solar_panels_handFor all solar energy investments, from basic roof-top installations to utility-scale photovoltaic systems, the need to accurately determine the solar resource is paramount. The amount and variation of solar radiation at your project site are key factors determining the profitability of your solar investment.

Solar irradiance is the “fuel” of all solar energy systems. Determining the potential of solar radiation at a given site is called "resource assessment".  Two main components of solar radiation are direct normal (or beam) radiation and diffuse radiation. Solar photovoltaic panels convert both types of radiation into electricity. Solar thermal systems, on the other hand, rely mostly on the direct normal radiation. As a rule of thumb, clouds absorb about 20% of the incoming radiation. Thus, determining the long-term characteristics of cloud cover (its “climatology”) is an essential part of solar radiation modeling.

The challenge of finding good solar data

Best investment decisions are made by understanding the characteristics of your solar resource. Unfortunately, finding good quality datasets is one of the biggest challenges of project development. There are very few operational ground stations which measure solar radiation around the world, and getting access to existing datasets is a big challenge. Even if your project site is close to a ground station, research shows that beyond a 25-km radius from a station, satellite-based methods are more accurate.

At Sunmetrix, we use a combination of ground and satellite data to give you the best of both worlds. For long-term average values, Sunmetrix Discover includes a dataset developed by NASA incorporating both ground and satellite measurements. For near real-time analysis, Sunmetrix GO uses its own sophisticated algorithms and satellite imagery to characterize the cloud cover and combine this information with solar radiation models. Satellite data is frequent, goes back to more than twenty years and covers the whole globe. The combined capability of Discover and GO can give you a significant advantage when there are no datasets available for your area of interest, or when the datasets at your disposal are outdated.

Understanding the variation of solar energy

When it comes to renewable energy we are all at the mercy of Mother Nature. Just like wind energy and hydroelectricity, the amount of solar energy available at any given time varies drastically at hourly, daily and annual time scales. Thus, in order to provide an objective evaluation of your solar resource and accurately quantify the energy potential of a site, we need to estimate both the long-term average values and the variation around this average. It’s not unusual to see variations of up to 10% from one year to the next, but over a typical solar investment horizon of 20 years, the annual ups and downs are likely to cancel each other out.

How to make the best investment decisions for solar energy?

Getting your solar resource numbers is important, but it's not the only key factor in making good investment decisions. Financial aspects and technical choices are equally important. Understanding your buy or lease options and government incentive programs are critical for making the best financial decision. Likewise, understanding the technical trade-offs when it comes to panel and inverter selection is critical.

Combining all of these factors (solar resource, financial aspects and technical choices) and making the right decision may look daunting at first. But we are here to help! Stay tuned for many more informative posts in the coming months.

 Image credit: