Household Electrical Loads & Efficiency

One of the first steps in any home-scale solar-electric project is doing what you can to make your household as energy efficient as possible. Every watt-hour you save is one that your PV system doesn’t have to generate, leading to a less expensive system. All the light bulbs in my house are energy-saving compact fluorescents, and it’s been that way for fifteen years or so. Over the past five years, I’ve upgraded all my major appliances with the most energy efficient ones I could buy.

Even with these measures in place, I still use a lot of electricity—about 1,400 kilowatt-hours per month, on average, which sets me back between $100 and $160. While I do my best to conserve energy, I have three computer servers, and three workstations  24 hours a day. This equipment uses a lot of electricity day in and day out, and accounts for the majority of my electricity use. But for the time being, it allows me to work from home for my employment, and for my own personal Web and programming work. I also enjoy woodworking as a hobby, and the 2 to 3 hp electric motors in my shop guzzle electrons whenever the woodchips are flying.

Sizing Up the System

After surveying the site for solar access and shading, and getting a handle on my electrical use, I asked to have put together a bid for a PV system that was within my budget, and would offset about one-half of my present electricity use. His quote of $21,500 (before incentives) was higher than I’d anticipated, but it wasn’t out of the ballpark. Even so, I ended up hemming and hawing for several months over the initial cash outlay before I signed the contract in March2005. We tentatively scheduled installation for the summer.

Ready, Set, Install

In June, the trees came down and the PV system went up. My installer and his associate made quick work of the installation, and I’d recommend them to anyone looking for pro solar installers in southern New Jersey area. A 3700-watt array was mounted on half of the roof and wiring from each array was run in conduit down to the inverter. One of the nice features of the Aurora inverter that was specified for the system is that it can independently track and optimize the power outputs of two separate series and go on to the computer for tracking

Production of electricity.

Grid-Tied PV System

Tech Specs

Overview

System type: Battery less, (no battery’s) grid-tie solar-electric

Location: South Toms River NJ

Solar resource: 5 average daily peak sun-hours

Production: 416 AC KWH per month (first 12 months

of operation)

Utility electricity offset: 50 percent

Photo voltaic

Modules: 22 BP BP 170 SX,  26.3 Vmp

Array: Two 11-module series strings, 3,700 W STC total, 236.7 Vmp

Array installation: UniRac mounts installed on south-facing roof, 30-degree tilt

Balance of System

Inverter: Power-One (formerly Magnetek) Aurora PVI-3600-US, 600 VDC maximum input voltage, 90–530 VDC MPPT voltage window, 240 VAC output

System performance metering: PC-based inverter monitoring with custom code for windows operating system. Two strings of PV modules.

In my case, this was a worthy feature, since trees to the east and west of the house, cast some shadows on one array or the other in the early morning or late in the afternoon when the sun is low on the horizon.

The inverter will also function down to 90 VDC. So except during extremely hot summer conditions, when the modules’ operating voltage is low, I can essentially lose the output of five of the nine modules in a string to shading and the Aurora will still produce energy. Since these shading conditions only exist at the beginning and end of each day, this low operating voltage capability doesn’t add all that much additional energy to my system’s total production. But I figured that it made sense to optimize my PV system’s performance in every way possible, which would also optimize my financial investment.

We had to delay the final commissioning of the system for two weeks, so that our local utility could inspect the system prior to bringing it online. This delay was the only one that did me no good; after more than a year of anticipation, two weeks of perfectly good summer sunshine wasted on inoperative PVs was almost too much to handle! But on June 27, the system came online, and the modules and inverter went to work making electricity from sunshine.

System Monitoring & Performance

My techhead tendencies drove me to create a seamless way to monitor the PV array and inverter output, and automatically display the data on the Web. Being a Nwtwork System Administrator and a windows user, I was not overjoyed to hear that the Aurora inverter came with software that only ran on Windows operating systems. But with some help from the inverter manufacturer, I was able to sort through the inverter’s communications protocol and write the necessary code that enabled monitoring via my Web-based computer network. I’ve been collecting performance data since the system came online, which is available for viewing on my Web site (email me for a reservation for access).

One thing I immediately noticed after reviewing some of the early system output data was that the modules were often operating below their rated output during the summer. After talking with the tech at Magnetek (Power-One has since purchased the Aurora line of inverters), I learned that the higher the ambient temperature is, the lower the voltage produced by the PV modules will be. Despite long, sunshine-filled summertime days, the array experiences a higher peak array output during the shorter, colder days of late fall, winter, and early spring. My best single generation day to date was April 5, when the system cranked out 24 AC KWH. But the bottom line is that cumulative energy is what I’m after. While peak power or the energy produced on a given day is often higher during the colder months, the long days and mostly clear weather during the summer is when the system generates the most energy.

The Big Payback

So far, my PV system has produced more than 5 megawatt-hours of electricity, and knocked close to $900 off my electric bills. Produced 10 SREC’S 5 sokd for 250 each and 5 sold for 245 and I still have 3 to sell. Originally, I’d predicted a Six to seven year financial payback for my PV investment. After living with the system for awhile, it looks like I may end up on the low side of my original estimate. Since then the state has raised the SERC price to $750 each so my system will offset my original cost even sooner. My modules are warranted to generate electricity for another twenty three more years, and will likely continue to do so for ten or more years beyond that. After the six-year mark, it’s all free electricity and monet making SERC’s. And that’ll be right around the time I’ll be thinking about retirement. Perfect.

A  year later the system worked so well that I want more panels. I put an order in for the other half of roof.

My installer said that they could fit 20 more panels that equates to 3500 kilo watt more or the other half of my electric use.

I expect to offset 100% of my electric and have it pay off in six more years.

South Toms River Borough can do the same thing and make a revenue stream of $100000 and free electricity .