Panel System Specs

[amarsinha]

Hi everyone,

I'm trying to install my first solar panel system and am trying to figure out the specs, and would appreciate if someone could confirm if I am on the right track with sizing the system because some of it is not lining up to my eyes.

I am trying to power two 1500 W greenhouse heaters - https://www.amazon.com/dp/B06XCJ7Q3S?psc=1&ref=ppx_yo2ov_dt_b_product_details

They will be heating two greenhouses in the winter when I receive around 4-5 hours of peak sunlight per day, and will run a total of approximately 6 hours.

Taking that into consideration and accounting for 3 days of autonomy, I have calculated the following:

• 1,500 W x 2 = 3,000 W x 6 hrs = 18,000 Wh
• 18,000 Wh * 3 DoA = 54,000 Wh
• 54,000 Wh / 0.85 ~= 64,000 Wh (accounting for inverter losses)

So this would mean that I would need a battery bank of at least 54 kWh, right?

And using that I would be able to calculate the size of the solar array as:

• 64 kWh / 4h of sunlight = 16 kW

The math seems right to me, but when I map out the battery bank needed for this, it seems a bit overkill? I'm thinking a 24 V system with two parallel strings of batteries with each string providing at least 2800Ah, to be able to store at least 68 kWh. This would also mean that even if I use 450 W solar panels, I would need a string of at least 36 panels to make up the 16 kW solar array.

If someone can validate my calculations that would be really helpful, as I'm really curious that if this is the case, how houses can run off of solar power with what seems like much less than 30 panels installed on their roofs.

Thank you!
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*Updated to account for inverter losses.

 

[Tomthumb62]

You forgot to account for inverter efficiency losses, which averages at 85% :

54000/0.85= 63,529 Wh

 

[amarsinha]

You forgot to account for inverter efficiency losses, which averages at 85% :

54000/0.85= 63,529 Wh

Thank you, that slipped my mind - have updated the calculations to account for that!

 

[Tomthumb62]

how houses can run off of solar power with what seems like much less than 30 panels installed on their roofs.

Because they’re not using electric heat for hours every day. Running an induction burner to cook up some food for 20 minutes is way different than running 2x1500 heaters all

 

[Rocketman]

That size of solar array will refil 3 days of battery useage in one day. You may be able to use a smaller array - maybe half as much - if you are good with only recharging 50% in a day Or maybe 2/3rds…

Another idea is get a small generator and have only 1-1/2 days of battery- the battery is the expensive part.

Also with that size of system go to 48v.

Good Luck

 

[OzSolar]

If someone can validate my calculations that would be really helpful, as I'm really curious that if this is the case, how houses can run off of solar power with what seems like much less than 30 panels installed on their roofs.

All electric homes aren't 100% solar in the winter. 50% at best.

The challenge with solar and heating is the the peak requirements are opposite the resource peak of the resource. Multiple short cloudy days in a row cannot be overcome with any sort of affordable battery bank.

 

[Sirtate]

What about storing the energy as heat?
ie; Heat water with sunshine, either photovoltaic or just a black panel warming the water.

and when the sun goes down, run a little hydronic heating system of photovoltaic battery storage. Those little circ pumps don't take much wattage, and if the water is heated with solar, it accomplishes the same task as those resistance heaters.

A greenhouse doesn't require much heating on a sunny day, it's the dark of night that gets cold.