1. The solar-mains hybrid lamp

Within the April 4, 2024, problem of EDN, the design of a photo voltaic mains hybrid lamp (HL) was featured. The lamp receives energy from each a photo voltaic panel and a mains energy provide to activate an array of LED lamps. Even when solar energy is broadly variable, it provides a relentless mild output by dynamically drawing balanced energy from the mains provide. Additionally, it tracks the utmost energy level very intently. 

Wow the engineering world together with your distinctive design: Design Concepts Submission Information

1.1 Benefits

Some great benefits of the HL are as follows:

1. It makes use of all of the solar energy generated and attracts solely the mandatory energy from the grid to keep up fixed mild output.
2. It doesn’t inject energy into the grid; therefore, it doesn’t contribute to any grid-related points.
3. It makes use of a localized energy circulate with quick cabling, leading to negligible transmission losses.
4. It makes use of DC operation, leading to a easy, dependable, and low-cost system.
5. Generated PV energy is utilized even when the grid fails, thus performing as an emergency lamp within the occasion of a grid failure through the daytime.
6. It has a prolonged lifespan of 15 years with minimal or no upkeep, leading to an excellent return on funding.

1.2 Disadvantages

The constraints of the HL are as follows: 

1. It doesn’t present mild if the grid fails after sundown.
2. Solar energy will not be utilized exterior of workplace hours or on holidays.

As talked about above, the HL’s utility could be absolutely realized in locations reminiscent of hospitals, airports, and malls, as it may be used on daily basis of the week.

In places of work which can be open for work solely 5 days per week, the generated PV energy shall be wasted on weekends and outdoors of workplace hours (early mornings and evenings). 

For such purposes, to totally make the most of the generated PV energy, a battery backup scheme is proposed. It’s designed as an non-compulsory add-on characteristic to the present HL. The PV energy, which might in any other case go to waste, can now be saved within the battery at any time when the HL will not be in use. The saved power could be utilized as an alternative of mains energy on workdays to cut back the electrical energy invoice. In instances the place the grid fails, it can work as an emergency lamp. 

2. Battery backup block diagram

The block diagram of the proposed scheme is proven in Determine 1. It consists of a HL having an array of 9 LED lamps, A1 to A9. Every HL has 5 1-W white LEDs related in sequence, mounted on a steel core PCB (MCPCB). For extra particulars, check with the earlier article, “Photo voltaic-mains HL.” Right here, the HL is used as is, with none adjustments. 

The PV voltage (Vpv) is provided via a two-pole two-way swap S1 to the HL. Swap S1A is used to attach the PV panel to both the lamp or to the battery. As proven within the determine, the PV panel is related to the battery via an Overvoltage Cutoff circuit. This circuit disconnects PV energy when the battery voltage reaches its most worth of Vb(MAX). 

A single-pole two-way swap S2 is used to pick out both MAINS or BAT to feed energy to the VM terminal of the HL. When S2 is within the BAT place, battery energy is fed via the undervoltage journey circuit. At any time when the battery voltage drops to the minimal worth Vb(MIN), the HL is disconnected from the battery. Swap S1B is used to disconnect the battery/mains energy to the HL when S1 is within the CHARGE place.

Determine 1 The proposed add-on battery backup system for HL.

Be aware: This straightforward battery cutoff and journey circuit has been applied to show the idea of battery backup utilizing the present HL. Within the ultimate design, the Overvoltage Cutoff circuit ought to be changed with a photo voltaic cost controller, which is able to observe the utmost energy level because the battery costs. Available off-the-shelf photo voltaic cost controllers could possibly be used. The number of a photo voltaic cost controller is given in Part 5.

Listed here are the lamp specs: 

1. Photo voltaic PV panel: 30 Wp, Vmp = 17.5 V, Imp = 1.7 A
2. Adapter specs Va = 18 V; Present 2 A
3. Lead Acid Battery: 6 V 5 Ah. (3 batteries related in sequence)
4. Battery nominal voltage Vb = 18V, Vb(MAX) = 19 V, Vb(MIN) = 17 V
5. Lamp energy output: 30 W

3. Overvoltage and undervoltage circuits 

The circuit diagram of the battery Overvoltage Cutoff and Undervoltage Journey is proven in Determine 2. Three lead-acid batteries (6 V, 5 Ah) related in sequence are used for storing photo voltaic power. The battery is related to the photo voltaic panel Vpv via a P-channel MOSFET T1 (IRF9540). The Schottky diode D1 (1N5822) is related in sequence to stop the battery from getting discharged into the photo voltaic panel when it isn’t producing any energy. 

T1 is managed utilizing comparator CMP1 of IC1 (LM393). The battery voltage is sensed utilizing the potential divider R6 and R7. The reference to the comparator non-inverting pin (3) is generated from a +12-V energy provide applied utilizing the IC2 (LM431) shunt regulator. If the battery voltage is decrease than the reference voltage, the CMP1 output (pin 1) is excessive. This activates transistor T3, which activates T1. The inexperienced LED_G signifies that the battery is being charged.

Determine 2 The circuit diagram of Overvoltage Cutoff and Undervoltage Journey circuits.

The battery is related to the load via MOSFET T2 (IRF9540). T2 is managed utilizing comparator CMP2 of IC1. The battery voltage is sensed utilizing the potential divider R14 and R15, and is related to the non-inverting terminal (Pin 5). The reference voltage is related to the inverting terminal (Pin 6). 

As long as the battery voltage is larger than the reference, the CMP2 output stays excessive. This drives transistor T4, which activates T2. When the battery voltage drops beneath the reference, T2 is turned off, thus disconnecting the lamp load. LED_R signifies the battery voltage is throughout the Vb(MIN) and Vb(MAX) vary.

Determine 3 reveals the PCB assembled in response to the circuit diagram in Determine 2. The connections for the photo voltaic panel Vpv, battery Vb, and battery output Vb+ (via the MOSFET T2) are made utilizing three 2-pin screw terminals. 

Determine 3: The assembled PCB for battery overvoltage cutoff and undervoltage journey circuit.

Determine 4 reveals the interconnections of the battery charger circuit with the HL.

Determine 4 A high view of the interconnections of the battery charger circuit with the HL.

The modes of operation of this circuit are captured in Desk 1. When S1 is within the CHARGE place, the PV voltage is provided to the batteries for charging. On this mode, the place of S2 doesn’t have an effect on the charging course of. 

When S1 is within the PV place, the HL turns ON. Utilizing S2 we will choose both mains energy or battery energy.

Desk 1 Working modes of the battery backup circuit: battery charging, hybrid with mains energy, and hybrid with battery energy. 

4. Integration and testing

Determine 5 reveals the combination of the battery safety circuit with the HL and three batteries. The cable from the PV panel is related to the 2-pin screw terminal labeled as Vpv. Three 6-V batteries in sequence are related to the screw terminal Vb. A DC socket labeled Va is mounted for plugging into the adapter pin. Within the {photograph}, S1 is in CHARGE place, so the battery is being charged utilizing PV energy. On this case, the place of S2 is irrelevant and won’t have an effect on the charging course of.

Determine 5 A picture of the circuit in Battery Charging mode. The inexperienced LED signifies the battery is being charged from the PV panel. The purple LED signifies battery energy is on the market to be used.

Determine 6 reveals the HL turned on utilizing PV energy and a battery. On this case, S1 is within the PV place, and S2 is within the BAT place. Be aware that the LED lamp array (A1 to A9) is going through downwards. On the HL PCB, there are 9 purple and 9 inexperienced indicator LEDs. Every pair of LEDs represents 11% of the full energy. The {photograph} reveals 4 inexperienced LEDs are ON, which suggests 44% of the facility is coming from photo voltaic. The remaining 55% of energy is being drawn from the battery. The inexperienced and purple LED mixture adjustments as the daylight varies. 

Determine 6 The lamp in Hybrid mode. 4 inexperienced LEDs point out 44% of the facility is coming from the PV panel. 5 purple LEDs point out 55% of the facility is being drawn from the battery.

5. Design Instance of a 90-W HL with battery backup

Right here, the design of a 90-W HL with a battery backup is proposed. The nominal working voltage chosen is 48 V. 

5.1 HL specs

The specs for the HL design are as follows: 

1. Photo voltaic Panel Specs: Energy = 30 Wp, Vmp = 17.5 V, Imp = 1.7 A
2. Variety of Photo voltaic Panels related in sequence: 3
3. Photo voltaic Array Voltage: Vpv = 3 x 17.5 = 52.5 V; Voc = 60 V
4. Variety of LEDs in every MCPCB (A1 to A9): 15 white LEDs of 1 Watt every.
5. Ahead voltage of LED: 3.12 V
6. Voltage throughout every lamp (A1 to A9): 15 x 3.12 = 46.8 V
7. Present via LED lamps: 0.2 A (chosen) 
8. Present limiting resistor [1]: R1 to R9 = (52.5 – 46.8)/0.2 = 28.5 Ω (choose 27Ω/2W)
9. Adapter specs: 48 V, 2 A

As said earlier, this lamp can be utilized with no battery backup in services which can be open all seven days every week. In these purposes, the solar energy generated is absolutely utilized, so the price of this lamp is minimal. The deployment of a lot of such lamps can considerably scale back the electrical energy invoice. 

Nevertheless, in places of work that function 5 days every week, the facility generated throughout weekends goes to waste. In instances the place one other load can make the most of the accessible PV energy on weekends, reminiscent of a pump, vacuum cleaner, or a battery that wants charging, the PV panel’s output could be related to that load. This manner, we will nonetheless use the HL as is. Nevertheless, if there is no such thing as a different load that may make the most of the PV energy, then we should resort to battery backup.

5.2 Battery choice

The battery choice could be as follows: 

1. Lithium-ion Battery: 13S (13 cells in sequence), Nominal voltage 48 V
2. Battery voltages: Vb(MIN) = 42 V, Vb = 46.8 V, Vb(MAX) = 54.6 V
3. Vitality storage capability (24 Ah):  48 x 24 = 1152 Wh
4. Photo voltaic power era per day: 90 W x 6 hrs = 540 Wh
5. Battery storage: 1152 Wh / 540 Wh = 2.1 or 2 days  

5.3 Photo voltaic cost controller specs

A variety of photo voltaic cost controllers is on the market available on the market. To pick out an acceptable cost controller, the next specs are supplied as tips:

1. Battery Kind: Li-ion, Life-Po4
2. Nominal Voltage: 48 V
3. Controller kind: MPPT
4. Most output present: 5 A
5. Protections: Battery reverse polarity, photo voltaic panel reversal, quick circuit safety, battery overvoltage cutoff, battery low voltage journey.

Be aware that the open-circuit voltage (Voc) of the photo voltaic array is 60 V; subsequently, the chosen parts ought to have a voltage ranking better than 60 V. 

This design is for a 90-W HL; nevertheless, higher-wattage lamps may also be designed. In that case, the lamp MCPCB chosen ought to have a better energy ranking. Alternately, the variety of MCPCBs could be elevated to round 16. This manner, the array could be organized in a 4×4 structure. With an elevated variety of arrays, each the {hardware} and software program of HL must be upgraded. 

It might be doable to attach two MCPCBs in parallel to extend the lamp energy. Nevertheless, on this case, the 2 MCPCBs ought to have an identical LED array ahead voltage. This may guarantee equal division of lamp present. 

5.4 Scheduling

The design proven right here makes use of handbook switches which could be changed with semiconductor switches. On this case, the operation of the HL could be automated with a weekly programming cycle. On weekdays, it can work in hybrid mode. On this mode we will both choose mains energy or battery energy. The period of battery energy consumption could be deliberate to make sure that battery is on the market for charging throughout weekends. 

6. Storing the HL’s extra power

The solar-mains HL proposed earlier, gives fixed mild regardless of the daylight circumstances. It’s a very cost-effective design and could be deployed in giant numbers to cut back electrical energy prices. Nevertheless, if it isn’t used on all 7 days of the week, then the solar energy will get wasted. To keep away from any energy wastage, a battery backup system has been proposed right here as an add-on characteristic. Utilizing batteries, the surplus photo voltaic power could be saved. The battery backup makes this lamp work as an emergency lamp, additionally throughout grid failures.  

Vijay Deshpande not too long ago retired after a 30-year profession centered on energy electronics and DSP tasks, and now works primarily on photo voltaic PV programs.

Associated Content material

• Photo voltaic-mains hybrid lamp
• Photo voltaic day lamp designs use passive and lively present limiting circuits
• Photo voltaic day lamp designs present low-cost lighting options, Half 1
• Photo voltaic day lamp designs present low-cost lighting options, Half 2

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