Portable solar applications

Hello all. I’ve been spending a bit of time investigating solar and getting an understanding of all the elements needed to create a portable solar installation. I have thought of a few applications for the sort of size of installation that could be fitted, say, to the roof of a van. I’m getting my head around the various numbers, but struggling a bit with the units and the calculations. Are there any experts out there that can assist or can anybody point me to a decent guide for a non-electrician?

One application I have in mind is to power the sound system that I use for gigs and festivals. Modern amps and line-array speakers don’t use as much power as the big old boxes and the switch to LED stage lighting might make this a viable alternative to hiring noisy, smelly and polluting generators.

I’d be interested to hear of any applications you can think of where a van-sized amount of solar energy could be put to use in a remote location.

Hi @James. Great question. Do you have any idea what your total power requirement (watts) for your festival sound system / lights is?

Actually I don’t. It does seem to be a good place to start, but it’s quite hard to calculate. The tech sheets for the main gear talk about the RMS output power of the amps (4x1200W), but not the power consumption. On top of this there are powered foldback speakers and various other bits of tech, some containing fans which could take a bit of power. Is there a good way to measure it?

@James next time you set up all your kit, you could try plugging it through some sort of meter. You can pick up one for 6 - 15 quid (perhaps something like this? ) This would give you a baseline measurement of the power consumption. You can then use this to calculate your battery / solar PV requirements. It’s probably easier to measure the actual usage than to guestimate from the spec of the components.

Great idea. I would probably need several though. Going back to my original questions, assuming I can work out the wattage pull, what next?

I’m assuming that you need several because your system cannot run off a single 13A supply right? ie. max power output is over 3kW?

Going back to your original question, once you have a value for the power that you need to run your system (kW). You can then decide how many hours you need to run it for and calculate the KWh needed to supply it.

I’ll run through an example here but first a disclaimer: I am not an electrical engineer or in any way qualified to advise you on this. What follows is cobbled together from a few dim recollections of school physics lessons. :crazy_face:

Say your system needs 1kW to run. Let’s say for the sake of the example that solar PV can generate around 200W per sq m in bright sunshine. This would mean that you would need 5 sq m of panels to power the system from the sun alone (5 sq m x 200W = 1kW).

However, you probably want the system to be able to run for some time on cloudy days or at night so say that you want to be able to run it for 3 hours in darkness. This would mean that you would need 3kWH (3 hours x 1kW) of battery storage. Assuming that you opt for a lead acid battery with 100AH at 12v . 100AH x 12V = 1200WH = 1.2 kWH. Lead acid batteries have a maximum recommended discharge of 50% so you might need 5 or so of these batteries.

Hope this helps you along a bit. I’m sure that there are loads of people here who are more qualified to fill in the details than I. Maybe @Greg_Kirkby can help?

I would need several because it’s not normally possible or sensible to plug everything in to one socket. Not necessarily because of load, but because physically it’s installed over a wide space (a problem I would have to solve with a solar power source). Also some equipment can cause a mains hum through speakers when plugged into the same ring main.

I get the basic calculations, thanks. However then you start to bring in items like your solar charge controller (rated in amps) and your inverter (rated in V). For a 1kW drain you’d need at least a 1kW inverter I guess. How do you size the controller? It would be good to get a split charger as well so the battery could also be charged while driving. Any thoughts? (Thanks for this btw).

The inverter should be rated for the load that you intend to put on it. The charge controller should be rated according to the power output of your panels but I’m afraid I’m now totally out of my depth. There are other specific issues about matching charge controllers to battery types as well. This link has a step by step guide for an 800W PV + 600AH battery system. Hope that helps.