Solar for Electric Vehicles

Without doubt solar is expensive. If you are paying under .10 a kilowatt hour I would not consider solar as it would take you 20 years to see 100% return on your investment. It could be a much longer payback period if you live in a location where you see lots of cloud cover.

If you live in a location with lots of sun where tiered billing is used then solar may be a good option for you. Your combined car and house usage may place you in the top rate tier. At .10 kwH it may not be worth installing solar, but if you are paying .20 or more then it would definitely be feasible.

The most frequent solar question asked of me by neighbors is concerning storing electricity. The big question is how do I get my electricity at night after the sun sets. The answer is net metering. Briefly, unused energy is fed back into the grid during the day, spinning the meter in reverse. At night I purchase electricity from my utility. Since demand is lower at night, electricity is cheaper then. If you have a digital meter you can opt for time of use metering where you pay less during the night and more during the peak daytime afternoon hours.


This interesting estimate presents a picture that my 7k system will generate throughout the year. Notice the months with surplus generation. I receive credit and get to use them during the summer months when I use more energy than I generate.

Solar systems are typically rated in kilowatts. Solar firms will refer to in their bids as offering a 3 kwh or 5 kwh system. What this means is in a perfectly efficient installation the system should generate 3 or 5 kilowatts of electricity each hour. Don't expect that as these numbers assume that the panels will always be perfectly aligned with the sun, at the perfect angle, and the outside temperature will be at the most optimum value. Result will vary. In actuality you could probably multiple that times four to get an approximate total. Your solar installer's bid will give you a better calculation based on your specific installation.

There are a number of decisions to make regarding solar systems:

System Size
If money is tight then maybe install a smaller system on the most optimum slope of your house. That way you are getting the biggest return for your dollar. At minimum your goal should be to reduce your usage from those upper expensive tiers. The lower tiers might only be costing you .12 kwH and payback for the system will be longer. Also, examine your roof orientation. You might find a small one will fit an entire south facing slope, but a large system will require placement on a north facing slope. That north facing slope may be 40% less efficient than the south facing roof. It may not be worth the outlay for that big system if it is only operating at half efficiency.

Panel Efficiency
Not all panels are created equal. Panels may be the same size, but some output more electricity per square foot of surface area than others of the same dimensions. You pay more for higher efficiency. The lower wattage panels are not necessarily inferior construction, they are just built to different specifications than the higher efficiency version.

Inverters
Some installation companies use micro inverters and some use a master inverter. An inverter is a device that converts the incoming DC power generated by the panels, and converts it to 240 volts AC that is distributed by the utility.

A central inverter is a large box that mounts to your house. Strings of solar panels are fed into the inverter which converts the DC to AC. A typical installation may have two strings. With micro-inverters each panel receives its own inverter.


Here is an example as to why micro-inverters are a good solution. My brother was kind enough to share his system statistics with me. His system uses a central inverter. Look at the graph and notice the jump in solar production after 9:30am. In the morning hours production is limited by shading. This particular system is rated at 4.9 Kwh and was installed by Solar City.


Look at the aerial image showing the array placement. This is the actual house shown in the graph above. When the sun climbs high enough away from the chimney and palm tree the array finally outputs the maximum energy. If this system had micro inverters only the panels being shaded would be affected.

Micro-inverter Pro's: each panel is independent so if one degrades the entire array is not affected, if your array is partially shaded by chimney or tree only those panels shaded will have reduced power output, one less box mounted to the wall of your house, 20 year warranty.
Micro-inverter Con's: Many more points of failure, more expensive than a central inverter.

Central Inverter Pro's: Only one point of failure
Central Inverter Con's: If one panel is degraded the whole string is degraded, most offer 10 year warranty, when the single inverter fails your solar system will be off until it is repaired or replaced. Takes up a sizeable portion of your outside wall or garage.


I am a micro-inverter fan. The unit mounts underneath each panel.

Roof and Racking
The easiest installation is installing the rack mounted system onto a composite roof. If your roof is concrete tile then placing them requires pulling up and reinstalling the tiles. Some municipalities also require engineering when placing panels on a concrete roof. If your roof is more than 20 years old consider paying a little extra to have the solar company repaper the area where the panels are to be placed. You don't want to have to remove the panels in a few years when roof starts leaking just to replace the paper.

My solar company replaced my concrete tiles with composite. Once the panels are installed they will place the concrete tiles up to the edge, giving the illusion of an all concrete roof, but in reality it is composite. The nice aspect of this type of installation is I received a new roof under the panels.


Racking system showing a pair of panels, enphase micro-inverters, and copper bonding wire. The roof received new composite roofing showing concrete tiles around the perimeter.

Solar Installation
I am a technonerd and originally I had planned to perform my own installation. I priced out the equipment and figured I could probably install a complete system for under $15,000. When it came time to get my roofer to bid on the roofing part he dragged his feet and I never could nail him down. In the end I chickened out. It was probably a good thing as this project would have dragged on for months as there is a lot of work involved.

I received six different bids and in the end I went with a local company named. They not only had the best price, but they proposed the best equipment and their plan to perform the project was most logical. I also received bids from the biggest of installers including Solar City, Verengo, and Rec Solar.

One problem I had with the big companies is the disconnection between the sales and production staff. This seemed to be a common feeling with the big companies. I would suggest choosing a local reputable company to perform your installation. With the big companies you don't know the competency of the crew installing your equipment. With a small company often the guy selling you the system will be the guy installing it on your roof.

My installation took four days to complete. They had 4-6 guys working on the job each day from 8am until it got dark. After watching them work I am thankful that I opted to hire a company to do the work.


View showing composite roofing material being laid down.


Here is why micro-inverters are the way to go. As you can see in this photo the array is being shaded by the chimney. With a central inverter the entire array will be degraded. With microinverters only the shaded panels are affected.


While most people might focus on the roof, there is a lot of wiring that takes place on ground level. This raceway was installed in my garage next to my electric vehicle charging station.


Racking installed and ready for the remaining 25 panels.

My installation encompassed the entire south facing roof. Besides putting a new composite roof on, they had to replace my attic vent with a new low profile version. They also rerouted my plumbing vents beyond the panel installation. Other companies will try to avoid this extra work by installing around these vents. Sometimes this works against you as they may place your panels next to the vents or chimney that extend above your panel, thus shading it during the day.


Installing a solar system is tough work. These guys worked a 9 hour day with a short lunch break. We fed our crew a nice lunch on one of the days as a goodwill gesture. My wife and I always try to take care of workers at our home as happy workers result in better quality work.

Installation Costs
Here we are at the bottom of the article and the question you are asking is how much did this system cost?

My system consisted of 27 260 watt Solar World panels and 27 Enphase micro inverters. The grand total for the system was $32,655. That was my out of pocket. Then there are the rebates and tax credits that bring the price down further. Federal tax credit was $9,348 and California energy rebate was $1,494. So the grand total was $21,813.

For $22,000 I will have a system that will produce almost all of my electricity. It won't be enough to power everything. I also have an electric vehicle meter for charging my Chevrolet Volt that is outlined on this web site. However, in retrospect I could have gone onto a time of day billing system and enjoyed similar savings without the hassle of installing the electric vehicle meter system.

Originally, I had only planned to install a 5 kwh system, but discovered for $5,000 more I could get a system that was 40% larger. For a little more I was able to scale up my system to provide almost all of my electricity.

I wrote this article in February 2013 and costs are subject to change. As the rebates and tax credits fade away expect to see the cost to remain about the same as installers adjust their prices to remain a competitive option entirely for homeowner funded systems.


My daughter hung out on the roof with me while I examined the installer's work.

I am a believer in buying the solar system outright. If you cannot afford a purchase then maybe a lease system is the best solution for you. However, realize that if you sell your home the new buyer will be expected to accept the lease terms. Some buyers may not want to accept these terms. Think it over before deciding which kind of purchase or lease plan you choose.


My roof showing all 27 panels. By removing the concrete tiles under the panels the installer was able to get the system mounted closer to the house. It looks like part of the roof. The doohickey extending up at the roof peak is my Davis Weather Station.


With micro inverters each panel operates independently. This output is from the Enphase Enlighten web monitoring feature that allows you to graphically see what each panel is producing, along with the daily, monthly, and lifetime total for the installation.


My house contains a smart meter that has the ability to report via Zigbee protocol. This device manufactured by Rainforest Automation reports real time energy generation flowing to the power company. The difference with this over the Enlighten software is the microinverters report generation. The Rainforest monitor reports a combination of your usage and energy being sent to the grid.

Photo tour of installations in my neighborhood