# Solar Estimator: Use of PVWatts

Solar & Wind Energy Calculations

Solar Estimate has created an improved solar calculator by taking the production data provided by PV Watts and adding information about the average cost of installed solar systems and also up to date information about solar rebates and solar incentives that you are entitled too. This means the solar estimate solar calculator can give you a more accurate idea of the financial returns from going solar not just the amount of energy that a solar system will produce.

Our Solar & Wind Energy Calculator and financial analysis software is driven by **PVWatts** together with our extensive databases of solar and wind ratings, regional weather conditions, applicable solar and wind incentives and utility rates.

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## Solar Calculations: PV Watts analysis

**Solar Electric (PV):** We use PVWatts to help develop solar energy calculations: analyze solar ratings and photovoltaic (PV) array performance for a given location. Then our solar analysis software sizes your system, estimates cost, applies local, state, federal and utility tax, purchase and use (power production) incentives. Finally, the solar estimator outputs a summary of results, including detailed financial analysis of a solar electric (PV) system suggested to meet your needs at your specific location.

**Solar Thermal (water, pool, spa heating):** We use PVWatts to determine solar ratings for a given location. Then the solar estimator software pulls from our extensive database of local weather data to estimate monthly low, mean and high temperatures at your location to make solar energy calculations. The solar estimator then sizes your solar thermal system, estimates cost, applies local, state, federal and utility tax, purchase and use (power production) incentives. Finally, the solar estimator outputs a summary of results, including detailed financial analysis of a solar thermal energy system to meet your needs at your specific location.

### About PVWatts

PVWatts is a solar energy system performance calculator for Grid-Connected PV Systems.

PVWATTS calculates electrical energy produced by a grid-connected photovoltaic (PV) system. Researchers at the National Renewable Energy Laboratory developed PVWATTS to permit non-experts to quickly obtain performance estimates for grid-connected PV systems within the United States and its territories.

In a grid-connected PV system, PV modules, wired together to form a PV array, pass DC electricity through an inverter to convert it into AC power. If the PV system AC power is greater than the owner's needs, the inverter sends the surplus to the utility grid for use by others. The utility provides AC power to the owner at night and during times when the owner's requirements exceed the capability of the PV system.

## Wind Calculations: Wind Resource Data

For wind turbine calculations we utilize a wind rating based upon the average monthly wind speed (m/s) near your location (nearest latitude and longitude derived from your postal code or zip code). Our data reference source is the NASA Surface meteorology data from the Atmospheric Data Center. This data is based upon satellite-derived data over a 22-year period. The data is compiled for each degree of latitude and longitude (each degree represents about 69 ground miles).

#### Weibull Shape Factor

We use the Weibull distribution to estimate the energy recovered by a wind turbine using a shape factor (λ). We default to a shape factor of 2 (the "Rayleigh" distribution). The higher the value of shape factor (from 1 to 3) the higher the median wind speed - i.e. locations with lots of low wind speeds as well as some very strong winds would have a value of shape of below 2, locations with fairly consistent wind speeds around the median would have a shape value of 3. Typical Weibull distributions are shown below. On this graph, one (1) represents the average and the graph shows how wind speed is expected to vary in probability around that average.

**Rayleigh Distribution** (where λ = 2) is shown below.

Suggested Books to Help You Learn More | ||
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Photovoltaics |
Solar Water heating |
Wind Energy |