How to predict the roof load before installing PV power plant?

- Aug 09, 2018 -

With the rapid development of the photovoltaic industry, the number of PV power plant installations is increasing day by day, and how is the roof load of photovoltaic power generation predicted? What are the classifications of photovoltaic power roof load? How much do you know about the roof load of photovoltaic power generation?

When the development of distributed photovoltaics is in full swing, the problem of roof load of distributed photovoltaic projects, especially the load problem of steel structure color steel tile roof which is easy to form a large project scale, has become the most important pain point in project development. Before the proof of the load is issued, how to predict the bearing capacity of the photovoltaic power generation roof to roughly determine whether it meets the requirements of the photovoltaic project?

1. Classification of photovoltaic power roof load

Classified by time: permanent load (constant load), variable load (live load), accidental load (special load or accidental action). The photovoltaic power plant system is a new constant load.

Classification of active surface sizes: uniform load, concentrated load, linear load.

Classification of action direction: vertical load, horizontal load.

2. Loads involved in roof distributed photovoltaic projects

The weight of the roof roof solar mounting structure: the weight of the reinforced concrete floor, the weight of the roof steel beam, the weight of the roof insulation, the weight of the roof insulation and the original weight of the roof and the equipment (constant load).

Photovoltaic power plant system load: PV modules, solar mounting brackets, foundations, cables, combiners, etc. (belonging to new constant loads).

Wind, rain, and snow loads: The wind, rain, and snow loads are increased due to the construction of photovoltaic power plants.

Construction load (late operation and maintenance load): During the construction phase, the impact of the equipment, such as lifting, transportation, construction personnel, construction equipment, etc., is a live load.

Earthquakes are not a load, and earthquakes are a kind of function. For the regulations and check calculations of earthquakes, see GB50011-2010 "Code for Seismic Design of Buildings".

3. Predicting the load

Simulation calculation of drawings: Through the structural drawing of the building, use software (such as MTStool, rational structure toolbox, etc.) to initially calculate the main force components (such as purlins, slabs, etc.).

Site survey: The actual building is compared with the design drawings, and the new load outside the design drawing or the load changed due to the later expansion and expansion is found.

Outdoor: Equipment room, elevator room, air conditioner or antenna equipment, fire or ventilation pipes, etc.

Indoor: whether there is a large area of water leakage, beam plate column cracking, rust and damage, new ceiling members, roof interior hanging equipment, roof opening, new indoor track cranes, etc.

If you want to obtain reliable load data, you should go through the site survey, combined with the actual load on the site, and then perform the system modeling and other system accounting.

4. Predicting the load on concrete roof

Reinforced concrete roofing: The acceptance rate of the bearing capacity of the newly added photovoltaic system is greater than 80%. The solar panel mounting structure is more suitable for installing photovoltaic power generation systems.

Paying attention to the problems: privately built buildings, old buildings with long-term construction, tofu projects with cut corners, and private expansion and expansion have affected the original building structure, and communicated with the homeowners. Is there any roof structure renovation and expansion plan in the future? .

Concrete prefabricated roofing, prestressed double T roofing, and saddle roofing, by selecting suitable installation forms, such as proper reduction of installation inclination, avoidance of sensitive areas, installation of deflectors in arrays, reduction of weight and weight of weights, etc. A photovoltaic power plant system can be installed.

The concrete roof photovoltaic system is installed according to the optimal inclination angle of the single-row assembly, and the concrete weight is considered to be about 0.45KN/m2.

5. Predicting the load of metal roofing

Metal roofing: The pass rate of the new photovoltaic system is less than 50%. The structural bearing capacity is insufficient, and it needs to be carefully checked before use.

Focus on the question: whether it is designed for the formal design unit, whether the original design drawings can be obtained, whether it is built privately, whether the steel grade has been replaced during the construction period, and the private expansion and expansion affects the safety of the original building structure and communicates with the homeowner whether the future There is a plan to renovate and expand the roof structure.

The color steel tile roof solar mounting system is installed on the slope of the roof of the roof according to the component, and the bracket strip is clamped on the metal roof corrugated board, about 0.15KN/m2.

6. Rapid pre-judging method for metal roof load

Experience method one:

The design of informal design institutes, the construction of informal construction units, and the construction of drawings without drawings or drawings are basically unusable. Because its structure is uncontrollable, there are many hidden dangers in barbaric construction, and the materials are shoddy. For example, Q235 material is used instead of Q345 material.

Experience Method 2:

The span of the purlin is about 6 meters, the model of the purlin is less than 180, and the accounting is easy to exceed the limit;

The span of the purlin is about 8 meters, the model of the purlin is less than 220, and the accounting is easy to exceed the limit;

When the span of the purlin is more than 6 meters and the strip between the purlins is only one, the purse is easy to be laterally unstable.

The above is mainly for pre-judging the common type of steel frame structure of the C-type or Z-type purlin. In the above case, the stress ratio exceeds the limit or the deflection exceeds the limit.

The above methods are only for reference during development. In the actual design of photovoltaic power generation projects, the design of the roof, especially the color steel tile roof, should be verified by the design institute to ensure the safety of the project.

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