Wisconsin’s rooftop solar photovoltaic (PV) marketplace is still in its infancy. In 2020, rooftop solar generating capacity was approximately 104 megawatts (MW), representing about 1/3rd of one percent (or 0.333%) of all the electricity produced in our state.
However, Wisconsin’s rooftop solar market is growing, with over 10 MW of solar installed on residential homes last year, compared with approximately 5 megawatts in 2019. The combination of Wisconsin’s current rooftop solar capacity and adoption rate in the solar marketplace prompted Wisconsin’s Public Service Commission (PSC) to request a Rooftop Solar PV Potential study. The study provides both technical potential and simulated market adoption analyses.
Technical Potential Study
Nearly 37 gigawatts (GW) of technically feasible rooftop solar capacity would be possible in Wisconsin by 2026. By 2034, another 2 GW of solar would be possible on Wisconsin rooftops, for a total of 39 GW, enough to provide around 70% of our total statewide electricity needs. Unfortunately, only 1.6% of this is projected to be adopted by 2034, given our current set of economic and regulatory factors.
The technical potential study considers all rooftop square footage in the state with less than 20% shade. It does not view houses and facilities that need structural upgrades, electrical upgrades, or new rooftop materials. Nor does it factor in the host utility’s net-metering capacity maximum. Essentially, the study represents the theoretical maximum amount of Wisconsin rooftop solar capacity.
Market Potential Study
The PSC market potential study focused on a business-as-usual scenario and four new economic scenarios that would help drive solar adoption. The new scenarios are as follows:
- A statewide, net-metering policy
- Increased Focus on Energy incentives
- “Attractive” financing (reducing interest rates to 2.5% and requiring no down payment)
- Extending the Federal Investment Tax Credit (ITC) at 26% until 2026.
The statewide net-metering policy demonstrated the best hypothetical outcome for rooftop solar adoption of the four potential scenarios. This net-metering policy would include a 500 kW net-metering cap and an annual “true-up,” meaning excess solar energy could be passed on or “banked” from month to month instead of only day-to-day.
Each of the potential scenarios resulted in increased solar adoption from baseline scenarios, but the standardized net-metering policy resulted in the highest adoption levels. While the other three scenarios represented a 5 – 15% increase in solar capacity, the net-metering approach resulted in a nearly 30% increase in adoption.
The majority of solar potential is concentrated in the residential sector, primarily among single-family homes. Approximately 62% of the technical solar potential comes from single-family homes, with the market-simulated study showing residential solar making up 50% to 70% of the total rooftop solar capacity.
Technical and Residential Potential – Under an ideal technical scenario, Wisconsin could reach 265% of its electric capacity and approximately 70% of our total annual electricity production from rooftop solar alone. The technical study doesn’t consider battery storage and other demand-side measures, which could make rooftop solar an even more efficient source of energy than it currently is today.
The potential for rooftop solar in the residential sector is substantial. Utility bills make up a large percentage of many household incomes, especially with more people working from home. Demand-side measures and other energy-efficient upgrades can reduce household utility bills further, speeding our energy transition even more quickly.
Jobs and Equity – Solar installer is already slated to be one of the fastest-growing jobs in the country, and this rooftop solar potential could place additional strains on worker demand. Wisconsin solar contractors are already challenged to find enough qualified employees, especially electricians, and the possibility of adding so much renewable energy to the grid means we’ll need to find people to fill these roles.
Wisconsin will need all hands on deck to build our clean energy future, which will mean making sure underrepresented communities are recruited into this robust workforce. It will be necessary to engage and train rural residents, people from impoverished areas, and people of color. Job programs like Madison’s GreenPower Program are essential to training tomorrow’s workforce, but we will likely need more programs like this moving forward.
Incorporating gigawatts of rooftop solar will also improve the health and futures of Wisconsin residents. In particular, studies have shown that fossil fuel generation sources, like coal and gas plants, are much more likely to be sited in lower-income communities, resulting in many poor health outcomes for members of those communities. Adding widespread, distributed rooftop solar to our energy mix will allow many fossil fuel plants to be decommissioned and taken offline. Plus, marginalized communities will share in the economic benefits that rooftop solar can have on utility bills.
Net-metering potential – From an economics perspective, net-metering is a highly beneficial tool for behind-the-meter solar installations, especially in the residential sector. Net-metering has positive impacts for both the consumer and the utility; rooftop solar provides additional capacity value for utilities when the grid needs it most (typically afternoons). It allows customers to receive credit for the excess electrons they produce and provide to the grid. This is why RENEW Wisconsin has advocated for a standardized, statewide net-metering policy for customer-owned solar arrays.
The findings in this report related to net-metering show the true value net-metering has on rooftop solar systems, especially those installed on residential dwellings. The net-metering scenario creates around 650 MW of new solar production, nearly 40% more than a business-as-usual scenario which only yields about 450 MW of rooftop solar capacity. This study shows a standardized net-metering policy would also have more dramatic and long-term effects on household utility bills than other scenarios considered, including increased tax credits or higher Focus on Energy incentives. This is especially true among income-qualified households, where a significant portion of monthly income goes towards utility payments.
RENEW hopes that the technical and market potential study findings will help bolster much of our regulatory work on the Parallel Generation docket at the Public Service Commission. RENEW advocates for an all-of-the-above approach to transitioning away from fossil fuel. Both utility- and customer-owned renewable energy sources will be needed to decarbonize our energy sector. This study shows that rooftop solar has a much more significant potential than previously thought and demonstrates how vital these installations will be over the next few decades.
 These increases in projections were primarily due to load growth and efficiency improvements in solar panels.