Several people have IM'ed me asking to document my solar installation that I had done this summer.

The Math behind the Science

The primary reason that I wanted to go solar was to save money rather than saving the planet. The power here is pretty reliable but still I have a pair of portable gasoline fed generators - an 8500 watt and a 2000 watt. I wanted a grid-tied system with mono-crystal panels and was interested in going with micro-inverters if possible. The advantage of micro-inverters is they don't degrade as much if shaded, an array using them is easier and cheaper to expand, and if one inverter fails the rest continue to produce power. The disadvantage is they are more expensive than a single larger inverter mounted near ground level.

I researched and found three top rated solar system installers who were licensed, bonded, and insured. When the first company came by we had to pull my power usage from the local provider Southern California Edison. Their web site was down and I've been on paperless billing since 2003 so I had to pull a 12 year old bill to get my account number. The SoCal Edison customer service representative gave me the number of kilowatts used per month as well as my monthly bill.

I noticed that despite going all LED and fluorescent lights, upgrading my AC unit to a very efficient two speed compressor/variable speed fan unit, and upgrading my major appliances I used about 12% more power in 2015 than I did 12 years ago. My bill went from $50 to over $200 in those 12 years.

Over the last 12 months my average power use was 11,160 kilowatt hours (WH) per month or 930 KWH a month. My average bill was $205 or about $2460 a year. My average delivered cost per kilowatt hour was $0.22 - this is the number I'm using for pay-off calculations.


Using a chart the solar system salesmen showed me that my area of Southern California could expect 5.5 to 6.5 solar hours per day. The sun shines more than 6.5 hours but since the panels would be stationary the sun didn't directly shine down upon them mean a loss of some of the light. We used 6 hours as a good number but I'll get more than that in the summer when power demand is higher due to the air conditioner and lower in the winter time. My home faces due south and the roof is sloped at 22 degrees which are both nearly ideal favoring the collection of power in the summer a bit more than the winter.

The math isn't that hard. 6 solar hours a day times 30 days in the month is 180 hours to collect power. 930 KWH divided by 180 hours is 5.16 kilowatts. In theory that sized array would zero my grid tie system out. The panels are 280 watt so that means about 18 panels. And in a perfect world I would feed into the power grid exactly what I pulled out. There are some fine points on the math - the conversion of the solar power from the panel into AC isn't perfect so there are some losses. An average efficiency numbers for systems run 75 to 85%. My system has been doing about 83% so far.

Locally there are four tiers of electrical power with tiers one and two being fairly cheap and tiers three and four much higher. Tier one is $0.15, tier two is $0.19, tier three is $0.25 and tier four is $0.31 a kilowatt hour. The local power company has put in "smart meters" which will allow them to day part billing with rates of $0.11, $0.26, and $0.35 per kilowatt hour for super off-peak, off-peak, and on-peak pricing. They haven't yet implemented that but it's just a stroke of a pen away from happening. Ideally I want to take the cheap tier one power and stay out of tiers three and four at all costs.

When the other two companies representatives came by I provided the array size of 5 KW and simply asked probing questions on their warranty period, panel type, panel build location, inverter type, and asked them how long they'd been in business and how big the company was. I took the three bids and took the middle one who happened to offer a 25 year parts and labor guarantee, used micro-inverters, US made mono-crystal panels, and required zero down and no payment until I was 100% satisfied with the job.

The initial wait was 7 weeks for the local city to approve the engineering plans and permits. Because of local building code I required an $1800 upgrade to my electrical power panel. The upgraded panel put physical space between the array’s breaker and the homes. The electrician put in new modern breakers replacing my 1980’s models.

The total bill with parts, labor, and permits was just under $27,000. There's currently a federal tax rebate of 30% so I'll get $8100 back from my taxes next year leaving a system cost of $18900. My power bill should be zero or very close to zero so I'll figure a savings of about $2400 a year meaning the array will pay for itself before its 8 years old. If the cost of power goes up in the next 8 years like it has over the last 12 the array will pay off sooner.


The panels are 280 watts each and are US made (Oregon).

With a normal home improvement the county assessor raises the assessed tax value of your home so the following year there's a matching increase in the real estate taxes. California law prohibits that from occurring for a solar panel installation. I put $27,000 into my home and the panels ought to increase the value of the home about $20,000 but unlike say a brand-new kitchen the solar array is going to make electrical power every day "paying" it's keep.

Typical mono-crystal solar arrays are rated to retain 80% of their output even after 20 years. My grid is expandable by adding more panels and microinverters.

The Build

I had a big tree that I had to have removed as it shaded the future home of the lower of the two arrays.


(above) Had to cut this tree out which wasn't easy because of it's location.  


On the day of installation a team of three men arrived. Two were focused on mounting and the third on wiring. A pair of electrical panels were mounted to the wall next to my existing power panel and a conduit was run up the wall and to the two portions of the array. The concrete roof tiles were lifted, a series of mounting brackets were screwed into place, and rails were mounted to those brackets. Finally the 18 two hundred and eighty watt panels and 18 microinverters were mounted. The panels and microinverters came pre-wired and simply plugged into each other.


(above) The brand of microinverters I went with have a built-in monitoring system which will allow me to monitor the array's health and output from a computer or cell phone.


(above) The look on the house is very nice. The panels and mounting rails are a high-tech looking black. The company painted the power boxes and conduit to match the side of my house and the roof tiles. The panels put a great portion of my roof in the shade meaning the summer sun will not heat that part of the house up as much as before.


(above)  The old fuse box still in place with the new one ready to be installed. I had to call Southern California Edison to have them unlock the electrical power meter and the solar power company to returned to finish the panel upgrade and run the wires through the conduits to fire the array up.

The solar company submitted the engineering diagrams and permits to the local power company to get my Customer-Owner Generation System connected to their grid. The system has been running for a few weeks now and we’ve had one cloudy day and couple of days with an early morning fog. Overall I’m generating about 29 KW per day.

The results

(above) A sunny day showing a nice smooth power production.


(above) A cloudy day with periods of heavy clouds blocking the sun.

During the day the meter runs backwards – even on hot days where the AC is running hard. In the evenings following the sunset I draw power back out of the grid. So far the balance looks like its slightly in favor of the power company and I’m burning about a dollar’s worth of power where in past years I was burning more than seven dollars’ worth. Once the summer heat breaks and the AC takes a break I expect the balance to tip into my favor more.


(above)  The power is being drawn out of the grid when above the line and being put into the grid when below the line.


(above) The meter running backwards sending 1.33 KW into the grid even with the AC on.

The micro-inverters connect to the Internet reporting their health and use to the manufacturer. In theory the installer will inform me if something goes wrong with one of the panels. I’ve been checking the system every day. The inverters feed their production information to a password protected web site that allows me to check production on a PC or my smart phone.


(above) The summary grid with harder blue being lower outputs and lighter blue being higher output hours. You can see the clouds from August 6th and 13th and the fog on the 16th, 20th, and 21st.


(above) One of the foggy days where the morning fog didn’t break until 10 AM. Each bar represents 15 minutes worth of production. The highlighted period is 12:45 PM where the array produced 1.024 KW. That's a bit more than 4 KW/hr so +80% efficiency.

So far in 17.5 days I've generated 534 KW worth about $117. I haven't seen a power bill but the way they work is that power company will let my account slide adding and subtracting power until the end of the year where they zero everything out and I will have to cut them a check for the balance.

Survival Use
So here's the rub. In the event that the power grid goes out the micro-inverters sense that and stop making power. Otherwise the 5 KW array on my roof would attempt to provide power back into the grid to feed the closest few hundred homes. That's not possible and they would fail. I spent 24 years in the Navy and retired as a Master Chief Electricians Mate and understand power. Don't try this unless you know what the hell you're doing. You'll damage your equipment for certain and possibly hurt someone working on the grid if you do this wrong.  In the event of a grid failure I would pull the breaker connecting my home to the grid. I would next fire up my 14 KW UPS and feed AC power into my building - the array's micro-inverters would see this and assume that the grid was back on and start making power again. The power produced would feed the USP charging system ... and minus the losses I'm making power. Additionally I have the two generators which could do the same thing while making a bunch of noise.

There's a 6" or so square pad that screws to the roof. The installers lifted the tiles above, put down some tar, and then screwed each pad. There's a piece that sticks up to which the rails are then mounted to. The installers spend a bit of time leveling the rails and cutting the ends off. How the panels attached to the roof was part of the engineering plans spec'ing out how many mounts, how many screws, and how long and big the screws were.

I used 865 last December but 1300 in August.

I draw 1 KW every hour just cruising on a freezer, refridgerator, and my UPS system charging.

I did did price a 20 and 22 panel systems. The bitch here is that the power company is in the business in selling power ... but not buying it meaning any extra panels installed would go to waste as the local company won't buy it from me. There are a couple bills before the CA legislature one pro, and one con for solar panel owners. The one pro bill is to have the power companies statewide be mandated to buy surplus power from residential providers. The one bad bill would have solar system owners pay $15 a month in a minimum charge for grid access - there's a 20 year grandfather provision in the bill currently but until it passes you can never be sure.

I'll let the system fly for few more months before looking at adding more panels. The company said that additional panels would be about $1000 each installed and there's room for five more without too much effort.

Thanks. We haven't gotten to the point where I start hacking the system.

OMG ... well pump, swimming pool pump, and five teenagers?

I have 2300 sq.ft. 1985 home that has only fair insulation and 18 panels is perfect. My bill from yesterday where it hit just 85 degrees ... 400 watts worth of power I had to buy which is less than a nickle's worth. In the last 30 days I've generated about 920 KW or bit more than 30 KW per day.

My little 14KW UPS will do that.

1. Pull the main breaker from the panel and "red tag" lock it out.
2. Connect the UPS 5KW inverter into the AC of the building.
3. The solar panels will sense the inverter and fire up.
4. The solar panels 4KW will feed the AC to DC power supplies back feeding the UPS.

-- I haven't tried this yet. An earlier post stated that the micro-inverters were frequency sensitive. I have an oscilloscope and a frequency counter so I can run test. I have a big bulky 5 KW inverter and a tiny 400 watt pure sine wave to play with.  

If in the last 15 years we had lost power for more than the two times for less than two hours combined time I'd be more aggressive with the testing. My city has there own series of generators separate of the CA grid. They can connect into the grid and buy power or generate their own price depending.

That's a very cool project, Paul.  

Got my first power bill with solar ... in the middle of a Southern California summer with the AC set at 76/78 ... $3.93.

Some people pay a hundred times that much.

Winning!!!11