarkdale44

##### Member
Thank you guys for all the information you have shared.. I just have one last query..

Suppose,

I have 600w panals with around 35 amps output (4x 150w 8.86 amps 12v in parallel) and connected to a pwm charge controller rated for 30 amps and that is connected to a 150 ah single battery and that battery is also connected to a dc to ac inverter 1000w 230v 50Hz . Is this setup correct or do i need one more 150ah battery connected in parallel.

I basically wants to run my 400 - 450watts load during day time from solar power and store the extra juice into the batteries. Can i do that with just one 150ah battery or do i need to add one more?
There may be times when no power is being used from the solar and all 600watts will be fed to the battery at about 25 to 30 amps until it gets fully charged if the charge controller is efficient enough which i doubt.

Let me summarize it again.. What i am trying to ask is whether or not i can use 600Watts solar panals with only single 150ah battery?

Last edited:

#### nsaspook

##### Well-Known Member
On the narrow question of simply charging the battery.
It depends on the type of battery.
If it can accept a possible C/5 recharge without problems then a 150Ah battery can utilize the full capacity of the (no other loads) solar when discharged. Now you could reduce the C/5 rate to C/10 by doubling the Ah capacity to 300Ah, keeping the SOC above 50% so the effective battery is 150Ah. This will give you a safety buffer and prolong battery life if you can keep them full charged daily.
http://batteryuniversity.com/learn/article/what_is_the_c_rate

The wider question of will it work in practice with loads depends on the usual solar energy storage off-grid energy in/out calculations.

Status
Not open for further replies.