Have you been thinking about installing solar panels for your home, but been discouraged because the cost is too high? Here in Montana, my family and I saved 40 percent on the cost of a solar electric system by buying a kit and doing the installation ourselves.
One notable feature of our solar power system is that it uses the relatively new micro-inverter technology. With this system, each photovoltaic (PV) panel has its own grid-tied inverter that is mounted right by the panel. This kind of system is easier for do-it-yourselfers to install, and has other advantages, such as less sensitivity to partial shading, power output optimization for each PV panel, and the flexibility to start small and grow the system as time and budget allow.
We decided to go with a grid-tied system, which is much more cost effective than an off-grid system. One advantage is that you don’t have to buy batteries, which are expensive and have to be replaced from time to time. You can also choose to install a smaller, less expensive system that generates just a portion of your electricity. On the downside, grid-tied systems provide no electricity when the power grid is down.
Planning the Solar Electric System
The first step to planning your system is to evaluate rebate options and obtain permits. Your local power utility has rules you must follow when you hook the finished system to the grid, and building codes may also apply. In addition to federal incentives, states (and even some cities) offer rebates to help with the cost of the system. Understanding the local rules before you start will save you frustration later.
Most utilities will have an information package and a person who specializes in the utility requirements. We found our local utility and code inspectors helpful and friendly. We didn’t pick up a hint of resistance from them regarding the idea of a homeowner-installed PV system. Permit costs and turnaround times were small. Check the Database of State Incentives for Renewables and Efficiency (DSIRE) for information on rebates in your state.
Deciding the size of your system is the next step. With a grid-tied system, size is less critical, because the grid supplies power when your PV system falls short. Systems as small as a couple hundred watts are practical, but you can also install panels that will produce enough electricity for all your needs. Review how much electricity you use now, and then estimate what you will be able to save by applying conservation and efficiency measures throughout your home. This will give you an idea of how big a system you’ll want to build. You certainly can build a system smaller than this, but it may not pay to install a larger one. Look up your state on DSIRE to learn about net metering rules where you live, including how much you can get paid for generating excess power.
Figuring out ways to use less energy in your home is almost always more cost effective than putting up a larger PV array. We started with a monthly usage of 1,000 kilowatt-hours (kwh), which is about average for a U.S. household. We got this down to about 500 kwh by spending a bit more than $1,000 on efficient lights, power strips with switches, a new fridge and a few other strategies (see 8 Easy Projects for Instant Energy Savings). Compare that with the PV system, which saves us 250 kwh per month but costs $6,000 — it’s clear where the best return is. Take the efficiency measures first, then buy the PV system.
We planned for a PV system that would cut our current usage by about half (i.e., a system that would generate about 250 kwh per month, or 3,000 kwh per year). We used the National Renewable Energy Laboratory’s PVWatts calculator to estimate the size of a system that would produce 3,000 kwh per year in our area. PVWatts came up with a system size that was a little more than 2 kilowatts. The system we ended up installing has an estimated production of 2.15 kilowatts.
Our system uses Enphase micro-inverters, but other brands may also be available. We have 10 PV panels rated at 215 watts each, and each has a 190-watt inverter that converts the direct current produced by the panels to alternating current, which is the standard system for electricity in homes in the United States. We ordered the system as a kit that included the PV panels, micro-inverters, mounting rails and a number of other parts. The kit was a good choice, but don’t expect an “insert-tab-A-into-slot-B” sort of kit. Basically, you get a box full of parts. You’ll soon become familiar with the websites of the companies that manufacture the parts — especially the “download manuals” area.
Situating the PV Array
Ideally, the solar panels for your home would face south, and be tilted at an angle about equal to your local latitude. They would also be in full sunlight with no shading from about three hours before solar noon (the time when the sun is directly in the middle of its path across the sky on a given day) to three hours after solar noon. Performance will not suffer much if you can’t get the panels aimed straight south or tilted just right, but even a small amount of shading can have a serious negative effect.
A solar site survey will show you any potential shading problems for any time of year. You can do the site survey in a couple of ways. One way is a procedure in which you use a “sun chart” for your area and a simple sighting of objects that may cause shadows — this could be a fun family event to teach everyone about the path of the sun throughout the year. Another simple method is to model your PV array and potential shading objects in the free Google SketchUp drawing program. SketchUp has a feature that will show you shading patterns for any time of day and year.
Micro-inverters offer an advantage in partial-shading situations because, in this system, each PV panel has an inverter that provides maximum power point tracking to get the most possible power out of that panel, whether it’s partially shaded or in full sun. For conventional string inverter systems, partial shade can cause the voltage of a string of panels to drop to the point where the inverter shuts down and power output drops to zero — a big effect, indeed. If you have serious shade problems that you can’t amend, PV is probably not a good choice for your situation.
We opted for the ground mount rather than a roof mount because it made the installation easier (and less scary), and we won’t need to remove the panels if the roof ever needs to be replaced.
Solar Panel Installation
It’s time for the fun part — installing the system! You could build or buy many types of PV panel mounting systems, but the PV panels will probably last 30 years, so choose a mounting system that can endure wind and weather for a long time. We made our own mounting rack from 4-by-4 treated wood posts and concrete footings, then installed the panels on aluminum rails designed specifically to support the panels over the wood frames.
With some help from the neighbors and a borrowed concrete mixer, we installed the mounts fairly quickly. It’s important to make sure the mounts are aligned well. We used temporary 2-by-6 frames behind the vertical posts to align all the support frames.
Be sure the joints in the wooden frame are reinforced with metal plates and that the footings are adequately sized. Apply an extra coat of wood preservative to all grain ends of the treated wood and the areas where the wood comes in contact with the concrete. In our climate, treated wood lasts a long time, but if you live in a wet climate, you may want to consider metal supports.
After the mount frames were in the ground, we installed the aluminum support rails. This was easy to do using the supplied L brackets. We then installed the micro-inverters on the rails, which required only two stainless steel bolts for each inverter.
Next, we installed the PV panels, starting at one end and working across the rails. Be careful! One slip may cost you a $600 PV panel. The panels are awkward to handle, so having assistance with this part is important. We temporarily clamped a 2-by-6 below each panel to support it while making the final adjustments. The mounting clamps simply slide into slots in the support rails. After the PV panel is in place, the clamps can be tightened to secure the panel.
Check the alignment frequently as you mount the panels. Small errors in alignment add up and tend to be noticeable. We tightened the panel clamps just enough to hold them in place, and later used a torque wrench for the final tightening.
PV System Wiring
The wiring for the Enphase system is relatively simple, but be sure to read all the instructions and understand the safety issues. You are dealing with high voltages, and the PV panels make the system “hot” even if it’s not hooked up to the grid. If you think this may be more than you want to tackle, you can team up with a local electrician to do the wiring. The actual labor involved in wiring is not much, so this shouldn’t add significantly to the cost of the system.
The output wires from each PV panel plug into the mating wires on the micro-inverters. The output cables from the micro-inverters are just daisy-chained together. The output from the final inverter goes first to a junction box at the PV array and then to a PV array disconnect switch located near the house meter. From the disconnect switch, the power goes to an unused circuit breaker in the circuit breaker box.
The PV array disconnect switch allows utility workers to disconnect the PV array from the grid. The switch must be lockable, it must be near your main house meter, and it must be clearly labeled. The circuit breaker that feeds PV power into the circuit breaker box must also be labeled.
I plugged in the PV panels and the new circuit breaker last, so nearly all the wiring was done on a “dead” system.
Grounding the System
Check all of your wiring, and be certain that you have everything grounded as required. All of these components (PV panel frames, PV panel support rails, micro-inverter cases, PV array junction boxes and the disconnect switch) must be grounded by an approved grounding method.
For example, even though the PV panels are bolted to the grounded rails, this is not an approved grounding connection. We used the Weeb grounding system for most of these, and it worked well.
In addition to safety issues, inspectors will look for proper grounding. If I were to do it over, I would use the Weeb system everywhere because it’s so easy.
More detailed construction information is available at Build It Solar.
Start Up the Inverter
For Enphase systems, a unit called the EMU communicates with all of the inverters by sending signals via the power line. The EMU provides information on how the system is functioning, checks the status and health of the inverters, and sends the data to the Enphase server through your home Internet connection.
After the inspector approves your system and the utility provider has installed the net meter, you can turn the system on and plug the EMU into a regular power outlet. The EMU will find your inverters and start reporting. At this point, the system is generating power, and the EMU will give you the basic stats. Sit back, have a beer, and watch the power roll in.
PV Performance and Savings
Our system has been operating since November 2009, and its performance has been good. We’ve experienced no failures, and the system hasn’t required maintenance. So far, the energy production is running about 10 percent ahead of the PVWatts calculator estimate. Check out the real time performance of our system anytime.
The cost of our system was $9,960, or $4.63 per watt — prices may be a little lower now. The 30 percent federal rebate plus a $500 state rebate brought the cost down to $6,470, or $3.01 per watt. Rebates in some states are much larger than those in Montana.
Professionally installed systems of this size are often quoted at $7.50 per watt, which would mean we saved about $6,000. If cost is your main motivation for assembling a system yourself, I recommend getting bids on installed systems and comparing them with the cost of all the parts you’d need for a similar system.
The savings on our electric bill the first year was $332 (based on about 10 cents per kwh), plus we reduced our CO2 emissions by 4,700 pounds. The simple payback period on the $6,000 we invested would be 18 years, but I expect it will be much shorter if the price of electricity continues to increase. For example, if rates go up 10 percent per year, the total payback time will be only 11 years.
Solar Power Sources
Gary Reysa has developed all sorts of DIY projects to harness power from the sun to heat his home, shop and domestic hot water — and to produce electricity. His website, Build It Solar, is an outstanding resource if you’re planning a project of your own.