Industry production of photovoltaic modules is growing annually, which allows more households to benefit from solar energy systems.

Financial incentives, such as those offered by the federal government and many states, provide the extra motivation for homeowners to have photovoltaic arrays mounted on rooftops or on the grounds. Maine offered rebates to solar photovoltaic and to solar thermal systems at one time but state government unfortunately has not authorized more rebates.

Two types of photovoltaic systems are most common. In early systems, batteries were connected together and served the house “off-grid,” meaning the system is self-contained. In the other option, the household system is connected to the electrical grid.

Before you begin you need to do some planning. Is the roof orientation correct? How much roof space do you have to mount panels? How much power do you want? How much money do you want to invest? Though systems can be installed in increments, there is a lot of economic advantage to larger systems installed at once. A small system, such as a 4 module (1kW, nominal) roof-mounted system, costs more than $5 per kW to install. Once you reach a threshold (typically about 3 kW), the cost per kW becomes more reasonable.

For a ground-mounted system, increased production can result using automatic sun trackers that will help offset the cost of the separate foundation and ground mount structure. When mounting on a roof, it is important to consider the structural integrity of the roof, the need for re-shingling, and that the attachments for the array don’t sacrifice the integrity of the roofing.

Two primary benefits of a photovoltaic solar array are its longevity and dependability. These arrays can last 30 years and most inverters can be connected to a wireless router to broadcast system production and communicate any system errors.

In my line of work, I occasionally do an energy audit for a homeowner who wants to have a photovoltaic array to supplement some of the electricity needed over the course of a year. The first thing I usually do after providing specific guidance about how to lower heating costs is to look at a year or two of electric bills for the house and figure a system that will power 90 percent of the annual power demands.

Following Maine’s net-metering rules, photovoltaic production in excess of what you use month-to-month is allowed to be credited to your bill at your per-kWh rate. This credit is carried forward for up to one year and used to offset times when your photovoltaic array doesn’t make enough power.

For example, a 3,000-W system of 12 panels, at 250 watts per panel, taking into account a number of factors, and $3.65 per watt installation, would cost approximately $11,000. With a 30 percent federal tax credit, the cost is lowered to $7,700. This would be save you close to $600 or more yearly.

Another factor in CMP’s service territory is a CMP charge each month, which can account for up to the first 100kWh of consumption. The savings increase as electricity rates rise.

Some people have been steered away from solar water heating systems for photovoltaic when a solar water heating system would be a much better investment (compared to a tankless coil in oil boiler situations, for example). I think it is important for all systems to be viewed with the other options (photovoltaic vs. efficiency vs. pellets vs. heat pumps vs. natural gas vs. solar water heating) to make sure the option best fits the homeowner’s goals in terms of financial return, self-sufficiency and environmental impact.

If the economics of these systems are a driving factor in your decision-making, be sure to have a detailed analysis of the economic benefits performed. The review includes using a shade analysis, modeling the system performance, taking into account your monthly usage patterns, and determining the benefit of the tax credit for your particular circumstances.

Lastly, always consult with an Efficiency Maine registered vendor and one who is certified by the North American Board of Certified Energy Practitioners. Always ask for references and request photos of comparable installations.

Clough Toppan is a member of Sustain Mid Maine Coalition’s board of directors as well as the Energy Team. He is a Maine licensed engineer who performs energy audits to homeowners and businesses as Toppan Consulting Services in Vassalboro. Email: [email protected]. Portions of this article are based on conversations with Vaughan Woodruff of Insource Renewables, Pittsfield, specializing in solar power installations. Email: [email protected].

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