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 homeowner (or business owner) looking to have a solar system installed on a roof of their house (office building/store/etc).

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 the 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 are true in your case, than a solar system is not for you.

If you do not know where the south is, use a basic compass 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 morning, noon and around 3 or 4 pm. If there is no shade, you are in good shape. If there is 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 course. If there is shade from a nearby building, 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 it 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, 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 out 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 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 supply 100 % of your electricity) you are looking at a system size of 5-6 kW.