Distributed rooftop PV survey belongs to the preparatory work of the project. Through on-the-spot investigation, it collects relevant information on the roof to prepare for the follow-up plan design and investment income analysis. The actual roof structure is diverse, and the owners are also very concerned about the feasibility of rooftop photovoltaics, installed capacity, investment returns, and cooperation models.
1, local resources
Distributed photovoltaic site selection should give priority to areas with large solar radiation, less rainy weather and less pollution. If the company is close to the sea, it is necessary to consider anti-salt spray, anti-corrosion and anti-typhoon measures; in areas where the company is located, dust and sand should be taken into account and measures to increase cleaning should be taken; if it is in cold regions, it is necessary to consider antifreeze and snow removal measures.
2. Local PV Support Policies
In order to promote the development of distributed photovoltaics, local governments have issued support policies at the provincial, municipal and even county levels. Project developers need to be familiar with these policies in advance in the early stage of project development. As a photovoltaic industry that currently needs government subsidies, the subsidy policy has a direct impact on distributed returns. Therefore, distributed projects with good local policies should be developed in priority.
For example, in the 13 years of Jiaxing Photovoltaic Industrial Park's personal distributed photovoltaic power generation project, Jiaxing Photovoltaic Industrial Park will give a subsidy of 2.8 yuan per degree for a period of 3 years, a drop of 0.05 yuan per year. At that time, according to this subsidy, distributed photovoltaics could recover investment in three and a half years!
3, the strength of the company and the industry
The life span of PV power plants exceeds 20 years. When the development of distributed power plants requires the examination of the existence of owners, priority should be given to the cooperation of owners with strong corporate strength, good industry prospects, and standardized business operations and formal finances.
The nature of the enterprise is preferably that of state-owned enterprises, listed companies, and foreign companies. These enterprises have a high degree of credit and generally do not have problems in the collection and settlement of electricity charges in the later period.
The business of the owners’ companies also has an impact on the construction of distributed photovoltaic power plants. If companies produce flammable and explosive dangerous goods, emit corrosive gases, emit large amounts of smoke, etc., they are not suitable for building distributed photovoltaic power plants.
The industrial and commercial roofs with high electricity consumption are among the best roof resources, such as large industrial enterprises, shopping malls, etc.; followed by owners with low electricity consumption and low electricity prices, such as schools and hospital roofs, municipalities. Building Hall, logistics center roof and so on.
4, the building roof situation
The ownership of buildings, design life, material, area and orientation also directly affect the feasibility and installation of distributed PV power plants.
If the property rights of the building belong to the owner of the enterprise or the local government, it is suitable for development; the leased plant is not suitable. At the same time, the roof of an industrial plant is generally a color steel plate. During the development of the project, it is necessary to understand the length of time the roof can be used, and the time limit is too short to be suitable for development.
The roof area of ​​a single company or a roof with a total area of ​​no less than 10,000 square meters (approximately 1MW can be installed). At the same time, it is necessary to measure the azimuth of the roof, the angle of inclination of the roof, and the height of the surrounding obstructions such as the parapet in order to determine the installed capacity of the system and the amount of power generation at a later stage.
5, building roof load
Roof load is divided into constant load and variable load.
The constant load refers to the weight of the structure and the dust load. The photovoltaic power plant needs to operate for 25 years, and its own weight belongs to the constant load. Generally, the photovoltaic system of a steel structure factory will increase the weight of 15 kilograms per square meter, and the roof of the brick-mix structure will increase the weight of 80 kilograms per square meter. During the project inspection, it is necessary to pay attention to the design value of the constant load in the architectural design instruction, and to determine whether or not to add additional loads such as pipes, lifting equipment, roof attachments, etc., in addition to the weight of the roof, and to determine whether the constant load is adequate. Quantity can install photovoltaic power plant.
The variable load is a load that is temporarily applied to the roof considering limit conditions, and is divided into wind load, snow load, earthquake load, live load, etc., and cannot be occupied. Under special circumstances, live load can be used as an option to share the load of photovoltaic power station, but it can not occupy too much and requires specific analysis.
When the project is inspected, the project developer is required to obtain the house structure from the owner to facilitate the calculation of the roof load.
6, roof bracket type
The roof of the building is mainly composed of colored steel tile, ceramic tile and steel mixed. The color steel tile is divided into a standing seam type, a bite type, a snap type, and a fixed type connection type. The first two require special adapters, and the latter two need to be fixed by drilling. The ceramic tile roof can use special adapters, or it can not be fixed with the roof, and be attached to it with its own weight and roof slope; the steel-concrete structure roof needs to make brackets. Foundations, foundations and roofs can take root or they can not take root. The key considerations are roof waterproofing, wind load resistance, roof design load and other factors.
7, distribution facilities and network points
The distribution equipment is one of the basis for the selection of grid-connected PV power plants. The main examination contents are:
1) Plant transformer capacity, quantity, bus coupler, load ratio, etc.;
2) Factory meter position, busbar specifications, switch specifications, etc.;
3) Whether the factory area is equipped with an independent power distribution room, and whether there is a backup interval for the power distribution equipment, if not, whether the busbar can be crimped;
4) Give priority to users with large transformers and large load ratios;
5) Check the capacity of the main switch into the line, consider the issue of income, the output current of the photovoltaic power generation system should not exceed the capacity of the household switch;
6) Considering the principle of convenient and costly cabling, consider the installation position of the inverter and the cabinet.
8, user power consumption and electricity prices
The most important issue of distributed photovoltaic power generation projects is the local consumption of generated electricity, so it is necessary to examine:
1) The company's annual, monthly and daily electricity consumption, electricity consumption during the day, peak hours and proportion of electricity consumption;
2) The price of electricity used by enterprises and the weighted price of electricity during the day.
9. Distributed photovoltaic development model
Distributed photovoltaic development model is mainly negotiated with the roof owners to determine the specific cooperation methods, the main model is to have a preferential price model, roof rental model. Need to comprehensively consider the project investment income, the owner's wishes and other factors to determine the investment development model.
A ball check valve is a check valve in which the closing member, the movable part to block the flow, is a spherical ball. In some ball check Valves, the ball is spring-loaded to help keep it shut. For those designs without a spring, reverse flow is required to move the ball toward the seat and create a seal. The interior surface of the main seats of ball check valves are more or less conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow.
Ball check valves are often very small, simple, and cheap. They are commonly used in liquid or gel minipump dispenser spigots, spray devices, some rubber bulbs for pumping air, etc., manual air pumps and some other pumps, and refillable dispensing syringes. Although the balls are most often made of metal, they can be made of other materials, or in some specialized cases out of artificial ruby. High pressure HPLC pumps and similar applications commonly use small inlet and outlet ball check valves with both balls and seats made of artificial ruby, for both hardness and chemical resistance. After prolonged use, such check valves can eventually wear out or the seat can develop a crack, requiring replacement. Therefore, such valves are made to be replaceable, sometimes placed in a small plastic body tightly-fitted inside a metal fitting which can withstand high pressure and which is screwed into the pump head.
There are similar check valves where the disc is not a ball, but some other shape, such as a poppet energized by a spring. Ball check valves should not be confused with Ball Valves, which is a different type of valve in which a ball acts as a controllable rotor to stop or direct flow.
A diaphragm check valve uses a flexing rubber diaphragm positioned to create a normally-closed valve. Pressure on the upstream side must be greater than the pressure on the downstream side by a certain amount, known as the pressure differential, for the check valve to open allowing flow. Once positive pressure stops, the diaphragm automatically flexes back to its original closed position.
A swing check valve or tilting disc check valve is check valve in which the disc, the movable part to block the flow, swings on a hinge or trunnion, either onto the seat to block reverse flow or off the seat to allow forward flow. The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle. Although swing check valves can come in various sizes, large check valves are often swing check valves. The flapper valve in a flush-toilet mechanism is an example of this type of valve. Tank pressure holding it closed is overcome by manual lift of the flapper. It then remains open until the tank Drains and the flapper falls due to gravity. Another variation of this mechanism is the clapper valve, used in applications such firefighting and fire life safety systems. A hinged gate only remains open in the inflowing direction. The clapper valve often also has a spring that keeps the gate shut when there is no forward pressure. Another example is the backwater valve (for sanitary drainage system) that protects against flooding caused by return flow of sewage waters. Such risk occurs most often in sanitary drainage systems connected to combined sewerage systems and in rainwater drainage systems. It may be caused by intense rainfall, thaw or flood.
A stop-check valve is a check valve with override control to stop flow regardless of flow direction or pressure. In addition to closing in response to backflow or insufficient forward pressure (normal check-valve behavior), it can also be deliberately shut by an external mechanism, thereby preventing any flow regardless of forward pressure.
A lift-check valve is a check valve in which the disc, sometimes called a lift, can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. A guide keeps motion of the disc on a vertical line, so the valve can later reseat properly. When the pressure is no longer higher, gravity or higher downstream pressure will cause the disc to lower onto its seat, shutting the valve to stop reverse flow.
An in-line check valve is a check valve similar to the lift check valve. However, this valve generally has a spring that will 'lift' when there is pressure on the upstream side of the valve. The pressure needed on the upstream side of the valve to overcome the spring tension is called the 'cracking pressure'. When the pressure going through the valve goes below the cracking pressure, the spring will close the valve to prevent back-flow in the process.
A duckbill valve is a check valve in which flow proceeds through a soft tube that protrudes into the downstream side. Back-pressure collapses this tube, cutting off flow.
A pneumatic non-return valve.
Multiple check valves can be connected in series. For example, a double check valve is often used as a backflow prevention device to keep potentially contaminated water from siphoning back into municipal water supply lines. There are also double ball check valves in which there are two ball/seat combinations sequentially in the same body to ensure positive leak-tight shutoff when blocking reverse flow; and piston check valves, wafer check valves, and ball-and-cone check valves.
Check Valves, Water Check Valves, Brass Check Valves, Sanitary Check Valves
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