October 28, 2014

Solar Power Forecasting: Photovoltaic (PV) Energy Production Estimates

Solar energy represents a vast, renewable resource that can be tapped to meet society’s growing demand for electrical energy. Everyone knows that solar can help the planet; many know it can also save money in the long run, but in either case, the question that often comes up is: “how much?” The amount of PV energy a solar array produces can help to answer this question. Solar power forecasting involves knowledge of the sun´s path, the atmosphere’s condition, the scattering processes and the characteristics of a solar energy plant which utilizes the sun’s energy to create solar power.

Solar integrators estimate the PV energy production of a solar array for your building using modeling tools that predict performance based on a variety of factors, such as past weather patterns, system design and other technical parameters. One common and basic tool that can initially be used is the PVWatts calculator provided by the National Renewable Energy Laboratory (NREL). This web application tool estimates the electricity production of a grid-connected roof or ground-mounted photovoltaic system based on a few simple inputs. The solar calculator’s financial analysis is based on energy bill savings you can expect and the net solar system cost after tax credits are applied. Though online tools like the PVWatts calculator have simplified initial performance estimates, the subject still remains much more complex. The field of solar and photovoltaic forecasting is rapidly evolving. An actual site assessment by one of our trained professionals will be needed to determine the actual costs and benefits of installing a solar energy system.

Solar Electric (Photovoltaic) System Calculations

(according to SolarEsitmate.org)

Estimating Solar Electric (PV) System Size

On average (as a general “rule of thumb”) modern photovoltaics (PV) solar panels will produce 8 – 10 watts per square foot of solar panel area. For example, a roof area of 20 feet by 10 feet is 200 square-feet (20 ft x 10 ft). This would produce, roughly, 9 watts per sq-foot, or 200 sq-ft x 9 watts/sq-ft = 1,800 watts (1.8 kW) of electric power.

Converting Power (watts or kW) to Energy (kWh)

One kilowatt-hour (1 kWh) means an energy source supplies 1,000 watts (1 kW) of energy for one hour. Generally, a solar energy system will provide output for about 5 hours per day. So, if you have a 1.8 kW system size and it produces for 5 hours a day, 365 days a year: This solar energy system will produce 3,285 kWh in a year (1.8 kW x 5 hours x 365 days).

If the PV panels are shaded for part of the day, the output would be reduced in accordance to the shading percentage. For example, if the PV panels receive 4 hours of direct sun shine a day (versus the standard 5 hours), the panels are shaded 1 divided by 5 = 20% of the time (80% of assumed direct sun shine hours received). In this case, the output of a 200 square-foot PV panel system would be 3,285 kWh per year x 80% = 2,628 kWh per year.

So with more solar energy coming onto the grid every day, how can you successfully integrate and take advantage of this intermittent resource? Contact us at 855-75-KMBDG. KMB Design Group is at the forefront of the escalating solar industry, and is considered a leading consulting firm in the renewable energy field providing photovoltaic design and engineering services. Licensed in 49 states, we have the ability to work nationally without limitations.