Another solar panel thread (Design considerations)

[wiltshirewonderer]

Hello

Bonus is in and it gives me just enough to install some solar on the roof. Based on my usage needs I can do with pretty much all I can get . Although I'm all low power & LED I do have a few luxuries that it would be good to power with solar when/where possible and off grid (Currently on hook up but don't see that as necessarily lasting forever)

I've started coming up with a plan to help me identify what I don't know. My first pass is below and I have already identified a few questions that I need to answer. I've spent a little time reading up on the forums and have experience of building a small set up a long time ago (To power a caravan) but definitely need to get myself educated on the subject.

What are your thoughts on game plan below? Are you able to point me in the right direction with any of the questions I have identified thus far?

1. Design top boxes

- Come up with a design for ‘sloped’ wooden top boxes with solar panels embedded in the top (to match lines of existing DB style dog box)

2. Map out roof and all fixed location extrusions

- Including ‘to be’ pump out location (Another DIY task)

3. Identify optimum solar panels and box design that matches both electrical and aesthetic requirements (See a bit of back and forth comparing panel characteristics/sizes and lumps on the roof before settling on something)

- Q: Any ideas on how to mount centre lines to roof with sufficient strength on port and starboard side? I have spray foam insulation and design that makes removal of internal roofing a PITA so anything that gets around both would be great!

- Q: Does anybody have a top box with solar panels that also had a mushroom vent underneath? Does the temperature under the panels cause any issues with circulation? (Assuming not?)

- Q: Any recommendations on good places to read up on different panel types and how to select right ones for needs and how to match to MPPT controller and installation design (Thinking max voltage considerations vs temperature etc.)

4. Identify optimum wiring of the panels to MPPT

- I’m going to be using MPPT. Don’t yet know whether I will be wiring panels in series/parallel etc. or single vs multiple controller - TBD

Q: Does having panels pointing in different directions (Like the doors on a dog box) create additional wiring considerations?

5. Identify optimum wiring of the MPPT to batteries

- I’ve got a Victron Multiplus 12/3000/120.

- In scenario where plugged in to mains I’d like solar to take priority and charger only to kick in if batteries discharging because solar not providing sufficient charge.

- Q: Is that possible?

- Q: If not, what’s the forums view on second best option (Looking for automatic rather than relying on me to check voltage, switch on/off chargers etc

6. Buy the stuff and build

Apologies, looking back that is a lot of questions. Hopefully others have got or will have similar questions so this isn't all about me!

[Detling]

I doubt that you will get the MPPT controller to trump the Victron charger. My Tracer adsorption voltage is 14.1 my Victron is 14.4 and always wins, neither voltages are readily changeable only the battery type which does change the volts but not for the best. It is not a big problem though as if you put a large12 volt load on, both chargers shove in current, it is only the last 10-15% of charge that comes mainly from the Victron.

[Justme]

One way you could get the Solar to be prioritised is to use a little known feature of the Victron.

 

You would need a grid tied inverter for the solar array. The output is fed into the boat side (the output) of the victron. The Victron supplies a mini grid for the grid inverter to lock on to.

 

Sound odd I know but it is ok.

 

What happens then is :-

 

a, any loads are supplied by the solar array via the grid inverter directly

b, if the array is making more than you are using the Victron will use it to charge the bats (see below)

c, if the load is bigger than the array can cope with the Victron will top it up from the bats

d, if the Victron has a shore power input it will sync to it & hence the array inverter will also sync to it.

 

Re b, above if the loads are small & the battery is full the victron can alter the htz to reduce the output from the grid inverter so you need a compatible grid inverter.

 

Other upsides are higher array & system voltages so thinner cables can be used for the additions.

 

Also remember you can use the virtual relay to turn things on or off so the shore power could be controlled or you could have the immersion run when bat are full.

[wiltshirewonderer]

One way you could get the Solar to be prioritised is to use a little known feature of the Victron.

 

You would need a grid tied inverter for the solar array. The output is fed into the boat side (the output) of the victron. The Victron supplies a mini grid for the grid inverter to lock on to.

 

That sounds very clever. Possibly also very expensive (I will check it out), but definitely clever!

 

Edit: Found a short document on the subject of the hidden stuff. Different solution but shows I have more options than I thought! Victron stuff looks more configurable than I ever knew....

 

http://philsolar.ph/wp-content/uploads/2014/05/Whte-paper-DC-solar-system-with-a-MultiPlus-inverter-charger-rev-01-EN.pdf

Edited August 28, 2014 by wiltshirewonderer

[Justme]

Also try looking at the Sunny Island units.

 

Combined with Sunny boys its a great combination.

 

Prices might make your eyes water.

[wiltshirewonderer]

Also try looking at the Sunny Island units.

 

Combined with Sunny boys its a great combination.

 

Prices might make your eyes water.

 

Eyes water? Yup! Think your FX80 is more the ball park I was hoping for (Similar solar output as well)

[wiltshirewonderer]

I found a diagram from Victron showing a Multiplus configured with a Blue Solar MPPT:

http://www.victronenergy.com/upload/documents/Hub-1-System-Layout-V3-4-8-2014ADR-.pdf

Victron switching policy: Disconnect from the mains where possible.

The multi/Quattro will normally be in invert mode. Only when the generated solar power exceeds the power needed to charge the batteries and feed the AC loads, the Multi/Quattro will switch to mains. All extra energy will then be fed into the mains. This way all solar power will automatically be optimally used for 'Self consumption'. When a large load is connected the unit will quickly switch to the mains. Use this option with a less reliable mains. This option requires the installation of anti-islanding equipment.

Interestingly the second AC output on the Multiplus on the diagram has a statement saying: 'Optional load shedding available on AC Out 2 Set points in Assistant'. This is getting me closer to using the immersion as a dump load...

Think I need to do further reading to see what the score is with feeding into mains, suspect it is a no-no in which case I need to figure out how to stop it.

[IainW]

We've got two top boxes with solar roofs. One sits over a mushroom vent and i haven't had any problems, but then i don't suppose it's the kind of problem you can 'see'. The top boxes themselves are well ventilated and just carry our bikes so perhaps there is enough airflow not to cause a prob? The vent itself isn't in bathroom or kitchen so maybe has less of a job to do?