Solar PV System Design

It’s been a while since our last post, but here we have a ton of solar PV design information and photos. First and foremost, this will be a generic solar system design that assumes installation of Solar PV panels on an average home in New England. This guide is aimed for the home owner (or business owner) looking to have a solar system installed on a roof of their house (office building/store/etc).

CCRI Solar PV experimental array

Just to let you know, it is highly recommended that you get a professional solar integrator to do this work for you. There are just too many things you need to consider when designing a solar array installation, and unless you are experienced in the field of electricity and roofing, leave it to the pros. This guide will help you understand what goes on from step one  (contacting a solar integrator)  to the final step – having a complete Solar PV array on your roof (or on the ground) and supplying you with “free” electricity. For a detailed overview of solar system costs and pay-off period, refer to Solar PV system design guide



 

Solar PV System – Basic design.

This is an essential step that determines the feasibility of having a solar system installed. For example, the solar system has to be positioned so that it faces south, and has as little shading as possible. If neither of these is true in your case, than a solar system is not for you.

If you do not know where the south is, use a basic compas to identify if your roof has a southern exposure. On a sunny day look at your roof to see if nearby trees and/or buildings throw off a shade on your roof. Do this in the mornig, noon and around 3 or 4 pm. If there is no shade, you are in good shape. If there is a shade from a tree, you’ll have to cut it. If it is you neighbor’s home, talk to them about removing the top floor of their house, mentioning that a shade will reduce your electricity production. This is a joke of courese. If there is shade from a nearby buildng, depending on how much of a shade it is and how many hours per day it is present, will determine if a solar electric system is feasible for you.

So, the site survey will be the first step, and a solar integrator you choose to work with will perform it. The site survey takes about 3 hours on site, and you can add driving time to it. Therefore it is safe to assume that the site survey will cost you anywhere from $125-200, depending on a solar company you are working with.

If you are not serious about getting a solar PV system installed, and just want to know how much it’s going to cost you, this guide is for you. Don’t waste the solar integrator’s time with something you can do yourself.

Basic solar PV system info:

An average household in the US consumes 500-750 kWh (kilowatt-hours) of electricity per month. To find ot how much electricity you use, gather your last 12 electric bills and add up all the kWh you used. Divide this number by 12 and you’ll have you monthly average electricity use. Notice that in the summer you use more electricity than in the winter (unless you have electric heat, which is the MOST expensive source of heat, and we recommend you change it before installing a Solar PV system).



 

We will assume that your monthly average electricity usage is 500 kWh. We take the lower end of the spectrum as most homeowners begin to use LESS electricity once the solar system is installed. They install energy-efficient appliances and lighting, turn off lights when they don’t use them and so on. Basically all the things they’ve never done before. This also allows them to have a smaller capacity solar array installed as the demand goes down.

How many KW will you need?

So, if you use 500 kWh per month, than your annual electricity usage is about 6000 kWh. As a rule of thumb, 1 kW solar array will produce 1000-1200 kWh of electricity per year, when it is installed in an unshaded area. This number accounts for all the rainy/cloudy days and grid power fluctuations, which may now out your inverter for a period of 5 minutes to 2 hours, depending on the quality of your electric lines and local transformer station.

An average residential solar installation is about 2.5-3 kW, and if your goal is to be 100% net-zero (to suplly 100 % of your electricity) you are looking at a system size of 5-6 kW.

Site Survey



 

Becoming a Solar Integrator – Day 1

Finally I got a chance to learn Solar Systems installation and design with lots of hands-on and theory!

This is the first in the series of reports to be posted this fall. Reports will include new technologies and methods of solar installation, as well as other renewable energy topics.

For the first time in 2 years, there is a Solar Training program running at the Community College of RI (CCRI). Their previous instructor moved to Maine, and there were no people willing and able to teach the class. There is now over 400 people on the waiting list, so I guess I’m one of the 15 lucky ones.

After reading through 100s of Renewable Energy websites and grasping all the theoretical aspects of Solar Photovoltaic systems, I had to finally get my hands wet. Unfortunately, except for one solar distributor out of MA, offering overpriced 1 and 2 day “Solar Training” programs, I could not find any college or tech school offering any courses in Renewables and Solar.

It all started over a year ago. Back in the summer of 2007 a course brochure from CCRI listed a Solar Training Program being offered in the Spring of ’08, but no detailed info was provided. Only a contact phone number of a person running a “Lifelong learning program”, an equivalent of a continued ed. program offered by most colleges for “working professionals”.



 

After making over 20 calls to CCRI and speaking to more than 30 people, most of whom never heard about this class, I finally got my name on a waiting list, that was aimed at electricians who want to install Solar PV systems. Myself being a roofer, I was not their target audience in the first place.

As spring of ’08 rolled on, there was still no instructor. By late may, after a few voice mails I finally received a call that the Instructor was finally found and the class was scheduled to run in the fall ’08. On one rainy June day, when I could not “roof”, I got in my car and drove to CCRI’s Lincoln Campus, only to find out that the person in charge of the program was at the Warwick campus, so I had to drive through half the state to talk to them, and secure myself a seat in the class.

As I got to the Warwick campus, the person I was looking for, left for the day (at 1 pm) so I had to run between 5 differnt offices to find someone else who new anything about the class. After talking to a few people I had them put my name on another list of people interested in the class. However, nothing was certain at that moment, as the registration for fall simester had not yet begun.

Finally in July I got a letter with a Course Brochure and a registration form, which I filled out and mailed back the same day. A week later my Credit Card was charged for this course, and now I am on my way to becoming a “Solar Installer and Designer”. Unfortunately, I cannot actually install any Solar Systems, since I’m not a Licensed electrician. But I can certainly design one, and then have the electrician do his part.



 

Things learned in todays class:

Besides the regular Solar System Design diagram that includes Solar Panels, wiring, the Inverter, disconnects, meters, breakers panels, etc., I actually learned that in New England an average angle at which a fixed solar system should be installed is 42 degrees. Optimal for the summer is 25 degrees, and for the winter is 55 degrees.

Also, whenever designing a roof-mounted solar array, a structural survey must be done to account for wind and snow loads.

Fortunately for us, we install roof-integrated thin film solar systems, so all these aspects do not really concern us, as there is no additional weight added to the roof, and since PV panels are part of the roofing systems, wind uplift is taken care of during roof installation.

Other valuable lessons:

Whenever a solar system is installed, a “power survay” should be done to reduce any power loads an install energy-efficient appliances and equipment to reduce electrical power consumption. Double benefit right there.

Things to discuss in next posts: Insulation and Energy Efficiency of your home.