Reducing the Cost of Solar

^{Photo by Gray Watson}

A recent report by the National Renewable Energy Laboratory (NREL) outlined several ways that the photovoltaic industry can lower design and installation costs for residential scale PV. Today we’ll look at a few products that meet at least some of the recommendations. As you’ll see, there’s a lot that’s already out there but there’s also plenty of room for new products.

Design Software

Before designing a photovoltaic system, one needs to determine whether PV is the most cost-effective solution. HOMER is a software tool that simulates a home under user-specified conditions and shows the effects of various renewable energy sources, including photovoltaic, wind, biomass, and microhydro. Both grid-tied and stand-alone systems are modeled. Although intended for professionals, a savvy homeowner could probably use HOMER to get a general idea of what types of renewables are best for his/her situation, and determine the size of the system that’s needed. The unsupported but fully functional version of HOMER is free; the updated and supported version is $99.

After the decision is made to go with photovoltaics, a designer has several tools to help with the design process. First you should do a site analysis. You can start with Google Earth to get an overhead view of the location. (Unlike Google Maps, Google Earth is a downloadable product that not only shows aerial views but also includes measurement tools.) This gives a general assessment of the solar resource at that location. A shading analysis comes next. I’ve used two products for that: The Solar Pathfinder and the Solmetric SunEye. The Solar Pathfinder is much less expensive than the SunEye, but not quite as user-friendly. Here are some videos that describe each product:

^{Video: Solar Pathfinder}

And of course, both of those tools come with their own PV design software. Each design software package allows the user to import the data gathered from the shading analysis.

If you’re designing a new building, you might be interested in the ZEROs software that I reviewed in September.

Plug-and-Play Components and Integrated Equipment

In order to reduce parts count, ensure compatibility, and ease the design and installation process, off-the-shelf systems are preferable. Many companies sell “AC photovoltaic modules” - PV panels that have built-in microinverters. Something more interesting to me is the TrinaSolar “smart” PV panel that includes an optimizer. The optimizer provides maximum power point tracking (MPPT) for each module (similar to a microinverter), but also offers remote control and monitoring via a WiFi connection and controlled output voltages to prevent overvoltage under cold weather conditions. The optimizer also works like an intelligent bypass diode for modules that are underperforming, possibly due to temporary shading conditions or panel aging. Instead of shorting out the module completely, it allows current from other series modules to pass around it, while still contributing whatever current it can. This way, it doesn’t waste the power from the underperforming module.

^{Video: TrinaSolar}

For those who want solar water heating as well as photovoltaics, you might consider a photovoltaic thermal (PVT) system. I examined the SunDrum system back in August, but there are other manufacturers of similar products.