Solar Math For Sizing The Right Solar Panel System

I think you will agree that understanding the math required to size a solar panel system for your home can be tricky.

It doesn't have to be if you follow the equations laid out in this article.

Discover the exact size of the Solar Panel System you need to power your home.

Understanding the size of the solar panel system you need is crucial to getting the right system installed for your home or business.  Knowing the math will do two things.  First, it will help you to understand how much energy you need to produce to counter the amount of energy you consume.  Secondly, it will arm you with information for when you are meeting with a solar consultant so you can test if they are being honest with you and recommending the right sized system.  For more information on checking out your solar consultant, I recommend reading my "Dummies Guide For Buying Solar" you will discover how to spot solar sales tricks and how to protect your family from them.

One of the best parts of solar energy is that it is math based.  That is a benefit you can figure out how much energy you need to produce down to the kilowatt hours (kWh), based on what you're using during the course of the year.  With this information, you have won 1/2 the battle.  You can then check your math with PVWatts.  PV Watts is a government sponsored site that utilizes calculations from NASA in regards to the amount of sunlight your area receives per day.  Which is an important variable in sizing your Solar Energy System?  In Central Florida, the average sunlight per day ranges from 5.34 to 5.60 depending on if you are located on the west coast in Tampa or inland in Orlando or in the east coast of Melbourne Florida.

Using the calculations included here will allow you to size the solar panel system you need for you home or business.  It will even help you to get and estimated the cost of your system.  Follow the steps and the math equations will take care of the rest.

Calculating Amount of Watts a Solar Panel System will produce

  1. Size of System being recommended – 6kw
  2. Times by the amount of sun per day – 5.6 (florida hrs)
  3. Times by 80% efficiency – 20% is lost by inverters and wiring
  4. times 365 days a year gives you annual production
  5. Divide by 12 for monthly number

Example :  6kw x 5.6hrs = 33.6 x .8(80%)= 26.88 x 365 = 9811.2 wpy / 12 = 817.6 wpm

Calculating System electricity savings

  1. Take watts per year
  2. Times it by electricity rate .12
  3. Divide by 12 to get monthly savings


Example 9811.2 wpy x $.12 = $1177.34 / 12 = $98.11 savings per month

Calculating System Cost

  1. Take the KW in System
  2. Times it by 1000 to get watts
  3. Times it by rate $3.5 per watt


Example 10KW x 1000= 100000 x $3.50 = $35, 000

Calculating The amount of Watts needed

  1. Get electric bill and add up the 12 monthly average daily usage rates
  2.  Times by 30
  3. Divide by 12 for monthly watts


Example 49+50+50+40+27+32+31+35+34+34+42+49+63=536×30=16,080watts

16080/12=1340 watts per month


Calculate Annual Electricity costs

  1. Take total annual watts
  2.  Times it by average electricity cost per watt $.12 FL
  3. For monthly average divide by 12


Example: 16080 x $.12= $1929 / 12 = $161 per month


Calculate How many Panels you need

  1. Take the total amount of KW system
  2. Times by 1000 kilowatts to watts
  3. Divide by efficiency of panels (Canadian Solar is 250)


Example 7.5 KW (system) x 1000 = 7500/250 = 30 panels

Calculate size of PV system needed

  1. Take your annual wpy and divide by 365
  2.  Take your watts per day and divide by amount of daily sun exposure 5 – 5.5
  3.  Take the daily KW needed and divide by a .72 efficiency factor


Example  16080 / 365 = 44.05 kwd /5 =  8.8 kw / .72 = 12.23 kws


Efficiency Factor of 72%

The 0.72 efficiency factor is based on the following assumptions: average solar access of 95% (shading derate factor); modules with a positive-only production tolerance; inverter efficiency of 96%; module temperature derate factor of 0.88; DC and AC wiring derate of 0.98 and 0.99; module soiling derate = 0.95; module mismatch derate = 0.98; system availability derate = 0.99:

0.95 × 0.96 × 0.88 × 0.98 × 0.99 × 0.95 × 0.98 × 0.99 = 0.72

Armed with this information you can find out the best way to size any solar installation project.  No matter if you are installing a solar panel system in Orlando Fl or anywhere else in the country.  just check for the usable sunlight hours.  You can always call Emerald Sun Energy Florida's Premier Solar Power Company to assist you in your equation calculations and have a Free In-home Solar Consultation.  Fully understanding this will protect you from dishonest contractors.  To find every dishonest contractor tip you can read our buyers guide "The Secret Guide to Buying Solar".


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