An article in the Oz prompted me to write the following.
The article referred to “solar saturation” of the power grid where excess solar generation is causing instability, primarily with over-voltage issues. Voltage needs to be kept within limits otherwise things like refrigerator motors fry.
In the article Energy Networks Australia are quoted as saying;
While it is not impossible for electricity to flow backwards, it is tricky for networks to manage the grid…especially where there is a lot of distributed electricity feeding back into the grid in the same area.
Domestic roof-top solar is touted as the answer to all our “bill problems”, and as the owner of a small system I can vouch for the effect on power bills, but I have a feed-in tariff of 56 cents/kWh and as long as this lasts I am doing OK. I recognise that non-solar households are subsidising me but that is due to political stupidity.
When the power system was designed,( by people who actually knew what they were doing), the model was to have large, centralised, reliable and economic power stations as close to the load centres as possible. Electricity was reticulated in a one-way system using various voltages which were progressively stepped down for ultimate consumption. Our houses use 240V. Main transmission lines run at 132, 256 or 500 thousand volts to reduce power losses due to line resistance, (Volts = I,(current) squared X R, (resistance)) so higher voltage give lower losses.
When it gets to our homes we want 240 volts so the local system draws from a High Voltage feeder, (usually 11,000 volts), through a transformer to get 240. In SA if folk look at the power poles in their street they will see 3 wires on top of the poles, (usually 11,000 volts), and 4 underneath – this is 415V 3 phase distribution system and the 240 volt supplies are taken off this. Every now and then there is a transformer between the 2.
Each transformer serves a “local” area containing a number of homes. Domestic solar systems can “share” their excess within the local area but nowhere else because the transformer will not permit a reverse flow when there is a higher voltage on the supply side. Electrical purists do not like water analogies but the best way to view the transformer is as a one-way valve.
If there is a power failure then solar systems will shut down as there is a need to ensure that there is no extraneous power supply that could endanger those who work to fix the problem. This is done by the solar inverter and it is a legal requirement that this happens. Once the inverter is off line a person’s solar system is no use to them and they will be in the dark until power is restored. A battery would be no use unless the system had the means to disconnect from the grid completely.
The article also states that the Clean Energy Council says 21% of the overall “power mix” is supplied by renewables. Each year the Department of Environment and Energy release statistics on generation and consumption. These are around a year late when released so the following comes from the 2016/17 release. The chart below shows the percentages of generation for all “fuel types”. I have lumped hydro in with “fossil” fuels because it is a mature method of generation and does not have the intermittency of solar and wind. As long as there is some water there is some reliable power.
There is a view that as long as there is daylight the solar system works. Earlier this year I submitted a post showing the vagaries of solar systems but it missed the cut. I will put a couple of charts below to illustrate. These were done in response to a request to see whether a 200 MW solar plant could power a remote mine-site. The load shown in the charts is the 200 MW that the mine needs constantly. Daily and hourly consumption is in MWh. I picked the “best” day and the “worst” day as well as the “best” month and the “worst” month.
Best day, hours 1 to 24:
Best month, days 1 to 31:
These charts come from an analysis using data for Kalgoorlie but anywhere is the same – perhaps a little better as you go North but not by much. The system used here had 2 axis tracking that gets the capacity factor up to about 25% but it needs power to operate. Most solar systems with fixed panels manage around 17% tops.
The charts show the variation in output over the year where the sun angle changes from summer to winter and also shows variations day to day usually caused by clouds. Every time the system is in deficit some other system has to step in to keep supply equal to demand. As the charts show, this is a frequent occurrence.
Domestic solar suffers the same vagaries of seasons and cloudy days.
In short, the idea of having “virtual” power stations using lots of rooftop solar systems is bullshit.
Electricity suppliers hate solar because they miss out on charging for the “free” power distributed by the rooftop solar systems but have to be ready to pick up the shortfalls and of course the 12 hours of the day when the sun does not shine. To counter this they raise their prices so more “renewables” leads to higher prices. It is a vicious circle that will not be broken until sanity prevails again and we get back to the dreaded coal for our power.
Getting power to “run backwards” is like squirting a syringe full of water into the end of a running hose and expecting it to get back to the reservoir, it is just bullshit.