Photovoltaics for cars: the best solution from the natural source to the wheels
There are important differences between the use of solar energy and all other modes of powering the cars. Solar photovoltaics is the only case in which the primary energy can be used on the car, coming directly from nature, in a sort of “short supply chain”. In all other cases, an “energy vector” is used: the primary energy is “incorporated” into a “vector” (fossil fuel, bio-fuel, electricity, hydrogen …), transported, distributed, sold and taxed.
It is a relevant difference: in fact, energy transmission always involves energy consumption and, in many cases, CO2 emissions, energy costs and emissions that would instead be avoided by using direct primary energy on the vehicle, through photovoltaics.
What contribution can photovoltaics make on a car?
Let’s now try to evaluate the savings that can be achieved by integrating the photovoltaic system into a vehicle. The skepticism that has accompanied the use of solar energy in the automotive field for a long time is due to the fact that the power of a solar panel that can be housed in a car with a normal size, of 300 W, is much lower than the power of a medium-sized car, of the order of 50-60 kW. But this observation is as elementary as it is misleading: it would be correct to think so if both systems always operate at maximum power. In the case of a car, this happens almost only when you run at Le Mans “24 hours”.
In reality, most of the motorists (about 50%) use the car mainly in the city, for no more than an hour a day and almost always with only the driver on board. In these conditions, the “average” power required in an urban environment is of the order of 8 kW, considering the partial recovery of the power needed to brake. If the car is used one hour a day, the daily energy required for traction is therefore equal to 8 kWh.
Now let’s go back to the solar panel: not even this, of course, always works at maximum power, at least because at night the sun goes away. However, if we consider a panel exposed in a sunny place, the energy obtainable is roughly equal to that obtainable in about ten hours per day operating at a power of 2/3 of the maximum power: in the case of a panel with a maximum power of 300 W , we can estimate the daily energy obtainable on an average day by multiplying the average power (200 W) for 10 hours, obtaining a daily energy of 2 kWh. The photovoltaic panel can therefore provide about 25% of the approximately 8 kWh per day required for traction, in a typical urban use, a value well over 0.5% that an apparently common sense but superficial analysis, based only on the maximum power , he would have attributed to him.