ENOW SOLAR TEST RESULTS:

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Melissa Richardson
5 years ago
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ENOW SOLAR TEST RESULTS: WINTER, SPRING AND SUMMER APU OPERATION Summary Results enow Inc. has been collecting data from three Class 8 Sleeper Trucks equipped with Battery APU systems.

1 ENOW SOLAR TEST RESULTS: WINTER, SPRING AND SUMMER APU OPERATION Summary Results enow Inc. has been collecting data from three Class 8 Sleeper Trucks equipped with Battery APU systems. Two of the trucks are equipped with a Solar Battery Charging system one is a 200 Watt (rated) system sold by a competitor and the other is a 300 Watt (rated) system sold by enow Inc. The third truck is a control truck, which is not equipped with solar. Based on the data collected during this period, we can conclude: - Battery APU A/C use was very low initially (Jan-Mar), but, as expected, Battery APU A/C use increased in the spring and summer (Apr-July). - Overall, solar maintained a higher average voltage (i.e., higher state of charge) for both the truck and auxiliary batteries over the test period. - The 300 W system generated significantly more solar on average than the 200 W system. - There is about 60% more solar energy that can be utilized if the Battery APU or other auxiliary loads are used more often. - In July, the Battery APU system was in operation during sunlight periods for 16% of the time, either because the sleep cycle entered daylight hours, or the Battery APU was used during the middle of the day. Test and System Design Overview enow worked with the customer s preferred upfitter to install enow s 300 Watt Solar Battery Charger to support the Battery APU systems and other auxiliary loads on a Peterbilt 579 tractor operated by Customer A. The 300 Watt solar system consists of a single 300 Watt panel, a MPPT (maximum power point tracking) charge controller, and all necessary cabling and electrical protection equipment. MPPT solar charge controllers extract the most power from a solar panel by scanning for the optimal power output given the light intensity. It will take advantage of shading and low light conditions where a traditional PWM (pulse width modulation) controller will become inefficient or not produce at all in lower light levels. The upfitter also installed a competitor s 200 Watt solar system to support the Battery APU and other auxiliary loads on another Peterbilt 579 tractor operated by Customer A. The 200 Watt solar system consists of two 100 Watt panels and a PWM charge controller used to charge the truck s auxiliary batteries.

2 In order to monitor the effectiveness of the Battery APU system with the addition of solar, enow and Peterbilt installed Onset HOBO data collectors, which record current, voltage, and temperature data from the truck s main (crank or starter) battery and the auxiliary battery banks. Data collectors were installed on all three trucks (i.e., control, 200 W, and 300 W trucks). The data is sampled from various sensors every 10 seconds, averaged, and logged in 5 minute increments. Thus, the reading at the time stamp is the average reading for the previous 5 minutes. The data is uploaded to the cloud every hour via the cellular network. If the tractor is not in an area with sufficient cellular coverage, the data is stored until the next good cellular service area is entered. The data may be downloaded into a CSV file format which can be directly opened in Excel. The data can be further analyzed and graphed. Although driver logs were not available during this period, it is our understanding that the tractors have been operated in long haul operations in the southern U.S., although the 300 W truck was initially driven by a team of two drivers and is now being driven by a trainer who is likely not operating in a typical long haul manner. Solar and Auxiliary Load Connections Both the 200 Watt and 300 Watt solar systems are mounted on the back half of the tractor s roof air fairing. For the 300 Watt system, a two-conductor cable connects the single solar panel to enow s solar MPPT charge controller located in the auxiliary battery box. Initially, the solar charge controller attached to the four AGM auxiliary batteries through a very short wire harness. More recently, the solar charge controller and connection were moved to the truck batteries as requested by Customer A. The solar charging does not interfere with battery charging directly from the truck engine s alternator. For the 200 Watt system, a two-conductor cable connected the two solar panels to a solar PWM charge controller located under the sleeper cabin bunk. The solar charge controller is attached to the four AGM auxiliary batteries through a longer wire harness. The Battery APU A/C is connected to the auxiliary batteries, but the Battery APU system has a battery separator (i.e., contactor) that connects the truck batteries to the auxiliary batteries. See Figure 1. Note that in the case of the Peterbilt 579 tractor, the sleeper cabin heater and the inverter (for hotel loads) are connected to the truck batteries instead of the auxiliary batteries. ALTERNATOR SEPARATOR AUXILIARY APU HOTEL LOADS FIGURE 1: APU CONNECTION TO AUXILIARY (CONTROL TUCK)

3 The 300 Watt solar system was originally connected to the auxiliary batteries (see Figure 2a), but, due to the operation of the battery separator 1, and the fact that the inverter and sleeper cabin heater were connected to the truck batteries, the truck batteries were in jeopardy of being discharged too low to start the engine. In order to evaluate a potential solution to the above situation, enow worked with Customer A to connect the solar to the main truck batteries instead of the auxiliary batteries (see Figure 2b). This modification occurred on March 20, This gives priority charging to the truck batteries, but when the truck batteries are fully charged, the battery separator will move energy from the truck batteries to the auxiliary batteries. When the battery voltages drop below a set point (i.e., 12.5 volts), the battery separator disconnects and the main batteries will charge from solar until they are fully charged again. SOLAR PANEL ALTERNATOR SOLAR PANEL ALTERNATOR CHARGE CONTROLLER CHARGE CONTROLLER SEPARATOR SEPARATOR AUXILIARY AUXILIARY APU HOTEL LOADS APU HOTEL LOADS FIGURE 2A: SOLAR CONNECTION TO AUXILIARY FIGURE 2B: SOLAR CONNECTION TO Performance Results Battery APU A/C Use Monthly Battery APU electrical demand presented in Table 1 and Figures 3 and 4 shows A/C use was very low initially (-March) on all three trucks, but, as expected, Battery APU A/C use increased in the spring and summer(april-july). We can also see from Table 1 that the average in-use current draw from the Battery APU A/C over the test period to date was around.6 Amps, which implies a duty cycle of 49%, based on a maximum current draw of 65 Amps for the Battery APU system. Note that the 200 Watt truck sensor didn t measure A/C use for March-May and the first 5 days of June due to a sensor failure, but we believe the A/C was used extensively by this driver during this period. 1. When the truck battery reaches 13.2 volts, the battery separator contactor closes and allows the auxiliary battery to be charged from the alternator; when the voltage declines to 12.5 volts, the contactor opens to prevent over discharge of the truck batteries when the Battery APU A/C is running off of the auxiliary batteries.

4 TABLE 1: MONTHLY APU A/C HOURS OF OPERATION AND ELECTRICAL DEMAND 2 APU A/C USE AND DEMAND CONTROL Hours Amp-Hrs Ave Amps 200 WATT Hours Amp-Hrs Ave Amps 300 WATT Hours Amp-Hrs Ave Amps February , March April , , May , , June , , , July , , , Total , , , Monthly Battery APU Use Use, Hours Control 20o Watt 30o Watt FIGURE 3: MONTHLY APU A/C USE 2. The 200 Watt truck monitoring system didn t measure A/C use from March through May and 5 days in June due to a sensor misalignment. The 300 W truck monitoring system didn t measure A/C use from March due to a power failure.

5 Monthly Battery APU Demand Demand, Amp-hours 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 Control 20o Watt 30o Watt FIGURE 4: MONTHLY APU A/C ELECTRICAL DEMAND enow also looked at the number of times the Battery APU was started in July for all three trucks. Both the Control and the 300 Watt trucks had a high start/stop count of 144 and 90 respectively. The average length of operation was 1.5 hours and.8 hours. The 200 Watt truck had 38 start/stops for an average of 7.7 hours of run time. The 200 watt driver is using the system only for over-night sleeping, while the Control driver used it for both overnight sleeping and daytime rest period use. The 300 watt driver used the system extensively during the day for rest periods, but rarely used it overnight. Battery Voltage Overall, solar maintained a higher average voltage (i.e., higher state of charge) for both the truck (Figure 5) and auxiliary batteries (Figure 6) over the test period to date. Higher average voltages can result in longer battery life and less likelihood of battery depletion events (e.g., dead batteries resulting in emergency service calls). Note, however that average battery voltages can also be affected by Battery APU and other auxiliary load use (higher loads decrease average battery voltage) as well as engine/alternator runtime (more runtime increases average battery voltage).

6 Monthly Average Truck Battery Voltage Battery Voltage Control 20o Watt 30o Watt FIGURE 5: MONTHLY AVERAGE VOLTAGES Monthly Average Auxiliary Battery Voltage Battery Voltage Control 20o Watt 30o Watt FIGURE 6: MONTHLY AVERAGE AUXILIARY VOLTAGES Solar Generation As can be seen in Table 2 and Figure 7, the 300 W system generated more solar energy than the 200 W system. The difference of more than 100% improvement is somewhat surprising considering that all things being equal it should be only 50% more production. Some of this can be explained by the better efficiency (i.e., MPPT charge controller) of the larger 300 watt solar system; and the July Battery APU usage during the day which draws directly from the solar. Other factors include geographic location and the need for solar charging (e.g., battery SOC). It should be noted that the 300 Watt truck recorded 62 fewer days in -April than the 200 Watt truck due to sensor failures. The especially high solar generation in February for the 300 Watt solar system is due to the fact that solar irradiance was particularly high on the 2 days the solar sensor was working that month. The average solar generation on the 200 W truck in May is probably understated due to a misalignment on the sensor. In June we only trusted 10 days of solar data on the 200 Watt truck.

7 SOLAR GENERATION RECORDED 200 WATT Days Watt-Hrs Watt-Hrs/Day 200 WATT Days Watt-Hrs Watt-Hrs/Day DIFERENCE 10 2, , % February 28 6, ,123 1, % March 8, , % April 30 8, , % May 9, , % June 10 4, , % July 8, , % Total (Jan-July) , , % TABLE 2: SOLAR GENERATION COMPARISON OF 200 WATT AND 300 WATT SYSTEMS 3 Average Daily Solar Generation by Month 1200 Watt Hours per Day o Watt 30o Watt FIGURE 7: SOLAR GENERATION COMPARISON OF 200 WATT AND 300 WATT SYSTEMS 3. The 300 Watt truck monitoring system measured solar generation intermittently from through April due to sensor failures and a power failure. Due to a sensor misalignment on the 200 Watt truck the May production numbers are an estimate and may be understated. The June represents accurate data collected for the last 10 days.

enow also looked at what the solar potential would have been for the 200 Watt and 300 Watt trucks if the solar systems were fully utilized assuming the truck or auxiliary batteries were at least

8 enow also looked at what the solar potential would have been for the 200 Watt and 300 Watt trucks if the solar systems were fully utilized assuming the truck or auxiliary batteries were at least partially depleted throughout the day. Using the National Renewable Energy Laboratory s PVWatts Calculator4 to estimate the solar power output for both systems in Kansas City, which we will use as a typical US location for this example, the 200 Watt system could have generated about 817 Watt-hours per day and the 300 Watt system could have generated about 1,225 Watt-hours per day on average for through July. This solar potential is about 63% higher than the average (or Total (Jan-July) ) that was measured during the 7 month testing period for both the 200 Watt (284 Watt-hrs/ day) and 300 Watt (558 Watt-hrs/day) trucks. This indicates that there is about 63% more solar energy that can be utilized directly if the Battery APU or other auxiliary loads are used more often, which we expect to be the case in the warmer summer months provided the operators use the Battery APU as intended for extended rest periods. Battery APU Use during Daylight Hours Starting in June we started to track when the Battery APU was used during daylight hours. Usually this was when the rest period carried into the beginning of the day, but there are several instances when the Battery APU was used in the middle of the day. For July 200 Watt truck had daylight use of 24 hours over a total of 284 hours giving a 9% daylight rate. The average solar generation during daylight was 2.95 amps per hour. The 300 Watt truck had a daylight use of 34 hours over at total of 76 hours resulting in a 45% daylight rate. The average solar generation was 9.5 amps per hour. Daylight use of the Battery APU is when the solar can reach its full potential as the solar can extend the Battery APU run time plus solar is most efficient by putting the power directly to the load instead of into the batteries. On-Board Monitoring System The HOBO monitoring system used for this test has been less than ideal. Problems have been encountered due to installation issues and repairs done in the field. The 300 Watt truck monitoring system didn t measure solar generation intermittently from through April due to sensor and wiring failures. These sensors were replaced and wiring fixed. The 200 Watt truck monitoring system didn t measure A/C use from March through May due to a sensor misplacement in the field. Also in May the 200 Watt solar measurements are probably underestimated. The 300 W truck monitoring system didn t measure A/C use, solar generation, or truck battery voltage from March due to a power failure when an installation technician cut through the HOBO power cable. Currently all sensors are working properly Hallene Road, Warwick, RI p: f: e: info@enowenergy.com enowenergy.com

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