Greenpower has always allowed the use of solar cells, it's just that now it has been expressly written down to encourage more people to research this area and feel confident about using them. Solar cells have indeed already been used on a Greenpower car before.

With the amount of extra charge that the solar cells will give I don't think you need to worry about there being a massive difference between the teams that put in solar cells and those that don't.

Greenpower is all about inspiring engineers and we'd really like to get the students investigating alternative energies and coming to conclusions about their usefulness themselves. If they really believe it will enhance the car then maybe they should start looking for sponsorship, I'm sure many companies will be chomping at the bit to get involved with young engineers who are going to showcase their technology at high profile motor circuits all over the country.

As for the speed issue, it is clear in the regulations that a speed limit will be imposed if the overall speed of a race is thought to be too high and at a dagnerous level.

There has already been a lot of discussion on this subject in another thread, so I suggest reading through that rather than starting all over again in a new thread.

"With the amount of extra charge that the solar cells will give I don't think you need to worry about there being a massive difference between the teams that put in solar cells and those that don't. "

Sorry to be blunt Em, but there ARE big issues here. A doubling of power budget WILL make a big difference in folks speeds. More importantly speed differentials between the "high tech" teams and the "low tech" ones will be bigger than ever. Cars will have worse weight distribution and be far more susceptible to winds. With the rules as they stand there will be a significant advantage to those who can afford fancy PV cells. All of these are BAD things.

Higher speeds (40mph+?)
More dangerous and difficult cars
Larger speed differentials
Richer teams have more power.

If things continue as they are now I forsee a repeat of the "everyone speeds up" followed by the "draconian rule changes to slow us down" necessitating scrapping of thousands of pounds worth of investment. It's not too late to try to avoid such damage by limiting the allowed PV contribution. If you wait too long, designs and purchasing will have happened and folk's pockets will be seriously affected.

I thought we had moved on from the ludicrous notion of racing with a speed limit (and I say that coming from the team that gained most from it last year....)

It will be very interesting to see how this goes ;^)

Though that's clear now Emma, it hasn't always been. For many years, the rule has been that all power should be drawn from the batteries and no other source of power, or charging was allowed during the race. My wording obviously. The new advice seems to contradict this.

Personally, we're unlikely to pursue solar cells for two reasons:

1 No money to re develop the cars and all our energy goes into tracking down sponsorship to be able to just turn up at races.
2 No sun in the North of England

I don't think this will set us at too much of a disadvantage as anyone can turn up at any track on a gloomy day and fail to qualify, solar or not. There may be regional disadvantages however, and if GP becomes a two tier race, of rich/well sponsored, southern teams winning on their brightly lit, long fast tracks and northern teams failing to qualify in the gloom, I have every faith that GP will respond appropriately to maintain parity. In those circumstances I would, for instance, feel for anyone trying to qualify on distance only racing at Alford.

Sorry to prolong the thread.

Nice idea , but unless you throw stupid amounts of money into high efficiency panels you might as well give all the cars a pair of pp3 batteries for the amount of use regular panels would be --- I feel myself agreeing with BobC here
lets put the engineering into better , safer ,cars and if you want more efficiency look at better quality motors !

Pete & Emma,
previous comments were in a general 2012 rules thread. I agree with the OP that this topic merits a thread all of its own. We're in the process of making expensive decisions regarding this very topic, right now.
And I agree that incorporating solar is a very intersting addition to the technical challenge which will be of great value to all team members (just in case I appear to be "down" on the whole idea....)

Perhaps you could have a Pv car with Two sets of batteries OR A non Pv car with three sets . Has Greenpower got a super new sponsor involved in Pv 's lined up ?

How about limiting the amount of energy you can get from the PV cells to say 50W (about 12% of current
usage) of power ?
This can be done using manufacturers data (~ area x panel efficiently) checked out with GP. This would at least limit the extra speed available, make it a marginal improvement (weight and aerodynamic factors would be affected), and keep the competing costs under control (expensive panels would be smaller and easier to fit but would not give you any more power). I think 50W is reasonably obtainable with low cost panels on a sunny day (few £100 pounds). Same as the bats really, limit the energy available to teams.

I wrote to SEC the company that makes our batteries and who also produce PV cells.

They said:

"Ben
Thank you for your enquiry re solar panels for Greenpower racing.
I think the limiting factor is going to be the size of solar panels that you can get on top of the car not the charge current.

For a start let’s look at using 2 No. nominal 12 volt 100 Wp solar panels SEC 1600S (100 Wp).- See data sheet attached
These panel are 18% efficient which is very good and will provide minimum size at 1037 mm x 527 mm two panels will have an area of 1.09 Sq m
The maximum charge current from this panel is 5.78 amp but in practice in the UK you will get a charge current of 4 to 5 amps.

So the question is can you get these two panels on the car?"

The panels suggested weigh in at 7.4kg each, and that's before any additional wiring or charge controllers, so to get a meaningful current would require significant extra mass, raising the CofG.

Another point to consider is the effect of shadows falling on the cells whilst lapping a circuit, since the performance of the entire panel is compromised if a single cell is in shadow.

Lastly the rules state that the current from PV must flow into the batteries (NOT the motor directly), so that in itself will surely limit the extra power available, since the batteries won't tolerate high power charging.

The fact that people are "in the process of making expensive decisions regarding this very topic" should serve as a warning to GP that IF the issues I've raised above are overcome, the disparity between teams will continue to increase. It's difficult enough as it is when competing against advanced computer managed electronics, two way telemetry (and engineers from CERN!) ;)

I honestly don't think we'll bother, barring a small panel to run a motor cooling fan.

Ben (was Mctavish, but decided that this forum didn't actually require anonymity!)

My initial reaction to the use of PV was similar to Topher's but having investigated a bit further I suspect it could be a lot of hard work to get back to where you started. The angle of panels on a car will limit their output to well under the manufacturers ratings to the extent that I'd be surprised if anyone gets more than 50% even on a sunny day on the south coast in June, and at the final in October....

Hah - you get more power out of PVs when they're cold (and they get exceedingly hot in "greenhouse" panels....) due to reduced resistance(mostly) & leakage.
I did some work on a 30kW installation in the early '80s & that maxed out on winter mornings.
Oh yeah - drivers of solar equipped cars will be weaving over to the sunny side of the track all the time (just to add to their "issues" ;^)

I think Farnorth was refering to solar intensity in Oct rather than ambient temp

Just to correct that perception, Ben, I am not an engineer at CERN (wish I was :) ), just a lowly engineer that has had the good fortune to work on some instrumentation there. Also I don't know about other cars with electronics, but RR's electronics is definitely not advanced, it is pretty basic and is well within the abilities of any school with teachers who understand electronics or has electronics helpers.
With the current flowing into the batteries, well it won't unless the motor is using less than the panels are producing, but the solar panels would need a degree of electronics to keep the charge levels under control when the motor is off. Cooling fan use is a good idea, I also think higher CofG's are likely ...

Correct Wheels. The angle of the sun at Goodwood in mid-October is only about 30 degrees above the horizon at the start of the F24 race and 9 degrees at the end, so for horizontal panels the available solar energy will range from 50% down to 16% of that available if the panel were directly facing the sun.

Thanks for these interesting replies. I have some thin light cells made by Powerfilm (http://www.powerfilmsolar.com/oem-components.php) intended for model aircraft and flexible. They are 0.3mm thick and weatherproof. They feel as stiff as a postcard. They scale up to only 30 W/m^2 but I have measured this output in Ullapool sunshine. Enough of these to cover 3 m^2 would weigh 728g so not a big weight penalty, and cost about £1400 at 2009 prices, but only make about 90W in direct sunlight. The very thin very flexible panels seem to have fairly low output per square metre.

On ebay there are 100W semi-flexible monocrystalline silicon panels weighing 5kg (aluminium backing, plastic covering, no glass, about 3mm thick) for £350. Four of these would fit on a max size car.

The more exotic cells are harder to find. Some of the cars in the Australian and South African solar races which are bigger than ours, I'm guessing three times the area, can develop 1.5kW from their cells in admittedly sunnier conditions.

Keep up the discussion and contribute any knowledge you may have, because solar car racing is alive and well in the USA (http://www.winstonsolar.org/challenge/photos.shtml) Australia (http://www.worldsolarchallenge.org/) South Africa http://www.solarchallenge.org.za/ and Japan and Canada too.

Which begs the question ------ Why apply this technology to a school Greenpower car ??? It seems to go against what most of us do Greenpower for

If I wanted to get involved with Pv cars I would switch loyalties to the University of Cambridge solar car

Thanks for that Terry, so not a CERN engineer, but a lowly CERN instrumentation engineer!? ;)

I think the electronics complexity is all relative. Our school does not offer electronics, or have any electronics helpers, so if we went down that route then we'd all have to start from square one (maybe two), and at the moment I feel that we have more to gain through the finessing of gearing, mass, rolling resistance and aero but perhaps one day.

Point taken about the current flowing through the batteries not being an issue, but it really wouldn't appear that the current could be high enough to exceed normal charge current in any case.

I do appreciate that you and your team have put in extraordinary levels of effort to the Rotary Racer cars, and the online documentation is extremely admirable and useful. (Is your web based VWT going to become open to others at some point?)

Congratulations on your win on Sunday!

I still can't see anything more than a token flexi panel appearing on RLR1 anytime soon...

I wish I was even a lowly CERN engineer, from my brief visits there it is probably one of the best environments for engineers as well as scientists !
Yes, all complexity is relative, from what I hear our school is lucky that all students get to do some electronics. Personally I think all schools should do some as well as some programming, but there you go and as you say the other areas of cars performance are far more important.
I would like to open up the VWT to other schools, and have tried to find ways of doing this but have hit a blank so far (I will have another go). Unfortunately it runs on computers at work and there aren't the resources to cope with more than a few teams there. Thanks on behalf of the team, note that although I am vocal in the forums, I am only one of the teams members. That win and rest were due to years of experience at CSS and the ideas and work of all of the teams members and mainly the younger ones.

Actually they are in Bristol today showing the cars at Bloodhound SSC's education centre opening day (S&B Automotive Academy) and trying to promote Greenpower (and get some sponsorship). I heard the BBC had filmed a couple of them, so they may be on the local news tonight. Hope they mentioned Greenpower ...

We are considering solar panels, if the rules permit them. Personally I think it would be good to expose the youngsters to this technology so they can see its pros and cons. But as with others, I think it needs some control.

They were on points west about 6.50pm.

I note that the American Solar Challenge 2012 regulations limit teams to silicon cells costing less than $10/Wp

http://americansolarchallenge.org/tech/tech-center-2012/ascfsgp-2012-solar-cells/

I'm still struggling with the "provided they are linked to the main batteries" comment. Does this mean the panel(s) must simply charge the batteries rather than using the energy directly? If so, what's the maximum charging current we can apply, and does that figure still apply if we're drawing 18A anyway? Say the charging current is 5A (and the panel(s) can supply that constantly throughout the race), does that mean we can run at 23A? I would assume we'd have to charge both batteries in series as using a panel per battery may result in one flat and one well charged battery if the light doesn't fall in our favour?

I'm regretting designing a very small car - virtually no panels I've looked at so far will fit with our current shape - the GP numbers don't fit flat on the side or the car - might have to redesign the bodywork! Suddenly a fully enclosed wheel arrangement makes a lot more sense...

A revised version of the 2012 regulations has now been published with some clarification on the use of PV panels. See http://www.greenpower.co.uk/node/253.

Admin.

Aaaaarghhhh well done lads and lasses, another meticulously crafted, concise, and unequivocal rule.... "wings or trailers are not permitted"
here's a def. from wikipedia
"In British English, the fender is called the wing (this usually only refers to the panels over the front wheel arches, in modern cars, since the rear 'fenders' are more an integral part of the car's body shape). The equivalent component of a bicycle or motorcycle, or the "cycle wing" style of wing fitted to vintage cars which is not integral with the bodywork, is called a mudguard in Britain, as it guards other road users - and in the case of a bicycle or motorcycle, the rider as well - from mud, and spray, thrown up by the wheels."
"wings are not permitted" is thus banning all but open wheel cars. I don't think that's what the organisers meant (maybe I'm wrong?)
I just wish they'd actually said what they meant, which is probably along the lines of "no solar cells can be outside the track of the vehicle". Again, maybe I'm wrong. clarification of clarification please...... ;^)
Bob

i think it means there can be no wings or trailers for the specific use of carrying solar cells (trailers are already banned by the rules involving number of wheels and ground clearance) because it's only mentioned in context of that rule. I imagine a pure aerodynamic wing would be allowed (although completely detrimental to performance)

If you need clarification about what is allowable with regard to PV panels then please contact us with your proposed idea which we will be very happy to examine. helpline@greenpower.co.uk

Admin.

OK I can interpret the rule as meaning "wings like on a formula 1 car are banned, but wings like on a ford escort are not" - I honestly read "wings are banned" and thought enclosed wheel cars were outlawed (half the field by the way...)
'fraid it's still a bad bit of rule writing, and should be amended, do you really want every design change on every car to be submitted for approval? & correesponding scrutineering arguments for ever....

I have to say that i am struggling to find the relevance of pv cells to electric road vehicles . Correct me if i'm wrong but i thought that the goal of greenpower was to encourage a new generation of automotive engineers - I cant see a major breakthrough in pv technology occuring that could even remotely be applied to road or even race cars within the realistic working lives of the students - after all we are still struggling with electric vehicles over 100 yrs after the first sanctioned land speed record was set by an electric car ( yes really !! ) - I am concered we are venturing into an expensive blind alley .

I see your point Tirgis but I thought the idea was to encourage engineering ( in any field) I believe anything the youngsters can learn from is worth persuing. Granted if the cost outways the benefit it should be looked at carefully buy looking at houses these days you see many with solar panels on. It may not be automotive but it's 'engineering', it's relatively new and expanding. I believe it's a good learning opportunity for them. Greenpower is an excellent platform from which 'engineering' in any guise can be learnt & developed, understood & applied in different ways/
Only my thoughts :)

Quite right Martin.. I agree whole heartedly.


CRL Dallas

I agree we are still developing electric vehicles, and we are trying to facilitate the learning of the next generation who will be grappling with climate change and the shortage of fossil fuels in a way we can only imagine. To take on the challenge of developing solar assisted cars in our Northern cloudy climate is a huge challenge, and will be enormous fun. Are we to pretend that climate change is not happening, and petrol will last forever?

Although not very practical as yet, I wonder if PV panels might start to be used on cars in the future when their efficiency improves. There are some PV cells rated at 45% efficiency in the labs. If you imagine a slow/light Smart Car type of vehicle with 2m^2 of these panels on the roof you could probably expect to get around 2.25kwh out of them, on average, during a day while sat in car parking areas (where cars spend most of their time). This would probably put enough energy in the batteries to power them for about 22 miles a day at less than 40 MPH. Enough for a lot of peoples daily commutes or would provide a fair proportion of the energy for the longer commutes as well. Mind you, for a lot of peoples journeys, cycling is cheaper and allows you to keep fit at the same time :)

What concerns me is the cost issue. Those with money/ influence may do well but what about the rest of the field? If the same few cars win all the time with no chance for newcomers to break through then the future will not be bright.

Following the reissue of the 2012 Regulations with some further clarification of the section under photovoltaics (PV), the Greenpower Technical Committee has received many further queries on the interpretation of the rules as written both in terms of the use of PV but also car body design incorporating them. Many designs both electrically and mechanically give great cause for concern with issues of safety even within the current rules as they exist. Understanding that teams want to progress with designing cars for 2012 and rather than producing complex regulations to further clarify this subject, Greenpower has decided to withdraw item T12.6 from the 2012 Regulations with immediate effect.

The Technical Committee will continue to consider the regulation during 2012 with a view to introducing PV in future.

Admin.

Thanks Admin.

i'm glad to see this rule removed! It caused alot of confusion, and made no sense in terms of power available. Maybe future integration will be possible but with more research on greenpowers part, for example a restriction of size e.g. metre squared and the solar panel wattage, so teams can benefit but not enough to out weigh the competition? I have mentioned that instead of feeding into the main circuit solar panels could be used to power onboard electronics, as there is still potential for learning, but not enough potential for unsafe speed etc?

Sam

I'm sorry to see this, although I can see there are issues which need to be explored. There are cheap light cells available on Ebay and it would have been fun trying to optimise a solar assisted car. I genuinely believe that PV could make a contribution to vehicle power even in our climate, and where better to demonstrate it than in Greenpower?

Let's hope that the Technical Committee can find some way to allow experimentation with PV because it is an interesting developing field crucially important to green engineering and to a future without fossil fuels.

Thanks Admin - I think that delaying Pv technology is the right thing to do at present - - perhaps revisiting the idea within a new formula and specification of car (introduction say 2017 ) with a lighter more efficient motor and poss one pair of lithium type batteries ( should be much cheaper by then ) . this should re balance any weight issues and allow for more thorough research into the relevance and feasability of the technology - any thoughts please --new thread if you like !!

Shame in that engineering the PV contribution would have been fun & instructive, but a bit of a relief because the rules as they were would have created a lot of aggro (and expense... I've been running a CFD "wind tunnel" model of zebedee with 4.4 sq m of photovoltaics on it...... probably about 300 real world watts on a sunny day with 15% efficient cells). CFD said 21N drag at 30mph, that's 281W in aero at 30...

Yes, shame, but I think right with the rules as they stand. Would have been quite a sight to see Zebedee with 4.4sq m of panels though ! It would be nice to integrate more optional engineering challenges into Greenpower and integrating PV somehow a bit sooner than 2017, as it is in vogue, is a nice idea. As Tigris suggests may be the people on this forum can come up with some ideas for rules to help Admin with their considerations for the future ?
As a starter I think limiting the maximum power from PV to say a manufacturers 65W (should give 50W in very good conditions or about 12% of current usage) would sort out most of the issues (speed, speed differentials, cost, size). Then perhaps stating they need to be attached to the surface of the bodywork with no gaps or edges and not extend past the wheel track across the car...

Tell you what over here in Oz we were dead keen to use PVs. Our car design was modified to give a flat top surface and some fellow schools who have run in the darwin-adelaide solar challenge had some great advice for us. Any chance Admin might give us a firm-ish date for PVs to be allowed? 2013 maybe?

looking forward, a potential path could be to ban auxilliary batteries for dataloggers/control equipment/sensors and the like, then give teams the choice of running them from the main batts or using a separate solar power system.

This sort of approach would have little to no effect on teams that are in the lower end of the field who struggle with money/resouces/experience/etc but would encourage solar development amongst the top teams who perhaps run some more compex electrical systems and usually have more resources to devote to it.

Just a suggestion here guys & gals - the motive power for all our cars comes from greenpower - this is what gives us the level playing field that means so much to the competition. Why not simply extend this to the PV arena? Greenpower could supply a set of PV cells (the ~4" square solar cells) for one car. Say 80 or 100 cells in a set. That way
1) everyone would have the same potential power
2) greenpower's bulk buy would make them cheap
3) the cells could be attached to any car body in a safe way
This does away with unsafe panel attachments and would render further rules unnecessary - the limited size of the "set" making extreme builds (e.g. 4.4 sq m of cells....) impossible.

I haven't thought about this so I fully expect to be shot down, but how about having solar panels allowed - but only in the battery quarantine area? (Which would have to be outdoors). Should we have different classes of car? How about starting with PV in F24+ only?

BobC's comment has a lot to recommend it, but in my limited experience of trawling ebay for solar cells the standard sizes are 6 inch by 6 inch, 5x5 and 3x6. The 3x6 are actually 80mmx160mm and 100 of them would make 180 peak watts. Allowing for a 5mm gap between cells the area would be about 1.1 square metres. Weight of the bare cells is 6.5g each, so maybe 2kg with wires and encapsulant. The cost currently for bare (unencapsulated) cells is £95 for 108 cells see http://www.ebay.co.uk/itm/3x6-polycrystalline-solar-cells-3-6A-1-8W-108-pcs-/270779430076?pt=UK_Gadgets&hash=item3f0bb634bc#ht_682wt_1110

RLR, don't think PV for the electronics supply would work that well. The PV's will probably provide 0W at
some races ! Mind you is that what you are after :) Also the electronics doesn't take that much juice to make it worthwhile. RR's electronics use about 0.48W which is 0.08% of total energy. Our original solenoid used to take 9.6W ...
Yes, Bob that suggestion sounds good. I think it may be better to have a smaller number of cells for a bit less
power and a smaller area so teams without PV are not so much at a disadvantage and more "dangerous" body shapes are less likely to occur. Might be a problem to be able to buy the same cells year on year though. maybe GP could supply alternatives based on watts produced. One possible option to reduce the speed differential between PV/Non PV is to limit battery heating on PV cars (double wammy green option :) )

Moving on to the debate about what would be a suitable peak amount of solar power available.....

There has to be an incentive to do this - otherwise it simply won't happen, so the car needs to be potentially, say, at least 3% faster.

3% speed needs up to 9% power, say 36W. 36W average from cells that are not pointed at the sun - we are talking about (rough guess) 100W worth of solar cells (at the peak power rating by which solar cells are described for sales purposes).

Let's say 5"x5" cells give 2W peak - we'd need 50 cells. That all seems reasonable to me. Reasonable size, cost and performance boost.

I don't buy the "lets try to keep it fair for those without PV" - if you frame the rules so you go as slow or slower with PV on NOBODY is going to do it & so the educational opportunity is lost.

Good point Bob. In fact peak watts only happen when the sun shines and no shadows fall on the panel, and get less as the sun shines at an angle which in our northeren latitudes is all the time. Also the weight and shape constraints penalise a car carrying cells even they are making no electricity which in overcast weather is a lot of the time. So to be worth doing one would need a lot of cells and even then it could end up being marginal.

So to be worth doing the gamble one would need quite a lot of cells. It's still an interesting gamble though.