How Many Solar Panels Do You Need? Follow This Easy Breakdown!

How Many Solar Panels Do You Need? Finally An Easy Answer!
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Trying to figure out how many solar panels you need is confusing! I found 5 different ways to calculate the number, and none of them were easy to follow. In this video, we'll take a look at the math behind this question and go through it step-by-step with an example to follow.

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[terrylane]

I am building an off-grid system for my house. During my peak month in December, I used 28 KWH per day. I live in Hawaii, so I put in my ZIP code to figure out number of hours of usable sunlight per day. It is 5.25 hours in December and 6.6 hours in July. I found bifacial Qcell panels that are 455 watts. There's a separate structure built just for solar generation that keeps the lines under 25 ft in length. EG4 18Kpv inverter and battery setup should keep me below 18% system loss. The structure was built to hold solar panels at 21° facing directly south. Accounting for albedo from clouds, I needed at least 9 KW with a 28 KWH battery.

[JDHarrington]

I've seen this formula listed on several Youtube videos. What I don't understand is the solar panel wattage figure. For example, the SILFAB-SIL-400 solar panel has a STC (best case) rating of 400 watts, but under normal operating conditions, it's rated for 298 watts. This is basically true for all solar panels. If you use the higher number, it would seem you'd be designing a system that would only produce approximately 75% of what was actually needed...

[beholdmatsikure]

This really helped with my school project

[crisg]

thank you for the information, was to useful to my

[inkdelencquesaing]

It's rare for a 100w panel to average 100w: in addition to the hrs/day not being an average of 12 hours on the equinox (4-6 hrs in summer in the southeast, due to clouds, or it's not getting full sun at 6AM-11AM, etc),
you should also multiply by 85%. because clouds or line losses also make it "only a 100w panel under perfect laboratory conditions".
I'd also go by your worst month (Aug-Sep in south, Jan in north), unless you have generator/microhydro for that month or for special occasions

[donfrank]

very good info. going to build a bigger system with solar /grid/battery, . built a 2 panel 100w solar system to charge my battery in my BBQshed last year for the fun ; I still ran 110v to a sub panel to run my refrigerator . thanks so much for the break down

[teemum.]

a house with electrical heating only uses 32 kWh per day in Finland. That´s 20 panels at 4 hours of sun per day. I don´t know what upper class American business elite uses 47 kWh per day. I would like to know how to get bare minimum for Panasonic heat pump, floor heating in two rooms, appliances, hot water and lights. Would 16 kWh per day and 10 panels suffice? I would use fireplace too.

[_jasonj_]

For panel sizing, panels never output their rating, more like 75-85% so I assume if you're really going for 100% offset, you need to use the NOCT values for each panel?

[bahmannosratollah]

Thank you so much for sharing your knowledge with everybody. Great explanation and easy to understand. Thank you.

[teemum.]

I want to power a 1.2 kwh heater + 0, 12 kwhheater (these are actual momentary usages) + 2.15 kwh sauna + 0.53 kwh water boiler + 0.62 kwh heat pump + freezer and fridge and others 1 kwh. How much do I use per year if these appliances take 5.62 kwh while running? How big inverter do I need? 6 or 8 kwh? How many panels will this amount to? In the winter we have 5 hours or daylight. In the summer we have 18 hours daylight. How can I send excess power back to the grid and get paid by the company?

[kashaanmahmood]

Thank you so much. I am an engineer but i didn't get calculate this right myself 😅

[irvingdomenech]

Thank you so much for that formula!!!! That way people don't get under sold or over sold on the necessary equipment.

[bradley]

A 400 watt panel will only pass 300 watts through the most commonly used micro inverter I have not heard of any micro inverters rated for over 300 so we are basically leaving 25% of the capacity of these big panels unused on the roof for ever none of the sales people ever tell you that do they ?

[giovanny]

THANKYOU!!! I have been looking for this and everywhere I go starts with a damm sales pitch and I just want to know how many panels I need, then I'll decide if I want to go to solar or not.

[mixedbeans]

How do you figure this out for a new build?

[jetmartin]

Nice video...Question: Are those kWh you've plugged into to spreadsheet. I'm asking because I only used ~3, 800 kWh all last year based on last 12 mos of data from the power company...So the huge discrepancy in your numbers vs mine makes me question whether I'm using the right numbers...My numbers are from each bill and listed as xxx kWh for the month....so each month on average is about 300kwh per month. That seems WAY too low compared to your numbers and that calculates to about 6 panels (rounded up).

[Goodellsam]

How do you figure that out if it will be new construction.

[bahmannosratollah]

I watched this video over 4 times, I should like it 4 times.

[michaelbrininstool]

Barely got through the first minute....before a common mistake was made: power is in units of Watts, while kWh is energy (not power). Power x time = Energy. Minor and common mistake, but should correct it moving forward.