Harden Electric Blog Why I will be putting Solar on my Project Car – And why Solar is not efficient enough yet to be installed on an EV

Why I will be putting Solar on my Project Car – And why Solar is not efficient enough yet to be installed on an EV

So this is one question I have had quite a few times online, will I be putting solar onto my Electric Car conversion?

Definitively, the answer is no. Well, at least not for the charging of the main battery pack.

So, for those that don’t know the terms, lets get some terms out of the way:

WhWatt HourA Watt Hour is a unit of measurement for power over a period of time (an hour), or in our case, a way of measuring capacity. One Watt hour is equal to one Watt of average power flow over an hour
kWhKilowatt Hour1 Kilowatt Hour is essentially 1,000 Watt Hours, and is what you get at 1,000 Watts, over a period of 1 Hour
Efficiency %N/AThis is how efficient the system you are using is, so if something is only 80% efficient, then 100% power going in = 80% power going out
VVoltsA “volt” is a unit of electric potential, also known as electromotive force, and represents “the potential difference between two points of a conducting wire carrying a constant current of 1 ampere
AAmpsAn amp is one unit of constant electrical current. “Amperage” is the strength of that current, expressed in amps (or “amperes”). If you were to think of electricity as water through a hose, amps would be the water.
Square MeterA Square Meter is a unit of area bounded by a square box measuring 1,000mm x 1,000mm
Table 1 – Terms

Now that above table should help you understand some of the basic terms that I will be using in this post, therefore where I can (read: Where I remember) I will try and convert these to Imperial units of Measure because I understand that American readers and some British readers will understand those terms better.

So where possible, I will try and convert m² to ft² just to help you conceptualise the units I am talking about.

Area to work with

Right, so I just went and measured my Jumbuck, and the area that I could conceivably use on the back if I fit/build a hard tonneau is 1,300mm x 1,300mm which gives me an area of 1.69m² (18.19101ft²)

Now, to help you conceptualise this, here is a render from Fusion 360 on this area on my Jumbuck.

Jumbuck Tonneau showing useable area
Jumbuck Tonneau showing useable area

As you can see, that’s not a lot of room to play with, especially when you consider that underneath that, I need support struts and such.

From here we can start looking at solar panels

Picking the Solar Panel

Ok, so I went digging through solar panels, and I realised quickly that I would need to find one that fitted my space, which isn’t great, as I do not have a lot of space to work with.

So in the end, I settled on the best one for the job (After about 10 minutes of earching) being this 150W @ 12v Solar Panel from Jaycar Electronics.

Yes, I know there are likely better ones, but I see this as an “easy to source consumer panel” that would be in the realms of an average owner.

So, at 0.69m x 1.35m you end up with an area of 0.9315m² (10.0265826ft²) or 148.725W/m² which isn’t great, but it’s “ok” for a consumer solar panel.

So given my area I can have 2 of these, for a total of 300W peak generation.

What is Peak Generation?

Ok, so here is the kicker, it’s sunny outside all day right?


Yes it is sunny outside, all day, but the PEAK generation is when the sun is high above you in the sky, and you are getting the maximum out of your solar panels.

Now, I have a weather station and monitor my solar that I get at my property, here is the graph.

Average solar radiation
Average solar radiation

So as you can see, I get some days where I get a really high amount of solar per m², and other days it is quite low, though my yearly average is 745W/m²

However when we look at the daily average:

Daily Solar Radiation

I was only getting the peak for that day between 9:15AM and 12:15PM.

I know what you are sayiong, there was clouds that day, yes, there was.

There can be clouds every day, and the average peak solar is estimated to be between 3 and 5 hours per day in most places, but the average is great, but our panels are only able to use anything above 148.725W/m² then I’ll look at when I was getting above that line.

So this gives us 1 decent block from 7:30 AM to 1PM, so we get around 5.5 hours

How this stacks up

So now we know that we have around 5.5 hours per day getting above our panels efficiency requirement, and we know we have 2 x 150W panels that can fit on the car.

So from here it is simple:

(150 x 2) * 5.5 = 1,650Wh of potential solar radiation, or, 1.65kWh


That regulator is a 12v regulator, and through my own testing with regulators and stuff, I found out that the regulator that comes with the system is only 80% efficient at taking that 150W and getting it to my batteries…

So, we can start at either end, but I’ll start with my final number, 1.65kWh and find out that only 1.32kWh makes it to my batteries

Oh, but wait, that’s 12v…


I need to make it at least 240v to get it into my EVSE and then into my PDM and into the car…

So Caravan Chronicles makes a really great writeup on this over in this article and they say that a good inverter is 92% efficient and a bad one is 50-60%

Let’s just go middle of the road and say that we are 75% there, as that seems to be where I got from my own research (No, I will not write a 10,000 word article on that alone, you are a grown up, you can search yourself)

After that efficiency loss, my 1.32kWh is now down to 0.99kWh

Now, thankfully, I am using an Off The Shelf charger, and I can find that the efficiency for a Nissan Leaf Charger is around 85%

So my 0.99kWh is now down to 0.8415kWh or 841.5Wh

But how practical is this?

Not very.

So, the Nissan eNV200 that I am using as a donor has an efficiency from it’s 24kWh battery pack of 170km which isn’t great to start with

This equates to around 140Wh/km or 226Wh/mile

Now I am going to stick it in an albeit lighter, but less aerodynamic car.

Honestly, let’s just say that I’ll get about 1.5x less efficiency, so I’ll end up around 210Wh/km or 339Wh/mile

So now that we know that a full day in the sun will net us around 841.5Wh that means that a full day of charging will give me just over 4km (or just shy of 2.5 Miles) of range.

So realistically, with 24kWh or 24,000Wh of capacity, if I was to become completely and utterly straneded at 100km from a charger, then I would need to sit on the side of the road for around 28 days to get a full charge.

Plus, given that my current energy plan at home is $0.16/kWh, that means that each day I save myself $0.13464

Now given that the panels are $406 each, and a good solar12v-240v inverter is around $500 then I’m into the solar by $1,318 it would take me around 9,789 good days of solar just to pay off the cost of installing the solar system.

This works out to be somewhere in the realm of 26 years…

Why I will be putting solar onto my Project car


I’m a simple man, I like my cars fun, and my beer cold.

I have a Dometic CFX35 Fridge sitting in my shed at the moment keeping my beers cold, and I would like to install that into the ute.

Sitting in my shed is a 1.2kWh AGM Gel Battery doing essentially nothing, I just make sure that I cycle it through the maintenance charger to ensure it doesn’t die on me.

Given that it uses 43Wh in use, that battery alone can net me 27 hours of use, and with the solar, my battery will be easily recouped from what the fridge uses daily.

Especially if I install a Redarc DC-DC and charge the battery when I am driving, or charging the car at home off the mains.


So whilst solar technology may not be there yet for charging your EV, at the end of the day, we can take solace in the fact that if I was to run into the shopping centre and grab cold meat, or I was to go and watch the footy, go to a friends house, or just need a fridge in the car for whatever reason, I can be rest assured that my beers will be cold, and my meat won’t spoil on the drive home.

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