1.14kw solar for greenhouse fans

steelheadguy

Hey everyone. Sorry to make my first post a question, but I really need some help or reassurance.

I run an off grid greenhouse. Currently I am running AC fans off of my honda eu2000 generator. I am switching to solar powered DC fans. I will not need an inverter to start.

So far I bought (4) 285 watt 24 volt panels.
I am powering (6) 30 watt and (4) 90 watt fans.
That is a 1140 watt array to power 540 watts. I included extra to help charge batteries.

Should my battery bank be 24 volt or 48 volt? I do not get many cloudy days so I only need about 12 hours stored. Would about 200 amp hours be sufficient? Which batteries and how many do I need?

Do I need a 30 amp controller? Please suggest one sized for me. I am really not sure about what type I need.

Thanks for any help. I plan to share my troubles and how I corrected them.

BB.

Welcome to the forum SteelHeadGuy.

Need to understand your loads first. Do you need to run the fans on cloudy days? 9 months a year? How much sun do you get in your location (nearest major city)? etc...

But as a start: Assuming you need to run the fans 1 day of clouds and 50% maximum discharge (that is pretty hard on batteries--But if you are doing seasonal growing of a few months a year):

• 540 Watts of fans * 12 hours per day * 1/0.85 AC inverter eff * 1/48 volt battery bank * 1 day of storage * 1/0.50 maximum discharge = 318 AH @ 48 volts

If you only need 1 day of storage, then you could also do a 635 AH @ 24 volts too... (as the battery bank AH rating gets over ~600-800 AH, you are usually better off going to a higher voltage rating).

And if this is a near full time greenhouse, say >9 months a year and you want to be a bit more conservative in your design, 2 days of storage:

• 540 Watts of fans * 12 hours per day * 1/0.85 AC inverter eff * 1/48 volt battery bank * 2 day of storage * 1/0.50 maximum discharge = 635 AH @ 48 volts

Note, this is not a small battery bank or a small amount of power usage. If you can find more efficient DC fans/improve natural airflow through natural convection, etc., conservation/reducing power usage will be your friend here.

Also, if this is a seasonal operation, then the Honda eu2000i may still be your most cost effective power source (plus "cheaper" AC fans).

Next, how much in the way of solar panels to power this load... We recommend 5% to 13% rate of charge (based on AH rating of battery bank)--And 10%+ rate of charge for full time usage. I.e., the larger the battery bank, the larger solar array you should have.

If we use the 1 day storage battery bank (the 2 day storage would be 2x larger solar array):

• 318 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,198 Watt array minimum
• 318 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,395 Watt array nominal
• 318 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,114 Watt array "cost effective" maximum

And then there is sizing the array based on power usage and number of hours per day of sunlight.... For much of the US, usually you will get 4.0 hours of sun for 9+ months a year:

• 540 Watts * 12 hours per day * 1/0.52 off grid power efficiency * 1/4.0 hours of sun minimum =3,115 Watt array minimum

And here is where you get "hurt"... Off grid power systems give only about 50-60% of the nameplate Solar Panel power Wattage listing.

Solar panels are, on average, about 81% of name plate, charge controllers are about 95% efficient, flooded cell lead acid batteries can be as low as 80% efficient, AC inverters run around 85% average efficiency, etc.

So, a lot of this depends on what your exact power needs are... For example, can you cut back on the number of fans on a cloudy day (smaller battery bank, smaller solar array). Is this going to be a 1-2 season operation (more sun) or 3-4 season (lower sun angles, more cloudy weather), etc...

The above is probably "way over kill" for your needs--The design is based on the assumption you need the fans every day, even when there is no sun (very dark/stormy skies may give you only 5% or so of clear sky power).

-Bill

mike95490

The DC voltage your fans operate at, should be the nominal voltage of the battery bank, But if they are 12V, you may as well backup and use cheap AC fans, and an inverter.
The fans you list, will, over 24 hours, consume (6) 30 watt 4320wh (4) 90 watt 8640wh for a total of 12,960 watt hours (13KWh) Only v 540 watts running, but Wow. That's for sure, 48V territory.
At 48V, that consumes 270Ah, for a 4 hour solar recharge, you need almost 7,000 nameplate watts of PV. So, you need to re-evaluate your running hours

Dave Angelini

Why do you need to run fans at night for a greenhouse?
24vdc fans are abundant and rare at 48vdc, so if you must do this 24vdc is the way. I however believe you could direct drive from the array to the fans with a controller and not use batteries. We do BTW.

BB.

For some indoor growing settings, I believe they use fans to mix the air around the plants. So the air circulating around them during the day.

-Bill

steelheadguy

I am not running the fans at night. The fans operate are variable voltage https://snap-fan.com/ . They are most efficient at 48 volts.
They are DC fans so there will be no inverter.
I very rarely get a cloudy day. Will these four panels charge a large enough battery bank for one day? Even if it takes a week to charge?

I ordered an Outback Flexmax 60 controller. Is this overkill?

steelheadguy

How do I direct connect the fans to the panels? Just to the controller?

inetdog

steelheadguy wrote: »

How do I direct connect the fans to the panels? Just to the controller?

No. To the panels themselves, possibly with a Linear Current Booster in between. In this configuration the fans would never run off the batteries. Only when the panels are producing.

Note that this is not an option if the panel voltage is too high for the fans.

steelheadguy

Hey everyone sorry to bring up this old post. I ran all of my fans for 6 months this season without a hitch. I connected them straight to the panels and they ran while the sun was up. Surprisingly even while cloudy. This year I am hoping to put in a battery bank. Before I start a new thread I figured I would ask here.

What is the largest battery bank a 1.14 kw array could charge? I know my array is larger than needed for my fans, so what can I be charging?

westbranch

steelheadguy said:

I am not running the fans at night. The fans operate are variable voltage https://snap-fan.com/ . They are most efficient at 48 volts.
They are DC fans so there will be no inverter.
I very rarely get a cloudy day. Will these four panels charge a large enough battery bank for one day? Even if it takes a week to charge?

I ordered an Outback Flexmax 60 controller. Is this overkill?

just looked at the spec sheets and i did not see 48 V mentioned, only 35 max...???

BB.

Well... Starting with the basic 5% to 13% rate of charge (typical for solar power systems). Assuming a 48 volt battery bank charging at ~59 volts:

• 1,140 Watt array * 0.77 panel+controller deratings * 1/59 volts charging * 1/0.05 rate of charge = 298 AH @ 48 volt maximum battery bank (weekend/seasonal use)
  
• 1,140 Watt array * 0.77 panel+controller deratings * 1/59 volts charging * 1/0.10 rate of charge = 149 AH @ 48 volt nominal (good for daily off grid system usage)
  
• 1,140 Watt array * 0.77 panel+controller deratings * 1/59 volts charging * 1/0.13 rate of charge = 114 AH @ 48 volt minimum battery bank

Note--If you are sharing the fans as a load with your battery bank--Then your maximum available charging current will be reduced by the current drawn by the fans... Which would decrease the supportable size of the battery bank.

-Bill

South Africa

BB, the charge rates are all 0.05 above, instead of 0.05, 0.10, 0.13?

BB.

Thank you South Africa.... I had forgot to edit the actual charge rate after the cut and paste.

-Bill

steelheadguy

I am planning with a .13 rate of charge for a good healthy charge. 114ah at 48v.

My 4 panels are 24v, I had them wired in 2 series for 48v. 

Sorry for the beginner question. But if I have a 24v bank instead of 48v, will this change the amp hours at a .13 rate?

BB.

Remember--If you have a set of batteries--No matter how you wire the set in series/parallel, the stored energy is the same:

Say you have 200 AH @ 6 volt batteries (golf cart)--4 of them:

• 4 in series:
• 200 AH * 24 volts = 2,400 Watt*Hours of storage
• 
  
• 2 in series, two parallel strings:
• 400 AH * 12 volts = 2,400 WH of storage

Adding batteries in series, raises voltage. Batteries in parallel, raises Amps (Amp*Hours).

Same thing for solar panels (series/parallel connections).

-Bill

steelheadguy

What I meant was

1,140 Watt array * 0.77 panel+controller deratings * 1/59 volts charging * 1/0.13 rate of charge = 114 AH @ 48 volt minimum battery bank

Is it still 114ah at a 24 volt battery bank? Excuse my brain is not working today.

vtmaps

steelheadguy said:

Is it still 114ah at a 24 volt battery bank? Excuse my brain is not working today.

No, it will be 228 ah at 24 volts.  --vtMaps