Like so many people, Joy Hughes wanted to do something for the victims of the July 2012 mass shooting in a movie theatre in Aurora, Colorado in the US. But while others held vigils and set up memorials, Hughes found herself scouting sites for solar gardens six days after the shooting in the Denver suburb.

‘It is something positive for people to focus on that might help with the healing process,’ said Hughes, who worked at Apple Computer and several Silicon Valley startups before founding the Colorado-based Solar Garden Institute.

A solar garden, also called community-shared solar, is a photovoltaic array that takes from the ideas of community vegetable plots, crowd source funding and energy aggregations. The garden is built near or within a community, where it is visible to its members. Local households and businesses come together to fund the projects through subscriptions, ownership of shares, or some other form of investment, sometimes using utility on-bill financing. Models vary, but the harvest usually comes in the form of electric bill credits, guaranteed utility rates, or some other type of financial compensation for the gardeners.

Helping a community through trauma is not a solar garden’s usual purpose, but then Hughes points out that the model opens up all kinds of possibilities not often associated with a power plant. ‘This is a way people can take individual ownership, individual responsibility for their power supply,’ she said. ‘lt becomes a symbol for sustainability for every community.’

Beyond the symbolism, the solar garden offers a sophisticated financial model that can leverage virtual net metering, bulk purchasing, solar power purchase agreements (PPAs) and tax equity credits to reduce solar costs and ensure all parties benefit from the deal. Moreover, solar gardens offer a way to attract investment from property owners who are otherwise disenfranchised from the solar boom.

Often solar gardens are built on public land, depleted agricultural plots, airports, school rooftops and other inexpensive pieces of property that are highly visible to the community. But it’s not just neighbourhoods that can benefit; the concept also can serve retail operations with multiple stores, as well as municipalities that pay electricity bills for schools, fire houses, water treatment plants and other facilities.

The results, say its backers, could soon be gigawatts of new photovoltaic installations.

Spreading Like Weeds

While solar gardens first emerged in the usual green-oriented states: the Pacific Northwest, California and Colorado, they are now spreading elsewhere, and the community model accounts for 60 MW, according to the Solar Electric Power Association (SEPA). Eight states have policies that specifically encourage community solar: Colorado, Massachusetts, California, Delaware, Vermont, Washington, Rhode Island and Maine. The concept is especially alive in Colorado where former governor Bill Ritter signed a bill in 2010 that allowed up to 6 MW per year of solar gardens. Changes in government policies, however, are not always necessary – solar garden models exist that can work in most states.

So far individual solar gardens have tended to be in the 1 MW range, but that appears to be changing, as existing gardens expand and new ones are proposed.

‘This is the way that we can bring solar to scale,’ Hughes said. ‘There have been two solar sectors up to now: one being the residential/commercial and the other being the utility scale. Now we are creating a third sector at a mid-scale size.’ Moreover, if pending legislation in California becomes law, solar gardening may take on gigawatt proportions.

California’s SB 843, the Community-Based Renewable Energy Self-Generation Program, would create incentive for up to 2 GW of solar garden installations, which could each be as large as 20 MW. The state Assembly Utilities and Commerce Committee voted 9-2 in favour of the bill in June, and the full legislature is expected to consider it by the end of August 2012.

‘This, I think is a potential game changer. If that bill passes, it will unleash innovation around these business models and the policies to support them. Keep an eye on California,’ said Hannah Masterjohn, policy advocate at Vote Solar, a US non-profit solar advocacy organization.

Net Metering Goes Viral

Solar gardens overcome one of the biggest obstructions to mass PV installation. While 90% of the US population says it wants to take advantage of solar energy, only 25% actually can, according to Masterjohn. The remaining 75% are precluded because of various obstacles: trees share their roofs, they don’t own the building, or they lack the capital or financing.

Using a community-shared model, households and businesses can participate in solar, and do so by taking advantage of the economies of scale offered through bulk purchase and aggregation. This reduces the already falling cost of PV installation.

‘What the customer sees is the cost savings; it is a modest cost savings at this point, but it could easily become a much greater savings over time as the installation costs of panels goes down,’ Hughes said.

Many solar garden programmes bring savings to customers through virtual or aggregate net metering, a concept modelled after conventional net metering, but able to spread the financial benefit of distributed generation beyond the building that hosts the solar panels. Virtual net metering provides bill credits for buildings not actually connected to the solar panels.

In a July 2012 webinar on community solar, Masterjohn cited the example of a college campus where a dorm building has solar panels on its roof. In the summer, when the students are away, the dorm consumes far less electricity than the solar panels produce. But administrative buildings remain occupied – and continue consuming electricity – over the summer. So they receive bill credits for the dorm’s solar production.

Similarly, in a neighbourhood with solar gardens, the facility feeds the power into the electric grid and local households or businesses reap the virtual net metering benefits, even though they have no physical connection to the panels. However, not all states allow virtual net metering. That is why the Clean Energy Collective has created a solar garden model that works without virtual net metering. Founded in 2009, the company has eight solar garden projects either built or in development in Colorado, Minnesota and New Mexico, and is talking to utilities nationwide about additional projects. The company expects to develop 5 MW – 10 MW this year and six to seven times that amount in 2013.