• Solar On EV

How to solar sizing an EV - of the car's roof...

Updated: Nov 16, 2021

If you can put solar on your EV, where would you put it? On the car's roof, maybe the bonnet too. OK.


How much space have you got? What power level do you get with that space? Does it worth the money? Does it provide a good return on investment? Or just good for the environment?


That is a lot of questions, just for sizing the solar system for your EV.



But, there is more...


How much distance do you drive under the sun each day? How long do you park during the day?


Why? Most passenger vehicles worldwide travel between 25-50km daily and are parked 95% of the time. There are always chances that you park under the sun (or can park under the sun).


We’re not driving a World Solar Challenge solar racing car that optimizes solar's flat surface area. The car we drive has a limited flat surface. The current “solar car” developing, Lightyear One, Aptera, SONO Sion, tried to increase the flat surface area while not sacrificing aesthetics and performance, etc.


If you’ve tried our “What IF – Solar Gain Calculator”. When you pick the power system, you’ll notice that it’ll also calculate the surface areas required. It’ll give you an idea of the surface area occupied on the solar system size picked.


So what’s the point? Are there other places we can put solar on your EVs?


Well, there are. There are ways to put solar on an EV, and so it affects the sizing.


Still not convinced? Let me show you the differences.



Flat Surface On Your Car


Let’s pick a sedan as an example, as shown below,


Areas illustration of a typical passenger car for comparison with EV
Possible solar surface area illustration of a typical sedan

There are generally two areas you would put (glue) the solar cell on a vehicle, the roof (area A) and the bonnet cover (area B). Area A is the surface all vehicle manufacturers will consider first as it’s directly under the sun and least affecting aesthetics. Area B is the bonnet cover with similar effectiveness as the roof; however, it affects the vehicle's overall aesthetics as people see the solar cell directly. In the picture above, there is also Area C which we will discuss later.


According to our “Solar Gain Calculator”, an area of 1.3 – 1.5m2 for an integrated solar system would result in a 200W solar power system. For the size of a typical sedan above, both the roof (Area A) and the bonnet (Area B) can install a 200W solar system separately. The solar benefit of a 200W system is minimal. If both roof and bonnet (A+B) are used, the output becomes slightly more helpful.


I wouldn't bother about the cost of installing solar on area A+B, affecting aesthetics, with minimal benefits. Would you?



What If This Is A Tesla


Let’s do the estimation on a Tesla Model 3 LR Dual Motor and a Cybertruck Tri-Motors


Model 3


For a Model 3, area A is roughly 1.4m2 and will fit a 200W system, while area B is 1.7m2, which may hold a 300W system (250-300W). This maximum of 500W solar on your Model 3 covered the bonnet and the panoramic roof. According to the “Solar Gain Calculator”, based on a 35km of avg daily driving distance and 500W solar gain on a Tesla Modle 3 LR Dual Motor will result:


A Good Mileage Gain


26 days of driving without recharging are equivalent to only 14 recharges required over the year from 26 recharges. The driving range also increased from 490km to 909km - an 85% increase in mileage performance.


Will you sacrifice your panoramic roof and the aesthetics for an integrated solar system that gives you a close to double mileage performance?



Areas of illustration shows the possible uses separately
Solar surface areas illustration for a Tesla Model 3 and a Cybertruck

Cybertruck


For a Cybertruck, areas A and B are 1.8m2 and 1.3m2, similar to a Model 3 total of 500W power outputs. Since Cybertruck is a more energy-hungry beast, a 500W power gain with a 35km average daily mileage will result:


29 days of driving without recharging are equivalent to only 12 recharges required over the year from 17 recharges. The driving range also increased from 750km to 1024km. A 36% increase in mileage performance.


A similar question again, “Will you sacrifice your panoramic roof and the aesthetics for an integrated solar system that gives you an increase of about 1/3 the mileage performance?”


Elon Musk Believes In Solar


Luckily, Elon Musk always wants solar on Tesla. This time, he made the Cybertruck tonneau cover with a solar option (Area C, 2.8m2). If we have the area A+B+C altogether, this is about 5.8m2 equivalent to a total of about 900W, which gives:


93% Mileage Gain


41 days of driving without recharging are equivalent to only 9 recharges required over the year from 17 recharges. The driving range also increased from 750km to 1447km. A 93% increase in mileage performance.


Well, I don’t believe that people with Cybertruck would be driving at average mileage of 35km daily. But let’s assume if this was right, it is close to double of mileage gain.


Will you consider it? Or this time, just the area C, the tonneau cover with the solar option?



A Mini Electric Car With Solar


What about some extra small EV? The Wuling Hongguang Mini EV, we compared with Aptera before. We lack the surface area informations for a Wuling; therefore, we’ll use something similar, Suzuki Swift, as a baseline for the calculation.


Areas illustrated for a Suzuki Swift to compare with Wuling Hongguang Mini EV
Solar surface area illustration of a Suzuki Swift

The Wuling is an EV with only 2.9m long compared to a Suzuki Swift of 3.7m long. However, I don’t see a massive difference with the surface area A and B from them, as Wuling is shorter in the front and back. We’ll use a Suzuki Swift to calculate the areas and assume a 10% off for the Wuling Hongguang Mini EV.


Therefore, area A for a Wuling is 1.5 x 90% = 1.35m2, area B is 0.7 x 90% = 0.6m2 with a total of 1.95m2, that is equivalent to 300W of solar system. Since Wuling is a Mini EV with a small battery of only 170km range, the solar gain will give:


Over doubles the Mileage Gain


10 days of driving without recharging are equivalent to only 35 recharges required over the year from 75 recharges. The driving range also increased from 170km to 360km. A 110% increase in mileage performance.


Impressive right! Thanks to its ultra-efficient energy system, it results in over 100% of mileage performance increase. But the question is, will you do it? Remember, this Wuling Hongguang Mini EV, priced only $6000.


In my opinion, I won’t. I might install the Cybertruck solar tonneau because it looks cool, but not any others. I want to help protect the environment. I want to contribute to CO2/GHG emission reduction.


It all comes down to cost-benefits. I think most people agree with that. Don't you think?



The Area C


It is the secret area, like area 51.


No. It is just the area of a portion of the vehicle from the top view. And yes, I’m talking about solar in this whole area.


Remember one of the articles we discussed before, Elon Musk wanted solar on Tesla since…


Elon Musk said he wants deployable solar charging on Tesla. I cannot agree more with that. He even wants solar “wings” for more area on Cybertruck.


“What if”, we can put deployable solar that spans slightly over the vehicle roof but within the vehicle width by the "wings".


All the area C diagram of the typical sedan, Tesla Model 3, Tesla Cybertruck and Suzuki Swift. The possible sizes for the Deployable Solar System
The "Area C" extracts from the above illustrated diagrams

If we translate this area into solar mileage gain at 35km daily driving distance, they are:


4 - 8 folds of Mileage Gains


Tesla Model 3 - 900W solar, i.e., 82 days (2.7 months) of driving without recharging, equivalent to only 4 recharges required over the year from 26 recharges. The driving range also increased from 490km to 2874km—a 485% increase in mileage performance (close to 5 times).


Tesla Cybertruck – 1500W solar, i.e., 109 days (3.6 months) of driving without recharging, equivalent to only 3 recharges required over the year from 17 recharges. The driving range also increased from 750km to 3799km—a 506% increase in mileage performance (5 folds).


Wuling Hongguang Mini EV – 90% of 3.5m2 is 500W solar, i.e., 40 days (1.3 months) of driving without recharging, equivalent to only 9 recharges required over the year from 75 recharges. The driving range also increased from 170km to 1413km—an 830% increase in mileage performance (more than 8 times).


Area C does not include the bonnet area (area B). What would happen if they were included:


For a bit more space, you're "Off-Grid"


Tesla Model 3 – infinite driving. It is totally “Off-Grid”; no more recharging from a 32% increase of surface area.


Cybertruck – recharge only twice per year, not far from “Off-Grid”. A 30% increase in surface area will make it “Off-Grid”.


Wuling Hongguang Mini EV – infinite driving. It is totally “Off-Grid”; no more recharging from a 20% increase of surface area.



How Realistic Is The Result


Of course, those calculations were based on several assumptions:

  • Daily driving over the year of 35km

  • 5 hours average of solar charging under the sun per day over the year (typical in US and AU)

  • 200W per m2, plus 20% of extra space for covering the area, efficiency about 23-24%

  • Recharging frequency and mileage calculate until the battery is depleted (I don’t think anyone does that).


There will be variations on factors that are affecting the results. Some may do better and others for worse, but achievable.


Solar cells efficiency increase gives the same Mileage Gains


If solar cells' efficiency increase by the same percentage as surface area, it gives the same results, “Off-Grid”. At a 25% solar cell efficiency, an 20% increase is 25% x 1.2 = 30% solar efficiency, a 30% increase is 25% x 1.3 = 32.5% solar efficiency. Such levels of solar cells are already on the market. We’re just waiting for the price to come down to more suitable for residential / vehicles use.


If we can have a more extensive coverage area for solar, a deployable system spans over Area C. The surface area increases vastly. It does not affect the vehicle’s aesthetics because it is put away when not used. It does not require “gluing” solar cells on the surface. It does not block out the beautiful panoramic roof. We can get valuable benefits while contributing to the climate.


Have you noticed that we didn’t include any trunk cover surface for calculations? Mainly windows and the roof.



Stop Waiting On Solar Car, Try Something Else Instead


If we want to put solar on EV, solar-powered cars, let's do it now. But not the way of the “Solar Car” idea by gluing solar cells all over our EV. Solar requires a flat surface, and the surface area available on the vehicle we drive nowadays is minimal. I mean, let’s keep researching the technology until it’s more ready for the market. And let’s focus on more practical research/solutions for putting solar on EVs, particularly "Solar Recharging System for Electric Car", or “Deployable Solar Systems for Electric Car”.


Deployable Solar. I think this is a topic we should dig into further.

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