Can someone check my plan

tunis0101

After a lot of research I think I'm finally ready to buily my solar system.
I only want to power on my pc with monitor (350 watts) as cheaply as possible.
I will buy two chinese 190 watts solar panels.
And connect them in parallel and connect both with a 40 amps pwm controller using a 5mm wire that extends for 10 meters.
And connect the pwm controller to a 220 amps battery for a little use in the night.
Prices:
Solar panels 60$ each: 120$ total
Pwm controller: 30$
10 meters of 5mm wire: 40$
220 AH Lead acid battery: 40$
Total: 250$ 
Us there any miscalculation in my plan?
Is that the cheapest possible 400 watts system?

BB.

Welcome to the forum Tunis0101,

Part of the planning--What is your rough location? Syria or Tunisia or elsewhere? Hours of sun per day for solar harvest planning?

350 Watt PC+Monitor for how many hours per day? That is actually quite a bit of energy (10 hours per day is as much energy as a very efficient home uses in 1 day).

You know your computing needs better than I... But a laptop using 30 Watts and external monitor (if needed) will use about 1/10th the energy as the 350 Watt PC system.

Also, power usage for computers is highly variable... Measuring your energy usage with an Energy Meter is almost a necessity to plan a workable/cost effective solar power system:

https://www.amazon.co.uk/s?k=kill+a+watt+meter&ref=nb_sb_noss

Just to give you an idea of how much power your solar panels can supply:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Damascus
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 56° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.62	4.11	5.07	5.80	6.46	6.85
Jul	Aug	Sep	Oct	Nov	Dec
6.85	6.71	6.26	5.19	4.05	3.41

For March:

• 390 Watt solar panels * 0.61 best case efficiency daytime use * 5.07 hours of sun (March) = 1,206 WH per day
• 1,206 WH per day / 350 Watt PC = 3.4 hours of operation on "average day"

Much less in winter, and a bit more in summer... Typically we oversize the solar array to account for bad weather and such...

If you have a 12 volt @ 220 AH battery (USD$40 seems too "cheap"):

• 12 volts * 220 AH = 2,400 WH storage
• 2,400 WH * 0.50 depth of discharge = 1,200 WH "useful" (not recommended for daily discharge levels)
• 1,200 WH storage * 0.85 AC inverter eff * 1/350 Watt PC = 2.9 hours of "night operation"
• And it would take 1 day of sun (no PC use) to mostly recharge the battery bank (probably closer to 1.5 days)

Anyway--That is roughly what I see. Your thoughts/comments?

-Bill

MichaelK

The glaringly missing component that I do not see is an inverter?  What kind of power does you computer/monitor need?  Is it 12VDC, 60Hz-120VAC, 50Hz-230VAC?  What?  Your battery can only supply power to 12VDC equipment only.  It can NOT power anything that plugs into a wall socket of your home. 

Is the 220Ah battery 12V or 6V?  Batteries of that Ah size are usually 6V, so you need two in series to get 12V.  Let's assume you use these two batteries in series for 220Ah at 12V.  Assuming you don't want to drain the battery more than 50% then you have 220Ah X 12V X 0.5 = 1320Wh of power, or enough to run your computer for 1320Wh/350W = 3.75hr.  Don't you want at least one light on at the same time you're working on the computer.  Add 100W for that.  1320/450W = 2.9hours.  Is that enough power for you?

tunis0101

BB. said:

Welcome to the forum Tunis0101,

Part of the planning--What is your rough location? Syria or Tunisia or elsewhere? Hours of sun per day for solar harvest planning?

350 Watt PC+Monitor for how many hours per day? That is actually quite a bit of energy (10 hours per day is as much energy as a very efficient home uses in 1 day).

You know your computing needs better than I... But a laptop using 30 Watts and external monitor (if needed) will use about 1/10th the energy as the 350 Watt PC system.

Also, power usage for computers is highly variable... Measuring your energy usage with an Energy Meter is almost a necessity to plan a workable/cost effective solar power system:

https://www.amazon.co.uk/s?k=kill+a+watt+meter&ref=nb_sb_noss

Just to give you an idea of how much power your solar panels can supply:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Damascus
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 56° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.62	4.11	5.07	5.80	6.46	6.85
Jul	Aug	Sep	Oct	Nov	Dec
6.85	6.71	6.26	5.19	4.05	3.41

For March:

• 390 Watt solar panels * 0.61 best case efficiency daytime use * 5.07 hours of sun (March) = 1,206 WH per day
• 1,206 WH per day / 350 Watt PC = 3.4 hours of operation on "average day"

Much less in winter, and a bit more in summer... Typically we oversize the solar array to account for bad weather and such...

If you have a 12 volt @ 220 AH battery (USD$40 seems too "cheap"):

• 12 volts * 220 AH = 2,400 WH storage
• 2,400 WH * 0.50 depth of discharge = 1,200 WH "useful" (not recommended for daily discharge levels)
• 1,200 WH storage * 0.85 AC inverter eff * 1/350 Watt PC = 2.9 hours of "night operation"
• And it would take 1 day of sun (no PC use) to mostly recharge the battery bank (probably closer to 1.5 days)

Anyway--That is roughly what I see. Your thoughts/comments?

-Bill

BB. said:

Welcome to the forum Tunis0101,

Part of the planning--What is your rough location? Syria or Tunisia or elsewhere? Hours of sun per day for solar harvest planning?

350 Watt PC+Monitor for how many hours per day? That is actually quite a bit of energy (10 hours per day is as much energy as a very efficient home uses in 1 day).

You know your computing needs better than I... But a laptop using 30 Watts and external monitor (if needed) will use about 1/10th the energy as the 350 Watt PC system.

Also, power usage for computers is highly variable... Measuring your energy usage with an Energy Meter is almost a necessity to plan a workable/cost effective solar power system:

https://www.amazon.co.uk/s?k=kill+a+watt+meter&ref=nb_sb_noss

Just to give you an idea of how much power your solar panels can supply:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Damascus
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 56° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.62	4.11	5.07	5.80	6.46	6.85
Jul	Aug	Sep	Oct	Nov	Dec
6.85	6.71	6.26	5.19	4.05	3.41

For March:

• 390 Watt solar panels * 0.61 best case efficiency daytime use * 5.07 hours of sun (March) = 1,206 WH per day
• 1,206 WH per day / 350 Watt PC = 3.4 hours of operation on "average day"

Much less in winter, and a bit more in summer... Typically we oversize the solar array to account for bad weather and such...

If you have a 12 volt @ 220 AH battery (USD$40 seems too "cheap"):

• 12 volts * 220 AH = 2,400 WH storage
• 2,400 WH * 0.50 depth of discharge = 1,200 WH "useful" (not recommended for daily discharge levels)
• 1,200 WH storage * 0.85 AC inverter eff * 1/350 Watt PC = 2.9 hours of "night operation"
• And it would take 1 day of sun (no PC use) to mostly recharge the battery bank (probably closer to 1.5 days)

Anyway--That is roughly what I see. Your thoughts/comments?

-Bill

Thanks for your thorough reply.
I am pretty sure that my pc consumes 350 watts because it's old technology and the core2quad processor alone consumes 110 watts when 100% active.
So according to your calculations I should get more panels to extend the daily (morning) usage right? 
The problem is, how would I know that the panels are providing more energy than the power I'm taking through the inverter, because if the energy I'm withdrawing is more than the panels are providing the charging would stop and the all the energy would be wasted, right? Because the battery is a one way power bank.
And yes I am from Syria.

tunis0101

MichaelK said:

The glaringly missing component that I do not see is an inverter?  What kind of power does you computer/monitor need?  Is it 12VDC, 60Hz-120VAC, 50Hz-230VAC?  What?  Your battery can only supply power to 12VDC equipment only.  It can NOT power anything that plugs into a wall socket of your home. 

Is the 220Ah battery 12V or 6V?  Batteries of that Ah size are usually 6V, so you need two in series to get 12V.  Let's assume you use these two batteries in series for 220Ah at 12V.  Assuming you don't want to drain the battery more than 50% then you have 220Ah X 12V X 0.5 = 1320Wh of power, or enough to run your computer for 1320Wh/350W = 3.75hr.  Don't you want at least one light on at the same time you're working on the computer.  Add 100W for that.  1320/450W = 2.9hours.  Is that enough power for you?

I have an old indian 1500 watts inverter that should be fine, and I'm not too worried about the power bank since my use would be only during the day and I'll only power some 30 watts leds and a wifi wouter during the night. 

BB.

A solar charge controller monitors the battery bank state of charge... The charge controller will (for example) will be programmed to 14.75 volts.

1. Bulk: Batteries less than ~80% state of charge--Charge controller allows all current from solar array to battery bank
2. Absorb: as battery reaches ~80% SoC and to 100% SoC, the controller allows enough current to hold the battery bank at ~14.75 volts. The battery bank "naturally" limits charging current from 100% available solar current to less than 1% of battery AH capacity (i.e., 220 AH, battery bank is "full" after charging current falls to less than 2.2 Amps @ 14.75 volts and/or when Absorb stage times out at 2-6 hours of Absorb cycle--2 hours if discharged to 75% SoC and ~6 hours if discharged to ~50% SoC).
   
3. Float: Once charge controller has determined the battery bank is "charged", then the charge controller will fall back to ~13.6 volts and held there (while sun is till up) to keep the battery full (and prevent over charging).

Off grid solar power systems are "over sized" to supply a given load... The idea is that the system can supply power (from the battery bank) at night and during bad weather as well as make up for various losses. A typical off grid power system will only supply about 52% of the solar panel's "rated" output (under standard test conditions). I.e.,

• 390 Watts of solar panels * 0.51 end to end AC system eff * 5.07 hours of sun per day (March) = 1,028 WH per day

The above assumes (mostly) charging during the day, and discharging during the night (the most losses).

Typical system losses:

• 0.81 losses due to Solar panels under full sun on a hot day (hot panels, lower Vmp-array voltage)
• 0.95 losses for charge controller
• 0.80 losses for charging/discharging flooded cell lead acid batteries (different batteries have different losses)
• 0.85 losses for DC to AC inverter conversion
• 0.81 * 0.95 * 0.80 * 0.85 = 0.52 end to end efficiency (52%)

In the USA, our utility power runs from $0.10 to $0.40 per kWH. And off grid solar typically runs $1.00 to $2.00+ per kWH (all equipment, replace batteries every 5 years, electronics every 10 years)... If you shop around and get good prices/used equipment and use most of the energy generated per day--May get down to $0.50 per kWH for a full time off grid system in a sunny climate--And managing loads daily (more loads when sunny, turn off loads when not much sun).

Refrigerators, computers, water pumps, fans, and other loads that run 12 to 24 hour per day use a lot of energy. Things that run for short periods of time per day (microwave oven, electric tea kettle, etc.) may draw a lot of power for 20 minutes per day--Not using as much energy overall.

For example, a 30 Watt light and 25 Watt router/WIFI base:

• 30 Watt light * 12 hour per night = 360 Watt*Hours
• 25 Watt router * 24 hours per day = 600 Watt*Hours
• 15 Watts Inverter Tare Losses (inverter "on" no loads) * 24 hours per day = 360 Watt*Hours
• 360+600+360=1,320 WH per day

Note that I am typing this on a cheap Chrombook computer that uses around 10 Watts, and I could network with my "smart phone" at 2 Watts:

• 10 Watts * 12 hour = 120 WH computer
• 2 Watts * 24 hours per day Phone Hot Spot = 48 WH networking
• 120+48=168 WH per day for laptop and networking

Or almost 1/10th the power consumption that a a 390 Watt array could produce in Damascus.

The battery bank, 2 days of storage, and 50% max discharge (for longer battery life):

• 168 WH per day (cheap laptop) * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days of storage * 1/0.50 max discharge = 67 AH @ 12 volt battery bank

The cheap laptop can browse the web just fine, and run videos+Zoom calls, etc... Cannot run large spreadsheets with lots of data/cells--Need a "bigger" computer to do that.

I know a small laptop (or tablet computer) may not meet your needs--But if it could, the savings in having a much smaller solar power system could possibly pay for the small laptop (or other low power computer+monitor).

In any case, as you can see, even a "few extra loads" used overnight/throughout the day, and it can almost double your power draw.

Details matter here.

-Bill

tunis0101

BB. said:

A solar charge controller monitors the battery bank state of charge... The charge controller will (for example) will be programmed to 14.75 volts.

1. Bulk: Batteries less than ~80% state of charge--Charge controller allows all current from solar array to battery bank
2. Absorb: as battery reaches ~80% SoC and to 100% SoC, the controller allows enough current to hold the battery bank at ~14.75 volts. The battery bank "naturally" limits charging current from 100% available solar current to less than 1% of battery AH capacity (i.e., 220 AH, battery bank is "full" after charging current falls to less than 2.2 Amps @ 14.75 volts and/or when Absorb stage times out at 2-6 hours of Absorb cycle--2 hours if discharged to 75% SoC and ~6 hours if discharged to ~50% SoC).
   
3. Float: Once charge controller has determined the battery bank is "charged", then the charge controller will fall back to ~13.6 volts and held there (while sun is till up) to keep the battery full (and prevent over charging).

Off grid solar power systems are "over sized" to supply a given load... The idea is that the system can supply power (from the battery bank) at night and during bad weather as well as make up for various losses. A typical off grid power system will only supply about 52% of the solar panel's "rated" output (under standard test conditions). I.e.,

• 390 Watts of solar panels * 0.51 end to end AC system eff * 5.07 hours of sun per day (March) = 1,028 WH per day

The above assumes (mostly) charging during the day, and discharging during the night (the most losses).

Typical system losses:

• 0.81 losses due to Solar panels under full sun on a hot day (hot panels, lower Vmp-array voltage)
• 0.95 losses for charge controller
• 0.80 losses for charging/discharging flooded cell lead acid batteries (different batteries have different losses)
• 0.85 losses for DC to AC inverter conversion
• 0.81 * 0.95 * 0.80 * 0.85 = 0.52 end to end efficiency (52%)

In the USA, our utility power runs from $0.10 to $0.40 per kWH. And off grid solar typically runs $1.00 to $2.00+ per kWH (all equipment, replace batteries every 5 years, electronics every 10 years)... If you shop around and get good prices/used equipment and use most of the energy generated per day--May get down to $0.50 per kWH for a full time off grid system in a sunny climate--And managing loads daily (more loads when sunny, turn off loads when not much sun).

Refrigerators, computers, water pumps, fans, and other loads that run 12 to 24 hour per day use a lot of energy. Things that run for short periods of time per day (microwave oven, electric tea kettle, etc.) may draw a lot of power for 20 minutes per day--Not using as much energy overall.

For example, a 30 Watt light and 25 Watt router/WIFI base:

• 30 Watt light * 12 hour per night = 360 Watt*Hours
• 25 Watt router * 24 hours per day = 600 Watt*Hours
• 15 Watts Inverter Tare Losses (inverter "on" no loads) * 24 hours per day = 360 Watt*Hours
• 360+600+360=1,320 WH per day

Note that I am typing this on a cheap Chrombook computer that uses around 10 Watts, and I could network with my "smart phone" at 2 Watts:

• 10 Watts * 12 hour = 120 WH computer
• 2 Watts * 24 hours per day Phone Hot Spot = 48 WH networking
• 120+48=168 WH per day for laptop and networking

Or almost 1/10th the power consumption that a a 390 Watt array could produce in Damascus.

The battery bank, 2 days of storage, and 50% max discharge (for longer battery life):

• 168 WH per day (cheap laptop) * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days of storage * 1/0.50 max discharge = 67 AH @ 12 volt battery bank

The cheap laptop can browse the web just fine, and run videos+Zoom calls, etc... Cannot run large spreadsheets with lots of data/cells--Need a "bigger" computer to do that.

I know a small laptop (or tablet computer) may not meet your needs--But if it could, the savings in having a much smaller solar power system could possibly pay for the small laptop (or other low power computer+monitor).

In any case, as you can see, even a "few extra loads" used overnight/throughout the day, and it can almost double your power draw.

Details matter here.

-Bill

Thanks for another informative reply, as you suggested think I'm going to sell the pc and buy a laptop, that way I can use it in the night too from it's own battery.
And I forgot to comment on why the battery is cheap, that's because it's a basic lead acid battery that's locally used from recycled lead, they last for nearly two years on 50% discharging.

BB.

You are very welcome... I know that I am 12,000 km from you typing on a keyboard. I don't pretend to know what your situation is, or what is "easy or difficult" for you to do/obtain (power meter, laptop, etc.).

Feel free to ask more questions as needed... I know that my guesses/assumptions may not be practical for you. But I hope they give you some ideas of how you can proceed.

Take care and good luck Tunis,
-Bill

BB.

I should add... Make sure you have everything planned out on paper first before you purchase any (more) hardware.

The pieces have to be "engineered" to fit and play together correctly. buying random stuff on sale may not plug and play well together.

-Bill