Solar Electric Systems (Photovoltaics)

Solar Electric panels (also known as photovoltaics or PV) convert sunlight directly into direct current electricity.  As most of the devices that use electricity in our homes require AC (alternating current) power, a solar electric system is composed of more than just the panels.  At a minimum you have the panels and a grid connected inverter (the inverter changes the power from DC to AC, a grid connected inverter feeds the power into the utility grid) and a cut off safety switch.  The safety switch is required for all grid connected systems, and prevents your system from feeding electricity into the electrical grid during a power outage.  In the past, utility workers have been killed or severely injured attempting to repair power lines that were supposed to be dead but turned out to be charged by someone's solar electric system.  These systems can produce dangerous amounts of power, so remember - safety first. 

A basic stand alone system (one not connected to the utility grid) has panels, an inverter and some type of batteries for electricity storage.  Systems can have more than one inverter, or multiple battery banks, or provide some AC and some DC power - it's really up to the designer and the load requirements.  My brother-in-law has a small grid tied system with a battery bank.  He uses some power as it is produced, charges his batteries and if there is any excess feeds back to the grid.  Since he is also signed up for off peak electricity rates (he pays less for power used on evenings and weekends, more for power used during the work day), he also charges his batteries off peak when needed and then draws power from them during on peak periods.  (He's pretty handy with electrical stuff.)

Building integrated photovoltaics (BIPV) are photovoltaics that are integrated into the structure itself and may take the place of conventional building materials.  I feel that is one of the most promising areas of photovoltaics, as there is potential for reduced overall system costs because the system displaces standard building elements, so "double costs" are not incurred.  Also, when used in office buildings or other buildings that have peak loads during daylight hours, the use profile is a better fit for the available sunlight (as opposed to a residential dwelling where the homeowners are gone during the day).

There are also commercial scale systems that produce electricity using solar thermal, but these are not currently available on a residential scale (and are not likely to become available).

Right now, even with federal tax credits and state incentives, solar electric systems have a much longer payback period than solar thermal systems.  In our area, you're looking at over a decade.  To quote my brother-in-law, "If you install a PV system right now, you're not doing it to save money."  Take for example the Bircher home, which has two 275 watt (AC) PV panels with built in inverters.  The installed system cost was $4800.  The estimated annual energy savings is $37.  This gives a payback period of just under 130 years.  Obviously, none of us are going to be around this long, and even if electric rates triple it's still going to have a long payback period.  The good news is that it still saves you more money than those granite countertops that are currently so popular, plus you get bragging rights with all your environmentally conscious friends and acquaintances.

I love the elegance of photovoltaics, but from a strictly monetary perspective solar thermal is the way to go.  They can have a payback time of less than ten years, especially if they are supplementing an electric water heater and you qualify for a utility rebate (in Wisconsin the Focus on Energy Program may cover up to 25% the system costs).  (Just in case you're checking the numbers, the Bircher Solar Hot water system supplemented a natural gas water heater back when natural gas prices had bottomed out.  They also are not home during the day to use the hot water when it's being produced, further reducing their savings, plus the cost did not include any utility rebates.)  The economics for PV are more favorable if you're building a home at some distance from the utility grid - line extensions are outrageously expensive.  If you can roll the system cost into your mortgage the numbers are also improved.  We do eventually hope to add PV, but we'll add solar thermal first.

Links

WisconSUN - WisconSUN promotes solar energy projects by marketing, reducing barriers, and helping participants. We support projects during planning, design, and installation. We also provide the information, training, and project management assistance needed to implement these systems successfully.

Does going solar pay off for homeowners?  Even as states ramp up incentives, investment payback remains elusive - an article from MarketWatch.

Building Integrated Photovoltaics (BIPV) by Steven Strong, Solar Design Associates - This article provides an overview of what the systems include and basic system design elements, as well as links for additional information.