Is there a quick calculator to determine panels/batteries/inverter needed?

[zzzgregzzz]

Hello!

My plan is to create an attic fan.
The current solar versions do not push enough air for the price you pay. I have a pretty big attic in an old brick home.
I am looking at AC versions for due to their CFM values.

Example: via Amazon
Broan 353 1140 CFM Gable Mount Powered Attic Ventilator

Specs:
120V
3.4 Amps

In this case I will need :

• A Panel
• Inverter
• Battery
• Charge controller

**I know...I know... it is probably cheaper just to run it on AC...but my birthday is coming up so I can have some family member buy some things **

Soo...how would one calculate what is needed?
Where do you start first?
I don't want to spend extra on things if they are not needed...ex. buying a 5000watt inverter just because 5000 watts sounds cool.

1. What is the bare minimum to keep that fan moving air during the hot months of summer?
2. How do you calculate if things would change...ex add a second fan?

Thanks!
Greg

[Naptown]

Hello!

My plan is to create an attic fan.
The current solar versions do not push enough air for the price you pay. I have a pretty big attic in an old brick home.
I am looking at AC versions for due to their CFM values.

Example: via Amazon
Broan 353 1140 CFM Gable Mount Powered Attic Ventilator

Specs:
120V
3.4 Amps

In this case I will need :

• A Panel
• Inverter
• Battery
• Charge controller

**I know...I know... it is probably cheaper just to run it on AC...but my birthday is coming up so I can have some family member buy some things **

Soo...how would one calculate what is needed?
Where do you start first?
I don't want to spend extra on things if they are not needed...ex. buying a 5000watt inverter just because 5000 watts sounds cool.

1. What is the bare minimum to keep that fan moving air during the hot months of summer?
2. How do you calculate if things would change...ex add a second fan?

Thanks!
Greg

There is a calculator here

http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design

But unless your are paying a US $1.00 or more a KWH hour just do a standard electric one.

[zzzgregzzz]

Let me try this....

Thanks for the response....

Let me try my luck at figuring this out based on the guide...here we go
Be nice if I make a mistake.

1. Worst Case Factor (PA Location)

• I need the fan to run for 8 hours (note: thermostat may make it run less)
• This fan at 3.4amps/120 volts - I think translates to approx 408 watts
• Will need to run in the 5 months (May - October)
• 408 Watts * 8 Hours = 3264 watt hours

2. Fudge Factor

• 3264 * 1.5 = 4896 watts

3. Solar Isolation/hours

• I will average to 6 hours

4. Size of Solar Array

• 4896/6 = 816 = 900 watts

5. Battery Size

• 3264 x 5 = 16320 or 16,000Kwh
• 16,000/12v =1333 Amp Hours

6. Charge Controller

• 900/12 = 75 or 7.5amp?

Soo...If I did this correctly...
I will need to obtain 900 watts in solar panels and 1333 amp hour battery system to run a fan for 8 hours during a day...wow....maybe I should stick with running on AC.

[Naptown]

Thanks for the response....

Let me try my luck at figuring this out based on the guide...here we go
Be nice if I make a mistake.

1. Worst Case Factor (PA Location)

• I need the fan to run for 8 hours (note: thermostat may make it run less)
• This fan at 3.4amps/120 volts - I think translates to approx 408 watts
• Will need to run in the 5 months (May - October)
• 408 Watts * 8 Hours = 3264 watt hours

2. Fudge Factor

• 3264 * 1.5 = 4896 watts

3. Solar Isolation/hours

• I will average to 6 hours

Too high even in the summer Go to Gaisma to get the true insolation


4. Size of Solar Array

• 4896/6 = 816 = 900 watts

Again too low


5. Battery Size

• 3264 x 5 = 16320 or 16,000Kwh
• 16,000/12v =1333 Amp Hours

6. Charge Controller

• 900/12 = 75 or 7.5amp?

Actually 80A

Soo...If I did this correctly...
I will need to obtain 900 watts in solar panels and 1333 amp hour battery system to run a fan for 8 hours during a day...wow....maybe I should stick with running on AC.

See my point?
Now go with a Home depot fan and $.15 a KWH and see what that costs to do.

Better idea is to go with a grid tie system where there is at least a chance of a return on the investment.

I hope your family members are wealthy. batteries alone will be well over a grand

[Sunking]

Soo...If I did this correctly...
I will need to obtain 900 watts in solar panels and 1333 amp hour battery system to run a fan for 8 hours during a day...wow....maybe I should stick with running on AC.

You did it correctly but used way too many sun hours. Based on your location and time of year use 3.8 Sun hours which pushes your panel wattage up to 1300 watts and that forces to use a 24 volt battery, and 60 amp MPPT Charge Controller. So you are looking at around $6000 with $3000 of that in batteries you have to replace every 3 to 5 years.

[zzzgregzzz]

UGH....Fun just ran out of the building...

OK, never in my wildest dreams would I think that running a $62 attic fan via solar/batteries for 8 hours a day would translate into a >$5000 investment cost?!?!!
My Elect cost is 8.636 cents per kWh....on AC the cost is $0.28 cents per hour x 8 hours $2.24 a day.
sigh.

Thanks for the feedback!
greg

[Sunking]

My Elect cost is 8.636 cents per kWh....on AC the cost is $0.28 cents per hour x 8 hours $2.24 a day.

Huh? How does $0.08636/Kwh go up to $0.28/Kwh. What am I missing here?

[inetdog]

Huh? How does $0.08636/Kwh go up to $0.28/Kwh. What am I missing here?

You just take 3264 watt hours per day, multiply it by $.0836/kWh to get $.2818 per day, then lose track and think that what you got was $ per hour instead of per day.
Easy as pie. (He said $.28 cents per hour (!?!) not per kWh.)
You are so good at doing the right calculations that you do not always recognize what went wrong.

[SunEagle]

You just take 3264 watt hours per day, multiply it by $.0836/kWh to get $.2818 per day, then lose track and think that what you got was $ per hour instead of per day.
Easy as pie. (He said $.28 cents per hour (!?!) not per kWh.)
You are so good at doing the right calculations that you do not always recognize what went wrong.

The fan is 0.408kw x $.08636/kwh = $.03523/hr x 8 hr = $.2818/day x 365 day/yr = $102/yr. Pretty cheap for me to run it on AC instead of solar.

[Sunking]

The fan is 0.408kw x $.08636/kwh = $.03523/hr x 8 hr = $.2818/day x 365 day/yr = $102/yr. Pretty cheap for me to run it on AC instead of solar.

That is why I was asking, he even got AC power wrong and made it %350% higher than what it really is. Initially I thought maybe he meant his Air Conditioner (AC) uses 3.2 Kw or a 4 ton unit.

[philsaudio]

Fan spacing

Beside matching CFM, to get the right ventilation you need to space attic fans every 10' or so, no matter what CFM they pull.

wage peace

[russ]

Beside matching CFM, to get the right ventilation you need to space attic fans every 10' or so, no matter what CFM they pull.

wage peace

Why? That makes no sense at all.

[SunEagle]

Why? That makes no sense at all.

Unless he is selling attic fans.

Oh. Don't forget the big hole at the other end of the attic so your supply cfm matches you exhaust cfm. Wouldn't want to suck air out of the house now.

[Mike90250]

Unless he is selling attic fans.

Oh. Don't forget the big hole at the other end of the attic so your supply cfm matches you exhaust cfm. Wouldn't want to suck air out of the house now.

Well, you do if you want to open a bedroom window, and suck cool nighttime air in, through the attic hatch, and then out the roof. I've done that with a 20" box fan zip-tied into the attic hatch hole. Works like a charm. No noisy fan in the bedroom either! It's a $20 whole house vent sytsem.

[SunEagle]

Well, you do if you want to open a bedroom window, and suck cool nighttime air in, through the attic hatch, and then out the roof. I've done that with a 20" box fan zip-tied into the attic hatch hole. Works like a charm. No noisy fan in the bedroom either! It's a $20 whole house vent sytsem.

My first house had a big attic fan and a louver in the ceiling. Opening a window on the shady side of the house did bring in cooler air since we did not have Air Conditioning.

I have see people put in a lot of fans but forget to provide enough opening to provide the make up air. Then they get a lot of negative pressure in the attic which then try to find ways through other openings in the roof to equalize the pressure. Not a good thing to let happen.