We now had a working grid tied solar electric system. But we didn’t let it operate all the time. Why not?

The salespersons for these solar installers usually claim that after installing their solar electric systems, your power meter could run backwards. This may be true of the old spinning-aluminum-disk type power meters. But it isn’t true of the typical new digital readout power meters, at least the ones Progress Energy uses. The new standard digital meters can’t tell which direction power flows. So you get billed for all the power that flows through the meter, whether you are consuming electricity or you are generating electricity and putting it back on the power grid. You need a special bidirectional meter installed which can detect which direction the power is flowing.

How did we determine this? Normally, our house uses an average of 3 kWh of electricity a day. The installation of the grid tied portion of our system was finished around 11 AM in the morning. The inverter indicated that the PV (photovoltaic) system generated about 10 kWh of electricity for the rest of that first day of operation. Yet our power meter indicated that our consumption was about 11 kWh over the same period (about eight hours of sunlight). The only things running in our house during that time were the refrigerator, a clock, and a telephone answering machine (and the utility power meter, which consumes about the same as an answering machine; you didn’t realize that the power meter draws power and you are paying for it, did you?). No lights, water heater, computer, modem, TV (we haven’t had a working TV since 1982), oven clock, microwave oven clock and controls, doorbell (ours is powered by lithium batteries), heat pump controls, garage door opener controls, or any other “phantom” loads were running, which is typical in our house and one big reason our electric use is so low. So, from experience, our use over that eight hour period, one third of a day, should have been less than 1 kWh. The less than 1 kWh that the stuff in the house was using plus the 10 kWh generated by the solar system equals 11 kWh, which is what the power meter indicated.

I have never seen any information from the power company warning that their typical meters can’t tell which direction the power is flowing. Is this just another way “the man” is trying to screw the little guy?

Not really. They probably wanted the cheapest power meter that met their needs to minimize their, and their customers’, costs. At present, for at least 99.9 % of their customers, the power only flows one way, into the customer’s house or business. As an electronics engineer, if I were given the assignment to design this power meter, none of the easiest and cheapest ways I can think of can determine which direction power flows. It takes a little more circuitry and cost to determine which direction the power is flowing. So the power company’s meter choice makes good sense for them and the majority of their customers.

So, until you get a new bidirectional power meter, that is, a meter that can record how much power is flowing in each direction, you will be billed for ALL the power that flows through the meter, whether consumed or generated. But the meter only measures the NET power flowing through it, that is, the difference between what is generated and what is consumed. For example, if your PV system is generating 2 kWh and you are using 3 kWh, your meter will indicate 1 kWh has flowed through the meter. So, in this case, your PV system has saved you the cost of 2 kWh of electricity. But if your PV system is generating 3 kWh and you are using only 1 kWh, your meter will indicate 2 kWh has flowed through the meter and you will be billed for that 2 kWh, even though you generated it.

So, if you are certain that you ALWAYS consume more power than you generate, you can leave your PV system running even with the standard power meter and it will save you money. But if you usually use less power than your PV system generates, then you are better off with your PV system shut down until you receive a new bidirectional power meter, unless you have battery backup and can run offline, that is, disconnected from the power grid.

Consequently, until we had the battery back up portion of our PV system installed, we had our PV system turned off except during times when we were certain we were continuously consuming more power than our PV system was generating. An example of such a situation was when we were running our electric clothes dryer, which consumes about 5 kWh per hour of operation and typically runs 1.5 to 2 hr per load. Remember, our system has a peak power output of about 2 kW.

Figure 1 shows what the bidirection power meter we finally received from Progress Energy looks like. To Progress Energy’s credit, we received this new meter withing two days of dropping our application in the mail. Since I suspect virtually none of the power company’s customers are aware that they are being billed for the electricity they generate while they still have the old power meter (I found no mention on the Internet of these power meters not being able to determine the direction of power flow), Progress Energy could have waited until the legal limit to replace the meter (in Florida, they have ten working days after they receive a valid application to replace the meter) and potentially collected a few extra dollars. But the goodwill and impression of being a “green” company by responding very promptly are far more valuable than those few extra bucks that they may have got by delaying swapping meters. This makes good business sense.

As Figure 1 shows, the new bidirectional meter has two readouts. Though I have yet to receive an explanation from the power company on how to read the meter (probably with the next bill), reading it is fairly obvious. The smaller leftmost reading is the readout mode and the bigger rightmost readout is the total power in that mode. The readout switches between modes every couple seconds. When the mode is “00,” the rightmost readout is the total net power drawn into the house. In this case, the meter shows that a net of 69 kWh has flowed into our house since the meter was installed. When the mode is “01,” as shown in Figure 2, the rightmost reading indicates the total net power output from the house, which in this case is 155 kWh since the meter was installed. Incidentally, the meter was installed around 10:25 AM Feb. 3, 2010, and both pictures were taken around 9:48 AM Feb. 26, 2010. So, in this case, the meter indicates our house has generated over twice as much power as it has consumed.

Why is this obvious? Well, for one thing, the rightmost reading in the “01” mode absolutely NEVER changes at night. It only changes during the day and in proportion to how sunny it is. In fact, the change in the “01” mode reading is always slightly less that the total power generated by my solar array, as indicated by my SB3000 inverter, unless I have some unusually heavy (for us) loads running that day, such as our clothes dryer (only once during this period) or our geothermal heat pump (only about four hours during this time period and always after sunset). Also, the “00” mode reading changes pretty much as our old power meter did whenever I turn on and off some unusually heavy load, such as the water heater.

Note that these readings do not indicate the total power used and total power generated over this period, but only the NET power flowing through the meter during this time. The power meter can’t tell what is happening inside the house. It can only measure what is flowing through it, which is the difference of what is used in the house and what is generated by the PV system. For example, if your PV system is generating 2 kW over a one hour period and you are using a constant 3 kW over that same period, the “00” reading will increase by 1 kWh over that one hour period and the “01” won’t change. If your PV system is generating 3 kW over a one hour period and you are using only 2 kW over that same period, the “01” reading will increase by 1 kWh over that one hour period and the “00” won’t change. This assumes the power used and generated is constant (not fluctuating too much) over these periods. So, over more than a day or two, both the “00” and “01” reading will almost always be less than what was actually consumed and generated, respectively, over that period, since some of that consumption and generation happened at the same time and canceled each other out before it was seen by the power meter.

So, the last week in October, 2009, I gave Harrimans Inc the go-ahead and a down payment for installing a solar electric system on our house. Three weeks later they notified me that they had all the plans, permits, and parts with one exception: They still hadn’t received the battery backup inverter, an SMA SI5048, which wasn’t expected for another couple of weeks. So they planned to install all the grid tie stuff first and add the battery backup stuff after the SI5048 was received.

They installed the photovoltaic (PV) panels, the grid tie inverter, and all the appropriate wiring and disconnects in less than a day and a half. Figure 1 shows the ten 200 Watt Sanyo HIP-200BA19 PV panels mounted on our south facing roof section. These panels are electrically identical to the older HIP-200BA3 panels, with the only change I could find being a slight change in width due to a slight change in the frame. These panels give the minimum of 2000 Watts total we desired.

Most all of the larger modern inverters have maximum power point tracking (MPPT), which automatically adjusts the load characteristics of the inverter on the panels so that the PV panels operate at the point where they are outputting the maximum possible power for the present light and temperature conditions. This maximum output power point can vary significantly with the type, orientation, and temperature conditions of the PV panels. Consequently, you want all the panels tied to a particular MPPT inverter to be matched as close as possible, that is, the same manufacturer and model and mounted in the same plane with approximately the same light and temperature conditions.

Figure 1 shows that these panels take up almost the entire south roof. We might be able to squeeze two more panels in with a bit of effort, but these additional panels would probably overhang the roof ridge caps. We wouldn’t want to add panels on the other roof sections to the existing inverter because these panels would experience much different light and temperature conditions, giving the inverter conflicting information on what the maximum power point should be. This would probably cause the inverter to operate in a condition that is not optimum for any of the panels, assuming the inverter is able to find a stable operating point and doesn’t start oscillating. Even mounting the additional panels on angled standoffs on the east or west roof sections so that they would face south and be at the same angle as the panels on the south roof section would still result in different temperature conditions for the added panels than those of the panels on the south roof. So ten panels is the practical maximum possible on our south roof, with twelve panels being the maximum possible with a bit of effort.

Figure 2 shows the two additional power disconnects added on the outside of our house by the power meter. One is for disconnecting the direct current (DC) output of the solar panels from the inverter. This is required by many communities so emergency personnel, such as firemen, can shut off all electrical power in the house before they perform their emergency tasks. The other is an alternating current (AC) disconnect between the inverter output and the rest of the AC circuits in the house. This makes it possible for the power company to disconnect the solar electric system from the utility power grid in case they have to do maintenance on the local grid. This disconnect is also often required in many communities, though the power company will probably just remove the power meter to absolutely guarantee that the solar installation can’t back feed the power grid during maintenance conditions.

Figure 3 shows the SMA Sunny Boy inverter mounted inside the garage by the main breaker panel. The inverter’s 240 VAC output goes to the outside disconnect first, and then to an added breaker in the panel before tying to our AC power within the house. The smaller box at the bottom of the inverter provides a DC output disconnect for the sloar panels that is inside the garage.

Figure 3 - SMA Sunny Boy inverter mounted inside the garage by the main breaker panel.

The inspections, an electrical and a structural inspection, both went without any problems. This particular electrical inspector was exceptionally thorough, removing the covers off of everything and tracing all the wiring against the permit drawings, which was commendable and unusual. But one thing he missed and I didn’t notice until the inspection was that Harrimans installed the wrong inverter; they installed an SB4000 and the contract and permit drawings called out an SB3000. The SB3000 and SB4000 are the same size and shape and look identical, with the only external clues to distinguish them being a very small print label on the side of the unit and the model number being flashed across the screen for a few seconds during power up.

Now in most cases this would not be a problem and would actually be a free upgrade, as the SB4000 costs about 25 % more and handles 33 % more power than the originally specified SB3000. The SB4000 could allow significant future expansion of the number of solar panels. But, as discussed previously, we have little room for expansion on this south roof. Also, I ran our particular Sanyo PV panels through the inverter manufacturer’s compatibility software (http://www.sma-america.com/en_US/products/software/sunny-design.html) and found out that the total output voltage of the PV array would vary from 240 VDC to about 374 VDC over worst case conditions. The SB3000 was specified for correct operation between 200 to 400 VDC, whereas the SB4000 was specified for 250 to 480 VDC operation. So our particular PV array would operate well within the SB3000 specifications but outside the SB4000 specs.

I contacted Harrimans about this. They said they checked the compatibility of the panels and the SB4000 with SMA software and found the SB4000 was compatible with between 4 to 8 Sanyo HIP-200BA19 PV panels per series string, with my system having 5 per string. It turns out they used SMA’s online software (http://america.sma.de/newstringsizing.aspx), which you run online from the SMA website, whereas I used SMA’s download software, which runs on your own computer. I tried the online software and got the same result as Harrimans. But then I noticed a “Predicted Outputs” button in the lower right hand corner of the results. I clicked on this button and the resulting data showed that the minimum voltage at 104 degrees F outdoor temperature from these Sanyo panels would be 236 VDC, lower than the 250 VDC minimum shown for the SB4000. In fact, this data showed that only 6 to 8 of these Sanyo panels per string was compatible with the SB4000, which conflicts with the 4 to 8 panels per string results shown on the previous web page. This same software showed that the SB3000 was compatible with 5 or 6 of these Sanyo panels per series string, as the downloaded software did.

I called SMA’s toll free help line and the technical person who responded was very emphatic about using the SB3000 and not the SB4000 in our installation, though she wouldn’t say what the consequences of using the SB4000 would be. So I called Harrimans and pointed out that the data for both compatibility software programs indicated that the lowest possible voltages out of the Sanyo PV array was outside the specified operating range for the SB4000. They agreed to replace the SB4000 with the originally specified SB3000.

Note that the system was operating correctly at that time with the SB4000. But it was also the end of November, when temperatures tend to be cooler in Florida. The low voltage condition would tend to occur during hotter temperatures, such as those typical during the Florida summer. In fact, most people would probably never notice the problem, but may only notice they weren’t getting as much power out of the system as expected during the summer. But without any previous experience with PV systems, most might think this is normal.

Note also that I don’t blame Harrimans for this problem as they did check for compatibility and the SMA software did initially indicate that five of these Sanyo panels per string was compatible with the SB4000. The problem is really with SMA in that they have inconsistent results in their software, which SMA needs to fix. Once the problem was pointed out, Harrimans did swap the inverters with no fuss.

So now we had a working grid tied solar electric system. But we didn’t let it operate all the time. Why not? The answer to that is the subject of the next article.

How do you find and select an installer for a photovoltaic system for your home?

I considered installing it myself. But the state rebate program, as well as the power company (if you are going grid-tied) and my homeowner’s insurance insist that the system be installed by licensed professionals. Also, when I compared the cost of doing it myself, including permits and getting engineering drawings approved by licensed engineers, with the various quotes I got from licensed installers, there wasn’t much difference in price, not enough to justify all the extra work and risks on my part for installing it myself. The installers are probably getting much better discounts on the components than I could get, with the difference almost covering their labor costs.

You could find an installer by doing a net search for your area, looking in the telephone book, or attending various home shows or environmental expos in your area. The problem with these methods is that anyone can present their business through these methods, including amateurs and fly-by-night outfits. It would be better to select from a list that has been at least somewhat prescreened.

The ASES (American Solar Energy Society) has been offering a tour of solar installations one of the first weekends in October for the past few years (www.NationalSolarTour.org). They feature various solar installations in your area. The installers are listed for all the installations on their tour. You get a chance to see an example of these installers’ work. They also often provide a list of other installers in your area. But you don’t have to wait for a tour as they do have installer lists and other helpful info on their website.

In Florida, the Florida Solar Energy Center (FSEC) is another good source. By Florida law, all solar installations must be approved by the FSEC. They have a list online of the systems they have approved and the installers (http://www.fsec.ucf.edu/en/industry/testing/PVsystems/certified_systems/index.htm). You can check out the installers on this list that are in your area. One problem with this list is that they don’t appear to be updating it regularly on the website.

I used the last two mentioned resources for finding installers in my area. My preferences were installers that have been in business at least 10 years, with at least 50 photovoltaic installations, and can show that they have experience installing grid tied systems that have battery back-up.

As a reminder from my previous blog articles, I was looking for a system with a minimum of 2000 W of panels, grid tied, with at least 10 kW-hr of battery backup. See my previous articles for the reasons for these requirements.

I contacted around a dozen companies. Some no bid because they didn’t feel my system was big enough to justify the distances they would have to drive for the installation (these were mostly Orlando-area companies). Some just gave bids over the phone or Internet without even seeing my house. This didn’t give me a lot of confidence as they had no idea what my shading, roof construction, attic access, etc., was like, so they were quickly rejected, especially since their quotes weren’t much different than anyone else.

All the quotes fell between $22,700 and $25,900 except one (a company that didn’t visit my house) which was about $30,000. These quotes were received in October, 2009. I narrowed it down to three companies:

Solar Source was by far the cheapest. They are also the largest solar installer in Pinellas County, where I live (population just under 1 million), with probably more installs in this county than all the other installers combined. I could find info indicating they have been business since the mid 1980’s, so they probably wouldn’t disappear next month.

But a number of things bothered me about my contacts with the company. First, their salesman insisted they could only install the panels on my west facing roof section (I have a hip roof with slopes in all directions with no gables). My studies indicated that that was the most shaded section of my roof with the least average hours per day of direct sunlight. I really wanted the panels on my south facing section of my roof, which is typically best in the northern hemisphere, though my analyzes indicated that a south orientation would only get me about 8 percent more power than an east or west orientation, since I have a shallow 14 degree roof slope. This assumes no shade. But the south roof section has a lot less shade and the shade that is present I have more control over and can significantly reduce if I need to. When considering shade, my analyzes indicate that I would get between 30 to 50 % more power from panels on the south roof than on the either east or west roofs (the sun exposure on my east is not much better than on the west). My sizing study indicated that I could fit 2000 W of panels, though not much more, on my south roof. The others who saw my house and gave me quotes also felt they could fit the panels on my south roof.

The only reasons I could figure out for the Solar Source representative’s insistence that the panels be mounted on the west facing roof is 1) that is the second biggest continuous roof section, since the longest dimension of my house runs north-south, so it would make their installation the easiest, and 2) the front of my house faces west, so panels on the west roof would be the most visible to the general public and give them the most advertising. These seemed like very poor reasons for me to take a significant hit in the output of my solar installation.

I was also having a hard time getting them to list exactly what major components (manufacturer, model numbers) they would be using for my installation. Their attitude appeared to be “We’re the experts. Trust us, you’ll like whatever we give you.” But this is the second biggest purchase I’ve ever made in my life. If I were having a room added to my house, hearing the contractor say “Trust us, it will be this many square feet, have a floor, four walls, and a roof” would not be too assuring to me that I would like the room they build. I would want to know the room’s dimensions, how many and what kind of windows and doors and light fixtures and outlets and closets, etc. And a solar electric installation cost as much or more than the typical room addition. When I did finally get them to give me some specifics on the components they intended to use, I ran the panels they proposed through the inverter manufacturer’s compatibility software (http://www.sma-america.com/en_US/products/software/sunny-design.html) and found out that the panels they proposed would apply too much voltage to the inverter they proposed and potentially damage the inverter. So they obviously weren’t going to use these panels in this installation.

I suspect the reason they were reluctant to list specifically what they were going to use for my installation was so that they could have the flexibility to choose the cheapest equivalent components at the time of my installation to maximize their profit. But that would not assure giving me the most efficient system for my location and money. The importance of all this will be more apparent in future articles on this blog.

All this does not imply that Solar Source is a bad company. As I mentioned earlier, they have by far the most installations in my area, so they must be doing something right. I could find no complaints about them. The things I mentioned above are probably what allow them to bid so low and still make a profit. They were on my final selection shortlist, partly because they were the cheapest, but also because from what I learned about them I was confident that whatever they installed would work. It just would not be what I would consider optimum for my property. So, if you have a more ideal situation (big south facing roof with no shade), they are probably the way to go as you will save a lot of money with them. But with my far from ideal situation, cheapest is not necessarily the best.

Harrimans Inc. was the second company on my shortlist. My research indicated that they have been in business since the early 1970’s. They provided a list of about 75 references, with addresses and phone numbers, of photovoltaic installations they have done the previous two years. I saw one of their grid tied, battery backed-up installations on the solar tour. They are installing about two PV systems a week (as of winter 2009-2010), making them one of the largest installers in Florida. They were also the second most expensive of all my quotes.

Harrimans was confident they could install 2000 W of panels on my south facing roof. They proposed using Sanyo HIT panels, which are the most efficient panels readily available on the market, and consequently take up the least roof area for a given power out. These Sanyo panels also tend to perform better than most panels under shady and cloudy conditions, giving even a little more power output. They are also a bit more expensive, which probably accounts for part of the higher price of Harrimans quote.

Harrimans also did give me a detailed list of the major components they intended to use and listed them on the proposal/contract. They also only wanted about 25 % of the money up front with the rest due upon satisfactory completion of the job. Their salesperson also didn’t try to bulls–t his way around any technical questions, like some others did. If he didn’t know the answer, he immediately called whoever he felt in his company would have the answer. So, even though they were a little on the expensive side, I couldn’t find anything wrong in what they proposed and felt confident the job would be done right.

St. Pete Solar was the third on my shortlist. They had only been in business a couple of years and had only installed five grid tied systems as of Oct. 2009. They had never done a battery backed up, grid tied system. These facts don’t seem to support my initial requirements for an installer. So why were they on my shortlist?

One thing that has always bothered me about most solar installations is that the PV panels are mounted on the roof. Roofs eventually need to be replaced. Though I had just replaced my cement tile roof about less than seven years ago and it should be good for at least another 30 years (my first cement tile roof lasted 44 years), I still felt uncomfortable about putting the panels on my roof. St. Pete Solar was the only company that proposed putting the panels on a free-standing awning-type structure and they actually had experience with this type of installation (shown on their website).

This free-standing structure would have to be put in the area between my house and the southern border of my yard to avoid shade issues. Unfortunately, I have an easement there that prohibits any permanent structure there. During initial talks with the head county zoning official, he said he couldn’t outright approve a variance for putting these panels in the easement and that it would have to go before the zoning board, though the official said he would support such a variance if my neighbor to the south of me was OK with it, which he was. But, after thinking more about it, I realized a few other things:

1) Most modern solar panels are self-leaded with snap together connectors. These wires would be exposed in an awning installation. The inspectors may require these exposed wires to be in some sort of protective conduit, which would be difficult. If mounted on a roof, this is not usually an issue as few people have access to the roof and the wires are sandwiched between the roof and the panels so they aren’t really exposed. I didn’t really want to fight this battle.

2) Mounting on the roof does provide some shade for that roof area, which reduces air conditioning requirements a little.

3)The panels themselves are less likely to be damaged on the roof than they would be on an awning type structure that people could and would be walking under.

4) After talking with some people, I found out that removing and reinstalling the panels is much less expensive and not as big a deal as I originally thought it might be, though, with my relatively new roof, this may never be a concern in my lifetime.

So having the PV panels mounted someplace other than the roof was looking less attractive. Also, the cost of going with St. Pete Solar was not much cheaper than going with Harrimans and they had never done a grid tied, battery backed up system before. If they were significantly cheaper, like $6000 or more, which would more than pay for a potentially fried inverter, these concerns could probably be lived with. But the risks and extra hassles for my particular installation weren’t worth saving just one or two thousand bucks. But if I would have been going strictly grid tied with no battery backup and didn’t have the zoning issue, I probably would have gone with them as they seemed quite knowledgeable and I liked a lot of the things they did with their installations and they would have been a lot cheaper than all but maybe Solar Source.

So I ended up choosing Harrimans. It was worth it to me to pay a little more for a lot more power generated.

The most basic instinct common to virtually all, if not all, creatures is the survival instinct, the drive towards self preservation. This survival instinct, as well as the desire to reproduce, dominate the lives of most all creatures. But, curiously, this instinct seems to be disappearing in most Americans.

Some common examples that triggered this observation:

1) Many Americans these days will walk into a street without even looking to see if they may be walking into the path of some vehicle. I was taught as a child to look both ways for any traffic before entering a street. Many American adults apparently never learned this or even thought of it. And this problem is not just confined to pedestrians, for this problem also seems to be very prevalent among bicyclists.

2) Many Americans try to drive a motored vehicle while their minds and bodies are focused on some other task. Everyone is familiar with those who are too busy talking on their cell phones or text messaging to worry about driving. But I have also seen people eating, reading a book or newspaper, putting on make-up, changing a diaper, dancing (I assume that is what they were doing when they have both hands above their heads and they are moving in a rhythmic fashion), and even appearing to have sex while driving.

3) Many people will attempt to do some strenuous adventure, such as a hike or paddling trip, without any training or far beyond their skill level, that are well beyond their physical abilities, without consideration of their present health, the weather, political conditions, and/or without the proper gear, maps, or planning. I have seen many people like this on trips I have been on that the rest of the group have to “babysit” to get them though the trip. I have also heard many people like this bragging about their adventures, wondering how they ever managed to survive. Then we all have read or heard in the news those who weren’t so lucky, often jeopardizing the lives of others and/or causing big political crises.

4) Instead of buying the minimum home that meets their needs and that they can afford with some margin, many people buy the absolute biggest and fanciest house they can manage to convince someone to loan them money for, even if it is a stretch to make the payments and there is no margin for potential future problems.

5) People deliberately live in questionable places and do little to protect themselves. For example, much of New Orleans is below sea level and the city has flooded at least 27 times in its less than 300 year existence, yet people still insist on living there. People also live in the flood plain of rivers that are known to flood on a regular basis. And few Floridians have done much to protect their houses from hurricanes, even after the rather disastrous storms of 2004 and 2005.