Community Solar – Better on the Roof?

Date: 22 Oct 2010 | posted in: Energy, Energy Self Reliant States | 3 Facebooktwitterredditmail

When we released our report on community solar power last month, we expected a few comments on the grades we gave to the nine featured community solar projects. We also generated a really robust conversation about the location (on buildings or on the ground) of community solar PV projects and made a disheartening discovery about the cost of roof repairs when a solar PV array is present.

 

In the report, our criteria for solar PV location gave high marks for rooftop solar PV systems because of their use of existing infrastructure, lower marks for ground-mounted systems in brownfields, and the lowest grades for greenfield systems. In one particular case, we gave a ‘C’ grade to the Clean Energy Collective’s project because while it used otherwise unusable land near a sewage treatment plant, it was still ground-mounted.

The response to their ‘C’ grade made us re-evaluate our grading system. On reflection, there are three major considerations for the location of a community solar (or any distributed renewable energy) project.

Location Criteria for Community Solar

  1. Preservation of Open Space 
  2. Use of Existing Grid Infrastructure 
  3. Lifetime Cost for Participants 

 

Open Space

The open space issue cannot be ignored, as demonstrated by the opposition to centralized concentrating solar thermal power and solar PV power plants in the Mojave Desert and San Luis Valley in Colorado. Projects that use rooftops will rarely encounter resistance on environmental grounds (although there can be issues with historic districts). From the perspective of open space, there is still a higher value in a rooftop project than a ground-mounted one.

Existing Grid Infrastructure

The issue of existing grid infrastructure is not as clear cut. In general, distributed solar PV projects minimize the need for new grid infrastructure by plugging into the grid at low voltages and in a variety of places.

Rooftop solar would seem to have an advantage in this.  With few exceptions, a rooftop solar PV system can easily interconnect through the building’s grid connection. A rooftop solar PV system doesn’t change the capacity required by the local grid connection because net metering limits typically mean that no one installs a system that produces more than the building consumers.

But our error was to assume that ground-mounted systems would not take advantage of existing infrastructure, as well. In fact, the Clean Energy Collective solar project connects to existing infrastructure at an adjacent sewage treatment plant. Several other community solar projects in the report were constructed by utilities and presumably built next to existing substations where the new generation could easily be absorbed into the local grid. In other words, we should have graded this location criteria separately from the open space issue.

Lifetime Costs

The third issue – and one we’d never considered – is that rooftop PV systems may have to be removed and reinstalled if the roof needs replacement or repairs. While PV systems typically lose a small portion of their potential output (< 1%) each year, the systems can operate for decades, far longer than the typical residential or commercial roof (20-25 years in Minnesota). In other words, there’s likely to be one roof replacement during the life of a PV system.

Reinstalling a residential rooftop PV system could cost $6,250 or 25% of the installed cost of the system

In our investigation, we found that moving residential PV systems to accommodate a roof replacement could cost as much as 25% of the initial system cost (and over 35% of the net cost after the application of the 30% federal tax credit).  Moving systems on a commercial roof was less expensive, on the order of 15% of initial installed cost (around 25% of the system cost after the tax credit).   

The following chart illustrates the range of costs we found relative to an initial installed cost of $5.00 per Watt for commercial and residential PV systems.  

But this chart is somewhat disingenuous, because solar PV owners never pay the full installed cost.  Instead, there are a slew of tax credits and rebates that reduce this initial price.  The next chart shows these roof repair reinstallation costs relative to the net cost after the 30% federal tax credit.  

The cost issue is also complicated by various ownership arrangements. If the building owner also owns the array, the cost of moving the PV system is their responsibility. But what if they lease the solar array? Does the leasing company bear the cost of system safety when the roof is repaired or replaced or is it still the responsibility of the building owner? Will that cost be assessed when the roof is repaired or escrowed from the start of the project?

A CEC representative noted, “I guarantee you that a building owner (lessee) will never sign a long term lease that requires them to pay the costs of reinstalling a system after roof repairs, etc.” If CEC’s recently completed 77 kW community solar array had been built on a rooftop and required a move, the cost to its individual investors would likely be around $2,000, increasing the upfront cost for those individuals by nearly 30%. In addition, CEC couldn’t have offered the utility or its customers a 50-year service level agreement.

Conclusion: Location is Complicated

Obviously, there’s much more to the ground v. rooftop issue than meets the eye, from interconnections to roof repairs. Look for a transformation in our Community Solar Report in the next few weeks reflecting on this complex issue.

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Better smart grids serve consumers, not just utilities

Date: 20 Oct 2010 | posted in: Energy | 0 Facebooktwitterredditmail

But what’s most interesting is the state’s desire to make sure that investment in smart grid technology will pay off not just for utilities, but for consumers as well. For instance, Hawaiian environmental groups are apparently pushing for rooftop solar panels, a more green approach, than simply better managing supply and demand via a network-enabled smart grid.

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Distributed, Small-Scale Solar Competes with Large-Scale PV

Date: 19 Oct 2010 | posted in: Energy, Energy Self Reliant States | 1 Facebooktwitterredditmail

Distributed solar photovoltaic (PV) proponents have recognized that solar is not without economies of scale – larger installations generally have lower installed costs per Watt of peak capacity.  But new data suggests that these economies are significantly smaller than previously believed.  This is good news for solar and great news for the renewable energy movement. First … Read More

Policy to Maximize On-site Use from Distributed Generation

Date: 4 Oct 2010 | posted in: Energy, Energy Self Reliant States | 1 Facebooktwitterredditmail

Distributed generation (DG) puts energy production close to where it is consumed, often on people’s homes or in their backyards.  But just having a rooftop solar module doesn’t mean that every kilowatt-hour produced from sunlight is used in the home.  In fact, it’s often less than one-third, with the remaining energy production flowing out into the … Read More

Utilities take a shine to (distributed) solar

Date: 21 Oct 2009 | posted in: Energy, Energy Self Reliant States | 0 Facebooktwitterredditmail

Rooftop solar is no longer the playground for granolas and Germans. But even when utilities join the solar PV game, they find that the distributed nature overcomes many of the technical and political barriers. A 2008 change in federal tax policy opened the door to utilities to invest in solar PV and utilities like PG&E are planning sizable installations (250 MW). PG&E will do a ground-mounted field of modules in the desert, but other utilities are finding distributed PV makes more sense:

Southern California Edison already plans to scatter 1 MW and 2 MW rooftop PV installations across its service territory, part of its goal to deploy 250 MW of PV over the next five years. Minimizing transient spikes is one reason. A second is that transmission remains the No. 1 barrier to renewable energy growth in California, says Mike Marelli, the utility’s director of renewable and alternative power contracts. “We can implement smaller systems with little or no transmission” additions, he says.

It’s hard to argue that transmission is a barrier when you’ve got 250 MW coming online without it! The good news is that the distributed solar also helps overcome some of the variability issues with solar power:

“During cloudy periods, the output from PV can get noisy with spikes,” which can have an effect on the grid, says Kelly Beninga, global director of renewable energy for WorleyParsons. PV installations around 20 MW in size can be managed without too much trouble. Larger than that and portions of the grid can be affected by passing clouds… To better understand the issue, NV Energy is studying power output variations that may result from deploying PV in and around Las Vegas. The study won’t be complete for another year, but Tom Fair says early data suggest that geographic dispersion helps dampen variability. A second finding is that solar facilities need to be placed on strong parts of the grid. “That leads us away from having huge amounts of PV at any one site,” Fair says. Ten to 20 MW at any one site might be the limit.

The utility interest in solar PV may help remove some of the stigma, and show that even small-scale modules can have a big-scale impact.

Photo credit: Schroeder, Dennis – NREL Staff Photographer

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When Local Became the New Organic

When Local Became the New Organic By David Morris, originally published in Minnesota Law and Politics, August 2008 We can pinpoint with some precision the date the local food movement came of age: Dec. 15, 1997. That day the United States Department of Agriculture finally issued the organic standards that Congress had said it required back … Read More

New Report Argues For A Renewable Energy Policy That Puts Rural Communities First

Date: 16 Mar 2008 | posted in: agriculture, Energy, Energy Self Reliant States | 0 Facebooktwitterredditmail

For Immediate Release PRESS RELEASE CONTACT: 612-276-3456 NEW REPORT ARGUES FOR A RENEWABLE ENERGY POLICY THAT PUTS RURAL COMMUNITIES FIRST   Minneapolis, MN—(September 8, 2008).  The next 20 years could generate as much as $1 trillion in new renewable energy investment in rural America. But as a new Ford Foundation-sponsored study by the Institute for Local … Read More

Give Ethanol a Chance: The Case for Corn-Based Fuel

Date: 15 Jul 2007 | posted in: Energy, Energy Self Reliant States, environment | 0 Facebooktwitterredditmail

Working Assets is my long-distance phone company. I love it dearly for its combination of business efficiency, social responsibility and progressive politics.

Each month, my phone bill carries alerts that urge me to take action on a specific issue or two. Recent Citizen Actions suggest the gravity of the issues chosen: "Save Our Constitution," "Impeach Dick Cheney," "Close Guantanamo."

This month Working Assets urged me to "Say No to Ethanol."

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