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Because I often get questions about our solar electricity system, I am migrating this post from DosGatos.net. This was written in late 2009.

Well, we finally did it - we installed a solar electricity system on our house.  I say "finally" because we've been talking about solar for a couple of years but I couldn't overcome my inertia to call some contractors.

First, a short review of solar electricity for home use.  Photo-voltaic (PV) solar panels generate electricity when exposed to sunlight.  They generate Direct Current (DC), the type of electricity generated by batteries.  Your house uses Alternating Current (AC) electricity so an inverter must be used to transform the DC from the panels to AC for use in the house.  Electricity that is generated but not consumed on the premises (excess) feeds into the power grid and helps power everyone else.  When you are generating excess electricity, you get a credit from the power supplier, in our case, Pacific Gas and Electric Company (PG&E); this is what happens when your electric meter spins backwards because you are generating onto the grid.  When the meter spins backwards, it subtracts from your kilowatt hour usage, giving you a credit.  You will use some or all of this credit when the sun goes down and you are no longer generating any electricity at all.  In this way, the power grid sort of acts like a virtual battery to store the electricity you generate so you can use it later.  Actually, the meter spinning backwards doesn't actually happen any more because PG&E uses new, smart digital meters for solar installations that do not have that spinning wheel, but you still get the credit via electronics.  If you are a PG&E customer, you can get your last two years of electricity usage in kilowatt hours by month on their web site.  This is useful in planning the capacity of your solar system.  PG&E also has some energy audit stuff on their web site but it mostly deals with stuff you probably already know. 

To help determine the real power usage of some of the devices in the house, I use a "Kill A Watt" model P4400.  I picked it up on Amazon.com for 20 bucks.  You plug it into an electrical outlet and then plug the device you want to measure into it.  It gives a variety of readouts but the two most important are the watts consumed in real time and a cumulative kilowatt usage over time.  Using it, we have determined that we need a new refrigerator and computers that are not in use should be turned off or put to sleep.

In July, I started my search for contractors and began my education on solar electricity.  There is a wealth of information about solar electricity on the internet.  The California Energy Commission (CEC) maintains a list of solar contractors on their web site.  The list can be searched using various criteria; I asked for contractors that did business in Santa Clara County and then I looked at their web sites to get a feel for their capabilities.  I settled on four contractors and started calling.  The four I chose were: Horizon Energy Systems, Renewable Energy Concepts (REC), ReGrid Power, and Vista Solar.  All of the companies except REC sent out a representative that was a salesman that also did the pre-engineering work on the system design; REC sent a person that was sales only.  Ultimately, they all made proposals but I eliminated REC early on because their proposal was made without measuring the sunlight available and the price seemed to shift around a lot.  ReGrid was very late with their proposal because their rep got sick; unfortunately that dropped them out of consideration.  Vista and Horizon had very similar bids but Horizon's plan produced more power by using photo-voltaic panels that produced more power.  We accepted the Horizon proposal but I want to stress that we could have done business with Vista or ReGrid just as easily.  I liked all three of these companies; they were all professional, courteous, knowledgeable, and patient.  REC was the only company of the original four that made me uncomfortable.

I'm going to discuss the price here because I think most people considering a solar electric installation would like to know what it might cost.  Each installation is unique but should be in the same ballpark as our cost for an equivalent sized system.  Our installation was relatively standard:  a south-facing roof with a few shade tree issues.  Our system is probably larger than average at 6.7 KW DC (5.5 KW AC).  It consists of 30 Sharp photo-voltaic panels (model ND-224U1F) that are rated at 224 watts DC, a Fronius IG Plus 6.0 240 volt inverter, a couple of circuit breakers, rails and hardware for the panels, and all installation labor.  Also included with our system was a thermostatically controlled attic fan to help reduce our air-conditioning load in the summer.  The price, with tax but before rebates and credits was $38,711.  The California Solar Initiative (CSI) rebate, paid directly to the contractor, reduced this by $7,683.  We paid Horizon the remaining $31,028 but will receive a 30% federal tax credit of $9,308 when we file our income taxes next year.  That reduces that actual out of pocket expense to $21,720.  Based on current electricity price trends and our own usage patterns, the system should pay for itself in a little over seven years.  It also adds about $40,000 to the value of our house.  I'm not including about $2,800 in tree work as we had a severe shade problem at the west end of our roof.  We topped some trees, removed three trees, and planted three more trees to replace the removed trees (the new trees are a shorter variety so they won't cause the same shading problem).

The installation was done in mid-October and took four days.  The working crew size varied from seven (on the first day) to three (on the last day).  Part of the work included relocating three plumbing vent pipes in the roof.  They spent a lot of time getting the rails straight on our somewhat wavy roof.  Here are some progress pictures. 

First, the roof before any solar work:

Day 1 - a driveway full of Horizon Energy trucks:

Day 1 - a roof full of Horizon Energy workers:

Day 1 - the first rail is getting installed:

Day 1 - the first rail is complete:

Day 1 - two rails are installed by the end of the day:

Day 2 - the rest of the rails are installed:

Day 3 - 30 Sharp photo-voltaic panels arrive:

Day 3 - Fronius inverter installation:

Day 3 -panel test fitting; also, this was the day the vents were moved:

Day 4 - about half the panels are installed and wired together by noon:

Day 4 - testing a string (10) of panels; that's a 250 VDC 9 amp spark:

Day 4 - securing the tops of the panels at the end of the day; the shade in this picture is now gone after some tree work:

First day of operation - 6 KW from the sun:

The solar system has been operating a couple of weeks now and we have generated more electricity than we have used.  When you connect a solar system to the PG&E grid, your electric billing changes to an annual reconciliation.  A year's worth of generation is subtracted from a year's worth of usage and if you used more than you generated, you pay PG&E.  However, thanks to a shiny new law in California, if you generate more than you use, PG&E pays you.  I think we will be a little short on generation this year but we might be able to conserve our way into the black.  In any case, our carbon footprint just got a whole lot smaller.