What is solar PV system?
Solar photovoltaic system or Solar power system is one of renewable energy system which uses PV modules to convert sunlight into electricity. The electricity generated can be either stored or used directly, fed back into grid line or combined with one or more other electricity generators or more renewable energy source. Solar PV system is very reliable and clean source of electricity that can suit a wide range of applications such as residence, industry, agriculture, livestock, etc.
Major system components
Solar PV system includes different components that should be selected according to your system type, site location and applications. The major components for solar PV system are solar charge controller, inverter, battery bank, auxiliary energy sources and loads (appliances).
&#;&#;&#; PV module &#; converts sunlight into DC electricity.
&#;&#;&#; Solar charge controller &#; regulates the voltage and current coming from the PV panels going to
battery and prevents battery overcharging and prolongs the battery life.
&#;&#;&#; Inverter &#; converts DC output of PV panels or wind turbine into a clean AC current for AC
appliances or fed back into grid line.
&#;&#;&#; Battery &#; stores energy for supplying to electrical appliances when there is a demand.
&#;&#;&#; Load &#; is electrical appliances that connected to solar PV system such as lights, radio, TV, computer,
refrigerator, etc.
&#;&#;&#; Auxiliary energy sources - is diesel generator or other renewable energy sources.
Solar PV system sizing
1. Determine power consumption demandsThe first step in designing a solar PV system is to find out the total power and energy consumption of all loads that need to be supplied by the solar PV system as follows:
1.1 Calculate total Watt-hours per day for each appliance used.
Add the Watt-hours needed for all appliances together to get the total Watt-hours per day which
must be delivered to the appliances.
1.2 Calculate total Watt-hours per day needed from the PV modules.
Multiply the total appliances Watt-hours per day times 1.3 (the energy lost in the system) to get
the total Watt-hours per day which must be provided by the panels.
Different size of PV modules will produce different amount of power. To find out the sizing of PV module, the total peak watt produced needs. The peak watt (Wp) produced depends on size of the PV module and climate of site location. We have to consider &#;panel generation factor&#; which is different in each site location. For Thailand, the panel generation factor is 3.43. To determine the sizing of PV modules, calculate as follows:
2.1 Calculate the total Watt-peak rating needed for PV modules
Divide the total Watt-hours per day needed from the PV modules (from item 1.2) by 3.43 to get
the total Watt-peak rating needed for the PV panels needed to operate the appliances.
2.2 Calculate the number of PV panels for the system
Divide the answer obtained in item 2.1 by the rated output Watt-peak of the PV modules available
to you. Increase any fractional part of result to the next highest full number and that will be the
number of PV modules required.
Result of the calculation is the minimum number of PV panels. If more PV modules are installed, the system will perform better and battery life will be improved. If fewer PV modules are used, the system may not work at all during cloudy periods and battery life will be shortened.
3. Inverter sizingAn inverter is used in the system where AC power output is needed. The input rating of the inverter should never be lower than the total watt of appliances. The inverter must have the same nominal voltage as your battery.
For stand-alone systems, the inverter must be large enough to handle the total amount of Watts you will be using at one time. The inverter size should be 25-30% bigger than total Watts of appliances. In case of appliance type is motor or compressor then inverter size should be minimum 3 times the capacity of those appliances and must be added to the inverter capacity to handle surge current during starting.
For grid tie systems or grid connected systems, the input rating of the inverter should be same as PV array rating to allow for safe and efficient operation.
The battery type recommended for using in solar PV system is deep cycle battery. Deep cycle battery is specifically designed for to be discharged to low energy level and rapid recharged or cycle charged and discharged day after day for years. The battery should be large enough to store sufficient energy to operate the appliances at night and cloudy days. To find out the size of battery, calculate as follows:
4.1 Calculate total Watt-hours per day used by appliances.
4.2 Divide the total Watt-hours per day used by 0.85 for battery loss.
4.3 Divide the answer obtained in item 4.2 by 0.6 for depth of discharge.
4.4 Divide the answer obtained in item 4.3 by the nominal battery voltage.
4.5 Multiply the answer obtained in item 4.4 with days of autonomy (the number of days that you
need the system to operate when there is no power produced by PV panels) to get the required
Ampere-hour capacity of deep-cycle battery.
Battery Capacity (Ah) = Total Watt-hours per day used by appliances x Days of autonomy
(0.85 x 0.6 x nominal battery voltage)
The solar charge controller is typically rated against Amperage and Voltage capacities. Select the solar charge controller to match the voltage of PV array and batteries and then identify which type of solar charge controller is right for your application. Make sure that solar charge controller has enough capacity to handle the current from PV array.
series charge controller type, the sizing of controller depends on the total PV input current which is delivered to the controller and also depends on PV panel configuration (series or parallel configuration).For thetype, the sizing of controller depends on the total PV input current which is delivered to the controller and also depends on PV panel configuration (series or parallel configuration).
According to standard practice, the sizing of solar charge controller is to take the short circuit current (Isc) of the PV array, and multiply it by 1.3
Solar charge controller rating = Total short circuit current of PV array x 1.3
Remark: For MPPT charge controller sizing will be different. (See Basics of MPPT Charge Controller)
Example: A house has the following electrical appliance usage:
The system will be powered by 12 Vdc, 110 Wp PV module.
1. Determine power consumption demands
Total appliance use = (18 W x 4 hours) + (60 W x 2 hours) + (75 W x 24 x 0.5 hours) = 1,092 Wh/day Total PV panels energy needed = 1,092 x 1.3 = 1,419.6 Wh/day.
2. Size the PV panel
Actual requirement = 4 modules
So this system should be powered by at least 4 modules of 110 Wp PV module.
3. Inverter sizing
Total Watt of all appliances = 18 + 60 + 75 = 153 W
For safety, the inverter should be considered 25-30% bigger size.
The inverter size should be about 190 W or greater.
4. Battery sizing
Total appliances use = (18 W x 4 hours) + (60 W x 2 hours) + (75 W x 12 hours)
Nominal battery voltage = 12 V
Days of autonomy = 3 days
Battery capacity = [(18 W x 4 hours) + (60 W x 2 hours) + (75 W x 12 hours)] x 3
(0.85 x 0.6 x 12)
Total Ampere-hours required 535.29 Ah
So the battery should be rated 12 V 600 Ah for 3 day autonomy.
5. Solar charge controller sizing
PV module specification
Pm = 110 Wp
Vm = 16.7 Vdc
Im = 6.6 A
Voc = 20.7 A
Isc = 7.5 A
Solar charge controller rating = (4 strings x 7.5 A) x 1.3 = 39 A
So the solar charge controller should be rated 40 A at 12 V or greater.
A solar project smaller than 2.5 kW takes only a few days to design and install. The freedom and sense of accomplishment that such a project grants the home owner lasts for years. Photovoltaic systems give individuals the ability to become self-sustaining and to control the cost of their electricity - PV systems also teach a fundamental lesson of local production and consumption unlike any other experience. The California Energy Commission published "A Guide to Solar PV Design and Installation (pdf)" to enable more citizens to go solar on their own .
Don't be intimidated, it's easy if you are fully prepared!
To begin, We'd like to mention that you can consult with Greentech Renewables to assist with all of your system design needs by filling out the online PV Design Request form on our website.
We will list the basic steps for do-it-yourself solar enthusiasts. You don't have to be an engineer, nor do you have to actually purchase equipment at this stage. Just as a starting point, follow these 10 easy steps:
KINGSUN supply professional and honest service.
1) Know how much electricity (kWh) you consume and know your electricity rate
To understand the economics of installing a solar system it is important that you determine how much electricity you consume in a year. A summary of your electricity usage is on your utility bill, make sure you do not include natural gas usage in your calculations. Please note that a solar PV system would offset your electricity demands mostly in the summer months (Not because of the temperature, rather because the path of the sun varies with the seasons, it is optimal for PV systems during the summer). Also, note that most utility companies have a tier rate structure based on consumption patterns and state mandates. A small PV system could reduce your electricity needs enough to move you to a different tier, lowering your rates and saving you a large amount of money.
2) Know how much available roof space (sq-ft) you have
To determine how many solar panels you can actually use, it is important that you know how much roof space you have. Based on the size of your house, draw a diagram of your roof on a piece of paper. If you'd like to be more technical, you can use the free tool Google SketchUp or a free CAD program DraftSight. Once you have determined the size of your roof it is important to know how much of your roof faces towards the equator (South in the northern hemisphere [USA, Canada, etc.], north in the southern hemisphere [Australia, South America etc.]). Solar irradiance is strongest coming from the equator and you will want to maximize the efficiency of your system.
3) Know your solar radiation data and calculate how much energy you could generate
You can consult the NREL website (National Renewable Energy Lab) for official government statistics on your area. You can also use PV Watts&#; or Solmetric's solar calculators.
4) Know your shading issues
If there are obstacles like trees or buildings in the vicinity of your roof that might create shade, you need to be careful. Shading can reduce the output of your system and may also damage the solar cells. You can use Solar Pathfinder or Solmetric Sun Eye for detailed shading analysis. Some utilities rent or loan these devices.
5) Select an appropriate solar module
There are hundreds of different solar panels on the market, determining which is the perfect fit for you can be complicated. The size (surface area) of the module and the solar rating are the most important factors. Please note, although the solar ratings might be the same for some modules, the voltage and current output might vary (It is advised to select a lower voltage module for smaller projects [less than 4 kW]). Other differences, such as color and financial limitations may also be a factor.
6) Select an inverter
Similar to choosing a solar panel, selecting an inverter out of the many available is not easy. Consider using micro inverters that are easy to install and that generate AC power directly from the module. If you want to use a central inverter please read the linked article and use the string sizing tools.
7) Choose a racking system to mount your solar PV system on your roof
Remember that 10% to 25% of the total costs will be the racking system. Pay attention and take your time to decide which racking system is most suitable for your budget and for your roof. The racking system is going to last for at least 20 years and it's one of the key components since it protects both the roof and the modules. A small mistake with the racking can permanently damage the roof or injure people or property.
There are a number of different racking and mounting systems available in the market for roof mounted solar systems. Check the manufacturer's websites, read the installation manual. Be aware of the codes and plan how you are going to mount the racking system on the roof. Learn about flashing solutions; I mentioned some options in the linked article.
Using an inexpensive racking solution does not mean lower quality, it might require more effort to install it or the materials may be different. To have a glimpse on how to design a roof mount system, you can either refer to a previous article or you can use Unirac's roof mount part estimator.
Additionally, as the solar PV field matures unique racking solutions, such as hanging panels vertically along an exterior wall, become more applicable.
8) Learn your local and state incentives, calculate how much money ($) you could save
Check the DSIRE (Database of State Incentives) website. There are also a number of other financial calculators available online. Most importantly, you need to estimate your electricity generation and compare it to your utility rate. Note that different tier rates might apply depending on your energy consumption.
Call you utility company and learn about their solar programs. Learn the applications process. Make use of incentives and tax cuts.
9) Get your documents ready
Every city has a different permitting process. In order to apply for an incentive or to receive a construction permit, you will need to obtain the equipments' (module, inverter, racking) data sheets, and submit a roof drawing and electrical drawing. You can draw those on your own using the programs mentioned above, or ask a professional to draw them for you.
The electrical diagram requires some electrical knowledge in order to determine the wire sizes, voltage drops, AC and DC disconnects. Contact an electrician if you don't feel confident about it.
10) Go Solar!
Once you feel confident with your system, you can consult a sales person or distributor. If you want to install the system on your own, read some books about it first. Or just contact a local electrician and install it together.
It will take 5 to 15 hours of work to install a small solar system on your roof, which could be done in one or two days. Then you can watch your meter run backwards and enjoy clean energy.
Are you interested in learning more about Customized PV Module? Contact us today to secure an expert consultation!