Electricity from the Sun

On March 14, 2003, our 5 kW PV (Photo Voltaic) solar array began producing power and pushing our electric meter backwards during the day. This system fits neatly in a 6 by 6 array on the south-facing portion of the roof over the stables (approximately 35 feet by 17 feet).

This system is grid intertied: Meaning that we push any excess energy we don't use during the day back onto the grid (turns the meter backwards) and use energy from the grid at night. Our system also does not have any batteries, so if the grid goes down, we loose power just like everybody else even if the sun is shining. This is the most cost-effective way to install solar power.

We're paying 1/2 price for the electricity! Instead of paying Edison, we're paying the bank (with the usual help from Uncle Sam.) Our electric bill has dropped by approximately $175 per month. After counting the mortgage deduction, we're sending the bank approximately $85 per month. Save the planet and save money!

Installation of the PV system was done by Energy Efficiency Solar www.eesolar.com. They did a great job on the installation, and they took care of getting the California rebate directly so we did not have to put up the whole cost.

Here are some pictures of the install:

Stable roof before install	Unloading the PV modules	Measuring the stable roof before install
PV racks installed	PV modules being installed on the racks	PV modules on the racks (before adding facia board)
Red covers for the inverters... too bright!	so we got the white covers instead.	Pure ZEV miles!

Sizing the system:

Over the course of a year, if we use more energy than we produce, then we pay the difference. If we produce more than we use we do not get a check from Edison. Since you gain nothing for producing more than you use over the course of a year and gain the greatest benefits by getting your net power use under the baseline amount, you want to size your PV system to produce close to your yearly usage but not exceed it.

We looked at our electric bills since we moved in and saw that we were using an average of 30 kW hours per day of electricity. In Pasadena, we get an average solar exposure of about 5 hours per day, so divide 30 kW hours by 5 hours to get a 6 kW array to cover 100% of use. We decided to go for 5 kW for several reasons:

It fits very neatly on the roof. (Aesthetics count!)
Most efficient use of components. The inverters are rated at 2500 watts (or 2.5 kW) so we would need 3 for a 6 kW system.
Gives us a reason to be more efficient with our energy use.
Takes the biggest bite out of our electric bill.

Cost / Payback / Economics:

The total installed cost of the system was $38,854. California paid for 1/2 the cost of installation, so our out-of-pocket expense was $19,427. Our electric bills have dropped approximately $175 per month at today's energy prices. Let's say we finance $19,000 on a home refinance at 6.125% interest over 30 years, that makes the solar portion of our monthly payments $115 per month. That's $60 per month. You also get to deduct the interest on your home loan. For the first 5 years you pay between $97 and $90 per month in interest. Just to make the math easy, let's use $90 and a combined 33% tax bracket, that's an extra $30 every month of savings for a total cost of $85 per month.

California subsidizes the cost of a PV installation for several reasons:

Clean air benefits. PV solar produces 0 emissions and produces most power during the summer when California suffers worst from the effects of smog.
Help to take the PV industry to the next level. By lowering the installed cost of PV, the state is helping to create demand for PV panels. This in turn allows PV manufacturers to build higher-volume production facilities which drives down their cost, thus lowering the cost to future buyers.
Distributed power benefits. Producing power closer to where it is used keeps stress down on high-power lines. This is especially beneficial during high-heat times when airconditioning loads are high.

What's it made of?

The system consists of the following major components:

36 Sharp 165 watt multi-silicon PV modules. The PV modules produce power at a nominal 24 volts and are wired into 4 separate strings of 9 modules each. Each string runs at a nominal 216 volts.
2 Sunny Boy 2500 watt inverters with display. Each Sunny Boy inverter has 2 strings of PV modules wired to it. Output from each of these is at 240 volts AC and is a true sine-wave. This is "high grade" utility power.
Also included were power disconnects, mounting brackets for the panels, mounting panel for the inverters, conduit, wire, etc.

Tilt: The array was not given an additional tilt over the roof tilt in order to keep windage low and to make the aesthetics of the installation more pleasing to the eye. Besides, the relatively low angle of tilt should help to optimize the summer output when the panels are completely unshaded.

Shading: There is a large eucalypts tree on the neighbor's property that shades any given panel in the array for about an hour each day during the 'winter'. The first panels start to get shade around solar noon and shade leaves the last panels around 3 pm. The panels continue to produce power even while shaded, but only 1/3 to 1/2 the amount that they do when under direct sunlight. By 7 - 10 days after Spring equinox (early April) the panels were no longer shaded at any time. I assume that shading will begin again in mid-September.

Actual performance:

Meter Read Date	PV Generated per Month	Net Used/ Month
3/21/03	140 kW (est.)
4/21/03	765.4 kW (est)	141 kW
5/18/03	649.6 kW	198 kW
6/19/03	754 kW	120 kW
7/21/03	857 kW	30 kW
8/19/03	818 kW	-59 kW
9/18/03	746 kW	-21 kW
10/17/03	497 kW	214 kW
11/18/03	429 kW	674 kW (*)
12/18/03	360 kW	1378 kW(*)
1/17/04	357 kW	1060 kW(*)
2/17/04	472 kW	637 kW
3/17/04	465 kW	507 kW
4/18/04	664 kW	377 kW
5/19/04	907 kW	97 kW
6/19/04	700 kW	245 kW
7/19/04	734 kW	314 kW
8/20/04	966 kW	54 kW
9/23/04	734 kW	314 kW
27-Oct-04	457	303
21-Nov-04	369	387
18-Dec-04	336	633
24-Jan-05	304	953
20-Feb-05	321	557
26-Mar-05	577	300
29-Apr-05	837	86
22-May-05	598	151
30-Jun-05	1042	-12
24-Jul-05	699	188(**)
17-Aug-05	1398	188(**)
17-Sep-05	741	152
16-Oct-05	422.5	370.5(**)
14-Nov-05	422.5	370.5(**)
17-Dec-05	421	615
22-Jan-06	395	656
20-Feb-06	435	437
18-Mar-06	446	364

* Net usage from Nov 2003 through Jan 2004 was high because our gas heater went out so we were using electric heaters during that time.

** No readings taken on Jul 24, 2005 or Oct 16, 2005. These are mid-points between the previous and next actual readings.