The Solar Project – Site Assessment

[This post is part of a series about our net-zero residential solar project – see a list of links to the full series here, a list of frequently asked questions here or click here to bring up all Green-related posts. Next Post in Series / Previous Post in Series.]

Once the economic arguments grip you, the next question you have to face is whether your site is appropriate.  This is determined by a site assessment.  Free site assessments are commonly offered by solar installation companies, and they are your first real opportunity to interact with and evaluate a prospective solar installer.  The company I had chosen to work with was called Independent Power Systems.  I chose IPS for four reasons:

  1. They did an excellent job on the installation of my friend’s system, he recommended them highly, and I liked the company representatives I met at the event celebrating the switch-on of his system;
  2. They have been in business since 1996, operate in several states out West in addition to Massachusetts, and they have done over 1000 installations, so they appeared unlikely to go out of business overnight unlike many of the newer installers which have popped up more recently;
  3. They offer an industry-leading 15 year warranty on their workmanship (on top of that, the manufacturer gives 25 on the panels); and
  4. They are an Elite Dealer for SunPower panels which were the panels I wanted to use because of their excellent design and efficiency; in fact, SunPower was the only kind of panel they use on their jobs.

I had high hopes for my first interaction with Independent Power Systems.  I wasn’t disappointed – they sent a very knowledgeable and low-key representative out to my house to have a look at the site and figure out what might be possible.

He educated me about what made for a perfect site – a roof oriented perfectly to the south, with a slope of 42 degrees, and no shade.  This was a source of concern for me, especially since I had determined the economic arguments were strong and wanted to go forward, and earlier cursory remote assessments by other solar companies (done in some cases by telesales reps using tools like bing and Google Maps satellite view) had brushed our site off as too shady.

To my amazement and delight, the physical orientation of our site turned out to be almost ideal: the long side of our main roof is angled almost exactly 180 degrees due south – just mere 5 degrees off – and its slope is just a bit less steep than ideal.  The ideal pitch at any given spot is the latitude of that spot, so, for example, where we are, you want 42.3 degrees.  The pitch of our roof is the slightly less steep, but pretty typical 36 degrees you often see on a traditional house.  Being slightly off south was totally inconsequential – the onset of peak power might start 5 minutes earlier and end 5 minutes earlier each day.  And the pitch was also not an important issue; in fact, pitch is a seasonal compromise to an extent so of you are a little off in one half of the year, you make it up in the other.  Overall, our site was rated a 96 out of a possible 100, which is hard to beat.

I did have some tree shade issues though, which was a major source of concern.  The irony of cutting down beautiful CO2-eating trees, which are an excellent source of passive solar shade cooling, in order to install a photovoltaic power project was not lost on me, so I didn’t even consider it an option.

Luckily I didn’t have to.  The IPS rep and I talked about the situation and identified a number of good options.  The first option was to just live with the shade and make the best of things by using micro-inversters to make the system more shade-tolerant.  Micro-inverters allow you to convert each panel’s power separately with a small inverter on the back of each panel rather than linking the panels into strings and using one larger inverter for each string.  Since shaded panels have reduced current output, an inverter working on a partially-shaded string will produce less power for the whole string due to the reduced current from some of the panels – they act like a weak link or a kink in a hose.

A better option was to trim the trees a little.  My first reaction was horror, but when talking to the IPS rep, I realized that a relatively minimal amount of trimming would have a huge effect.  And because the sun is so high in the sky (it is the sun, after all), the trees could be trimmed at a very steep angle leaving them still very tall on the outward-facing side and allowing them to cast their shadow starting right from the gutter line downward, thereby allowing the sun to hit the panels while still protecting the whole side of the house from passive solar heating in the summer.

Once we realized we could really make our physical site work, we  went inside and sat down to make some calculations in terms of what might be possible, and what it would cost.

Story continues…  This post is part of a series about our net-zero residential solar project – see a list of links to the full series here, a list of frequently asked questions here or click here to bring up all Green-related postsNext Post in Series / Previous Post in Series.

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