8KW Solar Power System
Go solar! Keep your house cooler in the summer!! More on the benefits of solar cooling later, this review will discuss how my wife and I decided it was the right time to invest in a solar power system.
We've started noticing solar power systems installed on many homes over these past few months and honestly what stopped us from investing in a solar power system was simply the cost. It was more cost effective to get electricity from San Diego Gas & Electric - AKA the "grid".
Our first consultation discussed our power usage and some initial measurements were taken of our home. The salesperson took a look at our previous twelve months of power bills. Using a rather simple equation, he arrived at an appropriate sized system for our needs. Currently, we are a family of five - all boys ranging in age from 21 down to 17.49 years old, and do they love their electronics! (Just like their dad) Throw in a slightly underpowered air conditioning unit we use for about a month in late summer when our area can hit triple digits - 8000 watts was what we required. It's important to base your system size on your current electrical usage and what it maybe like in the future. For example, you may have a young family, which doesn't use much electricity. On the other hand, you could have a family with teenagers, which will use a lot of electricity! :) Maybe you're approaching an empty nest and are essentially at your peak of electrical consumption. Your home doesn't have central A/C but you'd like to install one at a later date, etc. This is the time to brainstorm about your future use.
We signed on the dotted line... We financed our system, and I won't discuss that process because each solar company has their own, maybe you'll use HELOC, etc.
This is the first step in the process - design. A technician was sent out to take careful measurements of our roof for available space, keeping in mind building and fire codes. Our first design estimate used 220 watt panels to reach 8000 watts. My wife and I decided to upgrade to 250 watt panels instead of the 220 watt panels recommended. Why?? The cost difference was not that much and it requires less panels to provide 8000 watts of power. That ended up being a very good decision on our part. If you can get away with higher output panels with a less number of them, it's beneficial to go that route because of shading of the panels. There's a good chance part of your home's roof will be shaded and if you can use less panels, you might be able to arrange them so they stay out in the sun longer. Also having less panels means less things to break over time.
Paying Attention to the Sun
This is something I never really thought about until I was up on the roof looking at how various trees would throw shade on the roof. We all take the sun for granted, it's up everyday and all, but not in respects of how it's shading our home. About 2/3rds of our roof faces south, so that's good. South facing panels are most efficient, followed by west facing. All this applies to my location in Southern California. Your location will be different! Take photos, make sketch drawings, etc, on how your roof is shadowed. What time of day will depend on your location, for our roof, it was around 2 PM. Every 30 minutes I went outside to check the roof and see where shadows were falling on the roof. We have a row of 40' tall cypress trees that cast shadows on the roof. This came in handy when the first design was presented to us.
Design Approval Phase
The next step in this process is to approve the design. Armed with the new found knowledge of how shadows fall on our roof, we were able to make an informed decision on our design. Here's the first design we reviewed:
After reviewing this design, we realized it wasn't optimum for our home. The top of the drawing is due north. It wasn't maximizing the number of panels facing south and the row of 12 on the west of the house would be shaded for the majority of the afternoon. Back on the roof we go to take more measurements. We decided to rotate the row of 8 & 6 into landscape position, which created enough room to move 3 panels from the row of 12 to south facing. That meant 750 watts of generation improved. The row of 6 at the top was pushed up to the centerline of the garage roof allowing one more panel to face south. We're up to 1000 watts of solar panels in a south facing location. That leaves 8 from the row of 12. I know the Cypress trees don't shade the lower left corner of the roof until very late in the day. We took the remaining 8 panels, landscaped them so they all fit into the south-west corner. Our approved design looks like this:
You can see how all the panels were rearranged to have as many south facing and in the clear. Driving up the street, our home looks like the International Space Station! Aesthetics are important too, my wife and I think it's cool looking. Your tastes will probably differ.
Design approved, financing approved & signed, permits filed, and all the equipment has been ordered. It's time for installation! Ours took 3 full days and the install team of J & C were simply awesome. I work from home and they were as quiet as they could be on Thursday and Friday, and finished up on Saturday. Here are photos taken during install.
Array 1 - Garage Roof South
The shadows seen are from the cypress trees that line our back yard. This photo was taken around 5:30 PM, you can see even that late in the evening, more than half of the panels are still out in the clear.
Array 2 - House Roof South
This is the string of 17 panels on the very south roof of the house. Due to the way the picture was taken, it looks like the roof is sloping down to the left - it's actually sloped to the right towards my shadow. What I like is the attention to detail J & C had during installation. Wires dressed, everything evenly spaced, minimal exposed wires, and a very clean job site. This photo was taken around 5:30 PM and you can see the long shadow of the cypress tree. This array is in sunlight starting from 6:30 AM until 6 PM until the sun sets behind the hill that's close to our home.
Array 3 House Roof West
This are the 8 panels that were spread all across the west facing roof, landscaped and pushed as far down on the west facing roof. As you can see, plenty of shadowing going on. This shadowing starts around 3:30 PM during this time of year (May/June). This photo was also taken around 5:30 PM.
There are two ways to mount to the roof for our installation. Guaranteed not to leak! DIfferent footings don't matter because once the solar panels are attached to the rails, they can't be seen.
Enphase Micro Inverter
Newer solar power systems installs the inverter right behind each solar panel. These inverters are call "micro-inverters" This design is far superior than the older method of tying all the solar panels into a single large inverter. These older designs are still around and they have a few drawbacks. One is the losses of sending the output of the solar panels to the inverter. Solar panels output direct current (DC) that needs to be converted into alternating current (AC) for home use. The problem with single inverter systems is there can be significant resistive losses in the wiring when it's a long distance to the central inverter. All panels in this architecture are in series - which means if one panel gets shaded, the entire system output drops. One panel breaks, the entire system stops producing power.
Micro-inverters solve fix all those shortcomings of a central inverter. Micro-inverters convert DC from the solar panels right at the back of the panel to AC, which can be sent very long distances to the service panel with very little resistive losses in the wiring. If one of the solar panels happens to get shaded or breaks, only that panel output drops, or produces no power. This means all the other panels will continue to produce as much as they can. The other added benefit is expansion, more micro-inverters and solar panels can easily be added.
Solar System Roof Pass Through
In the top photo all three arrays are tied together, where they are combined into a single feed that leaves the roof in the bottom photo. From there, it's connected to the main circuit breaker panel of our home. The McWire installers are high-end artisans of their trade. Very impressed with their installation.
The output from all the panels make their way back to the circuit breaker panel of our home. They occupy two "slots" inside and the power generated from the panels is fed through those breakers, which are connected internally to all the AC wiring inside our home.
Power panel information and warnings
Here are the photos of our completed installation.
Solar Array 1 - Garage Roof South
Solar Array 2 - Home Roof South
Solar Array 3 - Home Roof West
Monitoring System Performance
The micro inverters are designed by Enphase and they can be monitored via a Communications Gateway (CG) device to their Enlighten "Cloud". The CG needs to be installed as close as possible to our breaker box in order for it to communicate with the micro controllers. This communication is accomplished using the Zigbee protocol at 144 KHz over the AC wiring inside the walls of our home. This means the distance between the CG and the micro inverters is sensitive. The CG AC power cord needs to be plugged into an outlet that's electrically wired as close as possible to the breaker box. This may not always be the case with an outlet that is physically very close to the breaker box, that outlet could be on the end of a very long AC line inside the wall that will eventually make its way to the breaker box. Experiment by plugging the CG into different AC outlets and see which one can give you the highest signal strength, you won't hurt anything, plus you'll save patching holes in your wall if you've wall mounted the CG BEFORE testing for best signal strength. (Guilty as charged.)
In order for the CG to communicate with the Enlighten cloud, it also needs an internet connection. Luckily for our install, both the AC outlet and internet connection are very close together. If this isn't the case for your install, Enphase ships two devices called Power Line Communication adapters. This can be used to make the internet connection using the AC wires inside the house. The biggest drawback is that it now takes two plugs at the CG end and another outlet near the internet connection. Both of these adapters CAN'T be plugged into a power strip or UPS, they must plug straight into the outlet. Another option is USB wireless adapters if you have WIFI in your home. Our CG is cabled so I can't recommend any WIFI adapters.
The installer configured our Enlighten account with our solar install and we can monitor all kinds of cool performance metrics of our system. Here's what's publicly available:
Enlighten Solar Performance Graph
At the start of this page, I mentioned cooling our home using solar. How?? Well, the solar panels are blocking the sun from reaching about 50% of our roof. The solar panels do get hot - so far maximum temperature has been 107 degrees F. Our middle son has his bedroom on the south-west side of our home and it's by far the hottest one of the entire house. We had a few days near 100 degrees F and his room was probably 10 degrees F cooler. Not only can we produce enough energy to power our home, the solar panels will help us indirectly by blocking the sun from hitting our roof, cooling our home during the hotter months of the year.
Does the Meter Really "Spin Backward"??
In the not too olden days, the power meter on our homes had a dial that would spin around, indicating how much power was being consumed at a given time. The faster it spun, the more power was being consumed. When people started installing solar system, their meters' would start to spin backwards if they could produce more power than they were consuming at that time. Modern power meters don't have a dial, instead they have a set of blocks and arrows.
Power Meter Spinning Backwards
This photo was taken around 8:30 AM. If you look below the number 10, you'll see two blocks and a left pointing arrow. The arrow indicates power is flowing from our solar system back towards the street - or the "grid". If the arrow was on the other end of the blocks and was pointing right, we're pulling power from the grid. In this photo, we're producing power that someone else is using, and yes, SDG&E will keep track. This process is called Net Metering. Depending how fast the blocks and arrow are being displayed signifies how much power is going to/from the grid. The performance of our system has been very impressive. The system starts generating enough power around 8 AM to start spinning backwards. This keeps going all day until about 5 PM. Southern California is entering the peak production time of year too. Our peak output reached 7.1 KW! That's enough to power around five 1500 watt microwave ovens all at once!
Return on Investment (ROI)
We get this question quite frequently. Our old monthly power bill will be erased by this system - meaning we don't pay the power company any longer, we pay on the solar loan we took out to pay for the system. The state of CA doesn't give a big tax credit but the feds sure do. Our financing plan will allows us a one time "refi" to make a large payment to reduce the principal of our solar loan. This will reduce our solar payments below what we were paying the power company. Now the system is generating an income every year - depending upon how much we use during the year. Yes, it's still important to conserve energy!! We "square up" with the power company once a year. With our family, our kids are older and within a few years, the Mrs and I could be empty nesters. Our power usage will drop and our solar power system will have even more excess to send to the grid, generating more income.
The other aspect we kept in mind, this is an investment in our home. We're paying for something tangible - all the hardware on our roof. We plan on staying in our home a very long time. So, what's our ROI?? It's hard to really calculate. SDG&E has been approved a 7% rate hike starting September 2013. That rate hike won't impact us at all! Our power bill will stay at the monthly cost we have on the loan. Since these rate increases are unpredictable, we really can't say exactly what the ROI is on our system. One guarantee is that rates will continue to increase over time, especially as more people install solar on their homes and businesses. As revenues from people using solar go away, the power companies will have no choice but to raise rates in order to maintain the power infrastructure & profits. The good news is, as these rates increase, solar power becomes even more affordable.