It started inauspiciously ...
with an email from some do gooder group announcing "yes, you can have solar power. Just call xxx". I think Solar City I had thought about installing PV panels, but not seriously. The house site was surrounded by trees especially on the south side. However, I figured a contact wouldn't hurt, so I sent them an email.
The email reponse was within a day. They asked for my address, and within a few hours sent me a link to a page containing a google map of the neighborhood. I clicked on my house and submitted. A day later the reply: "sorry, due to the trees we aren't able to install panels on your property" (not enough sunlight-- not enough electricity produced). I sent a joking response about mounting the panels on 50 foot struts, but otherwise forgot about it.
A few months later I decide to do an energy audit, only $100 -- Pepco (the local electrial utility) subsidized, (details). I went ahead with many of their recommendations, starting with the most cost effective (attic insulation)... and then thought that maybe their install solar panels from Sungevity might make sense. For I had been on the roof and thought "I don't want to cut down the trees in front, but the back North facing roof seems to be out of their shade".
The EcoBeco audit was fairly thorough, including a house pressure test (to measure air flow in/out).
But how to check? I looked online and found a service that will examine the solar prospects of your property, using google images, etc. And, as I expected, a North roof mounted solar system was reasonable (details)
The remote analysis provided two sample layouts: simple and full. Note the shading analysis report, suggesting averages over 80% (a not terrible amount, and enough to qualify for tax rebates).Time to get serious and call solar installers. I called around; the big guys (like Sungevity) and some more local companies. And they all said, either immediately or after a site visit, that they were not interested in a north facing roof install. I also got contacts from one of the parents in my kid's bnei mitzvah group, a solar advocate named Scott Sklar. He gave me two. Both were much more willing to tackle this job, and I chose one that seemed to be the most interested: Kenergy of Takoma Park.
Moreover the company recommended removal of a few trees next to the house. Since trees-next-to-house isn't such a great thing anyways, I had it done: removing trees on west side (before and after) , trimming back a tree on the northeast corner (so as branches would not overhang back of house), and topping 15' or so off of large pine trees out front (to reduce shade and limit damage if they were to fall in a storm). We left a few bird-habitat branches!
I also replaced part of the roof. The flat roof was 20 years old, nearing the end of its useful life. The sloped roof was about 15 years old, so had another 10 or more. Rather than replacing all of the roof, I just replaced the flat part over the new addition (before and after). That also allowed me to add insulation (that could not be added by the insulation people, since they could not get their blowers into the small attic space above the flat roof).
They did their own on site measurements (details), which confirmed the feasiblity of the project.
Time to design ...
(details) My goal was to maximize the average cost of PV power (installing enough panels to spread the fixed costs out, but not so many as to require panel placement in not-very-good spots). After some back and forth, I contracted for a 6.5kw nominally rated system: consisting of 25 made-in-Wisconsin Helios PV panels (the label!) (Kenergy typically uses German made Mage, but with a $10k fed rebate expected, I figured I should buy American). So at the end of June I am ready to go! Or so I thought.
A PV system basically has two components: the panels, and some way of inverting DC power produced by the panels to AC power used by your house's loads.
Roughly speaking, there are two ways of accomplishing this inverting.
However, central inverter PV installations have a design issue. For several reasons (such as increasing voltage to reduce line losses), PV panesl are usually serially wired in strings. This makes them vulnerable to shade -- since the output of all panels in a string can only be as great as the worst (i.e.; most shaded) panel in the string! That means a branch partially shading just one of a dozen panels can cut the output of the whole array of panels by a lot!
Micro-inverter avoid this problem, since each panel is independent. There are ways of limiting this problem with central inverters, by having several inputs (so that each string is directly wired to the inverter), or by adding DC optimizers (at about a 20% cost increase per panel).
With an odd installation -- shade, or orientation at different angles -- these kind of problems are more important.
Fate intervened in the form of the July 1 derecho, which knocked out power for 4 days. Which brought home a limitation of most household PV installs: during power outages they don't produce electricity (details)!
Even though the total electricity consumption of a house is likely to be greater than the PV power produced, most of the time power produced from one's panels is not used. Power useage at night or during very cloudy days isn't provided from panels, and large loads (AC, stove, etc) can only partiallly be powered from the panels. Conversely, during the middle of the day when no one is home, only a fraction of the power from the panels is used.In Jan 2012 (after suffering 3 several day outages in 10 years) I had installed a generator with appropriate critical loads GenTran sub panel/transfer switch (manual), so I had power. But it was noisy and stinky and a pain in the neck. Maybe it is worth considering some kind of hybrid system that would provide power during an outage from combination of batteries, PV panels, and a generator? Such a system could also act as a most-of-house uninteruptble power supply. That means power to most devices (TV, computers, etc) would not be effected by transient outages. Thus, I wouldn't have to provide desktop UPS's to my several computers. That's a cost savings: these desktop UPS's wear out after 2 or so years, and I use several of them.
What to do? One could just waste the power, but that would be kind of nuts. If one was off-grid, battery backup is used. But batteries are expensive (often greater than the cost of the panels).
Instead, most PV installs in urban settings use a grid-tie architecture. Basically, PV power is fed directly to the main circuit breaker box. From there, it either goes to loads in the house (lighting, AC, etc) or if more power is being produced than needed -- it backfeeds to the grid. This means your meter spins backwards -- your house becomes an electricity producer, not a consumer.
In a sense, the grid acts as an infinite battery, able to take whatever excess power you may produce.
In most states, the utility is obligated to accept PV power produced by households, and to credit this power to your electrical bill. In other words, they pay retail for the power you (the PV equipped home) provide to them. The utiltities don't like this very much, they would much rather buy it from you at wholesale!
Actually, this grid tie architecture does complicate the utitlity's power management regime. The utilities have to be adjust production to demand across the grid. They are used to doing that with their centrallized generating facilities. Adding a whole bunch of small distributed facilities (homes with PV panels) makes the balancing more difficult. So long as the fraction of power supplied by homes with PV panels is small, it isn't a huge problem. But should this fraction grow, it could become problemmatic (i.e.; how to adjust centrallized generator output as clouds move in front of the sun).There is one concern: what happens during a power outage? If a bunch of PV panels continue to produce electricity and backfeed it to the grid, that means the lines (in the street) may be live during an outage. For utility workers, that is a major safety hazard!
Therefore, grid tie systems must have a safety feature: during power outages, no power is fed from PV panels to the grid. The simplest way to do that is to simply shut down PV production.
What does that mean? During the times when PV power would be very useful -- during outages -- it is not available! That seems wrong, but it is an inevitable result of using the grid as a battery. And since 99% of the time the grid is working, that's a tradeoff that can make sense.
Still, it does seem just wrong. It seems sensible to consider ways to finesse this problem, ways of building a hybrid system that uses both your own batteries and a grid-tie connection to the utility.
Interesting, but I didn't want to spend a lot on such a system. So I thought about it for a month, did a bunch of research (details), discussed some options with Kenergy ... and modified the contract in mid-August. Now, about 11kwh of battery backup would be added to the system. That meant changing the PV installation, and increasing the cost. We were ready to go -- 6 weeks or so for the installation (early October)!
Types of hybrid systems -- systems with both battery backup and grid-tie.The basic idea is to somehow keep PV panel production going during an outage. This requires some means of integrating grid power, PV power, and battery power. And it means somehow safely keeping PV production going during an outage.
The basic idea is to seperate the PV power from the main circuit breaker box. PV power is fed into an intermediate device which can use the PV power in 3 ways: charge batteries, feed to a sub-panel, or send to main breaker box (and hence to the grid). When an outage occurs, this intermediate device can quickly switch to battery power (it "inverts" DC power from the batteries to AC power). This battery provided power is sent to a sub panel that supplies the most important loads; such as refrigerator, heating system, and basic lighting. This sub panel is isolated from the main panel, hence from the grid. Furthermore, the PV panels "see" the AC power from this intermediate device and will continue to produce electricity.
This means two additional components are needed. First, an intermediate device -- such as an off-grid inverter. Secondly, batteries.
Batteries are not cheap. A good quality 200 AH 12V battery costs $600. Four of these yields about 9.6kwh of power. Actually, these are usually only discharged to 50% -- which means something like 5-6kwh of power. If you are frugal, that's about 6 hours of power.
Details galore: I ended up choosing an AC coupled system using Magnum off-grid inverter and about 11kwh of batteries. This was minimal: I anticipate using my generator to charges these batteries at night. Still, if it works this setup provides UPS protection for much of the house, protection against short outages, and a great reduction in generator run time.
And then things got slow.
By the end of February, most of the install is completed, but ...
While panel installation almost done, thes system was not producing power (Feb photos).
A flurry of work occurred in Feburary and early March (early March photos). After a few bugs (i.e.; shorted wire from inverter to AC cutoff causing scary short circuit)...
The problem of panels shading panels could be readily solved by tweaking the tilt of the front row, or raising the back row. The second was a mystery, one that Kenergy spent a hapless hour or two (checking things that were unlikely to be problems), and punted. And, where to get a proper battery enclosure.
Kenergy ordered a enclosure.and when it arrived it was... pathetic. And too small. After expressing displeasure, I decided that I would have to bite the bullet and go over budget -- I would offer to pay for most of a good battery enclosure. That meant about $1000 for a solid steel construction from Midnight Sun. After some convolutions, where I paid for it even though Kenergy ordered it, the order was placed in early March.
And I waited until middle of May for delivery. Seems like this was a proposed product from Midnite Solar, rather than something that was regular inventory -- they hadn't gotten the bugs ironed out. Indeed, when I finally got it, a hinge was missing from the door. It took 2 weeks, and some embarrassment by the production line manager, for that to get mailed. But it is a very sturdy enclosure!
While waiting for the enclosure, Kenergy did nothing. Even though there were thing to be done, such as figuring out why an entire string was not working. And by April, I was just tired of it. So I gave them a 4 week deadline, wherein I sent 3 registered letters. With no response.
It seems obvious that they were no longer interested in finishing the job. Fine by me.
Why couldn't Kenergy do the job? My current thoughts are there were 3 complications, and that was too many. (details)
My theory is that this project required solving 3 non-typical challenges. First, the "tilted" panels (on N facing roof). 2nd was battery backup that was somewhat undersized. 3rd was a battery backup using non-typical inverter setup (i.e.; minimal Magnum ac coupling rather than Radian based battery charging or Sunny Boy based integrated AC coupling). I think that was one challenge too many. In the sense that solving them was multiplicative in difficulty, rather than additive. So it took a lot of labor time, and became a drag.
Of course, my sympathies are limited: these challenges weren't that big, only one of them was a requirement, and I am paying more than average.
Replacing the contractor ...
It isn't easy to get someone to step into a mostly finished job. I tried the electrical contractor who had worked with Kenergy (Plus Electric). I got one response email from him, and then after I sent several replies -- nada. Who needs to deal with more of that?
Per usual, the larger companies had no interest. So I figured I would try Capital Sun Group -- the other company that had expressed interest in May 2012. After some negotiation, we settled on a cost plus contract, with a max of $9,200 (note that I owed Kenergy $5,000, so this represents up to $4,000 extra).
This included installing Tigo maximizers. From what I could tell, the uneven shading on the roof seemed to depress output, something that Tigo maximizers might alleviate. And, these maximizers provided the ability to monitor each panels output. Lastly, the controller for the maxiziers had a DC cutoff switch, something that was a good safety feature.
Capital Sun wasn't that fast, but just about the time I would get really annoyed, they would show up. By Sept 1 the PV panels were fully installed. Inspection, and Pepco approval still needed.
What work did Capital Sun do...
PV install completed and legal...
Just because everything is working doesn't mean it's all done. County and Pepco inspections etc were still needed.I can now turn on my invx:erters, and use the electricity from the solar panels, or sell it back to Pepco (and watch the meter run backwards)!
Images and layouts
Solar Renewable Energy Credits ...
Solar Renewable Energy Credits (SRECs) are designed to help utilities meet regulatory requirements to produce a specified fraction of their power via renewable means. The utilities can achieve these requirements either by producing solar electricity themselves or by purchasing SRECs from other parties producing solar energy.
What does it mean to sell an SREC? The SREC is not the same as a watt of electricity! Rather, it is a fact about how the watt was produced. Thus, the watt and the SREC are seperate.As of mid-May 2014, still waiting for a first check.
The original plan was to have a battery backup system installed, which would automatically kick in and provide power
to selected critical loads in the event of an outage....
The battery backup system would be integrated with my current generator, so that I could recharge the batteries using the generator. Furthermore, some of the PV panels would run during outages, providing power to the house and helping to recharge the batteries (as noted in the AC coupling discussion).
Once the PV installation was legal (mid October 2013), the next step was to install the battery backup. I had the necessary equipment (batteries and boxes and inverter). Shouldn't be too hard, shouldn't take too much time? Of course, it took 7 months.