Solar Generation

Molly has three solar panels located on her roof. In theory these combined can generate 154 x 3 or 462 watts of energy. This is under ideal conditions, and we have never generated this much power. Or have we?

Molly came with a Blue Sky Energy Solar Boost 3024iL MPPT solar charger with its IPN Remote. We added to this setup a Universal Communication Module (UCM), also from Blue Sky Energy. The UCM allows us to connect our computer to the Solar Charger and monitor energy generation and charging mode. And answer the question of how much our panels are generating.

Solar charging can be a fickle business, and understanding how the charger is charging the batteries is our objective. Also it is fun to see how much green solar energy we are generating.

Wiring Up

The UCM gets its power from the Solar Charger via the 4 core IPN Network cable. And we connected the UCM to the network via the RJ45 ethernet cable. It took a little fiddling to change the factory set IP address, but once done, the UCM presented nicely on our local network. The ethernet connection is more powerful than the RS485 connection, as it also presents a web interface for a browser and an ftp interface to download file. So, this is the direction we went.

The Raspberry Pi connects to the UCM via node-red and a TCP based MODBUS adaptor. Configuration was unusually easy, and took less than 10 minutes to configure.

Although there are many variabes we can monitor, we are only monitoring the following

  • Charge State. Off, Absorption, Float, Equalize or Bulk
  • Battery Volts
  • Output Amps from Controller

We might add more parameters later, but these are the key ones for now.

Early Results

We have only had 2 days of test so far. On a bright sunny day we can generate about 4.5 times our base load. Our base load is about 65 watts, and we can generate about 290 watts. Not quite the promised 452 watts. But this is 64% of the rated output for the solar panels, so we are in the expected ballpark.

In theory we should be able to recover most of the power lost during the night during the following day, assuming a a nice sunny day with a good view of the sky.

Further Monitoring

Further testing in a variety of different conditions, revealed similar results. In very hot conditions, the solar panels can just about recover what we use during the day. When the solar panels are not baking in a hot sun, then they do a little better and can more easily recover our typical consumption.

If the sky is overcast, or we are parked under the shade of a tree or if snow is covering the roof, then the solar panels have no hope. Even if we added more solar panels to the roof, it is unlikely they would help much. It is hard to make hay when the sun ain’t shining.

The Solution

The solution has two components. more solar panels and more batteries. More solar panels for conditions when accessing to sun is hard and more batteries for when the sun is very hard.

However the extra solar panels will not be placed on the roof, because the roof might be in the shade. So instead we purchased two 100 watt potable panels, which we can move around depending on where the sun is. The new panels need their own solar charge controller, and we choose the Blue Sky Energy Solar Boost 1524iX.

The batteries were upgraded from 540 hr AGMs to 600 Ah lithiums. Even with no sun, this increased battery capacity should last around 3 days.

Sizing

Ideally we want enough battery capacity and solar generation to achieve

  • 3 days with no sun
  • 5 days on just our portable solar panels so Molly can stay in the shade and
  • at least a week on our roof-top solar panels, assuming they have a clear view of the sky

Anything beyond this will mean we have to run the alternator (or connect to shore power). Our daily consumption (in non freezing conditions) is a very generous around 2,250 watts per day. With 200 watts of portable power producing 125 watts effective power for 7 hours per day and 462 watts of roof top solar panels producing 290 watts effective power for 5 hours per day, means we need around 600 Ah of battery capacity to achieve and exceed our targets. In fact we will get 3.2 days of no sun, 5 days with just portable panels and 9 days with just roof top panels. If we could drop our day consumption to 2,000 watts, then we could get away with 500 Ahr of lithium.

With both roof top and portable solar panels deployed and good weather, we can generate as much as we consume, and a 200 Ahr battery is enough to get through the night.

Lithium is expensive. And clearly extra lithium is useful for the no sun days. But it is also useful to have extra capacity when using high current draw devices, like our coffee machine.

Solar Charger with new UCM module (not installed permanently
Computer connected
Added solar generation with the new portable panels. Here we are generating 450 watts.
New portable solar panels. Perfect for when Molly is under the shade of trees.