Monday, March 20, 2017

Island Solar Power

This post is intended to provide some information for a family cabin in the wilds of Canada.

All, I have been investigating some stuff on the solar power system. I have spoken with a few places and I have come to several conclusions.

1. You need to have a capacity meter added to your system. 
There may be an easier path to this in your existing system. I only took a picture of your SolarBoost 50 MPPT (SB50) unit, so I was working from that. The company that makes your SB50 also sells a remote monitoring display that you could add to your system and mount inside the main cabin. It will interface to the charge controller itself (SB50) and also has a power shunt that you install inline with the battery pack to measure the amperage going into and out of the battery pack. This unit will show you the state of the charging unit (same information you get when look at the SB50 directly in the shed) AND the amount of power left in your batteries. It also monitors the batteries and over time will make better predictions on how much capacity you actually have left.

There are also stand-alone battery monitor units that you can add to your system. Stand alone units only monitor the Amps going into and out of your battery pack and do not interface to the charge controller. You program it with specifics about the batteries and the capacity and it will tell you the capacity left at any time and how fast the batteries are being charged and a bunch of other information about charge rate, full charge, etc. This is just like the unit above, but it does not interface to the Charge controller. This can be a plus, however, because if you ever replace the charge controller, you would not need to replace the battery monitor. It is also cheaper even when you buy the shunt (sold separately). 

2. You have to move the panels out of the shade in the morning.
For the same reason above (averaging), one panel in the shade kills the average power produced. They need to be moved down the roof and out of the shade of the birch. I would recommend turning them longways and moving them down to the other side of the skylight right next to each other. The additional distance will make no impact on the power delivered to the charge controller.

3. You need to move the solar panels together.
When you connect the panels the way you have, you are averaging the output of all the panels. The angle at which the sun hits the panels makes a huge difference in their output. So in the morning when the sun is hitting the 2 panels on the front of the cabin, it is barely hitting the 1 in the back. This means that instead of charging with 2 panels plus a little from the back panel, something like 2.25, you are actually charging with the average of the 3, which is (1+1+.25)/3 = .73. This is actually less than 1 panel! When the sun works it way around to mostly hitting the back, it is even worse - (1 +.25 + .25)/3= .46.

So, it would seem that just moving the one panel from the back to the front would allow pretty good charging all morning and into the afternoon, and since they all point in the same direction, the average would be the same for each.

4. You should probably replace your panels.
We know that you have added panels over the years, and this is pretty bad for your particular system. When you use panels of differing amp capacity and (slightly) differing voltages (they change with age) your MPPT controller cannot calculate the most effective voltage/current to use to get the most efficient charging. There are many choices for panels out there, and I think with the prices dropping so much, you can probably replace the 6 you have now with 4 that will work better and charge your batteries faster. I think your system is rigged using 2 12 Volt panels together for 24 volts, so you will need to buy 2 at a time for a similar setup. I think that your best bet is to just get 4 new high current panels, mount them on the other side of the skylight all together and remove the old ones to another use. (more on that later). 

5. Add new panels and 2 new MPPT charge controllers to your system.
If you want to keep your existing panels (after moving them out of the shade) you could create a system that has 2 strings of panels each controlled by their own MPPT charge controller. In order to do this, you would need to get 2 matching MPPT controllers (so that they charge the batteries the same way) and get rid of the one you have now (or use it elsewhere). This is preferred way to add new (and different) panels to an existing system. It is also the way that you would mount 2 sets of panels on two side of a roof. As the sun moves from one side to the other, the two MPPTs work together to give you the best charging and remove the canceling effect you now have.

6. (Optional) You can rack mount the panels together.
If they face directly South they will be more efficient. This would afford the most solar flux for the longest time per day. The angle of the panels should be set to be best Spring, Summer, Fall since in the winter there is no electricity usage.

7. (Future) May need to Expand Capacity
After you install a battery meter, it might start to be clear that you need to expand your reserve capacity (number of batteries).

8. (Possible) Use the Old Panels on Opa & Oma Cabin
If you replace the panels on the main cabin, you could take the 2 best panels from the old system and mount them on the Opa & Oma cabin roof with a separate battery and charge system intended to just power the devices in that cabin.

I hope this helps a little and arms you with some information if you talk to SOLARMAN!

The pictures below show the panels in shade and the current then when they are in bright sun and the current.

Panels in Shade (Morning)

Current when in Shade (2.2)

Panels in Light (mid day)

Back Panel in light (mid day)

Current when in light (11.2)