How Many Solar Panels Do I Need? Sizing a Solar System

Customers always ask us, how many solar panels do i need? We take a lot of factors in consideration for sizing solar. The below information will allow potential solar consumers make an educated decision on what system size they need:

How many solar panels do i need?

What are you solar system expectations?graphic with a sun and lightning bolt

Every HESOLAR system is custom designed to fit the customer’s needs. Our first question for the consumer is, what do you want to accomplish with solar power? The answers can usually be categorized in to off grid power supply, financial savings, and environmental reasons.

  • Off Grid Power Supply: Understanding the difference between grid tied solar, solar w/ backup power, and off grid solar is important for this article. This article will focus on grid tied solar.
  • Financial savings: Most consumers invest in grid-tied solar for the financial benefit.
    • Small to medium solar power systems will knock a chunk out of your electric bill without risking over production.
    • Large solar power systems can completely offset electrical consumption but risk over production.
    • Over Production is when your solar produces more than your home or business consumes. Some utility providers will pay a very small amount for any solar production produced over the user’s consumption. For example, if your home uses 1000 kWh and your system produces 1100 kWh. The utility may only pay offset fuel cost for the 100 kWh your system produced above your consumption.
  • Environmental and Health: Solar panels produce reliable, maintenance-free, energy without producing harmful by products! Consumers that are mainly interested in the environmental benefits are usually happy to hear that HEsolar uses high quality products that are made in America. American production facilities are held to higher environmental and safety standards than most overseas solar manufacturers!

How many solar panels will fit on your property?Roof layout showing solar panels location

1) Estimate the area: Often available area is the limiting factor when sizing a solar array, especially in urban areas. Consumers have the option of a solar roof, ground mounted solar array, solar carport, or custom solar structure.

    • Take a rough measurement of the roof or land space where you plan on placing the solar panels.
    • Make sure roof faces east, south or, west. (Low slope northern facing arrays can utilize tilt leg systems to get southern exposure.)
    • Receives at least 6 hours of sun exposure
    • Roof Mount: Note any roof penetrations. (tip: walk off the base of the home or building to determine roof length, and make an educated guess on the vertical depth)
    • Ground Mount, Carport, and Structures: Make sure the area is a reasonable distance to an electrical panel, up to 250ft (Greater distances will require additional equipment).

2) Fit solar panel rectangles in the area: Once you have a general idea of the available space, you can estimate the amount of solar panels that will fit in the space. The most common solar panels on the market are roughly 40″ x 65″. Figure how many of these rectangles can fit in to your space. Keep in mind that panels can be placed in portrait (long side up) of in landscape (short side up).

3) Calculate system size: Once you have estimated the amount of solar panels that will fit you can calculate the estimated system size. 40″ x 65″ solar panels come in many sizes:

    • 210 Watt: Thin Film modules are less efficient but very cost effective.
    • 250 Watt: Crystalline modules in the 250 watt range are the most cost effective and widely available on the market.
    • 270-280 Watt: Solar World and LG offer premium quality modules in the 270-280 watt range.
    • 300 Watt: LG has a 300 watt line that is a bit pricey and currently unavailable in North America (August 2014). Most suppliers are claiming availability in January of 2015.
    • 327 Watt: Sunpower offers ultra high efficient modules that are often 50% more than 270-280 watt solar panels. Most consumers are not interested in spending 50% more for a 20% power increase.

How much power do you consume?solar panel illustration

Previous electric bills are the easiest way to determine power consumption. Consumption changes with the temperature so try to analyze a full years’ worth of consumption. If the home or building is new we can assist in determining estimated power consumption. The following items should be kept in mind for future consumption:

  • Occupancy change: Will your family or business be growing? The system can be sized larger or smaller to accommodate expected occupancy changes.
  • Electric Vehicles: EV’s consume a large amount of electricity and are becoming more common in the automobile market.

How much will the solar produce?

The following table will help you estimate the amount of solar production you can expect from 1000 watts of solar (1kW).

Month 1 kW – East 1 kW – S. East 1 kW – South 1 kW – S. West 1 kW – West
Jan 67 kWh 89 kWh 100 kWh 91 kWh 70 kWh
Feb 77 kWh 95 kWh 103 kWh 96 kWh 78 kWh
Mar 101 kWh 117 kWh 122 kWh 120 kWh 111 kWh
Apr 109 kWh 117 kWh 126 kWh 124 kWh 113 kWh
May 119 kWh 122 kWh 126 kWh 128 kWh 127 kWh
Jun 130 kWh 129 kWh 129 kWh 132 kWh 134 kWh
Jul 137 kWh 137 kWh 137 kWh 139 kWh 139 kWh
Aug 127 kWh 133 kWh 136 kWh 134 kWh 128 kWh
 Sept 104 kWh 117 kWh 124 kWh 120 kWh 108 kWh
Oct 94 kWh 114 kWh 124 kWh 117 kWh 97 kWh
Nov 67 kWh 89 kWh 99 kWh 91 kWh 70 kWh
Dec 58 kWh 80 kWh 91 kWh 82 kWh 61 kWh
Total 1191 kWh 1340 kWh 1417 kWh 1374 kWh 1236 kWh

Assumes 26° tilt (6/12 pitch), Central Texas location, and 80% AC to DC ratio

Use this general data to estimate the size needed to offset your electric bill.

For Example: If you consume 14,000 kWh and have room on a southwestern roof then you can calculate 14,000 kWh divided by an annual southwestern production of 1,374 kWh, for a 10.18 kW solar power system. ( 14000 kWh / 1,374 kWh = 10.16)

Remember that your system size may be limited to available space. Solar systems do not have to completely offset the user’s consumption. In fact, most customers end up purchasing systems that cover 40 – 80% of their consumption needs, greatly reducing their electric bill.

 

-Eric Hoffman