OFF GRID Solar system

Transcription

1 OFF GRID Solar system

2 Off-Grid solar system Off-Grid solar system has 5 components as follows: Solar panel - Solar panel is used to collect the sunlight energy and to convert it into electricity Battery - Battery saves the electrical energy to be used by the electrical appliances or else Charge controller (regulator) - Charge controller is used to protect the battery against over charging, so the life time of the battery will be longer Load - Load could be electrical appliances or others such as lighting, fridge, air-conditioning etc. Inverter Inverter is used to convert the DC electricity from the battery into AC electricity.

3 We have to be careful in selecting a solar panel A solar panel that will be used for a 12 volts system will have a voltage output of volts A solar panel that will be used for a 24 volts system will have a voltage output of volts

4 Sizing off-grid solar system How many solar panels do I need and what size should I buy? The first step is to work out your load requirements. In our example there are two types of load - DC appliances and - AC Appliances. 6 x 11W 12v DC Lights - used for 4 hours per day 1 x 150W 240V AC Television. Example is based on Philips 32PF " Widescreen LCD TV - used for 6 hours per day

5 Sizing off-grid solar system Calculate both the DC and AC Loads Determine the DC Load - Lighting - 6 x 11W DC Lights - used for 4 hrs per day = 264Wh per day Total DC Load in Watt Hours = 264Wh per day Determine the AC Load - Television - 1 x 80W - used 6 hrs per day = 480Wh per day Total AC Load = 480 Wh per day Total Load = DC Load + AC Load = 744 Wh per day. There will be energy losses to account for so add 20% to the load as this will account for the losses and emergency power use outside of the specified times. Total Load + 20% Energy Losses = 892.8Wh per day.

6 Sizing solar panel Due to UK weather conditions and for this example, we shall use 1.5hrs of Peak Sunshine (Peak Sun Hour = PSH) Please note: You do need to know the weather conditions for your area as this will affect the size of the panel or array. Required solar panel input = (892.8 Wh / 1.5h) = 595.2W. You will need solar panels that will generate watts per hour. Select the solar panels to provide a minimum of or 600W. Always round to the nearest 10. Any combination of solar panels can be used to provide the required 600W 3 x solar panels.

7 Sizing solar panel Let us assume: Kyocera solar panel KS200GT specifications are as follows: Power max = 200 watts Current max (at power max) = 7.61 amperes Short circuit current = 8.21 amperes Each solar panel will provide an output of [Pmax] at 7.61 Amps [Current at Pmax] As the output of solar panels vary with temperature we do need to know what the rated short circuit current of the chosen panels. Rated Short Circuit Current of solar panel 3 x solar panels arranged in parallel Each solar panel has a rated short circuit current of 8.21 Amps

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9 Sizing the deep cycle battery The simplest way to determine the total battery amp hours required is to determine the total watt-hours required by all loads and then divide by the DC system voltage. This will result in the amount of amp hours needed to operate all loads for a given period. The battery size is determined by the DAILY WATT-HOUR requirements and the desired number of DAYS of storage capacity required AND the assumption that the battery will never be discharged less than 20% - (80% remains of its capacity). 12 V battery is used The Average Daily Load = 892.8Wh per day. Add 20% for system losses and safety. Thus load = 1071Wh per day. If no inverter is used then the {Average Daily Load (1071Wh) / System Voltage ()} = 89.2Ah per day

10 Sizing the deep cycle battery Now take: For example we choose to use 100 Ah batteries (20 hours) The Average Ah per day (89.2Ah) x Days of Battery Storage (Eg 3 days in case there is no sunlight everyday) / Battery Discharge Limit (0.8) / Battery Ah Capacity of your choice = {(89.2 x 3/(0.8 x 100)} = Number of batteries in parallel connection = 4 nos of battery (3.345) If we are using 24 VDC system DC System voltage / battery voltage = Number of batteries in series = 24/12 = 2X For this 24 VDC system Total Number of batteries required = batteries in series X batteries in parallel

11 12 Volts 24V 24V If we are using 24 V battery we need 2 nos in parallel If we are using 12 V battery we need 4 nos in parallel If we are using 12 V battery we need 4 nos in series & parallel

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13 POWER REQUIRED PER-DAY Electricity consumption per-hour = 37.2 watts In 24 hours, the electricity consumption = 24 x 37.2 = watts-hour Add 2% of losses (battery etc) = x 1.02 = watts.hour 12 volts system voltage Amp.hour/day = : 12 = amp.hour BATTERY: 12 volts system voltage Battery back-up = 3 days With 50 % of depth discharge x 3 : 0.5 = AH If we are using battery with 100AH capacity Battery quantity = /100 = 4.55 nos Arrange 5 numbers in parallel SOLAR PANEL PSH = 1.5 hours Solar panel used = 200 Watts Capacity of solar panel/day = 1.5 x 200 : 1.55 = watts 12 volts system voltage Safety multiplier = 1.55 Nominal solar panel voltage = 16 volts One solar panel amp = : 16 = 12.1 amp Amp.hour/day = amp.hour Total of solar panel = : 12.1 = Arranged 7 numbers of solar panel in parallel

14 Example system Charge Controller Battery 100AH 100AH 100AH 100AH 100AH Solar Panel

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16 POWER REQUIRED PER-DAY Electricity consumption per-hour = 37.2 watts In 24 hours, the electricity consumption = 24 x 37.2 = watts-hour Add 2% of losses (battery etc) = x 1.02 = watts.hour 24 volts system voltage Amp.hour/day = : 24 = amp.hour BATTERY: 24 volts system voltage Battery back-up = 3 days With 50 % of depth discharge x 3 : 0.5 = : 0.5 = AH If we are using battery with 100AH capacity Battery quantity = /100 = 2.28 nos Arrange 3 number in parallel (24 V batteries are 2 numbers of 12 V batteries arranged in series) Total = 6 numbers of batteries! SOLAR PANEL PSH = 1.5 hours Solar panel used = 200 Watts Capacity of solar panel/day = 1.5 x 200 : 1.55 = watts 24 volts system voltage Safety multiplier = 1.55 Nominal solar panel voltage = 32 volts One solar panel amp = : 32 = 6.05 amp Amp.hour/day = amp.hour Total of solar panel = : 6.05 = 6.27 Arranged 2 numbers of solar panel in series 3 rows in parallel (for safety 4 rows)

17 Example 24V system Charge Controller Battery 100AH 100AH 100AH 100AH 100AH 100AH Solar Panel

18 Sizing PWM charge controller/solar regulator The purpose of the solar regulator or charge controller is to regulate the current from Solar panels to prevent batteries from overcharging. A solar regulator senses when the batteries are fully charged and stops the current flowing to the battery and also prevents the battery from feeding back into the solar panel at night when it is dark. Most solar regulators include a Low Voltage Disconnect feature, that senses the battery voltage and if the battery voltage drops below a a pre-determined level (cut-off voltage) the solar regulator will switch off the supply. Solar regulators are rated by the amount of current they can receive form the solar panels. Important note: The solar regulator should be capable of handling the total short circuit current of solar panel. From the example shown above we have 3 x solar panels arranged in parallel (voltage not increase but current increase) and the solar regulator must be able to handle the increased rating of the short circuit current. Thus, the short circuit current = 8.21 [A] x 1.25 [increased rating/safety factor] = Amps we can choose a PWM charge controller with 15 amps capacity NOTE: Always increase the solar regulator and add an additional 25% capacity to allow for growth and the fact that the solar panels may exceed their rated output. NOTE: Always allow for future growth so size the regulator accordingly.

19 Sizing MPPT charge controller/solar regulator For example, we could have a 3,000 watt solar module array that operates at 91.5 volts DC and your battery bank is 48 volts DC. MPPT charge controller are rated by the output amperage that they can handle not the input current from the solar module array. To determine the output current that the charge controller will have to handle we use the very basic formula for power in Watts: Power = Volts x Amps Here we know the power is 3,000 Watts, the battery bank is 48 volts, so: 3,000 Watts = 48 volts x Amps which gives us: Amps = 3,000 Watts/ 48 volts Amps = 62.5A We still want to adjust this value by 25% to take into account any special conditions that might cause the solar module array to produce more power than it is normally rated for (e.g. due to sunlight's reflection off of snow, water, extraordinarily bright conditions, etc). So, 62.5A increased by 25% is 78.13A. In this case we'd probably choose a 80 Amp MPPT Charge Controller

20 Example

21 Another benefit of MPPT charge controller Because MPPT charge controllers can handle a higher input voltage from the solar module array than the battery bank's voltage, you can also use these charge controllers with solar modules that have voltages that don't match your typical system voltage (i.e. 12, 24 or 48V). For instance, you could have a solar module that has a nominal voltage of 30.5 volts and charge controller and battery bank that's 48 volts efficiently with an MPPT charge controller. Keep in mind that MPPT charge controllers have a maximum system voltage limit that they can handle from the solar module array. It's important that you make sure there is no condition that the solar module array voltage will go above this limit or you could potentially harm the controller. You want to make sure that the open circuit voltage of the solar module array does not go above this value. You also want to give yourself a little bit of a margin for safety to take in account for the potential that an array's voltage will actually increase the colder it gets. If you give yourself a 25% margin of error you will be alright.

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24 Another benefit of MPPT charge controller Here's an example: We'll use twelve Sun Module Pro Series 30.5 volt 250 Watt solar modules with four parallel strings of three in series for a nominal voltage of 91.5 volts and a 48 volt battery bank. If we look at the solar module's specification page we see that each module has an open circuit voltage of 37.6V. That means the array has three times that because there are 3 modules in series. So the array open circuit voltage is 37.6V x 3 = 112.8V. We'll increase this by a safety factor of 25% and we get V. We can take a maximum of 150 volts MPPT charge controller

25 Sizing the inverter Inverters should always be chosen that would be more than capable of supplying the maximum anticipated AC load. This is always taken to be the combined maximum load for all AC appliances running at the same time. Always allow for loads that have a surge rating, such as motors and fluorescent lights etc. It is advisable to use pure sine wave inverters where possible. Generating AC from a DC supply source requires an inverter Converting DC to AC results in a loss of efficiency for the inverter and energy losses are assumed to be 20%. We therefore achieve an inverter efficiency of 80%. Thus 892.8Wh / 0.80 equates to 1, Wh per day We can choose a 1200 Wh inverter!