The panels I am using are a bit different, they are light weight semi flexible panels. Their stated specs are:
Rated Power 100W,
Vm 17.7V
Im 5.62A
Voc 21.6V
Isc 5.97A
In the sun they get hot, full sun they get to 70+ degrees. Thus I have decided not to mount them directly on the roof, but to put them on top of 10mm of foil board, reduces the roof temperature by up to 30 degrees, but it does not stop the panel heating up.
The Temperature Coefficient PMax is -0.38% so at 70 degrees the power will drop to about 83W.
For Voc -0.27%, so max volts will drop to 18.98V.
For Isc it is 0.05% so current will rise slightly to 6.1A
Even with tjat drop it is more than enough for our needs. Especially when you consider that my 1,200W of panels weigh a total of 16.2Kg.
brian said
09:19 PM Feb 8, 2014
Would perforated board work better at keeping the panels cooler?
Plendo said
09:48 PM Feb 8, 2014
Sorry Brian,
I was using a brand name (see link below), it is actually a specialised insulationproduct, it consists of 10mm of closed cell foam (polystyrene I think), with a layer of foil on each side. It works well as an insulator, and to be honest I am not worried about the loss of performance from the panels. I have about twice as many as I need anyway.
Our van is being built ot be efficient, with the exception of our fridge which is a compressor fridge, and I expect it to draw about 100ah / day on the 12v circuit. so 55Ah @ 24V (assume some loss on conversion). The air con is an inverter split system drawing up to 2.8A when running. I expect 1,200W of panels will mean I can run the air con, and charge the batteries during the day, then run the air con for most of the night if we wanted to.
http://www.foilboard.com.au/
Murray J said
11:24 AM Feb 9, 2014
Thanks Brian that is very comprehensive.
Mr B2 said
12:40 PM Feb 9, 2014
Dont put solar panels directly on the roof, They get excessively hot,
Sit the panels up about 75 mm minimum off the roof, The draught underneath keeps them cool.
Plendo said
01:46 PM Feb 9, 2014
Thanks Brian,
The panels I am using are not the traditional stiff panels in the allow frame with a sheet of glass at the front. They have the solar cells bonded into a semi flexible 3mm thick sandwich of TPT and a clear material. As I mentioned earlier they get hot, and when they are hot they become very flexible, thus need to be supported.
Sitting these particular panels on top of a 10mm thick piece of polystyrene works for them, and insulates the roof, but I would not recommend it for traditional panels where it makes far more sense to use their structure and set them up with an air gap as you recommend.
baysidetas said
12:22 AM May 10, 2014
There is a very good reason to use a DC to DC charger rather than rely on the vehicle alternator. The DC to DC charger will bring your batteries up their full SOC whereas the alternator will not achieve this.
If you find yourself in a series of bad solar days and you have to run the engine to top your batteries up you will be very pleased to get the extra charge from the DC to DC charger.
One thing to be careful of with DC to DC chargers is their standby current which is a drain on your vehicle battery. Best to wire it up through your ignition system so that it is only connected when the engine is running.
oldtrack123 said
12:12 PM May 10, 2014
baysidetas wrote:
There is a very good reason to use a DC to DC charger rather than rely on the vehicle alternator. The DC to DC charger will bring your batteries up their full SOC whereas the alternator will not achieve this.
If you find yourself in a series of bad solar days and you have to run the engine to top your batteries up you will be very pleased to get the extra charge from the DC to DC charger.
One thing to be careful of with DC to DC chargers is their standby current which is a drain on your vehicle battery. Best to wire it up through your ignition system so that it is only connected when the engine is running.
HI
Well actually you may find that is not the best way to get a quick charge into the house battery ,unless you have a HIGH current dc /dc charger!!
Depending on the vehicle system ,most alternators will put in more charge [ Ahrs] in a short time than a 20 or 49A dc/dc charger l
Of course this does require the charge circuit to be wired as it should be, with low voltage loss cabling
It is when the Alternator output voltage is reduced[ as in some late model vehicles] by the electronic engine management system, that a high current DC /Dc charger would be more likely to quickly charge the house battery
Of course that is understandable, as such a vehicle management system, is unlikely to really FULLY charge the vehicle battery so has no hope of even near fully charging a remote battery
THe final decision on which method is best ,depends on many factors.
It is not as simple as some would like to believe or make out
The panels I am using are a bit different, they are light weight semi flexible panels. Their stated specs are:
Rated Power 100W,
Vm 17.7V
Im 5.62A
Voc 21.6V
Isc 5.97A
In the sun they get hot, full sun they get to 70+ degrees. Thus I have decided not to mount them directly on the roof, but to put them on top of 10mm of foil board, reduces the roof temperature by up to 30 degrees, but it does not stop the panel heating up.
The Temperature Coefficient PMax is -0.38% so at 70 degrees the power will drop to about 83W.
For Voc -0.27%, so max volts will drop to 18.98V.
For Isc it is 0.05% so current will rise slightly to 6.1A
Even with tjat drop it is more than enough for our needs. Especially when you consider that my 1,200W of panels weigh a total of 16.2Kg.
Sorry Brian,
I was using a brand name (see link below), it is actually a specialised insulationproduct, it consists of 10mm of closed cell foam (polystyrene I think), with a layer of foil on each side. It works well as an insulator, and to be honest I am not worried about the loss of performance from the panels. I have about twice as many as I need anyway.
Our van is being built ot be efficient, with the exception of our fridge which is a compressor fridge, and I expect it to draw about 100ah / day on the 12v circuit. so 55Ah @ 24V (assume some loss on conversion). The air con is an inverter split system drawing up to 2.8A when running. I expect 1,200W of panels will mean I can run the air con, and charge the batteries during the day, then run the air con for most of the night if we wanted to.
http://www.foilboard.com.au/
Thanks Brian that is very comprehensive.
Dont put solar panels directly on the roof, They get excessively hot,
Sit the panels up about 75 mm minimum off the roof, The draught underneath keeps them cool.
Thanks Brian,
The panels I am using are not the traditional stiff panels in the allow frame with a sheet of glass at the front. They have the solar cells bonded into a semi flexible 3mm thick sandwich of TPT and a clear material. As I mentioned earlier they get hot, and when they are hot they become very flexible, thus need to be supported.
Sitting these particular panels on top of a 10mm thick piece of polystyrene works for them, and insulates the roof, but I would not recommend it for traditional panels where it makes far more sense to use their structure and set them up with an air gap as you recommend.
If you find yourself in a series of bad solar days and you have to run the engine to top your batteries up you will be very pleased to get the extra charge from the DC to DC charger.
One thing to be careful of with DC to DC chargers is their standby current which is a drain on your vehicle battery. Best to wire it up through your ignition system so that it is only connected when the engine is running.
HI
Well actually you may find that is not the best way to get a quick charge into the house battery ,unless you have a HIGH current dc /dc charger!!
Depending on the vehicle system ,most alternators will put in more charge [ Ahrs] in a short time than a 20 or 49A dc/dc charger l
Of course this does require the charge circuit to be wired as it should be, with low voltage loss cabling
It is when the Alternator output voltage is reduced[ as in some late model vehicles] by the electronic engine management system, that a high current DC /Dc charger would be more likely to quickly charge the house battery
Of course that is understandable, as such a vehicle management system, is unlikely to really FULLY charge the vehicle battery so has no hope of even near fully charging a remote battery
THe final decision on which method is best ,depends on many factors.
It is not as simple as some would like to believe or make out
PeterQ