Backyard power

The challenge of integrating solar energy into the grid

Backyard power
A typical 4-kilowatt rooftop solar electric array costs about $21,600, before tax credits.

So you like the idea of getting your electric power from the sun: It’s clean energy, it seems simple (no moving parts!), and it may lessen your dependence on the grid. 

But the truth is, residential solar power isn’t as simple as it seems, and unless you’re willing to invest in an expensive battery system and backup generation, the average household can’t sever its cord from the electric grid.

The sun shines only part of the day, but most likely you need electricity 24/7. For this reason alone, most homes with roof-top solar arrays need to remain connected to local power lines. But solar and other renewable forms of energy are popular, and they are changing the relationship between the grid and residential electricity users.

Distributed generation & the grid

Locally generated electricity is part of what the utility industry calls “distributed generation,” or smaller sources of power generation within a utility’s service system, separate from central power plants.

Until recently, power flowed just one way: from power plants through your electric co-op’s lines and into homes. But today, a home or small business with solar panels can generate electricity when the sun is shining — perhaps enough electricity for itself — and direct any excess power back onto the grid.

The rules governing distributed generation — in particular, payments for excess power that flows onto the grid — vary from state to state and utility to utility. Consumers who are interested in residential solar installation should always contact their local electric cooperative first. Cooperatives set any payment or credit for member-owned electric generation based on a rate determined by what it costs the co-op to integrate that power and maintain the grid for all members.

Distributed generation on power lines also raises a potential technical danger called “islanding.” This can occur when an outage brings down the local grid, but a line continues to be live because power keeps feeding in from distributed generation. Islanding can be a safety hazard for linemen working to get the power back on and can cause problems when the grid powers back up.

Another challenge of distributed generation is that solar power is highly variable. The energy generated regularly rises and falls during the day, hour by hour, depending on the weather. For cooperatives and other utilities, integrating this variable supply into the overall power requirements of a local system takes extra planning and scheduling.

Cooperatives are testing various ways to safely integrate new excess power into the grid, including battery storage, to smooth out the peaks and valleys that come with renewable generation.

Localized solar options

For homeowners and small businesses, a solar array can be an expensive proposition. Residential solar electric photovoltaic (PV) systems range in size from 1 to 20 kilowatts (kw). A 4-kw system is often a roof-mounted array or grouping of 16 to 20 PV modules. Costs vary across North Carolina. Advanced Energy, a not-for-profit research and engineering service in Raleigh, reports that an average cost for a residential PV installation is $5.40 per watt, so a 4-kw installation may cost about $21,600. Tax credits for systems installed before the end of 2015 can make PV systems more affordable.

To provide members with another option, some electric co-ops are looking into “community solar” systems. These are larger arrays from which members can acquire the power from one or more panels, or in some cases, just a portion of a panel. The co-op would handle the maintenance, and the member receives a credit for solar generation. Members buy just as much solar generation as they want or can afford. Community solar may open a new opportunity, offering “backyard solar” at a reasonable cost for consumer-members who may not have a site suited for solar.

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