sizing a pv system.ppt

7/28/2019 Sizing a PV system.ppt

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Sizing a PV system


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Content


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Systems


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Importance


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Steps


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Load evaluation


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Energy use profile of individual

appliances

Refrigerator Energy Consumption Profile


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They are very good candidates to enhance them with smartness.

The intermittent peak electricity use can be shifted in time, in order to reduce the

overall peak energy demand on the grid.

From the household perspective, time-of-use pricing will enable significant

energy bill savings.

However, the DR algorithms have to be implemented without incurringunacceptable consequences for the consumers.

The main benefits of utilities that arise from using DR include:

> automatic energy reduction without any inconvenience to consumers;

> precise control of appliance power usage on a network level a powerful

facility for sharing the load among participating consumers;> a clear, real-time view of the aggregated demand-side energy-saving

potential on the network that enables:

> the prediction of required supply;

> the setting of time-of-use and dynamic energy pricing;

> the ability to minimize the need for purchasing spinning reserve, thereby

lowering costs and significantly reducing carbon emissions

demand response (DR).


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problems related to loads

For all systems (AC and DC supply

systems): A1 - Wrong selection: some loads are non-adapted for

stand-alone PV systems.

A2 - wiring: substandard or inadequate wiring andprotection devices will also cause poor system response.

A3 Low efficiency: low electrical efficiency loads leadto over energy consumption.

A4 - Stand-by loads: stand-by mode of some loads

waste energy. A5 - Start-up: current spikes during the start-up of some

loads can create temporal overload of the system.


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problems related to loads:

Only for AC

AC1 - Reactive power: when appliances withcapacitive or inductive loads are used, realcirculating current differs from the consumed.

AC2 - Harmonic distortion: some electronicappliances with non-linear loads can createwaveform deformation of the inverter outputsignal.

AC3 - Mismatch between load and invertersize: Low overall efficiency can result fromoversized inverters operating at low-power forlong periods.


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A1 Wrong Selection.

For good energisation it is better not to use electricity for all types ofload.

For example, generally it is not appropriate to use PV electricity toproduce heat.

Example

The energy needed to take a shower is about 1 kWh, this daily habitaccounting 30 kWh/month, or 500 Wp of installed PV power*

Using thermal collectors to directly heat water is much more cost-effective for this usage (about 10 times cheaper than PV) *

Assuming a water temperature of 10 C, and raise it to 38 C; forheating 30 l of water to take a shower we need: 30 lwater * 4,18kJ/(kg*C) * 1 kg/1lwater * (38-10)C water * 3600s = 1kWh.

Calculation of installed Wp: assuming a daily average irradiation of4000 Wh/m2, and a performance of the system of 50%, the Wpneeded are: 1 kWh/day/50% * 1kWp/4hp = 500Wp


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A2 - wiring

Wiring is an important issue to guarantee correctperformance when using appliances. Havingundersized or damaged distribution cables, canlead to the following problems:

Problems:

If section of wires is undersized or selection offuses is incorrect, high current through these can

cause a fire ( by resistive heating). Undervoltage may detrimentally affect the

performance of some appliances.


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A3 Low efficiency

Generally speaking, inefficient appliances are cheaper tobuy.

Problems:

If the system was sized for efficient loads and, inefficient

devices are used, insufficient energy is available,resulting in:

Frequent cut-offs.

Frequent low SOC of batteries resulting in low life.

System undersized.

User unsatisfied and may even by-pass the controller. If diesel genset runs periodically, operating costs can

increase dramatically due to increase in demand/ orincreased demand.

i ith hi h


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saving energy with high-

efficiency appliances:


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A4 Stand-by loads

Problems:

When these appliances are left on stand-by forhours or even days, their cumulative effect can

become a significant part of systemconsumption. This may be reflected as lowcharge of the batteries and earlier cutoff of thesystem.

A recent study carried out in Japan estimatedthat about 10% of domestic electricityconsumption is used to power appliances onstand-by.


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A5 Start-up

Some appliances consume high electric power (several times its rated

power) at start-up. In case of AC current, the inverters should resist peaks of power severaltimes higher than its rated power value, during the short start-up periods.

The loads affected should have a starter, which could soften the start-up.

The problem would be solved using loads according to the availability ofpower, always considering energy-availability (e.g. water pump with less kWbut operating during longer time).

In case of simultaneous start-up of the appliances, the peak power wouldbe the sum of each one. Progressive start-up of the loads connected shouldbe done, controlled by the inverter or another device.

The last solution would be to use an alternative power source forproblematic loads (e.g. a diesel generator,...).

Specify the inverter continuous watts and surge watts by estimating the

surge requirements correctly. Use a linear current booster or use permanent magnets in pumpingsystems to assist start-up.

A starter used for a water pump could be a device, which produces afrequency variation of the output inverter AC signal, to improve the start-upof the water pump.


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start-up o f a refr igerato r


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start -up o f a water pump


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AC1 Reactive power

Problems:

The current to be delivered by the inverter is muchhigher than the real consumption,

resulting in a possible overcharging of the system.

Current through the cables is higher than necessary,resulting in the need to increase the wire section toreduce voltage drops. This will add to the cost of cabling.

The consumption of an electric motor can have a phasebetween current and voltage of 50 (cos(50)=0.64). Theinverter has to supply, in this case, 1 / 0.64 of the currentused by the load (1.56 x the motor current).


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AC1 Reactive power

Solut ions:

Reduce the need for inductive loads likeconventional ballasts, etc.

Use of synchronous motors instead ofinduction motors in the relevantappliances.

Install capacitors at the inductive load orthe distribution panel to provide therequired amount of capacitive reactance.


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AC2 Harmonic distortion

Problems:

This causes voltage deformation in the output signal ofthe inverter, which may occasion problems with the otherloads.

Harmonics can shorten the life of the appliances byvoltage stress and increased heating of electricalinsulation.

Some devices need to sense zero-crossings to controlinternal switching and could malfunction as the zero-crossings may appear to shift because of harmonics.

Solut ions:

Use of output filtering or use of inverters with highswitching frequency in situations where harmonics areexpected.

AC3 Mismatch between load and


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AC3 Mismatch between load and

inverter size

Problems:

The energy consumed is higher than the expectedone, resulting in:

Cutout of the system or permanent low SOC ofbatteries

High non-useful energy consumption.

Solut ions:

Use of a specific dedicated inverter for theapplication, or a modular inverter with workingpoints of good performance ranging from low toits maximum power.


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Smart Consumers

A key feature of the Hybrid grid is demand response (DR).

As defined by the Association of Home Appliancesmanufacturers (AHAM) in December 2009 in a smart gridwhite paper, DR refers to a set of scenarios whereby theconsumer, utility can reduce energy consumption during peakusage or other critical energy use periods.

It is critical to reduce peak demand to avoid the use ofhigh-cost and high-emission power-generating resourcesor when the utility encounters some other issue on the

electrical grid that requires the reduction of electricitydemand, it can send a signal to the home so that thesystem will reduce its electrical load during this criticaltime periods.


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Smart appliances

In the smart appliances concept, the appliances are nolonger passive devices, but active participants in theelectricity infrastructure contributing to energy reduction andoptimization of the electrical grid for greater compatibility withits greenest energy-generation sources.

On this line, by providing a variable load, smart appliancesconnected to the smart grid are ideal complements torenewable energy such as wind and solar power, which areinherently variable in supply.

First, the focus is on residential consumers, where thedevelopment of DR is more straightforward.

Developing the smart grid and linking it to smart appliancesand others products having DR capabilities will reliably andpredictably reduce appliance electricity consumption in realtime


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Smart appliances

The way consumers interact with the grid is essential.

Consumers must be able to choose when and how they want theirsmart appliances to participate in the smart grid.

The offer of financial incentive through time-of-use pricing or otherincentive plans will be the single biggest driver for consumers to

change their energy consumption habits. Therefore, the smart appliances concept provides benefits to

both the consumers that obtain direct economic benefits, andthe utility and society at large.

The best candidates for smart home appliances are: clothes washer,refrigerator, clothes dryer, dishwasher, water heaters and heating,air conditioning, battery charger (for electric cares).

In the next years the smart appliance market is expecting to recordan important grow.

S li b i i


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Smart appliances, by integrating

them in the Whirlpool Smart

Device Network (WSDN):


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Resource Evaluation


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Resource Evaluation


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Resource Evaluation


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Resource Evaluation


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Resource Evaluation


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Resource Evaluation


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Resource Evaluation


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Resource Evaluation


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Resource Evaluation


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Resource Evaluation


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PV Module selection [JRC]


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Connection


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Inverters [JRC]


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Inverters


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Inverters


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Inverters


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Losses in PV system


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Losses in PV system


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PV Yield


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Final Yield including losses


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Final Yield including losses


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Costs


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Project Example


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Project Example


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Project Example


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Project Example JRC


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Resource JRC


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Resource JRC


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PV Photon Database


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PV Photon Database


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Inverters Photon Database


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Module placement

sizing a pv system.ppt

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