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Home » Blog » Right choice of PV power plant

If you for a number of reasons (economy, ecology, power lines accidents) have thought of questions of renewable power use, namely generation of the electric power due to energy of the Sun, and at the same time you are not the graduate of power faculty in the technical university, the radio fan or the engineer with a 20-year experience, then you have at least 2 ways to define an optimum configuration of the necessary equipment: a way N#1 = simplest one — to address to specialists; a way N#2 — for people who want to master personally. If you have read up to this place and have decided to count personally: for calculation it is necessary to start the sheet Microsoft Excel, to open a notebook, or to prepare the clay plate. So, algorithm of a Solar Power Plant (further SPP) configuration choice:

Selecting the type of PV power station

At this stage it is necessary to decide for what specific goals you need your solar power plant:

The large on-grid solar power plants intended for power generation with the subsequent its sale to the state on so-called Feed-in-Tariff.

— Energy saving PV power plants generats electricity is made at the expense of solar radiation, partially replaces the electric power from the main grid. So, there is a direct dependence meanwhile, what share from the general energy consumption will be replaced by energy of SPP and in how many time less bill for the electric power to you will arrive.

— Intellectual solar farms for power saving and accumulation of the electric power. PV power plants of this type not only save the electric power, but also can accumulate it. This system will carry out also a role of uninterruptible power supply unit and the power filter.

The solar power plant power choice is a balance search between your desires and opportunities (financing, the available area and so on), which is regulated by several basic rules. For FIT solar farms power choice is limited only to the available volumes of finance and the available area. Before calculations power saving PV plants it is necessary to solve, whether you are going to sell excesses of the electric power using «green» tariff? Approach to calculations depends on this choice. This phenomenon is caused by surprising hostility of the company NEK «Ukrenergo» in unlicensed sellers of the electric power. That is, if in case of absence of the contract for a «green rate», and the power of SPP is picked up incorrectly (so that at any moment, generation is more than consumption), and the power supplying company will find an illegal overflow in its network, the economy can turn back lawsuit. For this reason it is important to observe accurately further recommendations for own calculations.

Algorithm of a SPP power choice:

1. We calculate quantity of the year consumed electric power of kWh/year (further Ep);

2. At desire to sell excesses of energy on a «green rate» we divide Ep on N — average annual number of maximum power generation hours (1070 — 1200 depending on area). We receive the optimum power of SPP (Ropt).

Ropt = Ep/1100 kW;

3. If you don’t want to sell excesses of energy on a «green rate», it is possible to add system with the power overflow monitoring system (POMS), which will not allow your electric power to overflow in the main grid. Or you can to calculate SOLAR POWER PLANT so that its power generation was ALWAYS less consumption.

3.1. When using POMS we calculate SPP power on next way: Popt (SPP optimum power) has to make 50% −60% of the power received in point 2:

Popt = (0,5÷0,6) * Ep/1100 kW;

3.2. In case of refusal from use of «a green rate» and POMS: it is necessary to calculate the minimum energy consumption during a summer season in the period of time from 10.00 till 15.30 (further Emin), kWh. It is necessary to consider thaton the days off and holidays the power consumption falls. SPP power is calculated:

Ropt = (0,75÷0,85) * Emin kW;

It is necessary to notice that specialists of the Rentechno company NOT RECOMMEND this approach to calculation of SPP power.



Intellectual solar power plant for power saving and accumulation of the electricity

The design of intellectual autonomous solar power plants differs from the previous types of «on-grid» systems, and conditionally consists of two parts or subsystems: PV modules array with charge controllers and off-grid (autonomous) inverter. Now we will consider algorithms of each of subsystems construction choice:

1) Define quantity of the electric power consumed by you within a year, kWh/year (further Ep).

2) Define average daily electric power consumption for summer and winter seasons (Es and Ew), for predesigns, it is possible to accept their equal among themselves and to calculate the next ways: — Take the electric counter data of the consumed electric power within several days and calculate an arithmetic average; — Take the monthly electric power bill and to divide on 30 or 31; — For new construction it is necessary to make the list of the following look — the name of electric equipment; its power P, kW; quantity of units N; an equipment operating time for day t, hours. Multiplication of positions PxNxt with the subsequent summing of results for all electric equipment will allow receiving desirable quantity of daily electric power consumption of kWh/days.

3) Let’s calculate the necessary power of PV modules. There are some options of approach to a power choice:

— Reach full autonomy of a power supply system of the house in independence from a season (in the winter SPP power generation 3 times less, than during the summer period):

РPVM =(0,95÷1,05)* Еs/1,5 kW;

Advantage of this approach is that you become completely autonomous from the main grid. Rolling blackouts and accidents on the power transmission line do not excite you anymore. Disadvantage — in the summer, more than a half of time SPP will work in the single mode in connection with considerable excess of energy.

- Reach partial autonomy of the house when solar energy during the summer period completely covers the house power needs, and during the winter period — partially:

РPVM = Еs/4,5 kW. Advantage of this approach is that all solar electric power will go to a covering of consumption and capital investment will be much less.

4) Inverter type and power choice:

The inverter power is defined by the power of electric devices which are powered from it. As parallel work with a network for this type of inverters is impossible, in case of excess of consumers load over the inverter rated power- protection will work and the inverter will be switched off.

The second way is removal the electric counter data for 1 hour of work in the period of the maximum power consumption.

5) Choice of number of accumulators in Battery Bank:

We can calculate number of accumulators on the following formula:

NBB= Еs*3/2400

The received number needs to be rounded to the next number, multiple 2. The received digit means number of the accumulators necessary for accumulation the quantitie of energy, that house consumes during 1 day.

In a case when all power consumers of the house do not need to be connected to the uninterrupted power source, we can calculate number of accumulators on the following formula:

NBB = Pn*t*3/2400, where Pn, kW — power of the equipment, which work must be reserved by means of accumulators; t — operating time of this equipment.



Choice of a place and mounting mode of solar power plant

It is possible to place an array of solar modules anywhere, it is necessary to follow some basic rules only: — The generating surface of PV modules as far as it is possible, should be turned on the South; — Shadowing of PV modules should be minimum; — PV modules should not be subject actions of the increased temperatures.

Let’s consider ways of calculation of the necessary area for solar PV modules installation. Depending on the location, the necessary area is calculated multiplication of the wished power on coefficient of placement of k: — At land placement, k = 14,8; — At placement on a flat roof, k = 12,6; — At placement on a cattle roof, k = 6; — At placement on biaxial dynamic tracker systems (one tracker is expected placement of 5 kW of PVM) k = 40.



Rentechno's leading PV system engineer, Alexey Fedyuk


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