Difference between revisions of "Minimum PV source size"
| Line 5: | Line 5: | ||
An off-grid PV system that depends upon the PV as its single charging source requires an array that is sufficiently sized to be able to generate sufficient energy to both meet the energy needs of the users and to recharge the [[Energy storage|energy storage system]] under less than ideal conditions. Any sizing decisions should therefore lean towards an oversized PV source. | An off-grid PV system that depends upon the PV as its single charging source requires an array that is sufficiently sized to be able to generate sufficient energy to both meet the energy needs of the users and to recharge the [[Energy storage|energy storage system]] under less than ideal conditions. Any sizing decisions should therefore lean towards an oversized PV source. | ||
| + | |||
| + | ====Step 1: Determine minimum PV source size==== | ||
| + | Finding the minimum size of the PV source will help to determine the appropriate PV module size and charge controller type. The power rating of PV modules is generated under ideal testing conditions in a laboratory (See [[PV module#Standard test conditions|Standard test conditions]]), thus to build a PV system that is going to generate the necessary amount of energy under less than ideal conditions it is necessary to requires that the estimated production that a PV module will generate is reduced to function under the anticipated conditions of use. There are many different parameters that need to be accounted for and without performing extensive testing each of these parameters will largely be an estimate on the part of the designer. It is important to use conservative numbers as an over-sized system is always preferrable to an under-sized system. | ||
| + | |||
| + | *'''Shading loss parameter:''' Parameter that accounts for any production losses that the system may experience due to [[Shading|shading]] from nearby obstacles - mountains, trees, other buildings - during the course of the year. The only way to get a accurate value for this parameter is to evaluate the shading at the site using a took like a the [https://www.solarpathfinder.com/ Solar Pathfinder]. The value for this parameter is completely site dependent. If it is anticipated that there will be no shading losses, then the value for this parameter should be 1. If there is a 5% loss, then a value of .95 should be used. | ||
| + | *'''Soiling loss parameter:''' Parameter that accounts for the build-up of dirt on the surface of a PV module, which reduces production as it doesn't allow light to reach the cells of the module. The appropriate value for this parameter depends primarily upon the climate and location in which the system is installed, but also the tilt and cleaning frequency of the PV modules. <ref name="NRELsoiling1">National Renewable Energies Laboratory - Time Series Analysis of Photovoltaic Soiling Station Data: Version 1.0, August 2017 https://www.nrel.gov/docs/fy17osti/69131.pdf</ref> <ref name="NRELsoiling2">National Renewable Energy Laboratories - Photovoltaic Module Soiling Map https://www.nrel.gov/pv/soiling.html</ref>Frequent rainfall helps PV modules to self-clean. If a system is installed in a location with minimal windblown dust that receives regular rainfall or in which modules are cleaned weekly, then losses may be as low as 1%. If a system is installed in a location with significant windblown dust that receives very infrequent rainfall or in which modules are never cleaned, then losses may be as high as 50%.<ref name="qatarsoiling">Qatar Environment and Energy Research Institute - PV Soiling Rate Variation over Long Periods https://www.nrel.gov/pv/assets/pdfs/2015_pvmrw_02_figgis.pdf</ref> With regularly cleaning of a system a value of 3% is recommended for locations with minimal windblown dust and a value of 7% is recommended for locations with significant windwblown dust. | ||
| + | |||
====Step 1: Determine a charge controller type==== | ====Step 1: Determine a charge controller type==== | ||
| Line 23: | Line 30: | ||
*Minimum PV source voltage: depends upon nominal voltage and charge controller type | *Minimum PV source voltage: depends upon nominal voltage and charge controller type | ||
*Maximum PV source current: up to 100A+ | *Maximum PV source current: up to 100A+ | ||
| + | |||
| + | ==Notes/references== | ||
| + | <references/> | ||
Revision as of 09:35, 20 November 2020
The size of the PV source, which is determined based upon the load evaluation and weather and solar resource evaluation will determine the necessary size of the charge controller. The charge controller must be selected at the same time as the PV source as the charge controller type - PWM or MPPT - will also determine the possible configurations of PV modules.
In this phase of the design process, more than in any other phase, it is necessary to explore different designs using PV module, series and parallel wiring configurations, and charge controllers in order to achieve the highest performance at the lowest cost possible. This phase may have to be performed several times.
An off-grid PV system that depends upon the PV as its single charging source requires an array that is sufficiently sized to be able to generate sufficient energy to both meet the energy needs of the users and to recharge the energy storage system under less than ideal conditions. Any sizing decisions should therefore lean towards an oversized PV source.
Contents
Step 1: Determine minimum PV source size
Finding the minimum size of the PV source will help to determine the appropriate PV module size and charge controller type. The power rating of PV modules is generated under ideal testing conditions in a laboratory (See Standard test conditions), thus to build a PV system that is going to generate the necessary amount of energy under less than ideal conditions it is necessary to requires that the estimated production that a PV module will generate is reduced to function under the anticipated conditions of use. There are many different parameters that need to be accounted for and without performing extensive testing each of these parameters will largely be an estimate on the part of the designer. It is important to use conservative numbers as an over-sized system is always preferrable to an under-sized system.
- Shading loss parameter: Parameter that accounts for any production losses that the system may experience due to shading from nearby obstacles - mountains, trees, other buildings - during the course of the year. The only way to get a accurate value for this parameter is to evaluate the shading at the site using a took like a the Solar Pathfinder. The value for this parameter is completely site dependent. If it is anticipated that there will be no shading losses, then the value for this parameter should be 1. If there is a 5% loss, then a value of .95 should be used.
- Soiling loss parameter: Parameter that accounts for the build-up of dirt on the surface of a PV module, which reduces production as it doesn't allow light to reach the cells of the module. The appropriate value for this parameter depends primarily upon the climate and location in which the system is installed, but also the tilt and cleaning frequency of the PV modules. [1] [2]Frequent rainfall helps PV modules to self-clean. If a system is installed in a location with minimal windblown dust that receives regular rainfall or in which modules are cleaned weekly, then losses may be as low as 1%. If a system is installed in a location with significant windblown dust that receives very infrequent rainfall or in which modules are never cleaned, then losses may be as high as 50%.[3] With regularly cleaning of a system a value of 3% is recommended for locations with minimal windblown dust and a value of 7% is recommended for locations with significant windwblown dust.
Step 1: Determine a charge controller type
There are two different charge controller types - pulse width modulation (PWM) and maximum power point tracking (MPPT) - each of which has advantages and disadvantages that are are detailed in Charge controller types.
Step 2: Deteremine a PV module size
The PV module size that is ideal for the system design will depend upon the amount of energy required each day, the type of charge controller chosen, and what module sizes are available in the market. An MPPT charge controller can function with any module size as long as the series configuration of modules meets the minimum voltage requirement for the charge controller so that it can properly charge the batteries.
PWM:
The PV source must be configured to operate at the charging voltage of the energy storage system and below the maximum PV source current rating of the charge controller.
- Nominal system voltage: 12V, 24V, 48V.
- Maximum PV source current: 6A-60A
MPPT
The PV source must be configured to operate below the maximum PV source voltage rating of the charge controller, above the minimum PV source voltage based upon the maximum charging , and below the maximum PV source current rating of the charge controller.
- Nominal system voltage: 12V, 24V, 48V
- Maximum PV source voltage: varies up to 600V
- Minimum PV source voltage: depends upon nominal voltage and charge controller type
- Maximum PV source current: up to 100A+
Notes/references
- ↑ National Renewable Energies Laboratory - Time Series Analysis of Photovoltaic Soiling Station Data: Version 1.0, August 2017 https://www.nrel.gov/docs/fy17osti/69131.pdf
- ↑ National Renewable Energy Laboratories - Photovoltaic Module Soiling Map https://www.nrel.gov/pv/soiling.html
- ↑ Qatar Environment and Energy Research Institute - PV Soiling Rate Variation over Long Periods https://www.nrel.gov/pv/assets/pdfs/2015_pvmrw_02_figgis.pdf
