Solar panels or modules (generally installed on the roof but can also be mounted on the ground or an overhead canopy like a parking structure) are made up of photovoltaic (PV) cells. A current is made when sunlight hits the cells, converting sunlight into power. Those solar panels’ direct current (DC) power is sent to an inverter. The inverter does precisely what the name sounds like – it inverts the current from DC to AC (alternating current) power, which is what your home and everything in it uses. The inverter also monitors your system’s performance and regulates the voltage coming into your home. It’s the “brain” of your solar array. Your inverter will also provide the monitoring of your system. Our Enphase systems come with lifetime free production and consumption monitoring through the Enphase MyEnlighten application.
The AC power then travels from the inverter to the electrical panel, often called a breaker box or main panel, and into your home. Anything that uses power, like your dishwasher, your kid’s video game system, or your TV, will draw it from the solar panels first. If solar is unavailable (because it’s dark or cloudy outside), you’ll get your power from the main power grid just like you do now. Everything in your home that runs on power will run exactly as it does now. Your air conditioner can’t tell the difference between running on dirty power and clean kilowatt hours, but your power bill and your lungs sure can! Unlike fossil fuels, solar power doesn’t emit harmful smog, waste chemicals, or noise to mess up the air or water. Your home will also gain value as now you have a power plant on the roof that runs on unlimited free fuel. No more rising utility rates for you!
When it’s sunny outside, you could even be sharing that clean power with your neighbors through Net Metering. Net Metering is how the utility pays you to send your clean energy back to their grid. Think of it like rollover minutes on those old cell phone plans before we all got unlimited talk time.
Net Metering in a Bar Graph: See the orange bars on the graph to the right. That’s solar production. See the blue bars? That’s power consumption. With Net Metering, the extra power you make in the spring, fall, and winter pays for the more considerable power demand in the summer.
In the spring, winter and fall, we have a lot of clear, sunny days. Most of us are not using our air conditioners, so our power use is way down. During those months, your solar system will usually make more power than your house needs. Whenever that happens, that extra power goes back through your meter, and NV Energy puts a credit on your power bill. That power is then delivered to your nearest neighbor that needs power right that second. Your meter will “spin backward,” and you’ll be banking up credits against your future power bills – just like those old plans would save unused minutes until you needed them. When summer rolls around, and the temperature soars, you’ll need more power than your solar is making. The power company will then use your banked-up credits to pay for it before they bill you. Thanks to Net Metering, if we can replace all your power needs with solar, you could have an average power bill of about $14 a month year-round.
NV Energy offers net metering on a Tiered system. Currently, the state is in Tier 4 at 75% of retail value buyback. At the end of the month, NV Energy will compare what you used (KWHD) with what you sent back (KWHR). What you send back wipes out what you used at 100%.
If you used more than you sent back, they bill you for the extra (KWHN).
If you send back more than you used, they will credit you for the excess energy sent back to the grid.
Any extra (KWHA) is purchased back from you at 75% of the current retail price per kilowatt hour. It’s a credit on your bill (Excess Energy Credit). Like rollover minutes on the old cell plans, the credits sit until you need them. The power company applies them as needed. They never, ever cash these credits out, so it’s important to size your solar to create the amount of power you need and not oversize it. Click here to learn more about sizing your solar system correctly.
Central or String Inverters are old-fashioned technology. With this setup, all solar panels are wired in series (or strings). All the power the system makes feeds from the panels, over your roof as high voltage DC, and down through one inverter to be flipped to AC and then fed into your main electrical panel. The inverter is usually a big box (about 1′ x 2′) and is mounted on your garage wall – hopefully in the shade as they tend to fail in high heat conditions. If you have a lot of panels, you might get stuck with two or more of these clunky boxes on your wall because each inverter can only handle so much wattage. Once it hits the string size limit, you must add another inverter.
Central inverters are the weakest link in your system. Because all the panels are connected in strings, that means if the inverter has a problem, the whole system stops working, just like those old-fashioned Christmas lights when one bulb burnt out. It also means that if one or more panels are in the shade from a roof vent, a tree, or a cloud, the entire string’s power output is reduced to whatever that lowest-performing panel is doing. Some companies will install a power optimizer on each module to overcome this performance loss and help the system compensate for shade, but that can’t overcome the single point of failure in the system. Power optimizers provide panel-level monitoring, but they are NOT inverters. If the inverter fails, the whole system stops working. In summary, these kinds of systems are much more complex to design. They are subject to a lot of limitations with string sizing. They are far more prone to failure due to the large mechanical cooling fan inside the inverters. Anything that moves can break over time. This is why central inverters typically come with a 12-15 year warranty instead of 25 years. When that fan goes, the unit must be replaced. You will pay to replace a central inverter at least once during the 25-year lifespan of your system. Central inverter systems, even with optimizers, produce less power over the system’s life due to the line loss from the long trip over the roof as DC. Centrals with optimizers are a kludge, not an equivalent to micro inverters.
With a microinverter system, each panel has its inverter. The DC is converted to AC right at the panel. This means the system is more efficient and produces more power over its lifetime because electricity loses strength the farther it travels before it gets flipped from DC to AC. Lower voltage AC moving across your roof is safer than high voltage DC. It also means that there is no single point of failure because the system is wired in parallel. If one panel or inverter were to fail, the rest of the system would keep making power. Micros also do not have ANY moving parts inside them, so there is no fan to fail. This is why they are warranted for a full 25 years. Robco recommends Enphase microinverters. They offer free lifetime monitoring with the Enlighten website and app and built-in consumption monitoring at no additional charge.
Having an inverter on every panel means each one is truly independent. If one or two panels are shaded or dirty, the rest of the system couldn’t care less and keeps making power at maximum capacity.
On a central inverter system, there has to be enough light hitting the panels to create the minimum voltage on the string for the inverter to wake up from sleep. Because microinverters are independent, each panel will wake up from sleep about 30 minutes earlier in the day and go to sleep about 30 minutes later in the evening. Burst mode is the technical term for this. That means you get roughly 1 hour more of production daily from a micro inverter system. Over 25 years, that extra hour can add up.
Mirco inverters have an expected lifespan of 25 years and are warranted (parts and labor) for all 25 years. Central inverters – even the ones with optimizers – typically last 12 to 15 years and often fail even before their expected end of life. These failures are widespread if they are not installed in a shaded area. While it is true that it’s pretty simple to replace a central inverter and does not require anyone to get up on the roof, they cost $3,000 or more every time they fail and will take 4-6 hours to replace. If you had to replace it twice in 20 years, you just added $6,000 to the sticker price of your system and added years to the payback time.
Simple. In the last eight years, Robco has installed over 40,000 Enphase microinverters. They have been through many punishing summers, and the failure rate remains less than 1%. You can verify this by checking our reviews; there are no mentions of inverter failures.
You may need more power than your system was sized to deliver at some point. Maybe you put in a swimming pool or buy an electric car. Once your system is up and running, you can add on as needed. Find out more about adding on here.
If you want to add to a central inverter system, you can only go up to the capacity limit of the inverter (3kw, 6kw, etc.). So if you have a 6kw system with a 6kw inverter and need to add on eight panels because you converted your garage into an office, you’ll need another inverter. Another inverter can cost upwards of $1,500 in addition to the added cost of the panels.
On the other hand, microinverter systems add a panel and an inverter together. With micros, you can perfectly size your system as your needs grow. No need to spend extra money on equipment you don’t need or pay the power company more than you have to. This design flexibility also means that your install team can easily alter your panel layout in the field if needed.
At its most basic, a solar panel is two sheets of silicon solar cells connected by bus bars encased in glass surrounded by an aluminum frame. Just as there are many kinds of cars with different price points and specifications, there are a lot of brands of solar panels with diffeotherifications and prices. The grade of the silicon and the wattage of the panels, as well as how those cells are assembled, all matter when it comes to lifetime power output and reliability.
All solar panels are made from silicon crystals. In a polycrystalline panel, each wafers used to make the solar cells is composed of multiple silicon crystals. The process used to make the silicon ingots is a bit like the one used to make particle boards in construction. A single crystal seed is placed in a vat with lots of chunks of silicon, and it’s all melted together. Many crystals grow as they cool. It’s cheaper to make and creates less waste, but the borders where the crystals meet make for a slightly rougher surface which causes electricity to move around less efficiently. This type of panel has a 13-16% efficiency rating. It also has that typical blueish hue due to the composite nature, where light bounces off the rougher surfaces and is reflected back to your eye.
In a monocrystalline panel, the silicon wafers are sliced from a single pure silicon crystal, giving them a much more uniform surface that converts sunlight into power at higher efficiency (15% to 22%+). Due to the more refined nature of the silicon, monocrystalline panels have a dark black appearance. They also perform better at higher temperatures – a big plus in our desert heat.
These days, most solar panels are at least 300 watts. That is the maximum rated generating capacity of the panel under perfect test conditions. On your rooftop, though, the output will depend on which way the panels face, how much sun is hitting them, what angle they are tilted at, how high the sun is in the sky, how much shade is present, and how hot it is outside. In practical terms, that means each panel will put out different amounts of power at other times of day and in different seasons. When your solar installer provides an annual power estimate, they consider all these variables. Higher wattage panels will produce more power over their lifetime than lower-wattage panels, even with these variables.
Silicon crystals break down over time. This is called degradation, and it is a natural quality of the material, so every single panel will lose a little bit of performance as it ages. Environmental factors and stress can increase it to the module structure – like someone walking on your solar panels. Your power output in year 25 will be lower than in year 1. How much will it drop off, and will you notice it? That depends. Manufacturers guarantee that the typical solar panel will produce at least 80% of the day one power at Year 20. Still, manufacturers can reduce degradation in several ways from using more and thinner bus bars to the surface of the cells to the actual composition of the cells themselves. Those technological advances mean that long-term power production from panels is improving. You should look for a panel that offers at least a 90% power output guarantee at year 25, just like our recommended LG NeON 2 panels.
A bifacial solar panel has a transparent back sheet. The cells used can create power from both sides. It produces electricity using the light that hits the front of the panel and reflected light hitting the back of the panel. When installed at an angle over a light-colored surface, like on a flat roof, in a parking canopy, or on a raised rack on the ground, these types of panels can increase power production. They are typically reserved for commercial installations. However, we may recommend them for flat roof installations