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How to judge solar energy resources in a place
- Apr 20, 2018 -

In the development of photovoltaic power plant projects, solar energy resource conditions should be one of the preconditions most concerned by investors. Because photovoltaic power generation depends on the weather, solar energy resources conditions directly determine the benefits of your project. How should we judge solar energy resources in a place?

First, the source of solar radiation data

There are many sources of solar energy data and the costs paid are not the same. Therefore, I always believe that different resource data can be used at different stages. According to the progress of the project, talk about the evaluation of solar energy resources.

1, pre-site selection stage

Before deciding to invest in photovoltaics in a certain place, the landlord must first determine roughly whether the local resource conditions can guarantee project profitability. Most homeowners have no financial resources at this time, and they do not have the money to purchase resource data. Therefore, it is necessary to use some free data, such as satellite data.

At present, the more commonly used satellite data is NASA and Meteonorm. Through the latitude and longitude coordinates of the project, the total amount of radiation at or near the site can be read for free. Using this resource data and the basic cost of the current photovoltaic power plant, it is possible to roughly estimate the project revenue. Although it is a relatively crude number, it is worth knowing whether or not it is worthwhile to continue investing in energy.

There are many other ways. 1) Now many websites provide software for fast-track measurement of photovoltaic power stations. As long as you enter locations, you can get project benefits. For example, comparing the "PV Bao" of the fire depends on the powerful database behind it. (From the design of the power station to the prediction of power generation and yield, it feels very powerful!) 2) If you have a power plant that is already built near the site you are selecting, and you have a good relationship with people, you can go and inquire about the measured resource data of the power plant. .

2. Feasibility study stage

Through the judgment of the previous step, the basic decision to be made here is to conduct a solid resource analysis, that is, a feasibility study of the project. According to the regulations, solar energy resource data should collect radiation data of each month for the last 30 years of the weather station, sunshine hours data, and measured radiation data of the project site for one year (weather stations and sites must have one-year data). Although there are few local changes in solar energy resources, I have always believed that accurate on-site observations are very necessary. It is generally believed that if the weather conditions in the two areas are basically the same (elevation, surrounding conditions, etc.), data within 50 km can be used.

1) 30-year data from weather stations

The number of meteorological stations with radiation observation in China is relatively small, and the weather stations near the project site often have no radiation observation data. In this case, the method of "climate method extrapolation" is generally used. In general, the sunshine hours or the percentage of sunshine is the monitoring data that every weather station has. Therefore, it is possible to make use of the percentage of sunshine in the two places and the total astronomical radiation.

There are three databases for solar radiation data in China: CMA Solar Radiation Database 1 (measured data), CWERA Solar Energy Resource Assessment Database 2 (climateological method derivation), and CWERA Solar Energy Resource Assessment Database 3 (satellite data). Therefore, if you do not have measured data at a weather station near you, you can obtain data using the “climateological method”.

2) Site measured data

The measured data of the site must rely on the owner's own observation. I have obtained a lot of measured data, but it is rarely accurate, and it is very different from the actual value. I discussed this issue with some experts seriously and felt that the measured data on the site was inaccurate. There were three main reasons:

Instrument quality problems. This question will not be discussed.

No calibration. Before using the metering equipment, it is best to do a calibration by the Multinational Meteorological Administration, otherwise the results may drift overall.

Poor maintenance. Meteorological station instruments are maintained by professionals every day. Some of the on-site observation equipment I saw was in the wild mountains and no one had to maintain it.

Second, the significance and role of each data

Collecting so much data, how do we use it?

Total radiation data for 1 and 30 years

The total radiation data is the most fundamental resource data, and it is also the basis for our calculation of power generation. Generally we will pay attention to four indicators:

1) Long-term trends. The operation period of the PV power plant is 25 years, and the owner must know what the local solar energy resources are in the long run.

Calculate the average of 30 years, 20 years, and 10 years.

If they are basically the same, the local resources are relatively stable and can be calculated using 30 years of data. If the downward trend is significant, it may be more accurate to use the data of the last 10 years.

2) Interannual stability. I usually calculate the relative deviation. Solar energy resources are divided into years and years, and the predicted power generation is an average value. Owners need to understand how the actual and predicted values of the project's annual electricity production may change within a certain range.

3) The size of the value. In a specific location, the value is large and the power generation is large; the value is small and the power generation is small.

4) Stability during the year. The ratio of the smallest month to the largest month. Through this value, we can determine the extent of changes in solar energy resources within a year.

2, direct ratio

The direct ratio should be a very important parameter, but since only one station has direct radiation observations, this parameter is always ignored.

Photovoltaic power generation mainly depends on direct radiation. With the same amount of radiation, the amount of positive power generated by direct irradiation is relatively large. The inclination angle of our fixed support is based on the incident angle of sunlight throughout the year. In places where the direct ratio is high, the angle of inclination of the matrix will be larger; where the ratio of direct radiation is low, the angle of inclination of the matrix will be smaller.

3, 30 years of sunshine hours data

1) Reflect the local solar energy situation. Radiation = sunshine hours × irradiance. Therefore, solar energy resources will be relatively good in places where sunshine hours are long.

2) Computation of climatological methods. According to the local latitude and longitude, the “astronomical radiation amount” and “lightable hours” of the site can be calculated; the sunshine percentage can be obtained from the measured sunshine hours and the available hours; using the reference station, the a and b coefficients can be calculated. In this way, the radiation amount can be calculated!

3) Design. Although the winter solstice day is the shortest day of sunshine, if the local average sunshine time in December is 7 hours, it would seem impossible to say that if you consider designing to ensure that there are no obstructions for 6 hours.

4. Field measurement data for 1 year

Only after self-testing the data at the site and comparing it with the weather data of the weather stations at the same time, the resource analysis work is solid and the results are the most accurate. The owner’s heart is practical.

5, other weather data

Temperature, wind speed, and the depth of frozen soil are all important meteorological parameters in the design and are not repeated here.