Photovoltaic Systems Engineering Ali Karimpour Associate Professor Ferdowsi University of Mashhad Reza Bakhshi Ph.D. candidate Ferdowsi University of Mashhad Ali Karimpour & Reza Bakhshi
Lecture 7 Off-grid components (part ) Ali Karimpour & Reza Bakhshi
Two types of photovoltaic systems Grid-connected, grid tie, On grid The balance between generated power and consumed power can be reached by Utility grid. So, utility grid is the virtual energy storage in this type. Electrical grid Local load PV array Solar inverter This type of photovoltaic system has been introduced in previous lectures. Ali Karimpour & Reza Bakhshi 3
Two types of photovoltaic systems Why Grid-connected? We do not concern about mismatch happens between PV generation and load consumption. This type has a lot benefits such as: Produce clean energy Load peak sharing Easy installation and usage, low maintenance and repair Higher reliability Ali Karimpour & Reza Bakhshi 4
Two types of photovoltaic systems Off-grid, Standalone This type of solar electric is not connected to the electrical grid. Therefore, it uses batteries to store generated energy and release it when needed. Charge controller Off grid inverter + - + - + - PV array DC loads Battery package AC loads This type of photovoltaic system is beyond our study for next sessions. Ali Karimpour & Reza Bakhshi 5
Two types of photovoltaic systems Why off-grid? Off-grid solar systems can be cheaper than extending power lines in certain remote areas. The target of off-grid system is to feed the local load with the minimum outage. However, some load are not critical and cannot be fed for some intervals. The batteries are applied to save generated energy by solar panels for use when the system is not generating enough to sustain household functions, for example, at night. Ali Karimpour & Reza Bakhshi
Off-grid photovoltaic systems Off-grid applications Power supply for rural or mountainous regions. Ali Karimpour & Reza Bakhshi 7
Off-grid photovoltaic systems Off-grid applications Urban furniture with solar system enables charging mobiles, bulbs power, etc. Ali Karimpour & Reza Bakhshi 8
Off-grid photovoltaic systems Off-grid applications Water pump Mobile solar station Ali Karimpour & Reza Bakhshi 9
Off-grid photovoltaic systems Off-grid applications Street lights Ali Karimpour & Reza Bakhshi
Off-grid photovoltaic systems Off-grid applications Back up supply (Civil defense) for sensitive loads such as hospitals, military stations, etc. Ali Karimpour & Reza Bakhshi
Off-grid photovoltaic pros and cons Pros Eliminates utility dependency Can work with wind or hydro power renewable energy generators Can be used in many applications Cons Cost Required high maintenance Need to replace batteries each 3-5 years Complex control strategy Ali Karimpour & Reza Bakhshi
Off-grid photovoltaic systems Charge controller: the charge and discharge of battery package. Battery package: compensates the deficit/surplus generated power Off grid inverter: converts DC power to the AC type for AC load consumption. Charge controller Off grid inverter + - + - + - PV array Battery package AC loads DC loads We want to know the detailed characteristics of mentioned elements. 3 Ali Karimpour & Reza Bakhshi
Off-grid elements (Charge controller) A charge controller controls the rate of adding or drawing electric current from batteries. They manage interactions and energy flows between a PV array, battery, and electrical load. 4 Ali Karimpour & Reza Bakhshi
Charge controller Duties Protects batteries from overcharging and may protect against overvoltage, which can reduce battery performance or lifespan. 5 Ali Karimpour & Reza Bakhshi
Charge controller Duties Prevents completely over discharging (deep discharging) a battery, or perform controlled discharges, depending on the battery technology, to protect battery life. Ali Karimpour & Reza Bakhshi
Charge controller Duties Maximum power point tracking (MPPT) in some cases. Maximum power point tracking manipulates the load or output voltage of an array in order to maintain operation at or near the maximum power point under changing temperature and irradiance conditions. 7 Ali Karimpour & Reza Bakhshi
Charge controller Charge and discharge regulation set points Battery charge and discharge can be performed according to its voltage. Charge regulation set points are the voltage levels at which the charge controller interrupts or limits the charging current from the array to the battery bank. Load control set points are the voltage levels at which the charge controller interrupts or limits the discharging current from the battery bank to the loads. 8 Ali Karimpour & Reza Bakhshi
Charge controller Charge and discharge regulation set points Battery charge and discharge can be performed according to its voltage. These set points are adjusted with controls inside the charge controller. 9 Ali Karimpour & Reza Bakhshi
Charge controller Charge controllers can control charging and discharging in parallel or series with battery and array. Shunt charge controllers control charging current by short-circuiting the array. Series charge controllers control charging current by opening the circuit from the array. Ali Karimpour & Reza Bakhshi
Charge controller Two most applied technologies adjusting charging rates depending on the battery's level, to allow charging closer to its maximum capacity are: Pulse width modulation (PWM) The PWM controller is in essence a switch that connects a solar array to a battery. The result is that the voltage of the array will be pulled down to near that of the battery. Ali Karimpour & Reza Bakhshi
Charge controller Maximum power point tracker (MPPT) The MPPT controller is more sophisticated and more expensive. It will adjust its input voltage to harvest the maximum power from the solar array and then transform this to the battery plus load. Ali Karimpour & Reza Bakhshi
Charge controller Maximum power point tracker (MPPT) vs. PWM The MPPT controller will harvest more power from the solar array especially in low temperatures. The PWM charge controller is a good low cost solution for small systems only, when solar cell temperature is moderate to high (between 45 C and 75 C). Also, the charging can be reachable rapidly in this case. 3 Ali Karimpour & Reza Bakhshi
Charge controller Datasheet 4 Ali Karimpour & Reza Bakhshi
References. www.victronenergy.com. Frank Jackson, Planning and Installing Photovoltaic Systems, nd edition, Berlin, 7 3. www.outbackpower.com 5 Ali Karimpour & Reza Bakhshi