How to Get Started with Solar Power

The following guide will help you start exploring the possibility of going solar at your house. Let’s first get up to speed on solar electricity basics with a few key definitions:

PV Module: aka a solar panel, converts energy from the sun into direct current (DC) energy. PV Modules come in varying wattages and sizes. Typical PV modules used on home installations are 200 watts and about 14 square feet.

PV Array: A number of PV modules wired together. Using 5 x 200 watt PV modules creates a 1,000 watt PV array. Typical array sizes range from 2,000 to 5,000 watts and up.

Inverter: Converts DC electricity into alternating current (AC) electricity used around the house. A 3,000 watt inverter will output 3,000 watts of AC electricity given enough PV input. Typical inverter sizes range from 2,000 watts to 7,000 watts.

Grid-Tied Solar System: An electrical system comprised primarily of a roof or ground mounted PV array and inverter, which are connected to and interact with the utility grid. Other devices called over current protection devices or OCPD are used for safety. Energy from the PV array goes fist to household loads and any extra power is stored on the utility grid.

Kilowatt Hour (kwh): One kilowatt (1,000 watts) for 1 hour = 1 kilowatt hour. The utility company charges you by the number of kwh you use.

The three main factors that will determine your eventual grid-tied solar electric systems are daily energy requirements, available shade-free space, and project budget.

Daily Energy Requirements: The PV array will be generating most if not all the energy your home needs, so looking at your own usage is a good place to start. Look on your utility bill or call your utility company to find out your energy use in terms of kilowatt hours per day or kwh/day. It’s best to use the average kwh/day for the last 12 months to account for seasonal variations in energy consumption. While you’re talking to the utility company, ask them for their “interconnection agreement.” This is essentially the contract you’ll enter with them when you connect PVs to their grid. Once you know your average kwh/day usage you can plug this number into simple calculations to determine system size and cost.

Shade-Free Space Available: PV modules need direct sunlight to produce electricity. Even a little shade on the PV array will cause significant drops in power generation. The PV array needs to be in a location where it will receive direct sunlight between 10am and 3pm. The early morning and late afternoon hours don’t really count for solar production because the sun’s rays pass through too much atmospheric debris to be “strong” enough to produce much power.

Every location on Earth has an average “Peak Sun Hours” ranging from 4-6hrs, or the yearly average number of hours per day for good solar production. These peak sun hours occur between 10am and 3pm, so shading outside this time is less of a concern. Tools like solar pathfinders and sun charts can be used to find out if that big tree across the street will shade the PV array in December/January. You might have more shade-free space than necessary or it could be the limiting factor in your system’s size.


Project Budget: Solar electric systems are not cheap and usually cost more than expected. Modest systems start at around 5K but the majority fall in the 20K-40K range. There are federal and state incentives and rebates to take advantage of that will significantly decrease out of pocket costs. It may not be possible to produce 100% of the energy you use and many systems are supplemental, producing as much as space and/or budget allow.

The cost becomes more reasonable when looked at as a long term investment. After all, you are pre-paying for your electricity at a fixed rate for what could be the rest of your life and providing free energy for your kids and grandkids. People often complain about a long payback period, but isn’t any payback whatsoever a good thing no matter how long? What’s the payback on the last car you bought? A PV electric system is a risk free investment with a guaranteed payback.

Easy calculations for system size and cost:

If you know your average kwh/day or know how many kwh/day you would like to produce, a simple calculation will determine system size and cost.

System size in kilowatts (kw) = (kwh/day) / 5hrs (peak sun) x 1.43 (system losses)
Step 1: divide average kwh/day by number of hours of peak sun, or (kwh/ay)/5
Step 2: multiply by 1.43 to account for system losses due to friction, heat and other inefficiencies.

Example: What size system is needed to produce 20kwh/day?

20kwh/5h = 4kw
4kw x 1.43= 5.7kw
5.7kw = system size to produce 20kwh/day assuming 5 peak sun hours

System cost = system size x $7,000-$9,000
Step 1: multiply system size by $7 for competitive system cost installed
Step 2: multiply system size by $9 for conservative system cost installed

Example: How much would a 5.7kw system cost?
5.7kw x $7,000 = $40,040 = competitive system cost
5.7kw x $9,000 = $51,480 = conservative system cost

We used to see an average cost of a grid-tied system to be about $9,000 per kilowatt (array size) installed, but with a growing market, systems are being installed for as low as $7,000 per kilowatt in competitive areas. Keep in mind that these costs are before any incentives or rebates are taken into account.

Hopefully this helped introduce you to some of the basic considerations needed before purchasing a solar electric system. There is far too much information to cover in a short guide and anyone serious about greener living should get their hands on a copy of the Solar Living Sourcebook. This guide, now in its 13th edition, speaks from 30 years of experience in the renewable energy field, covering everything you’ll want to know about renewable energy technology and sustainable living (available at www.realgoods.com). If you have more questions you can call the technicians at Real Goods at 1-800-919-2400.


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One Response to “How to Get Started with Solar Power”

  1. I really think that this blog can help people. Well done 🙂

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