Question about solar power

[Homer]

This is one for the solar power experts.

I know very little about solar power. I live in a small strata complex of 17 terraces in the inner city and our executive committee (of which I am a member) is proposing to raise a special levy to install solar panels on our roof (with battery storage like the Tesla PowerWall at the individual lot owner's expense). Apparently due to our available roof space and some other factors the best we will be able to get is 4kW each.

I support the proposal but as I have a 90kW Model S in the garage and a 4-level house with a/c running a lot of the time, the prospect of capturing 4kW doesn't sound like it will go very far towards meeting my family's consumption. So I was wondering whether any solar power experts on the forum might either be able to reassure me or else direct me to some methods of maximising the kW obtained?

 

[strykeroz]

With a north facing roof and 5.7kW of panels in Brisbane (hotter, so panels run less efficiently here than in Sydney, but also different cloud cover, frequent summer afternoon storms etc) we generate around 24kWh on average daily. Rainy days, 2-4kWh and peak autumn cool bright cloudless days 38+kWh...so if your roof was located at my place I'd expect around 16kWh/day as an overall average. However there are heaps of variables that will have an impact on the daily production you achieve over and above the panels you choose.

I suggest you checkout PVoutput.org (link to ours: gskctest 5.760kW | Live Output) and select some systems that are in your area to get an idea of what you're likely to achieve in your location.

 

[Homer]

Thanks! So let's say I was able to generate 16kWh on an average day, and store it, what would that power in terms of a typical house?

 

[strykeroz]

For that the best source you have is your own power bill. You'll also need to take into account the power consumed by the common areas in your complex.

 

[Homer]

Apparently the common areas will either continue to be drawn from the grid or may be supplied by a separate set of panels. I just checked my bill and our average consumption ranges from about 45kWh up to about 50kWh. So 16 kWh is only about one-third of our needs?

 

[WhiteStar]

One third of your energy requirements generated & stored in home batteries will definitely more than pay for itself over the lifetime of the system, especially with increasing energy costs. Avoiding the universal feed-in tariff theft with home storage makes all the difference. Also consider using Powershop (if you don’t already) as your supplier with way more transparent costs as well as the ability to select various renewable supply sources.

 

[raynewman]

Apparently the common areas will either continue to be drawn from the grid or may be supplied by a separate set of panels. I just checked my bill and our average consumption ranges from about 45kWh up to about 50kWh. So 16 kWh is only about one-third of our needs?

Your usage seems hungry; ours for a 4 bedroom apartment is an average of 16kwh per day (plus a daily average of 18 kwh per day for the car). May I suggest an audit on your usage.

 

[strykeroz]

Another thing I can attest to is once you have a system on your roof you'll start to use less power because you start paying attention. Every appliance we've replaced since has improved our situation. Compact fluros replaced older lights and have gradually been replaced by LEDs. Our clothes drier died, and it's stayed that way. Our A/C is used far less, and fans far more.

The other variable that your bill won't show you is the time of day when you use the electricity. Despite us typically generating more than we consume, every day (without battery storage) we buy at least 10kWh from the grid. Batteries will eventually fix that.

If there's an opposite to "buyer regret" that's what we've had for the past few years with PV on the roof.

 

[Homer]

Your usage seems hungry; ours for a 4 bedroom apartment is an average of 16kwh per day (plus a daily average of 18 kwh per day for the car). May I suggest an audit on your usage.

That's a good idea but I suspect it's accurate. My wife is a former Queenslander, so she likes to keep the house "comfortable" at 25 degrees in our winter... I think that's where a lot of our usage goes - on heat. Plus we have a house full of old-fashioned dichroic lights. Some of my neighbours replaced theirs with energy efficient LEDs and have noticed a big difference. We also have a lift and, while I take the stairs, the cleaner and the kids use it a bit. I think it's likely a bit power hungry too.

 

[Drewflux]

@Homer some thoughts.
If the strata is paying for the panels, who gets the solar rebate? Its been drastically reduced from when the scheme was set up.

If you dont get the rebate, can you claim the strata fee back on tax?

It could be an attractive offer if you only have to pay for the power wall and install, charging the wall on off peak rate, may have a cost saving benefits. Also as ray mentioned sounds like an audit is needed.
Led lighting, posible updated appliances with higher energy ratings, fans to reduce/ help the a/c use, curtains to reduce sun load to the interior are a few things that may help.

 

[Homer]

@Homer some thoughts.
If the strata is paying for the panels, who gets the solar rebate? Its been drastically reduced from when the scheme was set up.

The owners (i.e. us) would be paying via a special levy if the proposal passes. I will ask about the solar rebate as that hasn't been discussed to date.

I really appreciate the comments and suggestions here. Thanks team!

 

[paulp]

That's a good idea but I suspect it's accurate. My wife is a former Queenslander, so she likes to keep the house "comfortable" at 25 degrees in our winter... I think that's where a lot of our usage goes - on heat. Plus we have a house full of old-fashioned dichroic lights. Some of my neighbours replaced theirs with energy efficient LEDs and have noticed a big difference. We also have a lift and, while I take the stairs, the cleaner and the kids use it a bit. I think it's likely a bit power hungry too.

LED downlights (decent ones) are way better than dichroic and wont burn your house down (have a swap fitting rather than swap globe approach), and your lift uses bugger all power. They use a lot for a fraction of a second, then minimal for the rest of the journey. I'm agreeing with your wife. Keep the house comfortable, its only a few more dollars on the power bill. Ditch the kids, that will cut back your power bill more than any other action.
With solar, you get to tell onlookers that you have free fuel for your car as you charge with solar, especially if a dedicated circuit. Its worth it just for that.

 

[Mark E]

The amount you get from the panels would be very dependant on the site - shading makes a huge difference, as does aspect. In winter time you will get a lot less than in summer.

Your power usage is huge it that's your average all year round. I suspect your lights will have a bigger impact than you expect.

 

[Shock-On-T]

Agreed very high power usage. My house rarely runs over 20kwh/day, and has quite a few incandescent dimmer lights.

 

[Homer]

I've been going back over the bills and the usage drops back to 36kWh/day in the Spring quarter, which is when we run the a/c the least. So to me that indicates the impact of the a/c on our consumption. I have a feeling, based on comments by my neighbours who have replaced their lights with LEDs, that the lighting makes up another chunk of the cost. I will investigate replacing the lights; from memory it was around a $10K spend so, much like the solar, you get it back over time.

 

[Mark E]

$10k on LED replacements? You must have a LOT of lights in that apartment LED globes can be had from $5-30, complete replacements around $35 ea. Just looked up my old power usage, pre-solar panels with electric hot water, reverse cycle air, 24x7 computer equipment and my wife home during the days was 35kWh in winter, and between 17-25 for the rest of the year. 3Br house.

 

[Homer]

Yeah it's a four-level house, not an apartment. I did a quick count and there are more than 100 lights (all part of a home automation system).

 

[360C]

That's a good idea but I suspect it's accurate. My wife is a former Queenslander, so she likes to keep the house "comfortable" at 25 degrees in our winter... I think that's where a lot of our usage goes - on heat. Plus we have a house full of old-fashioned dichroic lights. Some of my neighbours replaced theirs with energy efficient LEDs and have noticed a big difference. We also have a lift and, while I take the stairs, the cleaner and the kids use it a bit. I think it's likely a bit power hungry too.

I have gone down the solar/battery storage route in a big way at home and work and have had systems running for about 18mths now.
You will get the biggest bang for your buck by far by making your house and appliances as energy efficient as humanly possible before you look at solar. Once this is done you can then look at your energy usage in detail and design an appropriate system for your situation.
You would likely be surprised how much energy is used by a big house full of old appliances and non LED lighting. As mentioned change to Powershop as your energy supllier. They provide you with some useful analytical data on the App that can help you see where your energy is being used.

 

[360C]

With solar, you get to tell onlookers that you have free fuel for your car as you charge with solar, especially if a dedicated circuit. Its worth it just for that.

This is a bit of a fallacy as it takes a very big solar/battery system to provide enough energy to charge a Tesla without falling back on grid power. I have a 10kw system with 24kw of battery storage and I can charge my Tesla off grid in some conditions; but most of the time it gets some degree of top up from the grid. Charging on single phase will draw about 8kw/h and on three phase obviously x 3.
If it is a sunny day, the 10kw system is generating well and the batteries are fully charged, off grid charge on single phase is possible for a top up of the Tesla battery. In any other conditions or using 3 phase will exceed the capacity of the solar system and grid power will provide the balance of power.

 

[Jimat]

This is a bit of a fallacy as it takes a very big solar/battery system to provide enough energy to charge a Tesla without falling back on grid power. I have a 10kw system with 24kw of battery storage and I can charge my Tesla off grid in some conditions; but most of the time it gets some degree of top up from the grid. Charging on single phase will draw about 8kw/h and on three phase obviously x 3.
If it is a sunny day, the 10kw system is generating well and the batteries are fully charged, off grid charge on single phase is possible for a top up of the Tesla battery. In any other conditions or using 3 phase will exceed the capacity of the solar system and grid power will provide the balance of power.

My MS85 is currently getting 32A all from my rooftop solar.
I have a fairly large PV array and we are off grid with a battery bank.
And it feels TERRIFIC!!
I think I will go into town today to burn off some electrons- just because I can.
HOWEVER.....unfortunately the whole system is NOT cost effective as I started 20 years ago and the payback period is probably still another 10 years at best. And we make a major effort to reduce power consumption in general- our "normal" power usage is about 10Kwh a day- no a/c , no kids, all LED lighting etc,etc.
HOWEVER (again) I didn't do it to save money- it's a greenies type thing. And owning a Tesla is the same philosophy- only a crazy person thinks they can save money driving a Tesla- if saving money was the objective I might have bought a Nissan Leaf. Yuck!