Our PV Solar Project


This page is intended to give a brief summary of the thinking behind our PV Solar project, and an outline of its general design and construction. I hope to be updating and expanding my Arrowflight Data (& Energy) Services site to reflect what I expect to be a growing professional focus on Energy consulting. There should be a number of pages there which will include more detail about the considerations which affected what we did, in the hope of giving others who are thinking about Energy issues at least a suggested structure in which they can organise their own thinking and planning. Everything on this page, and much of the material that will appear on the Arrowflight Data site, represents my own personal opinions. While I hope that these are reasonably well researched and thought out, they remain those of someone with no formal qualifications in any of the areas under discussion. I am an enthusiastic and increasingly well-read amateur - it will be a while longer before I can claim to be a certified solar guru!

Some Background

Without subscribing to 100% of the current near-hysteria about global warming, and while remaining somewhat agnostic as to the reliability and precision of the predictions being made by the prophets of doom about the extent of the changes we need to make to the pattern of our lives if we are not "all going to die" (sooner, rather than later!), we do feel that it is important to be good stewards of the earth and its resources. I hope that we have never been profligate consumers, but, over the course of the last couple of years, we have tried to move more actively towards a greener lifestyle. Some aspects of this are made easier by where we live - the Village of Lisle actively supports the recycling of paper, plastics, and yard waste with weekly curbside collections of these recyclables. Fortunately, too, our house's HVAC and hot water systems had been upgraded with energy-efficient major components by its prior owners, and we have now replaced these, as they reached the ends of their lives, with even more efficient models. We have also progressively replaced failing appliances with modern, energy-efficient, models, and, particularly over the first couple of years, started to pay much more attention to how we use electricity. These efforts resulted in a slightly less than 20% reduction in our annual electricity usage between 2008/2009 and 2009/2010. In 2009, we signed up for Commonwealth Edison's Real-Time Electricity Pricing Program, and being conscious of the timing of our remaining power usage allowed us to save a further 15-20% on our electricity bills (which is good for us!), as well as make a (very!) small contribution towards reducing the peak loads on the system (which is good for everyone). In 2010, following a detailed energy audit, we also sealed most of the major sources of air infiltration that it highlighted and enhanced the insulation in our roof and on our basement walls.

Why PV Solar?

Towards the end of 2009, I started to research the possibilities and costs of renewable power production at the household level. As well as reading and browsing widely, I subscribed to HomePower Magazine and joined the Illinois Solar Energy Association. I rapidly discarded the idea of using wind energy - however much of an wind enthusiast one might be under other circumstances, a small suburban lot, surrounded by trees and other buildings, is not a suitable site for a wind turbine! The choice between PV (photovoltaic electricity) and Thermal (hot water/space heating) solar power required a little more thought. The Thermal approach has lower up-front costs and is theoretically more efficient - thermal solar collectors can capture upwards of 50% of incident solar energy, against (2017 numbers) a bit more than 20% for the best commercially available domestic PV panels. On the other hand, the pumps, valves, and pipes of a Thermal system require much more maintenance and more frequent repairs than do the components of a no-moving-parts PV system, especially in the Chicago climate. This adds substantially to the longer term costs of a Thermal system. In addition, the theoretical efficiency advantage of a Thermal system assumes that you are going to be able to use all the collected heat energy within a relatively short time (hours) of its collection. The reality of a typical Thermal installation is that much of the energy available in the summer months will not be collected or used. It is considerably easier to store electricity when production exceeds use, and easier still to operate a grid-tied PV system, where the utility acts, in effect, as a "bank" for any excess production. These considerations, and the fact that a decline in price (over the last couple of years) and longer term improvements in efficiency of commercial solar panels have substantially eaten into the price advantage of Thermal systems, led me to focus in on the practicalities of grid-tied PV systems.

The Installation

We were again very fortunate in having two roof planes in the back of our house facing slightly to the West of due South. Although fixed PV arrays can face anywhere between SW and SE with relatively little overall loss of efficiency, an approximately due South roof facing is generally considered to be ideal. PV solar panels are, however, more affected by shading than are Thermal collectors, and we did have some substantial trees shading the roof planes. We had already been warned by an arborist that a number of tall spruces on the South and West sides of our back yard were nearing the end of their lifespans, so removing them sooner rather than later was not an issue. Unfortunately, it rapidly became obvious that a large locust tree that was in good health, but shaded both the suitable roof planes in the Spring and Fall, would also have to come down. That still left us with a a number of established deciduous trees in what had previously been a heavily wooded yard, and we replaced the spruces with some arbor vitaes (or should it be arbores vitae?!) - trees which would be expected to do better in the long term in the Chicago climate, so we don’t feel that we totally lost our green credentials in the course of the relandscaping!

With the aim of generating about 80-90% of our annual power usage, I originally hoped to be able to install a system with close to a nominal 5 kW output rating. Under the then and current rules for domestic co-generation in Illinois, any net power generated in excess of one's annual usage is effectively given to the utility free, making it foolish to aim for much more than that in a home with our current annual energy usage. Once I had settled on a contractor, however, it became apparent from our discussions and his calculations that it would not be possible to fit much more than 4 kW "worth" of panels on the larger, south-western, roof plane, while extending the system onto the south-eastern plane would, for a number of reasons, add complexity and cost disproportionate to the expected gain. We ended up settling on a 4.14 kW array, which fitted neatly on the south-western roof plane without needing any of the existing vents penetrating it to be moved, was relatively easy to configure and install, and is surprisingly unobtrusive (see the Solar Installation Photo Gallery).

Our contractor, Tom DeBates of Habi-Tek Renewable Energy Systems is a NABCEP certified PV installer, and (professionally speaking - he does have a life!) does nothing else. Strongly recommended! He and his team installed the system over the course of a couple of weeks in April, 2010. Kudos too to the Village's Works Department, whose staff took just over a week to turn round the permits for the project, despite the fact that it was the first PV solar installation application that they had seen. This was, of course, greatly helped by Tom's knowing what they would need. By April 17, 2013— three years from commissioning — the installation had produced just under 16 MWh (yes, that is MegaWatt hours) of power, and its production has continued to average just over 5 MWh/year through the present time (June, 2017).

We were a host site for the 2010, 2011, and 2012 Illinois Solar Tours.

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