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Adding automatic solar charging to an electric van By Roderick Boswell How far can an EV travel without having to visit a charger? We added solar panels to the roof of a Renault Kangoo ZE van, plus an onboard inverter. This gives us up to 18,000km a year of driving at no further cost! H aving built the solar van, we’ve achieved up to 50km of driving per day using just the solar panels. Multiply that by the number of days in a year to get the 18,000km figure, although that assumes nice sunny weather year-round, which is perhaps a little unrealistic. Still, sitting in the van watching the onboard batteries charge at 50A for the first time, it certainly was pleasing to realise that it was working as intended. There are surprisingly few reports of this having been done, so we thought we would create a company, “Solely Solar”, based on the concepts of autonomy and freedom. In this article, I will describe how the decisions were made, what we purchased, how we configured and tested it, the integration of the solar 58 Silicon Chip system into the van and the on-road tests. The solar panels Photovoltaic (PV) solar panels have been slowly improving over the past few years. It is possible to purchase single crystal silicon arrays with passivated emitter rear cells (PERC), which were invented by a team at UNSW in Sydney. They are cut in half to reduce the resistance and hence losses. These cells have an efficiency of around 22%, so with full sun delivering 1kW per square metre, you can obtain 220W from a 1m2 panel. So, off I went to eBay to check prices; I found a real Aladdin’s cave of solar treasures. Having purchased a few, I quickly discovered that the power they Australia's electronics magazine could produce was often overstated by as much as 100%. Unless you like opening protracted disputes with eBay (which I did to see how the system works; it does, sort of), be aware that the only reliable indicator of the potential power of the panel is its area. I learned this by spending money and testing the product, an easy task with a multimeter that can measure up to 20A. The two main parameters to measure are the open circuit voltage (Voc), which increases with the area of the panel, and the short-circuit current (Isc), which manufacturers try to keep as low as possible to reduce Joule heating (I2R). For example, I tested a 2m2 solar panel with a Voc of around 50V and an Isc of around 10A. Of course, multiplying those two siliconchip.com.au figures won’t tell you exactly how much the panel will produce since they are measured under different conditions. Still, it gives you a way to estimate the power and compare different panels. We decided to use Longi 510W panels that measured 2093 × 1134mm and weighed 25.3kg since they just fitted onto the roof of the Kangoo. Interestingly, some tests showed around 550W being produced per panel. There is an efficiency temperature coefficient of -0.25%/°C, with the stated performance being at 25°C. So, on a cold morning, with a temperature around 0°C, the panels will be 5% more efficient. Conversely, of course, during the afternoon in summer, the air temperature may be 40°C, and the panels will be so hot you cannot touch them, leading to a performance reduction of up to 10%. The van There are currently several very expensive electric vans on the market. Still, a couple of years ago, the only real option was the Renault Kangoo Zero Emission, although BYD slipped around 50 T3 electric vans into Australia as they were mucking about with distributors. I decided on a 2019 Kangoo ZE that had been used to drive from the Blue Mountains to Sydney every day and back, which had travelled around 85,000km. The Kangoo has a Mennekes Type 2 7kW onboard charger that requires a Type 2 to Type 2 cable, or a destination charging cable with a Type 2 on one end and a regular 10A 230V mains plug at the other. Two of us would have to drive to Sydney from Canberra, pick the van up, and drive it back. Since the top of the CCS (Combined Charging System) plug is a Mennekes Type 2 plug, we purchased a Type 2 to Type 2 cable. We made an unpleasant discovery when we stopped at a commercial charging station at Sutton Forest on the way back to Canberra. The top Mennekes socket of the CCS charging station was not connected! As night was about to fall, we swiftly returned to Canberra in the other car, leaving the Kangoo in the parking area adjacent to the chargers. Rats! After some research, we found that the commercial CCS charger providers wanted a fast turnover so their chargers only provided DC fast charging. The siliconchip.com.au The inside of the Renault Kangoo ZE van with some basic wiring for the solar panels. The onboard inverter and the other electronics required for the solar panels are stored in the large timber cabinet on the side that doubles as a kitchen. poor old Mennekes is generally limited to 7kW, resulting in a wait of several hours. The company supplying the chargers evidently didn’t want anyone sitting on their charger for that long, so they removed the Type 2 option. The following morning, we returned much wiser and drove the Kangoo to a local winery that had a couple of Type 2 chargers. We plugged in and then discovered that you have to download Australia's electronics magazine the charger supplier’s app on your phone to arrange payment before you can start charging. After doing that, it was finally charging, and we had four hours to kill. We had lunch at the winery and drove around the area, which was really quite beautiful, and got back to discover that a watched charger never boils. Eventually, we were back on the road again, popping into the Goulburn July 2024  59 Workers’ Club later for supper and another couple of hours of Type 2 charging. That got us home. At home, we used the cable with the Type 2 connector on one end and 3-pin mains plug on the other to recharge the van overnight. The dash instruments show the instantaneous kWh/100km figure, estimated range, distance travelled and instantaneous power usage. It also has a ‘fuel gauge’ that correlates more-or-less with the battery state of charge (SoC). At 1/8 SoC remaining, you touch the red line and a warning light suggests you look for a charger, as there is only about 30km of range remaining. A double red line follows at 1/16, and another light appears that the manual explains is to warn that you are about to go into ‘limp home’ mode. I checked this scheme out, down to 1/16th full, and all worked as expected. A few tests showed that the charger is about 90% efficient, with 10% lost between the mains and the van battery. The majority of the losses are from the inverter built into the Kangoo. I conducted a sequence of tests on range and efficiency at different speeds, with the main result being that the battery still had about 30kWh left of the original 33kWh. Not too bad after 85,000km! The best efficiency of 14-15kWh/100km was at 50-60km/h. It read about 17.5kWh/100km at 80km/h and over 25kWh/100km at 110km/h. It is interesting to get used to nearly one-foot driving with the regenerative braking. I performed another test in hilly terrain, taking the van to the Picadilly Circus pass through the Brindabellas, a voyage about 50km long and 1000m vertical. At the top of the mountain, the consumption had increased to 22kWh/100km, but on returning home, it had dropped back to around 15kWh/100km, having regained most of the energy used to ascend. This was with careful driving, trying to keep the efficiency indicator out of the red, even if it meant going at only 30km/hr on the steep parts of the ascent. The regenerative braking certainly is effective. To sum up the efficiency/range tests, keeping to 50km/h, I got a range of about 220km, but at 80km/hr, it drops to around 150km. These results agree with the USA Electric Vehicle Design Base (EVDC) range estimate for the Kangoo ZE of 160km. There is real optimism in Europe with the New European Driving Cycle (NEDC) that claims a range of 270km, while the Americans take a more realistic view. Attaching the solar panels According to the Australian Design Rules (ADR) for loads carried on The inside of the timber cabinet, which contains the Victron MPPT solar chargers, circuit breakers, busbars, battery charger etc, as shown in Fig.1 opposite. The eight batteries sit under a piece of wood on which the main circuit breaker is fitted. vehicles using public roads, an overhang of 1200mm without flags is acceptable both front and rear. For side protrusions, 150mm on each side is allowed beyond the vehicle’s width. This meant the Longi 510W panels were a good fit, so we decided on having three lengthwise on the roof, with the first in line with the top of the windscreen and about 500mm of overhang at the rear. MORID Pty Ltd did the design using the roof rack attachment points (three on each side). The main challenge was the roof loading rating of the Kangoo, which is just 100kg. Having three 25.3kg panels means that the whole roof rack structure could weigh only 24.1kg and had to be strong enough to hold the panels. A plastic 3D printer was employed to print the fittings for the prototype. We then attached them to the roof to verify their stability, size and appropriateness. Having passed this first hurdle, the design was sent off to PCBWay for machining out of aluminium. These guys are really good and they have never disappointed us. The six adaptors were finished and sent to us. Perfect! Assembling the panels into an aluminium frame, drilling holes in the roof and attaching them to the van took some time. We just managed to get it a few millimetres under the protrusion rules. We were then faced with the one task we had been avoiding: drilling holes in the roof to get the cables from the panels into the van so they could be connected to the interior electronics. We took the plunge, drilled the holes in the roof (sorry Mr Renault) and fitted the grommets. As usual, after the cables were slipped through and the connectors attached, we found that we had forgotten to slip a clip on the connector; oh dear! We had to desolder the connectors, attach the wayward clip, then resolder the connectors. The Maximum Power Point Trackers (MPPTs) The solar panels do not charge the Kangoo’s battery directly, as the onboard charger does not support charging from low-voltage DC. Instead, the solar panels charge a secondary 24V battery that we installed (more on that later), and that battery runs an inverter that feeds the onboard EV charger – see Fig.1. 60 Silicon Chip Australia's electronics magazine siliconchip.com.au Our solar panels put out about 50V and 10A, and we need to charge a 24V battery, so a conversion is necessary, conserving as much power as possible. By chopping the input voltage at around 100kHz, small inductors (or coils) and an electronic circuit called a buck converter can reduce the voltage without wasting too much power. As a result, the output current is higher than the input current. If we are charging the 24V battery at, say, 27V, the charge current would be 18A minus the losses from the buck converter, which are only around 5% nowadays (ie, 95% conversion efficiency). MPPT is needed to get the most power from the panels, as the voltage/current curve has a peak that moves depending on the ambient conditions. We want to manage the panel voltage to keep it at that point while doing the buck conversion. The MPPT chargers also continuously monitor the battery SoC to provide the correct charging profile. A few years ago, such circuits comprised lots of individual components and were pretty expensive, but now a single chip can carry out most of the operations and the price of MPPT chargers has fallen dramatically. It pays to shop around! The secondary battery Once again, this was a learning experience. For safety, we decided on Lithium Iron Phosphate (LiFePO4) cells since they are less likely to fail than Lithium Manganese Nickel cells (and if they do fail, it’s usually less spectacular). However, they have a lower energy density. The next choice was the voltage. Using a 12V DC battery would require high currents and hence significant Joule losses, so we went for 24V. Should we use a series/parallel arrangement of 12V batteries or build our own 24V system from 3.2V prismatic cells? If the latter, we would need a battery management system (BMS) to balance the voltages of all the cells and prevent overcharging and overdischarging. I tried both approaches and started by purchasing four 12V 135Ah batteries. These were bought at different times during the COVID-19 years, and we soon discovered that we needed to get a balancing system, so we purchased that as well. It worked, but it was a clunky solution, so off to AliExpress to purchase eight 3.2V 320Ah PWOD prismatic cells and a 24V BMS. These took some months to arrive, and we eagerly assembled them with the BMS attached to a 20A charger and waited until the BMS cut out. We then discharged it into a bathroom heater via an inverter and surprise, we only got 275Ah. We charged it again and only got 275Ah the second time, so what should we do? Messaging the PWOD AI was highly frustrating, as it was impossible to have a coherent discussion. They finally offered $26 off the next purchase, or we could send them back at our expense. Sigh. So we swallowed the bitter pill and realised how the price could be so low – caveat emptor. We would have to make do with 6.7kWh of stored energy, 14% lower than expected. The inverter There are a great many DC/AC inverters on the market. The first one I bought was from Victron and it is installed in our solar off-grid shed. Actually, I did buy a few smaller inverters before that for use in the car Fig.1: each solar panel has its own MPPT battery charger to maximise charging efficiency. The battery management system ensures the cells remain in balance and are not overcharged or overdischarged. siliconchip.com.au Australia's electronics magazine July 2024  61 and for camping, but nothing in the kW range that we were investigating. Pretty much all the inverters now use chopped voltages rather than heavy transformers, making them quite compact. We needed 3kW continuous and 6kW peak (for a few seconds), with a charger, and we got those capabilities for well under $1000. However, we soon realised that the inverter’s internal charger could only draw a maximum of 2300W from the wall (230V <at> 10A). Since it was to be used for charging the Kangoo, we purchased a second inverter rated at 4kW continuous and 8kW peak for around the same price. We tested the batteries and inverter before installation to verify that everything was operating as expected. With everything installed in the van and the solar panels connected, the isolating circuit breakers were flipped on and, hooray, the Bluetooth app on our Android phones showed the voltage, current and power being delivered by each of the three panels. The BMS showed the battery charging. Charging the Car The last step was to charge the car with solar panels. On the first try, using the 24V battery, inverter and 10A home charger, the car refused to charge. The charger was blinking; after reading the manual, we realised that the error was related the Earth connector on the socket. Most inverters have Earth wiring, however, most of the time, it is floating. To solve this problem, we connected the Earth and Neutral inside the inverter and the car started charging. Using only the 24V battery for charging the car, the inverter would draw around 90A and could add 6.5kWh (~40km range) to the car. Using a fully-charged 24V LFP battery and solar panels on a sunny day at the same time, the solar panels provide around 50A and the battery around 40A, adding up to 16kWh (~100km range) to the car in one day. You can’t do that two days in a row, though, as the secondary battery would be discharged at the end of the first cycle, and it needs to be charged initially to provide so much energy to the EV battery. be ideal for camping. Since micro-­ campers are popular, we took the van to Kata Camperbox in Sydney to do their magic. As can be seen from the photos, the fittings are all real timber, and the result is a true beauty to behold. There is a pull-out kitchen, a slideout fridge that runs from the 24V battery and a space large enough for two electric bikes that can also be used as a sleeping space. It is about the same size as a business-class bed on an aircraft. To get an idea if everything would work, we took a camping/cycling trip to the Orroral Valley campsite that had recently reopened after the bushfires. This 55km trip from Canberra was successful; all the subsystems worked, and nothing fell off the van. My electric bike fitted in the van OK. However, I must say that I am not a great fan of sleeping in enclosed spaces, even those at the pointy end of an aircraft. I know; first-world problems! Planning for a trip In Australia, the Bureau of Statistics has determined that the average passenger vehicle travels a smidgen over 10,000km a year, an average of a bit under 30km per day, well within the parameters of our Solely Solar van. The van would have to be left out in the sun all day; still, rooftop parking is generally the last to fill up, so perhaps that is not too much of a drawback. So what sort of a trip could be made with our little Solely Solar Renault Kangoo ZE, just relying on solar generation of electricity? The Kangoo has 30kWh in its primary battery and 6.7kWh in the secondary battery. Assuming you have solar panels on the roof of your house connected to a home battery, it is simple to just charge the Kangoo at home without paying for grid energy. You could have a separate solar system for charging the car, but then you could argue that you are losing around 10¢/kWh by not selling any excess power back to the grid power supplier. Then again, nothing is completely free. However, if you would like to travel further than a few tens of kilometres (eg, to work and back), you need to do a bit of planning, especially if you want to get back in under a week. And there are limitations on how the remote charging is carried out. As mentioned, the solar panels alone cannot supply the full power necessary for charging via the inverter; they need to be supplemented with power from the solar batteries. Arriving at a campsite in the evening, the solar battery will generally be full, allowing the 6.7kWh (ignoring losses) to be transferred to the traction battery in a few hours while it is dark. The next morning, the panels will start charging the empty solar battery and will absorb around 4.5kWh by midday, at which time the inverter can be brought into play, allowing both the solar electrons and the secondary battery electrons to flow into the traction battery for the daylight that remains. Given a sunny summer day, the solar panels would provide around 9kWh, so the Kangoo would need about 3½ days to fully recharge if exhausted. So, with judicious planning and good weather, you could take a long weekend and travel within a radius of around 180km from your house and return, paying virtually nothing for the trip. Not too SC shabby! The camper conversion Our group had some discussions and decided that the Kangoo would 62 Silicon Chip The van with solar panels being used for camping for the first time. Removing the bike frees up space to sleep inside. Australia's electronics magazine siliconchip.com.au