Electricity from the Sun

[Photo of PV solar panels on stable roof]

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:

[Photo of stable roof before install]
Stable roof before install

[Photo of unloading PV modules]
Unloading the PV modules

[Photo of measuring stable roof]
Measuring the stable roof before install

[Photo of PV racks installed]
PV racks installed

[Photo of installing PV modules on the racks]
PV modules being installed on the racks

[Photo of PV modules on the racks]
PV modules on the racks (before adding facia board)

[Photo of red covers on Sunny Boy inverters]
Red covers for the inverters... too bright!


so we got the white covers instead.

[Photo of CRELTRC and PV]
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.