Renewable Energy Workshops


Solar Hot Water Photovoltaics Sustainable Building

Full Workshop Schedule On-line


The Solar Water Heating System Built to Last

Tax credits and incentives in some states pay up to half the cost or more!

* Solar-powered pump

* Design life of over 25 years

* Designed for easy installation and reinstallation after re-roofing

* Residential and Commercial

* OG-300 and Bright Way certified

* Dealerinquiries are welcome!

No freezing! No visible plumbing!

No overheating! No parasitic losses!



Call (888) Sol-Rely (888-765-7359) www.So/Reliant. com

After Kathy Swartz and Kris Sutton bought their 5-acre property in Paonia, Colorado, they realized it needed a coop for future chickens—part of their overall plan for providing some of their own food and living as locally as possible. What they didn't realize was that the chickens would also help "grow" their own energy.

When we first looked at our pastured property with wide-open mountain views near the edge of the North Fork of the Gunnison River, there was a little red shed that we thought would make a great chicken coop. Little did we know that the seller was going to take it with him when he moved. Though we were disappointed at its disappearance, constructing a new coop became an opportunity to explore load-bearing straw-bale construction and passive solar design—as well as make room for a second, 1,750-watt grid-tied PV system.

In 2006, we installed a 1,440 W grid-tied PV system—sized to meet our budget at the time and approximately 50% of our electricity usage. But our goal all along was to produce 100% of our own electricity with renewables. The chicken coop, designed with a south-facing roof and nearly shade-free solar access, was a prime spot for the other PV system.

Mounted parallel to the roof plane, which sits at a 15-degree tilt, the second system takes advantage of the region's long, sunny summer days. The pitch is lower than recommended for optimal production, but the system will only suffer a 5% annual production loss as a result, which we find acceptable. However, the shallow pitch does not shed snow very well. In some parts of Colorado, this would be a problem, but since we experience less snowfall, it was less of an issue. After a heavy snow, we sometimes brush off the array with a broom to hasten melting.

Why Microinverters?

We decided to use ten 175 W SolarWorld modules with Enphase microinverters, one per module. As proponents of buying as locally as possible, it was important to buy U.S.-

Top to bottom: The PV mounting rails, ready to go; detail of the inverter mounting scheme; inverters appropriately spaced between the PV mounting bolts, with the AC wiring neatly tucked away; the modules in place and connected to their inverters (note the ground wires across the inverters, and behind and attached to the modules).

made PV products. Both of these companies are in California and just happen to be the closest manufacturers to us.

Kris is typically very cautious about buying equipment from start-up companies. But because the microinverters are so unique—and potentially industry-changing—we were excited to try this product.

Microinverters are fundamentally different from conventional string or central inverters—they have a one-inverter-per-module design. Individual inverters provide maximum power point tracking (MPPT) for each module in the system, resulting in higher system output overall. Though it doesn't apply to our sunny site, with the microinverters, any shading of one module does not influence another module's output. With a larger, central inverter with multiple modules in series, shading of part of one module can decrease the performance of the whole series string. Because of the individual MPPT, modules can be oriented differently or mounted at various tilt angles without affecting one another. Another benefit to a microinverter-based system is that you can put as many modules as you want or can afford in a system—matching module strings to inverters, as required with string or central inverters, is not necessary. Therefore, you can have exactly the number of modules that fit your roof or your budget—increasing the system size in the future is made easy.

Since modules are not connected in series, the DC voltages of the PV array are no higher than one module's open-circuit voltage, reducing (but not eliminating) the shock hazard for PV technicians. As a safety professional in the PV industry, Kris believes that this design is safer to install and service than most conventional PV systems. Plus, eliminating higher-voltage DC circuits meant that we saved approximately $200 and about one hour of installation time, since we did not have to use a high-voltage DC disconnect. Also eliminated are the fused DC combiner boxes required on larger systems with multiple strings in the array. Using microinverters saves wall space and a few hours of installation time by not having to mount a single, large inverter with accompanying disconnects and conduit.

For the size of our small system (and not including communication systems, other balance-of-system components, or installed labor differences), the Enphase microinverters average about $1.14 per watt retail for a 1,750 W system, offering a tiny bit of savings (about $0.02 to $0.16 per watt) compared to a similarly sized central inverter.

However, Enphase microinverters are not without their disadvantages. The biggest one is that they are a new company offering a product with a short track record in the field, even though the microinverters carry a 15-year warranty. They were introduced to the market in the summer of 2008. We don't know what the performance will be like in five or 10 years. And, of course, if the company were to go out of business, product support would disappear along with the company's Web-based data monitoring. But that's a risk that we take with all companies.

If one of the inverters fails, replacing it could be challenging depending on the accessibility to the back of the modules—for instance, if an array is mounted several stories off the ground on a steep roof. For our application, the modules are easily accessible, and this not a concern.

It can get pretty hot under PV modules in the sun and, in general, inverters and other electronics can fail early if they cannot handle the heat. This is also an issue with mounting standard inverters in direct sun or in contained spaces with no airflow. Enphase recommends a minimum gap of 1 inch above the roof for proper heat dissipation.

Putting the System Together

Our system installation started out like any conventional installation—first figuring out the module layout and then attaching mounting hardware to the roof. However, the step that differed was paying attention to the location of modules on the roof to determine where the microinverters would be mounted so they'd be evenly spaced between the module frames. The inverters must be mounted on the rails, between where the module's frames will lay against the mounting rails.

The inverters were then laid out on the roof to make sure that all of the prewired AC cabling would reach the next inverters' cables. Once their location was determined, we bolted the inverters to the PV mounting rails. The prewired AC quick-connect cables from each inverter were all plugged in together. Once the cables were connected, we secured the extra wire along the mounting rails (see "Installation Tip:

Tech Specs


System type: Grid-direct solar-electric Location: Paonia, Colorado

Solar resource: 5.85 average daily peak sun-hours

Record low temperature: -31°F

Average high temperature: 90°F

Average monthly production: 205 AC kWh

Utility electricity offset annually: 100% (includes existing 1.44 kW system)

PV System Components

Modules: 10 SolarWorld, 175 W STC, 35.8 Vmp, 4.9 Imp, 44.4 Voc, 5.3 Isc

Array: 10 modules, 1,750 W STC total

Array installation: Direct Power & Water mounts installed on south-facing roof, 15° tilt

Inverters: 10 Enphase M175-24-240-S02, 175 W rated output, 54 VDC maximum input, 25-40 VDC MPPT operating range, 240 VAC output

System performance metering: Enphase Envoy monitor with Enlighten Web site

PV Array:

Ten SolarWorld, 175 W modules, each wired to individual inverters, 1,750 watts total


Ten Enphase M175-24-240-S02, 54 VDC maximum input, 25-40 VDC MPPT range, 175 W rated output at 240 VAC


Ten Enphase M175-24-240-S02, 54 VDC maximum input, 25-40 VDC MPPT range, 175 W rated output at 240 VAC

Swartz-Sutton On-Grid Microinverter PV System

PV Array:

Ten SolarWorld, 175 W modules, each wired to individual inverters, 1,750 watts total

To Utility Grid:

120/240 VAC

kWh Meter il


To Enlighten Web site or personal computer kWh Meter

Internet Router

AC Disconnect:

May be required by some utilities or local inspectors

Array AC Disconnect:

Toggle switch, on roof

AC Disconnect:

May be required by some utilities or local inspectors

AC Service Entrance:

To 120/240 VAC loads

Communication Gateway:

Enphase Envoy

To Outlet:

120 VAC power & data

AC Service Entrance:

To 120/240 VAC loads

To Outlet:

120 VAC power & data

Microinverter System Costs

Item Cost

10 SolarWorld PV modules, 175 W


10 Enphase microinverters


DP&W PV mounts

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

Get My Free Ebook

Post a comment