Unit 1 plans included a solar power system so the appropriate wiring was laid during construction. But what exactly should we install? After much discussion about system sizing, location of solar panels and battery storage, we took the plunge. Gary (Sustainable Power Systems) and his crew spent some quality time on the roof and in the garage to get the job done.
Solar power system specifications.
Contrary to what Julie Andrews would suggest, let’s start at the very end and then talk about why we did what we did.
Our solar system has three main components:
- Solar panels – 26x300W SolarEdge smart solar panels fitted with optimisers
- Inverter/charger – SolarEdge 6000 StorEdge inverter with back-up power option
- Battery – LG Chem RESU 10H
Deciding on the number of solar panels.
Working out the capacity of a solar power array is not an open-ended question. These days installers probably won’t climb on the roof for anything less than 3kW. Obviously, the upper limit is set by how many solar panels fit up there. No point asking for a capacity that requires knocking on the neighbour’s door to borrow some of their roof space.
So, what works best between those two limits?
Environment Victoria recommend going big with solar systems for two reasons. Firstly, over the last few years the price of larger systems (eg 5kW) halved while the cost of smaller systems dropped by only a quarter. Secondly, feed-in tariffs increased to over 11c per kWh. Combining these factors means larger systems pay back quicker than smaller ones. In Melbourne, a 5kW solar array has a 6 year payback period but owners of a 2kW array have to wait another two years to cover the cost. Higher tariffs ensure homes exporting a significant portion of electricity production benefit from a larger system.
We decided to go for maximum generating capacity, based on the Environment Victoria advice and our need to regularly charge Libby’s Nissan LEAF EV. Gary found space for a total of 26 SolarEdge 300W smart panels. All up, the system has a nominal 7.8kW capacity.
The system is split into two strings with one row of 12 panels on the north facing roof and 2 rows of 7 panels on the south facing roof.
Why use SolarEdge panels?
Gary prefers SolarEdge smart panels because they do a good job and he likes their technology. They aren’t called “smart” for nothing.
Creating an effective solar array isn’t as simple as whacking panels on a roof and wiring them together. Shade or dirt on one panel can reduce the production of the entire string of panels. It might be sunny, but electricity production drops well below nameplate capacity.
Manufacturers reduce this pesky problem by installing Maximum Power Point Trackers (MPPTs) in the inverter. These devices work tirelessly to fight the shading effect by constantly adjusting voltage and current to maximise power production. However, as a standard inverter only has two MPPTs, there is only so much they can do.
SolarEdge decided to improve system performance by installing a power optimiser on each panel. In effect, every one gets its own MPPT. Overall array performance improves because each panel is doing its best to maximise production. They aren’t affected by what’s happening to neighbouring panels.
Hang on, south facing solar panels!!
Yes, you weren’t wrong. Over half of our panels are on the roof that faces south. Conventional wisdom is north or nothing. However, as Gary says, “South is the new North.” What he means is falling panel prices are making non-optimal orientations economically viable. More people are intentionally choosing panel orientations to fit with their electricity consumption patterns. For example, facing some panels westwards helps to meet the peak air conditioning power load during hot Summer days.
Solar Quotes publish a handy power loss predictor for panels facing away from the optimum northerly direction. Given a 10 degree roof pitch, south roof panel capacity should only drop by 20% compared to a panel on the north roof.
I recently checked this prediction and found the southern panels are currently operating with a 35% reduction. Solar Quotes says that’s not surprising given the Sun is lower in the sky as Winter approaches. I’ll be watching this number with interest next Summer. With the Sun high in the sky, I expect the south array to match the 80% prediction.
StorEdge inverter is the brains.
Those of you with an eye for detail probably noticed the solar panels have a nominal capacity of 7.8kW but the StorEdge inverter is only rated for 6kW. Are we being crazy? First it was south-facing panels and now it’s a solar array that’s too big for the inverter.
Fear not. Oversizing arrays is a thing. Solar Quotes explains that a well-designed inverter is good for 133% of rated capacity. After crunching the numbers, Solar Quotes showed that matching the array and inverter capacities produces about the same amount of electricity as a smaller capacity inverter connected to an oversized array.
There are a couple of other things to bear in mind for this system.
Although the 26 panels have a rated capacity of 7.8kW, south facing panels means it is more like 7kW. The 6kW inverter is unlikely to reach a design limit, even during Summer peak production.
Another interesting wrinkle is our electricity distributor limits household solar power exports to 5kW. However, we won’t waste the extra capacity available in our system. The battery soaks up excess production until it’s full. We can “stash” solar power in two other places – the battery in Libby’s Nissan LEAF and the hot water system. Running the heat pump to heat water in the storage tank is equivalent to storing electricity in a battery. There’s a lot happening on our side of the electricity meter which should minimise time spent bumping up against the 5kW export limit.
LG Chem battery minimises power imported from the grid.
Installing a battery provides a nighttime supply of solar power. Without a battery, solar electricity is a “use it or lose it” proposition. Excess production quite rightly goes to the grid to replace energy from non-renewable sources. At night, household demand is met with imported grid electricity. A battery acts like an electricity “bank”. Make a deposit during the day and a withdrawal at night.
The solar power bank is also open for business on cloudy days. If there isn’t enough electricity from the panels, the inverter tops up the supply from the stored energy in the battery. Grid electricity is a last resort.
Choosing an inverter limits battery options to compatible brands. In this case, SolarEdge works best with LG Chem RESU batteries. The smallest one currently on the market is the RESU 10 (nominal capacity of 9.8 kWh).
With a usable capacity of 8.8kWh, there is plenty of energy on tap to keep us going overnight. Maybe a bit too much some might say. Correct, but I have ideas on what to do. I’ll post about my plans after chatting to Gary about some minor alterations to the inverter operating profile.
While setting up the electrical system for Unit 1, Gary took advantage of the StorEdge inverter power backup function. This allows us to party on if there’s a neighbourhood power failure. The battery backs up our standard power and light circuits. Big power users like the induction cooktop and oven won’t be available but I’m sure we can manage.
What’s with the bollards?
As a finishing touch, Gary bolted two bright yellow bollards into the floor in front of the battery. He wasn’t making an artistic flourish, simply complying with the battery install guidelines for accredited installers.
Puncturing a lithium ion battery makes bad things happen.
What could possibly go wrong with a battery installed on the wall in a garage? It didn’t take the boffins long to insist on bollards to prevent a car hitting the battery. In our case, how ironic would it be for a Nissan LEAF electric vehicle to run into the battery?
Can we switch on the solar panels now?
With electricity, it’s better to be safe than sorry so there’s quite a bit to do between finishing installation and switching on the system. Time seems to drag when you’re waiting on inspections, paperwork reviews, meter modifications, etc.
Of course the “ready to go” email notification arrived on the day when I’d stopped my frequent checks. What a pleasant surprise! Libby and I rushed to the garage to flick the inverter ON switch. That was closely followed by an error message. Luckily, Gary was just a phone call away. He explained the battery had been decommissioned during the lengthy delay. All it took was a few instructions to bring it back to life and, voila, the electrons started flowing.
Sneak peak of the information on tap.
SolarEdge lives up to its reputation for smart technology.
Since each panel is fitted with a power optimiser, I can see individual performance data by day, week, month or year. I’ll know if any panel is off its game as soon as a problem occurs.
Instantaneous readings show where electricity from the solar panels is going. Are we charging the battery or just supplying the house. Has the load increased to the point where electricity is coming in from the grid? How much are we exporting?
A summary screen wraps all the data into a neat little graph. The following examples shows solar power production (green), self consumption (blue) and imports (red). On this particular day, most of the two big blue spikes was due to charging the LEAF. I’d like to use these graphs to minimise electricity imports.
There is so much to learn about making the best use of this system. I’m looking forward to the experience.