E

Hours: South-facing, Hours: West-facing,

On the RE Road

There are a few ways to size a photovoltaic system. In off-grid situations, the system is necessarily sized to meet all the loads on a sunny day. Typically, a small amount of backup generator time is factored in to alleviate the excessive costs that would otherwise be required to provide for total loads during extended cloudy periods. But system sizing is significantly more flexible for grid-tied systems, since utility electricity is available to make up the difference between PV production and load requirements. Usually, sizing a grid-tied system becomes a balance between budget and available mounting area for PV modules. In Kathleen's case, the roof area of her 2,000-square-foot, two-story home was the limiting factor in sizing the PV array. It was decided

The 1,950-watt, south-facing array with the San Juan Islands in the background.

Open for inspection: Two Fronius IG 2000 inverters (one for each array), the DC array disconnect, and a handy wiring "gutter."

The 1,950-watt, south-facing array with the San Juan Islands in the background.

Open for inspection: Two Fronius IG 2000 inverters (one for each array), the DC array disconnect, and a handy wiring "gutter."

to squeeze as much generating capacity onto the roof as was functionally and aesthetically reasonable.

While peak sun-hours in the area can dip below 1 per day in December and January, the summer months of June and July make up for it to contribute to an overall daily average of about 3.7 peak sun-hours. At 48 degrees north latitude, Anacortes experiences the most sunshine and highest peak sun-hours during summertime, when the sun traces a long arc through the sky, rising in the northeast and setting in the northwest. Kathleen's grid-tied PV system would rely on these long, sunny summer days to heavily weight its net solar production for the year. To maximize PV generation capacity, it was determined that, along with a south-facing array, a west-facing array would contribute significantly to the system's total energy production. The idea of installing an east-facing array was rejected due to shading from trees and neighboring buildings. Plus, in this coastal town, morning fog can reduce solar insolation—even in the summer months.

Choosing Equipment

With maximizing the PV array output as the goal and roof area as the limiting factor, high-efficiency Sanyo HIP-195BA3 PV modules were selected. These 195-watt modules fit in two rows of five on the south-facing roof and two rows of four on the west-facing roof. The dimensions of other PV modules that were considered didn't work well with the available roof space in portrait format, or would have required additional racking and mounting hassle in landscape format. (Savvy PV shoppers will recognize that the Sanyo HIP modules also come in 200- and 205-watt ratings with the same overall dimensions. However, at the time, these higher-rated modules were difficult to obtain.)

Tech Specs

Overview

System type: Batteryless, grid-tie solar-electric Location: Anacortes, Washington Solar resource: 3.7 average daily peak sun-hours Average monthly production: 278 AC KWH Utility electricity offset annually: 32%

Components

Modules: 18 Sanyo HIP-195BA3, 195 W STC, 55.3 Vmp

Array: Two, five-module series strings, 1,950 W STC total, 276.5 Vmp (south-facing array); two, four-module series strings, 1,560 W STC total, 221.2 Vmp (west-facing array); 3,510 W total

Array combiner boxes: Two GroSolar

Array installation: Direct Power & Water Power Rail mounts, 36-degree tilt (south-facing roof) and 30-degree tilt (west-facing roof)

Inverters: Two Fronius IG 2000, 500 VDC maximum input voltage, 150-450 VDC MPPT operating range, 240 VAC output

System performance metering: Fronius IG Personal Display and production KWH meter

The other major equipment choice was the grid-tied inverters that would convert Kathleen's solar-generated DC electricity into AC electricity. In turn, this renewable electricity would be used to power household appliances and charge the Zenn, with any excess sent to the utility grid. While there are several reputable manufacturers of grid-synchronous inverters in the market these days, two Fronius IG 2000 units were deemed a good fit. The west-and south-facing arrays would have different numbers of modules and different voltages at maximum power—221.2 and 276.5 volts, respectively. As such, one inverter would not have dealt optimally with these mismatched input voltages. Instead, two 2,000-watt inverters were installed side by side (one for each array) and paralleled on the AC output side.

The Photovoltaic Effect

Although Kathleen wasn't a complete stranger to smart electricity use before installing a PV system, once her Fronius remote meter was spitting out the daily totals for energy production, conservation became her new hobby. Even during the winter, when a day's total PV output can be less than 1 KWH, her new habits are making a noticeable impact.

Besides programming temperature setbacks to regulate her home heating, Kathleen has taken to drying clothes on a rack in the laundry room instead of in the dryer. "It only takes a couple of minutes to hang them up and they're dry in a day. This is not really about sacrifice: I still throw my towels in the electric dryer because I like them soft. Instead, it's about what we can do relatively painlessly that has a positive impact." And those positive impacts are paying off. Kathleen's December electricity usage was 25% lower than in 2006—even with the additional load of charging the Zenn. And that's not even counting production from the PV system.

Rooftop to Ground

On the south-facing rooftop, the PV modules are mounted on Direct Power & Water Power Rail mounts and wired in two series strings of five modules each. The two strings are wired in parallel in a combiner box mounted to the roof. The west-facing array of eight modules is mounted and wired similarly, but the series strings contain only four modules each. Six-gauge, bare, stranded copper wire was used between the modules for equipment grounding. The equipment-grounding conductors were transitioned to 10 AWG in the combiner boxes.

A single conduit run carries a pair of #10 conductors, plus the #10 equipment ground wire, from each array through the roof overhang and down to the balance-of-system components mounted on the house's exterior. The positive wire from each array passes through the DC disconnect switch before the pairs terminate at the two Fronius inverters. One inverter processes 1,950 watts (Pmax) at 276.5 volts from the south-facing array, and the other processes 1,560 watts (Pmax) at 221.2 volts from the west-facing array.

On their output side, each inverter produces 240 VAC. A quartet of wires exits each inverter—two hots, a neutral, and an equipment ground. The four hot wires pass through two, two-pole, 15-amp breakers that act as the main AC disconnects and overcurrent protection for the PV system. On the line side of these breakers, the four hots are paralleled into a single pair of hot wires and join one neutral wire for the journey to the production meter.

The production KWH meter is an additional component. In many grid-tied PV systems, a single, bidirectional KWH meter measures net production from the PV system as well as electricity consumption from the grid. In Kathleen's case, her utility meter doesn't deduct the PV-produced electricity from her utility electricity purchase. Instead, the designated production meter keeps track of the electricity produced by the PV system, which she is paid for. (See the "The Performance Connection" sidebar on page 32 for more information on how Kathleen's system pays her back.)

From the production KWH meter, the two hot wires, a neutral wire, and an equipment-ground wire continue to the AC service entrance. The hots enter a standard household AC distribution panel through a two-pole, 30-amp, 240 VAC breaker. There, the neutral and ground wires terminate at their respective bus bars. The energy produced by Kathleen's PV system either contributes to the mix of electricity powering her household loads or, if the system is producing more electricity than she's using, enters the electric utility grid through her utility KWH meter.

Root ^n-Grid PV System

■""""" iiiiuiiHiHiiiniuiii iiiinnjiiHiiiiiiuih iiiiuiiHiHiiiniuiii iiiiuiniiHimiii!!!!

0 giiiml 0 giiiml I 0 0IIHII 0 0IIHII

South-Facing PV Array: Ten Sanyo HIP195, 195 W each at 55.3 VDC; wired in two series strings of five modules each for 1,950 W at 276.5 VDC

PV Combiner Boxes:

Two, parallel series strings

PV Combiner Boxes:

Two, parallel series strings

PSE Net Meter

Customer PV Production Meter

West-Facing PV Array: Eight Sanyo HIP195,

195 W each at 55.3 VDC; wired in two series strings of four modules each for 1,560 W at 221.2 VDC

AC Disconnect:

PSE Net Meter

AC Disconnect:

Inverters: Two Fronius IG 2000, 2 KW each, 500 VDC max input, 150-450 VDC MPPT operating range, 240 VAC output

Wireless Remote:

Fronius IG Personal Display

AC Service Entrance:

Two-pole, 30 A breaker

Inverters: Two Fronius IG 2000, 2 KW each, 500 VDC max input, 150-450 VDC MPPT operating range, 240 VAC output

Wireless Remote:

Fronius IG Personal Display

A wireless remote meter helps Kathleen keep tabs on her PV system's production.

While Kathleen didn't actually climb on her roof to install her PV system, she was definitely involved with the planning and paperwork of the process, especially the permitting and net metering agreements. "I was amazed and inspired," she says, "with how patient and helpful everyone was." Skagit County Head Electrical Inspector Dennis Patterson readily answered technical questions in advance. Jake Wade, program implementer of the Renewable Energy Advantage Program at Puget Sound Energy (PSE), Kathleen's electrical utility, walked her through all the necessary paperwork to get her system signed up for production

A wireless remote meter helps Kathleen keep tabs on her PV system's production.

The Performance Connection

Of the more than 40 states that offer some sort of incentive for utility-tied renewable energy systems, Washington is one of only a handful that provides performance-based incentives (PBIs). While other states or utilities that offer PV incentives typically provide a one-time rebate based on a PV system's rated watts (capacity-based), Washington provides payment, though the utility, for the electricity actually produced by the system. Under the PBI scenario, payment is for every KWH that the system produces, whether it is actually fed to the utility grid or used immediately in the system owner's home. Most other net metering agreements often involve simply offsetting either monthly or annual electricity use with RE generated electricity. Any excess energy that those systems produce is either sold to the utility at retail rate, avoided generating cost (a fraction of the retail rate), or sometimes nothing at all (the system owner "donates" the excess electricity to the utility).

Although Kathleen received no incentive money up-front from the state to help her pay for her system, under the PBI program, for at least the next seven years, she will receive $0.15 for every KWH her system produces (about twice the utility retail rate). Based on her system's projected performance, it could earn $3,500 in those seven years. If these PBIs are renewed, Kathleen could expect $15,000 over the system's assumed 30-year life.

If she is using that PV-produced energy herself, then she's also offsetting the cost of utility-based electricity. In essence, when she's using her solar-generated electricity, Kathleen's PV system is paying for itself at a rate of about $0.22 per KWH. As the price of electricity goes up, the value of her own PV-produced offset goes up too.

In the future, it's possible that more states will transition to PBI incentive structures, rewarding system owners for their system's actual output, rather than just their rated potential. This means that more care will be taken to ensure proper system design and installation and more attention paid to properly maintaining the system's level of performance over its lifetime.

The PV production meter next to the system's AC disconnect.

Root PV System Costs

Item Cost

18 Sanyo HIP-195BA3 photovoltaic modules

$19,800

2 Fronius IG2000 grid-synchronous inverters

3,200

Direct Power & Water Power Rail PV mounts

1,600

Miscellaneous wire, conduit, etc.

Was this article helpful?

0 0

Post a comment