How Dwellvance Calculates Solar Production, Savings & Payback

What the Solar Calculator Is Designed to Do

The Dwellvance Solar Calculator is designed to help homeowners understand the potential size, production, financial savings, installation cost, and simple payback of a residential solar project.

It is a planning and educational tool. It is not an engineering design, installer proposal, utility approval, structural assessment, or guarantee of energy production or financial performance.

Methodology at a Glance

1. Solar Production: NREL PVWatts

Dwellvance uses the National Renewable Energy Laboratory (NREL) PVWatts model to estimate electricity production from a grid-connected photovoltaic system.

PVWatts uses location and solar-system inputs to model expected photovoltaic electricity production. Dwellvance uses the modeled monthly and annual AC production to calculate the production values used elsewhere in the solar calculator.

The production-per-kilowatt value becomes an important input for planning-level system sizing.

2. System Sizing

The current Dwellvance sizing method estimates the system size required to produce an amount of annual electricity equal to the homeowner's annual electricity usage.

The current V1 sizing target is a 100% annual production offset. This is a planning target, not a universal recommendation that every homeowner should install a system capable of producing 100% of annual consumption.

Roof constraints, utility rules, export compensation, future electricity consumption, system costs, and project goals can all affect an appropriate final system size.

3. Production Loss Assumption

Dwellvance uses a 14% default system-loss planning assumption in its solar production methodology. The assumption is informed by the PVWatts methodology but is used by Dwellvance as a planning input rather than as a guarantee of actual project losses.

4. Solar Savings

Dwellvance separates solar electricity production from the financial value of that electricity. The savings calculation considers electricity used by the home and electricity exported to the grid.

This means the same amount of solar production can have different financial value depending on the home's electricity rate and the compensation received for exported electricity.

5. Self-Consumption Assumption

When the calculator needs a planning assumption for the portion of solar electricity used directly by the home, Dwellvance uses a default self-consumption rate of 60%.

The 60% value is a Dwellvance planning assumption for a U.S. residential planning estimate. It is not a measurement of a particular home's actual hourly electricity-use pattern.

6. Export Compensation

Export compensation determines how the financial value of electricity sent to the grid is treated. Dwellvance supports three compensation modes in the calculation model.

The planning-estimate mode should not be interpreted as a verified utility compensation policy. Actual export compensation depends on the applicable utility and program.

7. Electricity Rates

Financial savings require an electricity rate. Dwellvance does not invent a rate when a verified or user-provided value is unavailable.

When the required electricity rate is missing, the calculator can still provide production information, but savings and payback should not be presented as if they were supported by a verified financial input.

This separation is intentional: a production estimate and a financial estimate are different calculations with different input requirements.

8. Solar Installation Cost

When a homeowner does not provide an installation cost, Dwellvance uses a residential solar planning benchmark from the U.S. Department of Energy.

These figures are planning benchmarks, not guaranteed market prices, installer quotes, or site-specific project costs.

If a homeowner enters an installation cost, that user-provided value takes precedence over the planning benchmark in the calculator's cost calculation.

9. Incentives and Net Installation Cost

If a homeowner enters a known incentive amount, Dwellvance subtracts that amount from the installation cost when calculating net installation cost.

The calculator does not assume that a homeowner automatically qualifies for a particular incentive. Incentives should be entered only when the applicable amount is known and verified for the project.

10. Simple Solar Payback

Simple payback compares the estimated net installation cost with estimated annual solar savings.

For example, if a project has a $18,000 net installation cost and estimated annual savings of $2,000, the simple payback is:

This is an illustration of the formula, not a prediction of the payback for a particular homeowner.

11. Long-Term Projections

Dwellvance can show cumulative savings and cumulative net benefit over 5, 10, 15, and 20 years using the calculated annual savings and net installation cost.

These are simple constant-savings projections, not financial forecasts. The current calculation does not model panel degradation, future electricity-rate changes, maintenance, financing costs, discount rates, or other changes that can affect long-term economics.

What the Solar Methodology Does Not Currently Model

Why Dwellvance Separates Estimates From Verified Inputs

Solar economics can look precise even when one of the underlying inputs is uncertain. Dwellvance therefore distinguishes between modeled production, planning assumptions, user-provided values, and verified financial inputs.

This approach is intended to make the result easier to understand and harder to misinterpret. A calculator should not create false precision simply because it can display a number.

Primary Data and Methodology Sources

Dwellvance also documents its planning assumptions and calculator behavior in its broader methodology and data-source documentation.

Use the Methodology With the Solar Calculator

The best way to interpret a Dwellvance solar result is to review the assumptions alongside the estimate. Start with your actual electricity usage and provide verified financial inputs wherever possible.