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Photovoltaic System

Bruce Barbour - June 2019

I have recently (at the start of March 2019) installed a photovoltaic (PV) system on my roof for the generation of solar electricity. The system is a nominal 4.3 kW system comprising 14 310 Watt Trina Honey Plus Monocrystalline Solar PV Panels and Enphase IQ7+ Microinverters. The panels are on three orientations. The system is grid connected with no batteries. You can view the electricity production and other details at this link. This system was a lot more expensive than many of the advertised systems I saw. By paying the additional amount I am hoping that I am buying quality - a system that will last at least 20 years without significant issues. Time will tell whether this decision pays off.

I have been satisfied with the operations of the system thus far. Although it is now (June 2019) at the start of winter on the majority of days it generates more electricity (kilowatt hour - kWh) than I use. My energy usage is fairly modest averaging about 6 to 8 kWh per day at the start of winter (less during the "shoulder" season when no space heating or cooling is needed). There is no gas connected to the property so electricity is used for all heating, cooking, lighting and other functions. Not having gas connected to the house means lower carbon dioxide production and also a saving in that I don't have to pay for gas usage nor the quarterly gas property service charge for the house - at around $320 per year, depending on the distributor chosen. The low electricity consumption is assisted by having the hot water heated by a heat pump system (Sanden) and the space heating provided by a reverse cycle air conditioning system (Daikin Inverter split system - 1 kW)) and a new refrigerator (LG - 300L) that uses about 0.66 kWh per day. The lighting in the most used areas is LED (batten fix). CFL lighting is used in other lower use rooms and will be changed to LED over time.

The Daikin reverse cycle system installed was smaller than recommended by the installation company - who suggested 1.5 kW. I had done the calculations on the house heating energy usage and had determined that 1 kW was a sufficient size. This has so far proven correct though it is still early days. Of an evening once the room has reached temperature it operates using between 200 to 300 Watts. However if the house has been unattended for a number of days and the thermal mass (mainly the floor slab) has cooled then the reverse cycle air conditioning system can struggle to bring the room quickly up to temperature - not an issue most of the time. I also only heat the main living area and not the bedrooms - a closed door slows the loss of heat to the rest of the house. I insulated (R1) the walls between the living area and the rest of the house during construction. I set the temperature of the living area to about 20 degrees (winter) in the evening which is fine for me so long as I have a jacket on, but may be too cool for some. The house itself has an energy rating of 7.2 stars and uses some passive design principles, although full implementation of passive design was restrained by site restrictions. Some further improvements could also have been made to the house to increase its thermal performance - which may be the subject of a future article. The house is also relatively small compared to many newly constructed houses. I still have not installed proper curtains and pelmets on the (double glazed) windows which when installed may further assist with the energy efficiency of the house.

The hot water system is set to commence heating at 11 am (Australian Eastern Standard Time) in the morning and can continue until 4 pm. I chose this time as by then the PV is approaching (at 88% of) its peak production, which is typically at around 12:30 pm on a cloudless day. Usually the system commences heating at 11 am and has switched off by 12:30 pm  The Sanden heat pump hot water system uses approximately 1 kW when on. On sunny days and even days with some light cloud cover the PV system is generating more than a kilowatt during that time - and I try to avoid other large power loads during that period. Usually the water is being heated with electricity from the PV system, though on overcast days it draws electricity from the grid. The system works well and I recommend this approach to hot water heating for people with a grid connected PV system (>4 kW).

Batteries

I had to decide whether I wanted batteries. This was fairly easy as most experts were saying (in March 2019) that batteries for domestic installation in areas with grid electricity available could still not be justified economically. Simple back of the envelop calculations showed that this was a correct assessment. I may consider batteries if their cost declines further, though some reportage suggests that as battery powered cars became more prevalent the batteries in the car may be able to be used to power the home when the sun is not shining.

A couple of more points about batteries. If I do elect to install batteries in the future I would probably install a small capacity battery pack, say 4 kWh, and still remain connected to the grid. This amount of batteries would allow me to draw no power from the grid for, say, 95% of the days. Remaining connected to the grid also allows me to sell my excess back to the grid. If I wanted to disconnect from the grid I would probably need to at least double the amount of batteries, to 8 kWh or more, and perhaps increase the number of panels. For this over doubling of the cost I would save the electricity imported from the grid on those 5% of days and I would save the electricity distributor's property service charge, approximately $360 per annum (June 2019). However I would lose the opportunity to sell my excess electricity back to the grid, which in summer would be well over 20 kWh per day (for over $2.20) on clear days. I will know more precisely when I have run the system over a summer. I am hoping the amount that I sell back will cover the cost of the electricity property service charge, plus a bit more to cover the cost of the grid electricity that I use. The other aspect of this is that it would not just be a loss to me, but a loss to the whole grid. If I was not connected to the grid the excess PV power generation (20 kWh per day in summer and more) would be wasted. My PV infrastructure, and its embedded energy, would be partially wasted. Additional infrastructure may have to be built in the grid to cover for the admitted small loss of my PV system to the grid. It is a waste that should be avoided.

The point of this is that I want to discourage people with PV systems that are currently on the grid from exiting the grid when the cost of batteries falls to a point that allows it to occur economically. Hopefully systems will be in place that will make it more economically advantageous to stay connected, such as where the distributor can access power from the householder's battery storage, at times of high demand and low supply, and pays the householder a premium rate for the privilege. Or a payment system might be developed where the householder can remain connected to the grid so they can still sell their excess PV electricity to the grid, but pay a heavily discounted property service charge as most of the electricity is leaving the property. Under this arrangement if the householder wanted to take electricity from the grid, to cover an electricity shortfall from their PV system in a period of low solar, they would have to pay for it at a premium rate per kWh.

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I will update this page if I have further observations to report.

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