IN THIS CHAPTER

Taking the time for proper evaluation and orientation

Using the right system components

Keeping an eye on the array and its associated equipment

Regardless of their varying reasons for installing a PV system, there’s one thing all people want to see from their investment: the maximum amount of energy production possible. Your job as the system designer and installer is to help deliver this maximum energy yield. Yes, each system will be slightly different, and each client will have varying needs, but at the core, the processes are similar for all PV systems. The tips presented in this chapter focus on a variety of stages, from system design and preplanning to installation and long-term maintenance, so you can give your clients the value they’re looking for.

Select the Right Site

It may seem like a silly (and obvious) thing to say, but selecting the proper site is one of the most important steps you can take to maximize a PV system’s energy production. All too often I see situations where someone just picked a random location for an array and never thought to stop and look around a bit for a different location. After all, some locations work better than others due to a variety of shading, structural, mechanical, and electrical issues.

With the components that are available today and the wide variety of system configurations you have to work with, you shouldn’t need to compromise on an array’s site. Take the time to walk around the site and gauge which installation location will work best. At the very least, keep an open mind when it comes to array locations and flip to Chapter 5 for advice on how to properly select a site for a PV system.

Orient the Array Correctly

An array’s orientation is the direction in which it points. Conventional wisdom says to orient the array to true south (when you’re in the Northern Hemisphere) and tilt it at an angle equal to your latitude. Although this strategy may yield a high amount of energy, it may not give you the maximum amount of energy the system can produce. A client’s PV system should be in place and operating for more than 25 years, so small gains in energy production can have a large effect when measured over the system’s lifetime. (To determine the best orientation for an array in your client’s location, turn to Chapter 5.)

When orienting a PV array, you need to evaluate both the structural and aesthetic effects. A rooftop PV array that raises the modules off of the roof plane in an attempt to point them in some direction other than that of the existing roof may boost the energy output, but it may also cause serious damage to the client’s roof due to the extra weight if the location is subject to high winds and/or heavy snow loads. And even though maximizing energy production is the main goal, you also want to help promote PV installations by installing good-looking arrays.

Configure the Array Properly

For maximum energy production, the PV array should be properly matched to the charge controller and/or inverter, which means you need to consider both the voltage and the current relationships.

All the components connected to a PV array have a voltage window that they must operate in. As I explain in Chapters 11 and 12, you must account for changes in voltage based on temperature; otherwise, the charge controller(s) and inverter(s) may shut down. On top of that, PV modules degrade over time, so you need to properly account for that eventual energy loss due to aging; if you don’t, you run the risk of the PV array falling outside of the voltage window due to natural degradation.

The amount of power a PV array can generate in comparison to the amount of power the electronics connected to it can process is another important comparison to make. Each manufacturer of charge controllers and inverters has a recommended amount of power you should put through its machine. Exceeding the recommended values results in excessive heat production and shortened life spans for the components. Chapters 11 and 12 show you how to properly account for these limits.

Work within the Limits of the Utility Voltage

Grid-direct systems are really at the mercy of the utility grid because their inverters have to follow the lead of the utility and go offline if the utility goes outside of the acceptable limits. Utility-interactive, battery-based systems have a little more flexibility, but the grid is still critical for them too. (See Chapter 2 for an introduction to both of these system types.)

When it comes to the utility grid and voltage, inverters are important for both PV system types thanks to the “follow the leader” approach the inverters have to take. The voltage window on the AC side of the inverters is much smaller than the DC side, and for safety reasons, the AC side isn’t adjustable. For all utility-interactive inverters, the acceptable range of voltages is –12 percent to +10 percent of the nominal line voltage. (I note the voltage windows available to inverters in Chapter 11.)

On top of that, the voltages delivered by the utility aren’t under your direct control and can fluctuate over time. When the grid’s voltage is off of the nominal value and the inverter has a long wire run before connecting to the utility, that narrow voltage window can disappear. In Chapter 13, I show you how to look at these conditions and minimize their effects on your clients by reducing the voltage drop in the conductors (wires).

Choose the Correct Inverter

The inverter is the brains of the whole PV system. Given this fact, you need to make sure the inverter’s power output level properly matches what the array can deliver. The proper inverter for a PV system that you’re installing is the one that delivers the right type and amount of information for the end user.

At a minimum, the client should be able to see the power and energy values on the inverter. Some people want to see voltage and current levels as well; if your client is one of these individuals, you can install a more sophisticated monitoring system for her. If the system owner is left in the dark in terms of the system’s operation, no one will be able to make sure all is well with the system (after all, the system owner is the person who has the ability to check the system on a daily basis). Chapter 9 introduces the basics of inverters; Chapters 11 and 12 present the inverter selection processes for different system configurations.

Size Conductors Appropriately

Conductors (which I introduce in Chapter 10) are the arteries that carry the precious cargo of solar-generated amperes down to the brains and bodies of PV systems so your clients can benefit from the power and energy. Yes, that was a little dramatic, but it made you think, right?

The conductors in PV systems have to effectively deliver power. If they don’t, then you’ve installed a rather expensive power-producing system that can’t deliver to its potential. A National Electrical Code® (NEC®) requirement is to size conductors so that they have the proper ampacity (ability to carry current) for the conditions in which they’ll be used. As I explain in Chapter 13, this means you have to estimate temperatures and derate the conductors’ ability to carry current due to the presence of multiple conductors in a single conduit.

Voltage drop, when voltage (and therefore power) is lost between the power source and the load, is the other part of the conductor-sizing equation. The NEC^® makes no mention of voltage drop as it relates to PV systems, but the PV industry has come up with generally accepted standards of no more than 2 percent voltage drop on the DC side of the system and 1½ percent on the AC side. You can evaluate these percentages for your specific application, but 2 percent for DC and 1½ percent for AC are good starting points.

Keep the Components Cool

All PV systems use some form of electronics to process the power they generate, and as with all electronics, they’re much happier when they’re kept cool and able to get rid of the heat they generate. In addition to their general happiness, you want to keep PV systems cool because as they get hotter, they have a reduced capacity to do the work they’re designed for. For example: An inverter rated at 3,000 W at 25 degrees Celsius (77 degrees Fahrenheit) may only be able to have a maximum output of 2,500 W at 40 degrees Celsius (104 degrees Fahrenheit).

Use proper mounting locations and techniques to keep inverters and charge controllers as cool as possible. In other words, don’t install a PV system in a location where it’ll be exposed to full sun.

For equipment with the proper ratings, installing components on the north side of a building is a good option. If the south or west sides of the building are the only options, put some sort of shade structure over the inverter to protect it in the afternoons when the temperatures are the hottest and the array is producing energy at maximum power.

Advise Clients to Monitor Their System

One of the reasons PV arrays are so great is that they produce power all day long without visible signs of operation. Most other forms of electricity generation have some sign of operation (spinning blades, humming motors, and the like). Then again, this plus also makes it difficult to tell when a particular component of a PV system isn’t working.

To ensure that any PV system you install is working at maximum power, advise your clients to monitor their systems regularly. A quick check of the daily energy production gives them the best monitoring option. Most inverters show that day’s performance as well as cumulative performance over various time periods. If a client says that checking the daily production isn’t an option, suggest she try a Web-based monitoring program offered by the inverter manufacturer. The information such programs provide give your clients exactly what they need: energy production values. (Refer to Chapter 9 for more on inverter monitoring and communications.)

Clean the Array Periodically

The amount of current (and power) produced by a PV array is directly proportional to the intensity of the sunlight striking the array. As dirt and dust (as well as leaves and other debris) begin to accumulate on an array, the intensity of the sunlight striking that array is reduced. This layer of dust covering the modules is described as soiling; in extreme cases, soiling can reduce an array’s output by nearly 20 percent. The level of soiling typically varies among installation sites and throughout the year. It therefore deserves consideration as part of an array’s ongoing maintenance.

Soiling on a residential roof-mounted array in an urban environment will be less than a ground-mounted array on farmland. The exact schedule and level of cleaning necessary is therefore dependent on the array’s location — as well as the value of the energy the array generates.

Generally, the system owner is responsible for cleaning the array periodically. Your main task for this portion of the maintenance process is simply to instruct your client that whenever she cleans the array, she should make sure to do so early in the morning. Although the modules use safety glass that probably won’t break when hit with a sudden blast of cool water, it’s not worth testing them. (Flip to Chapter 18 for more details on basic PV system maintenance.)

Inspect the Array Annually

PV arrays often get the “out of sight, out of mind” treatment. After an array is up and running, people begin to ignore it — at least in the sense of going out or up to it and inspecting it. What they forget is that the PV array is constantly being exposed to extremes. It sees extreme temperature swings on a daily basis, its metal components are constantly expanding and contracting, its conductors are blown around by the wind, it gets weighted down with snow, and so on. For all of these reasons, I strongly encourage you to annually (at a minimum) inspect the PV arrays you install, along with their associated equipment.

As the PV system designer and installer, you should be responsible for performing the annual inspection; be sure to tell your clients the importance of such an inspection so they’re aware of the additional annual cost of the system. During the inspection, you should look for conductors that have come loose and conduit that doesn’t seem properly supported; you should also put a wrench on the array mounts to check for proper tightness in the mechanical connections. If you have the proper tools, go ahead and verify the array’s power output too (I tell you how to do this in Chapter 18).

I suggest a nice, cool, summer or fall morning for your inspection. This way you can visually look over the array, get down on your hands and knees to check the underside, and bring a bucket of water to clean the modules. (You’re already up there, so why not give your client a break from the cleaning routine? That’s customer service right there.)