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Usable Roof Area

Rooftops within jurisdictions that have Light Detection and Ranging (LIDAR) data available can be clicked to determine the site's solar potential. The LIDAR data has been converted into a digital surface model (DSM) that allows the map to factor in shading, roof slope, roof aspect, and other factors that impact the feasibility of the site for solar. Sites without LIDAR data must use the "Draw Solar" tool, which factors in annual solar radiation in that location but not local shading, such as from trees or nearby buildings. To determine the usable roof area for solar in areas with LIDAR data, the following algorithm is used.

Roofs are divided into three types:

- "Pitched" if average slope is greater than or equal to 20 degrees
- “Large flat" if slope is less than 20 degrees and area is greater than 315 square meters
- “Small flat” if slope is less than 20 degrees and area is less than or equal to 315 square meters.

To determine usability, rooftops are divided into one-square-meter pixels. The usability of each pixel is determined based on the modeled incident solar radiation, the slope and aspect, the proximity to the edge of the building, and the height and shape of the building. To be considered usable, a pixel must:

- Receive at least 70% of annual maximum incident solar radiation;
- Have an aspect between 67.5 degrees and 292.5 degrees, if slope is greater than 5 degrees (i.e. not flat);
- Have a slope less than or equal to 60 degrees, if the roof is pitched;
- Have a slope less than 10 degrees, if the roof is pitched and the square meter is not considered an edge (we assume this criterion rules out the peak of the roof); and
- Be more than 2 pixels away rook-wise (i.e. connected along a full side, not diagonally) from a non-roof pixel if the roof is flat (i.e. there is a two-pixel setback along the roof edge, which approximates the Fire Code in New York City and common design constraints on larger roofs).

Pixels that are not 2 pixels away rook-wise from a non-roof pixel, regardless of roof slope, are classified as a “roof edge.”

Usable pixels are grouped into usable roof area patches. We assume that each usable roof area must contain at least 10 contiguous square meters of uninterrupted usable pixels. A pixel is considered in the same group as its neighbor if:

- The roof type is pitched and either pixel is an edge pixel (to counteract exaggeration of slope as roof edges);
- The slope delta between the pixels is less than 15 degrees; or
- The slope of the two pixels is greater than 15 degrees and the aspect delta between them is greater than 30 degrees.

Flat roofs on buildings less than 100 feet tall are assumed to be subject to New York City Fire Code section 504 rules.

System Size Estimates

Once a roof’s usable area is determined, in jurisdictions with LIDAR data, the optimal system size is determined from either the default energy consumption estimate or the available usable area.

If the building is flat, the assumed power density value of 10 watts DC per square foot is applied to all usable areas. If the building is pitched or a polygon is drawn, the assumed power density value of 14.7 watts DC per square foot is applied to all usable areas. These power densities applied to the usable area of a building produce the estimated max feasible system size.

The optimal system size displayed by the Map’s calculator can be limited by the average monthly electricity cost field, which serves as a proxy for annual energy consumption. The default estimated energy consumption of the building is estimated in kWh based on building square footage (see below). A user can manually change this input. Annual energy consumption is translated into the average monthly electricity cost value by dividing by 12, multiplying by the utility rate, and adding $20 in fixed charges. The default utility rate ($/kWh) is taken from utility data and provided as one of three average rates, auto-selected based on user input, for residential customers, non-residential customers on a non-demand rate, and non-residential customers on a demand rate.

When the average monthly electricity cost is manually adjusted, the estimated annual energy consumption adjusts according to the formula above. For the purposes of determining an optimal system size, the map assumes a kilowatt of solar will generate 1,238 kWh per year, based on PVWatts estimates. (Note: once a system size is determined, the map uses more precise calibrated estimates for system production using PVWatts and Daymet – see below.) If the system size (kW) required to produce the estimated annual energy consumption (kWh) is smaller than the estimated max feasible system size (kW), then the system size required to produce the estimated annual energy consumption is considered optimal.

If the estimated max feasible system size determined from usable roof area is less than the size of the system needed to produce the estimated annual energy consumption, then the estimated max feasible system size determined from usable roof area is provided as optimal. Either of these cases can be overridden manually.

Because optimal system size is closely tied to energy consumption, it is important to update your average monthly electricity cost to the approximate average monthly bill that you pay. Exact installation requirements and regulatory limitations include a number of criteria that cannot be evaluated based on available data, and the actual usable area on any rooftop is likely to differ slightly from this estimate. NYC Fire Code setbacks and allowances have been incorporated into map assumptions regarding available roof space. Additionally, setbacks from the roof peak that are commonly required in other jurisdictions around New York State have also been incorporated into map assumptions. However, please consult with a NABCEP-certified installer for a site survey to determine how much viable square footage is available for a solar system.

Solar Potential and Payback Calculator

The NY Solar Map contains a calculator that allows users to estimate the environmental and financial benefits of a solar energy system. The output of the calculator depends upon user inputs as well as the assumptions listed below.

**Disclaimer**: information provided to users through the solar calculator is provided on an as is basis. CUNY does not guarantee the accuracy of information regarding solar energy system performance, incentive eligibility, or financial returns of any investment.

Solar PV System Costs

**Installed Cost:** The installed cost of solar PV varies significantly depending upon site conditions, as well as changes in the market. As such, users are able to override the default cost and enter the appropriate values. The installed cost defaults to the average cost per watt in the local county over the past year for either residential or non-residential installations, based on the user’s selected user type. This data is reported from NYSERDA’s NY-Sun incentive program.

**Inverter Replacement:** The calculator assumes inverter replacement is required after 10 years. Assumed inverter replacement cost is assumed to be $0.15/Watt. Note: actual inverter lifespan and replacement cost depends on the make and model of the inverter. Microinverters and DC optimizers are often warrantied for 25 years while string inverters are commonly warrantied for 10-12 years.

**Operations and Maintenance (O & M):** Calculator assumes annual O&M costs are 0.3 % of total installed cost. Source: US Department of Energy. Solar Energy Technologies Program: Multi-Year Program Plan 2007-2011.

Incentives for Solar

There are federal, state and local incentives for installing solar in New York State, depending on the jurisdiction. The NY Solar Map calculator includes the following incentives: 30% Federal Tax Credit, Federal MACRS, NYSERDA NY-Sun capacity-based incentives, the New York State Tax Credit, and the NYC Property Tax Abatement. Pictured below is the assumed timetable for monetizing incentives. Note that the calculator assumes system owner has sufficient tax liability to take advantage of all tax incentives as soon as they are available.

Incentives Timetable | Year 1 | Year 2 | Year 3 | Year 4 | Year 5 | Year 6 | Year 7 |

NYSERDA NY-Sun Incentive | 100% | ||||||

Residential State Tax Credit | 100% | ||||||

NYC Property Tax Abatement | 25% | 25% | 25% | 25% | |||

Federal Tax Credit | 100% | ||||||

MACRS + 50% Bonus Depreciation in Year 1 | 60% | 16% | 9.6% | 5.76% | 5.76% | 2.88% |

For details regarding the incentives listed above, please see the Solar Incentives Page.

Taxes Due on Incentives

**Commercial:** Calculator assumes commercial customers pay income taxes on the NY-Sun incentive. Therefore, the total installed cost of a PV installation is the basis for calculating the federal tax credit. Source: Rickerson et al. CALCULATING THE IMPACT OF FEDERAL, STATE, AND LOCAL PHOTOVOLTAIC INCENTIVES USING THE RETSCREEN SOFTWARE: A Guide for New York State Projects. July 2009.

**Commercial federal income tax rate:** 35%

**Residential:** Assumes residential customers pay federal income tax on the State Tax Credit, but NOT on the NY-Sun incentive. Therefore, federal tax credit for residential systems is 30% of installed cost minus the NY-Sun incentive^{1}.

**Residential federal income tax rate:** 25%

**Modified Accelerated Cost Recovery System (MACRS):** Calculator assumes that basis for determining tax deductions is the total installed cost minus 50% of the federal tax credit, or 85% of the total installed cost of the system. Model does not include state depreciation. Source: Rickerson et al. CALCULATING THE IMPACT OF FEDERAL, STATE, AND LOCAL PHOTOVOLTAIC INCENTIVES USING THE RETSCREEN SOFTWARE: A Guide for New York State Projects. July 2009.

Financing Options

**Loan:** The default values for the calculator’s loan financing option are:

- Amount: Cost of system after NY-Sun rebate
- Down payment: 0%
- Life: 10 years
- Rate 6%

The monthly loan payments are determined via the formula: (-[monthly interest rate]*[monthly compounding interest rate])/(1-[monthly compounding interest rate])

**Lease:** The default values for the calculator’s lease financing option are:

- Term: 20 years
- Escalation: 1% annually
- Termination option: Renew lease

The monthly lease payments are determined by a formula that utilizes estimated annual solar savings for a purchased system. These savings are based on the estimated annual energy production of the system and the estimated annual energy consumption of the user. Excess generation above annual consumption is credited at the avoided cost of power rate of $.04/kWh. Generation less than the annual consumption is credited at the full utility rate for the selected region and user type with assumed panel degradation of 0.5% and utility rate escalation of 2.5% per year. These assumptions yield an annual solar savings value. Lease payments are determined via the formula: ([Average annual solar savings value over 25 years]/12)*0.55.

**PPA:** The default values for the calculator’s PPA financing option are:

- Term: 20 years
- Escalation: 1% annually
- Termination option: Renew PPA

The PPA rate is estimated as ([Gross system cost]-[NY-Sun incentive]-[ITC value]-[MACRS value])/[Total solar savings over lifetime of PPA]

Map Layers

Installed Capacity by County - constructed from NYSERDA data (updated weekly).

NYC/Westchester Solar Radiation - constructed from NYSERDA data (updated weekly).

Statewide Solar Radiation

Installed Capacity by County - constructed from NYSERDA data (updated weekly).

Cost Per Watt by County - constructed from NYSERDA data (updated weekly).

Completed Systems by County - constructed from NYSERDA data (updated weekly).

Num Approved But Not Completed by County - constructed from NYSERDA data (updated weekly).

Capacity Approved But Not Completed by County - constructed from NYSERDA data (updated weekly).

Installed Capacity by City/Town - constructed from NYSERDA data (updated weekly).

Unified Solar Permit Map - constructed from Sustainable CUNY research (updated quarterly).

Net Metering Capacity Available - constructed from Sustainable CUNY research (updated quarterly).

Solar Incentives: Commercial/Industrial - constructed from NY-Sun Data (updated quarterly), see NY-Sun website for more details.

Solar Incentives: Residential/Small Commercial - constructed from NY-Sun Data (updated quarterly), see NY-Sun website for more details.

Solarize Programs - constructed from Sustainable CUNY research (updated quarterly).

Solar Statistics

Solar Statistics are constructed from NYSERDA data (updated weekly).

Installed capacity in MW

Projects in queue versus completed

Local cost/watt vs state average

Installed capacity in MW

Completed projects by sector

Local cost per sector

^{1 Source: Rickerson et al. CALCULATING THE IMPACT OF FEDERAL, STATE, AND LOCAL PHOTOVOLTAIC INCENTIVES USING THE RETSCREEN SOFTWARE: A Guide for New York State Projects. July 2009.}