Another interesting question off group which I thought I would share for those that are interested in this technology......

Question

i suggest you contact nanosolar, Nanosolar: to see if they will coat your plane with solar cells for free as an experiment. then make a deal with them for the future. the solar cells could charge the batteries, extend flying time, and are very thin and light. you are welcome to my idea.

Answer

the problem is that solar panels simply do not produce enough electricity to be of any benefit. The total wing area of the aircraft is only 9.5 m². The very best solar panels available theoretically produce around 300 W per square metre. This has a total energy production of 2,850 W We require just under 10 times this amount for slow cruise. 20-22 kw in Australian heat and 18-20 kw in colder areas.

As you can see there is no benefit.

Let's say a solar system on an aircraft weighed 40 kg (the nano panels weigh 2.8 kg/m2 + inverter etc) then we would actually be going backwards because it would use more electricity than the system can produce to actually carry around the extra weight.

Please don't think we have not been down this road already, many times

mcoates - I'm interested in the difference between the 1000 charge cycles you quoted and the 300-700 charge cycles in the Pipistrel FAQ (to hit 75% health).

There is a pretty big difference in battery-related hourly running cost between 300 and 1000 when you are paying EUR12K for a cell replacement.

300 cycles would increase the battery-related hourly running cost to EUR40/hour (AUD$60/hour), assuming one hour per cycle.

Also, what is the AUD cost for the E12K cell replacement? E12K works out to about AUD$18K by direct conversion, but I assume we are adding GST plus whatever other costs Aussies generally have to pay in comparison to other countries?

The battery manufacturer claims a 1000 cycle for the units operating under normal conditions before they get to 75% of their manufactured original capacity.

Pipistrel have tested this latest battery chemistry we are using and have managed to get 700 cycles and they are still above 80 something percent so for this reason Pipistrel are guaranteeing a minimum 700 cycles because that is what they have tested this current battery chemistry to.

There are however some caveats and they have to do with operating the aircraft/batteries incorrectly and against the advice of the manufacturer which include long-term cold storage (think of winter in Canada whether batteries can come close to freezing) think of running the batteries below the stated minimum amount which is 20% charge (this is what we consider to be zero battery remaining). If you do this on a regular basis then you will reduce the battery life significantly. Pipistrel have tested in extreme cold conditions, trying to use frozen batteries etc. as part of their testing and they believe that this will reduce the recharge cycle down to about 300.

Part of the training you receive when getting an electric aircraft is to be aware of the limitations of the batteries. Think of it like a normal gasoline engine, if you don't warm up the engine before takeoff and you roll out of the hangar at full throttle you know that your engine will not make 2000 hours or whatever the TBO is and it is exactly the same with a battery system operated incorrectly. Failure to comply with the rules and recommendations on using the batteries reduce their effective lifespan considerably.

Also be aware that the pricing given for battery replacements etc. in my earlier correspondence is based on the pricing from October 2017. I suspect when somebody is looking for new batteries in two years time or three years time that the price will be significantly cheaper based on what we have already seen with this cell manufacturer.

It seems like a better option might be a solar charger kit that can be sold with the plane - but maybe it's cheaper to just install a regular solar power system and plug the charger into that. Hangars do tend to have no shortage of roof space, and the panels don't need to be anything fancy.

I did a few calculations a while back while pondering whether a conversion would be possible. The answer is "no, don't even think about it".

Consider a PA28 with an O-320 engine. The engine alone weighs about 125 - 130kg and produces up to 160hp. From the Warrior handbook, you'd expect to burn 5.5 GPH at 55% power (88hp, 66kW). With 48 gallons of usable fuel, you get just about 8:60 endurance (never mind reserves, ground handling, climb, etc).

I'll assume that an electric motor of the same power (160hp or about 120kW) would weigh about 25kg (a bit over twice what the Pipistrel one does, for a bit over twice the power). This leaves us with 100kg of batteries where the engine used to be, and with current lithium-ion power density (about 250Wh/kg for commercially available cells) this translates in to 25kWh of energy. 25kWh being used at 66kW gives you only about 23 minutes endurance, which is hopeless. However, this is just replacing the engine - not the fuel tanks. If you fill the Warrior's fuel tanks with batteries to achieve the same weight (original 50 gallons weighs 136kg) then that gives an additional 34Wh (31 minutes), for a total endurance of almost an hour.

You could fill the baggage compartment and maybe the rear passenger seats with batteries too. Reducing the available load to 200kg (440lbs) means that you can put another 500lbs or so of batteries in the Warrior (57kWh), which raises the endurance to a whole 1:45. Realistically this would be similar to the Pipistrel's one hour once reserves, taxi, etc are added. Of course, you're now hauling around an exceptionally heavy Warrior (it'll be very close to MTOW all the time due to the batteries) which is no longer a four-seater (back seats are full of batteries). Overhauls cost a fortune (you're replacing out four massive battery packs), probably much more than having the old O-320 done.

The only real advantage over the Pipistrel is the speed - cruising at between 92kts and 105kts depending on altitude. Of course, you won't be doing a whole lot of cruising with only an hour's cruise endurance.

Realistically, it looks like an electric plane has to be designed for the task, and a practical electric plane (at this stage) is probably only going to be a trainer. Pipistrel appears to have hit a pretty good spot, with an endurance just long enough for basic training, a cost low enough for flying schools to find it attractive, and a size/weight comparable to many other light sport aircraft.

We have already sourced a 7.5 kW solar panel system to be installed on a hanger roof. This system chargers an array of batteries which then runs through an inverter to run the supercharging system. It can be complemented any time by connection to the mains grid. This system is ready to go except it is impossible to find solar panel installers working over Christmas/New Year and will have to wait until February for this to be installed.

We are also ordering what is called the " EV ARC" system in the USA EV ARC? 4 ? Electric Vehicle Autonomous Renewable Charger | Envision Solar this is a complete standalone system and will be deployed in the USA originally between Los Angeles and Sacramento. This system is not connected to anything so it does not require any approvals because it is considered a mobile charging station because it can be packed up and moved in less than one hour

What all this shows is the extraordinary energy density in a litre of fossil fuel.

Unfortunately the alternative energy movement constantly glosses over this fact.

Does someone have a figure ? Is it 100 times more energy density compared to batteries. Or is it more than that?

From what I can find on the Internet 1 L of normal fuel is 34.2 MJ (megajoules) this converts to 9500 watt hours.

From there i get lost

We use 18-20 kw for normal level flight in the electric or approx 10 lph in the gas powered version

You go out and do an hour of circuit work, come back, plug in and debrief. How soon can you use the aircraft again for another hour lesson?

The book says 45 minutes to charge after one hour of operation.

We are finding however in Perth where the minimum temperature during our testing was 35° that it would take approximately 60 minutes.

The reason is, the charging cycle is slowed down because of high temperatures to prevent damage to the batteries. The same happens in low temperatures.

So, at 21°C you will get one hour use of the aircraft and the recharge will take 45 minutes.

At 35° you will get one hour use of the aircraft and the recharge will take approximately 60 minutes.

There is no point in comparing energy density of Batteries compared to liquid fuels,(in cars anyway) as electric motors are 5+ times more efficient,

yes, i own 2 electric vehicles..
one can travel 600Km on 100Kw of energy. the other 100Km on 15Kwh

1 Ltr of petrol/avgas has about 10Kwh of energy, so a comparable car running on petrol will use about 10Ltrs to go 100Km. so it needs 600Kwh of energy to go the same distance that 100Kwh in an electric car will take it.

you simply dont need to carry the same energy density to get the same output.

To simplify this, forgetting all reserves.

The electric aircraft will travel 1.5 hours at an economy cruise setting 85 knots.

The gasoline equivalent aircraft carrying the same weight as the batteries in fuel will get more than 10 hours endurance at a fast cruise setting 108 knots

The O-320 can deliver 75% power (120hp, about 90kW, or 90kJ/s) at 8.5 GPH (23kg/hr, 6.42g/s) according to Piper. 100LL Avgas gives 44MJ/kg, so the theoretical power available in this case is 282kJ/s. Efficiency of the O-320 at a 75% cruise is therefore just about 32%, and an extremely good electric motor might get close to 3x that efficiency.

I think that comparing the energy density does make a lot of sense. The avgas engine might be 1/3 as efficient as an electric motor, but for each kilogram of fuel (at 44MJ/kg for avgas, 900kJ/kg or 250Wh/kg for LiPo batteries) you get almost fifty times as much energy. Even taking engine efficiency into account, you're getting about 16 times as much useful energy from avgas as from batteries, per kilogram of fuel.

For small fuel loads, the relatively tiny weight of the electric motor helps a lot. However, as the amount of fuel rises and the weight of the engine becomes less significant, the advantages of avgas become unbeatable.


jack11111 - I think the idea would be that you pull the batteries out and plug those in to charge, then stick your spare set of batteries in the plane for the next flight.

It might seem expensive to have a second set of batteries, but if that means that each set is only doing three cycles per day rather than six then your battery life has just risen from about 100 days to about 200 days.

At 60 minutes to charge after a 60 minute flight, two sets should give you more-or-less continuous usage.


mcoates - a quick question: how's the heater? Plenty of places get cold enough in winter that a heater is desired, even just for circuits, and conventional electric systems (as a direct result of their efficiency) tend not to produce much waste heat.

Thank you for the question. The first aircraft are not fitted with a heater but it is something the company looking at.

The electric motor system is water-cooled and it will be possible to utilise this heat source to provide cabin heat in cold areas where it may be required.

I'm thinking this is not going to be a very hot or very cold weather aircraft. Hopefully it shall have very good ram air ventilation.

Batteries are happy in the Goldilocks temperature range, as are pilots.

The plane is operating in 38° over in Perth without any issues and it is certainly not hotter inside the cabin because you don't have a hot combustion engine in the front passing temperature through the firewall. So, it was about as comfortable as driving a car on the same day with the windows wide open because it does have really good ventilation.

It will go the opposite way in winter where you won't get the heat transfer that you would normally get with a gasoline engine. We have some flying in Switzerland they have not complained (yet) I guess, you just can't go flying in winter in a T-shirt and shorts. But, as I mentioned a heater of some description is under development.

I will be interested to see the hot and/or high performance. With naturally-aspirated petrol engines, you get a triple penalty when hot/high: the engine produces less power (because there's not as much air available for combustion), the propeller loses effectiveness (because the air is thinner), and the plane has to be going faster for takeoff (also because the air is thinner).

Presumably the first will not apply to the electric motor; it'll happily produce full power at 40degC or at 6,000ft. This may translate into a pretty significant improvement in takeoff performance at hot and/or high airfields.

mcoates. What is the cost of the Electro Alpha put together and delivered in say Melbourne ?. Any updates on the operating cost you mentioned earlier.

Are there really no Antares 18/20/23E in australia? Has been in production since 2003 and is using an electric propulsion system. Could have been the first electric aircraft in oz ;)

Of course, it is a powered glider and therefore only needs the electric motor for take off and climb, not for "cruise".

The price ex factory is Euro 118,000 plus shipping and GST, registration etc It would arrive depending on the exchange rate at around $200K In-line with many other high performance LSA aircraft.

There was one Antares here for a while, however a battery overheated while on charge and did enough damage that it was returned to Europe. Electric self launching gliders are going to increase in the future for sure. There are a number of new ones on order. Charging points at airfields is going to be something to be an issue.