Get Smart about Energy™


This article is published in collaboration with Soilar Man Dan, your guide to the world of DIY solar systems.

Last week we discussed the types of residential solar systems that are available for you (the consumer) to install. We ended our article with some guidance on potential pitfalls and the solar scams that seem to have overrun the solar cyber world.

This week we discuss the systems and formulas needed to accurately size a solar system to meet your needs. To begin I did a quick search on "DIY solar systems" to see if anybody was offering information on sizing a solar system?

The results made me ill. The 1st four sites were DIY solar panel scams, the 5th was a DIY supply store charging 300% over current available pricing, the next 2 were DIY solar panel scams again and finally the 8th site was a well intended person offering limited info on DIY solar systems.

Let me SHOUT FOR JUST A MINUTE! And hopefully somebody will listen!

Solar system DIY kits (from reputable dealers) have come down, way down in price over the last year. Unfortunately there are still way to many dealers on the web charging seriously inflated prices for DIY projects. (I will reference the good supply sites verses the bad ones at the end of this article) Nobody pays me for steering you one way or the other. My job is to point out the obvious and you can do your own price comparisons.

O.K. Back on topic. In order to accurately size your (grid tied) solar system, you’ll probably want to start with your electric bill. Usually on the 2nd or 3rd. page will be a rate structure breakdown with the amount of energy (in kWh) you consumed at each tiered level during that particular month. If your electric bill is in excess of 120.00 a month, then you are probably paying some upper tiered electric rates. The reason for pointing this out is that for some people it is more financially feasible to off set the more expensive rate consumption with a solar system thus leaving a smaller more manageable bill every month. There are also people who want to generate 100% of their energy needs with a grid tied system. Both (in the DIY arena) are financially sound decisions.

Now is a good time to gather 12 months (1yr) of electric bills, a note pad and a pencil and return to this article.

Step 1. Start 2 columns on your note pad. Label 1 “total kWh” and the 2nd “peak kWh”

Step 2. Add the total kWh consumed from all 12 bills and enter that amount in column #1.

Step 3. Add just the upper tiered kWh from all 12 bills and enter that amount in column #2

Step 4. Divide both columns by 365 (days of the year). The result is your daily kWh usage.

Step 5. Follow this link to visit the Performance Calculator for Grid-Connected PV Systems.

Step 6. From the atlas map, click on the country, state and then city that is closest to where you live.

Step 7. Scroll to the bottom of the page and Click "Calculate" - Using the "Results" section on the right hand side, scroll to the bottom and note the average solar radiation hours (sun hours) for the year. In the U.S. this should range between 3 and 7 hrs a day.

Step 8. Divide your daily kWh totals in each column (from step 4) by the average "sun hours" from step 7. The result from column 1 is the size of D/C system needed to meet 100% of your energy needs. The result from column 2 will generate the electricity to eliminate your higher tiered rates.

Step 9. The PVWatts Calculator automatically divides your D/C system sizes by the derating factor, approximately 0.8. Do make sure that this factor is included in your calculation of the system you go shopping for.

There you have it. We have applied sound mathematics to accurately size a solar system to fit your specific electric needs.

The two good solar supply sites that supply reputable products, great service and have honest pricing are:

1. Solar Electric Supply, Inc.
2. Sun Electronics

If there are any other good sites out there let me know, I’ll check them out and post them next week when we will discuss the best place to put your new solar system.

Thanks for following along. My name is Dan and I am a solar man.


Open4Energy - Get Smart about Energy™