Solar Panels

[Quickstatus]

No second bite at the cherry

Correct, it is a one time only rebate per premises.

 

[JessicaTam]

Remember the rebate is a once only per premises offer and proportion to the size of the system. No second bite at the cherry

Good point. Maybe I will go larger for the (pre-rebate) cost of smaller.

 

[Quickstatus]

Maybe I will go larger for the (pre-rebate) cost of smaller.

The c/kWh reduces progressively as battery size increases.

 

[AuSammy]

The c/kWh reduces progressively as battery size increases.

Yep a 19kw system is approx 50% cheaper per kW than 9kw from quotes I got

 

[NM]

I am still struggling with the numbers. With my 6.6kW of panels and 5kW inverter (the biggest for grid connection permitted in my area), I have setup my consumption to self-consume as much of my generation as possible, through scheduling major consumption activities as much as practical. But even in April, which is typically one my best months for excess generation, I averaged 57% self-consumption and averaged 12.25kWh/day feed to the grid, with only 14 days exceeding 13.5kWh (typical battery size).

With my current generation and consumption profile, I could only recharge (fully) a 13.5kWh battery 50% of the time. And there were some days where feed to the grid was VERY small (less than 1kWh). And that is during the "best" month.

So to make a battery work for me, I need to consider some changes:

• To the times that I operate high consumption appliances (i.e. hot water system, pool pumps, dish washer etc.)
• To my retailer tariff profile. Currently one usage tariff, but a 3-step TOD tariff may work better with a battery
• Consider top-up charge of battery from the grid during "low" rate tariff just before evening peak tariff commences on days when excess solar generation is insufficient

And with TOD tariff I only need the battery to address the consumption requirement during the afternoon/evening peak tariff period.

I have all my generation and consumption data available, so can so some historic analysis based on different tariff options. But the biggest unknown is how tariff options and rates will morph over the next 10 years, as it is anyone's guess. locking in the capital investment based on today's conditions can be dangerous when there is no guarantee or even expectation that how and how much the energy supplies will charge in the future.

I expect that to make it work in my favour I will need some smart control tools to manage the charging and consumption from the battery.

 

[Quickstatus]

Currently one usage tariff, but a 3-step TOD tariff may work better with a battery

Correct
Most people with TOU/TOD tariffs have a high peak tariff. In my case 48c/kWh peak and 21c/kWh off peak
So a battery covers the high tariff period

Consider top-up charge of battery from the grid during "low" rate tariff just before evening peak tariff commences on days when excess solar generation is insufficient

No, I would not do that. The cost of electricity coming out of the battery = cost of electricity going in + cost of battery on a c/kWh basis
It only makes sense if the cost of electricity going in is solar or if the retailer has an electricity plan which gives free power during a certain period from which you can charge the battery.

Battery only makes sense if you have excess power during the highest electricity consumption period and if you have TOU.
Having said that it would make sense to get a quote to see if the battery on a c/kWh basis comes in under your general tariff

You need:
Installation cost
Total kWh throughout during the warranty period.
Opportunity cost of capital at prevailing interest rates
Charging cycle 90%
Losses in charging and discharging battery 10%
FiT forgone in order to charge battery
Battery degradation - Im assuming 0% in the first year and 15% in the 10th year. So assume 7.5% less available capacity every year.

So if the warranty is 10 years and the usable capacity of battery is 13.5kWh per day
The available energy per day = 13.5kwh x 0.9 x 0.9 x 0.925 = 10.1kWh
Total over 10 years at 365 days /year = 10.1 x 3650 = 36900kWh

If battery costs $8000 then the cost of battery in c/kWh = 8000/36900 = 21c/kWh

Add in Fit - lets say 4c/kWh

Your cost of battery power is 25c/kWh
How dos this compare with your tariff at the moment

 

[NM]

No, I would not do that. The cost of electricity coming out of the battery = cost of electricity going in + cost of battery on a c/kWh basis
It only makes sense if the cost of electricity going in is solar or if the retailer has an electricity plan which gives free power during a certain period from which you can charge the battery.

If there is insufficient charge in the battery to supply my needs during the peak tariff period, then I am paying the peak tariff rate for the additional power consumed during that peak tariff period. As an example, my battery at say 2kWh (~15%) charge at the beginning of the day and its an overcast day and my excess generation is low for the day (say 2kWh), leaving my battery at 4kWh as peak tariff approaches.

If my peak tariff period consumption is say 10kWh, then I get the first 4kWh from the battery (free in terms of paid tariff) and then next 6 kWh come from the grid at peak tariff rate. So using your peak tariff rate of 48c/kWh, the excess consumption will cost $2.88.

But if I was to top-up the battery charge from the grid during low tariff period, that 6kWh of "top-up" would have cost $1.26.

Obviously, where possible the battery charge should come from solar generation, but I do not have sufficient excess generation every day to charge the battery to fully cover the peak tariff consumption. The goal would be to ensure there is sufficient charge (ideally fully charged) at the start of every peak tariff period so that my peak tariff period grid consumption is zero every day, and on days where I do not have sufficient excess solar energy to charge the battery to a capacity that will fully cover the peak tariff period consumption, then its better to buy the electricity at low tariff rate and store it in the battery for consumption during the peak tariff period.

I suppose its best that at the start of the solar generation for the day and during the off-peak or shoulder tariff period, direct all solar generation to the battery rather than just the excess solar generation, and during that time of battery charging from solar, try to limit high consumption appliances, until the battery is charged.

Currently, I have my home automation monitor the solar generation and uses this logic:

• When generation reaches 4kW (80% of the 5kW inverter capacity) or at 10:30am on very cloudy day) the hot water system turns on
• Then as soon as the hot water is heated (current to the HW system drops to zero) the HW power is switched off and the pool pumps/chlorinator starts and runs for 6 hours).

So maybe the logic with a battery should be:

• When solar generation starts in the morning and cheapest tariff is active, direct solar generation to battery
• When battery is full, or 90 mins before peak tariff starts, turn on hot water system (normally takes about 60 mins to heat once per day)
• When hot water is heated turn on pool pumps and run 6 hours or until peak tariff commences
• If pool ran less than 6 hours, turn pool back on for remaining time after peak tariff period completes

Battery only makes sense if you have excess power during the highest electricity consumption period and if you have TOU.
Having said that it would make sense to get a quote to see if the battery on a c/kWh basis comes in under your general tariff

You need:
Installation cost
Total kWh throughout during the warranty period.
Opportunity cost of capital at prevailing interest rates
Charging cycle 90%
Losses in charging and discharging battery 10%
FiT forgone in order to charge battery
Battery degradation - Im assuming 0% in the first year and 15% in the 10th year. So assume 7.5% less available capacity every year.

So if the warranty is 10 years and the usable capacity of battery is 13.5kWh per day
The available energy per day = 13.5kwh x 0.9 x 0.9 x 0.925 = 10.1kWh
Total over 10 years at 365 days /year = 10.1 x 3650 = 36900kWh

If battery costs $8000 then the cost of battery in c/kWh = 8000/36900 = 21c/kWh

Add in Fit - lets say 4c/kWh

Your cost of battery power is 25c/kWh
How dos this compare with your tariff at the moment

I see my numbers a little differently. While I do not dispute your logic, I know the reality will be somewhat different due to factors that cannot easily be quantified, such as when we get extended days of low generation (as we had hear early and late March with solar generation less than 10kWh for 5 consecutive days) and the completely unknown tariff projects over the 10 year projection. 10 years ago we didn't even have TOD tariff here, and when my solar was installed, FIT was around 17c/kWh. So pre-install projections over the life of the system are not going to be accurate after the first year or so.

So my goal is aimed at reducing what I pay to the energy retailer making the best use of my solar generated energy (self consumption and storage for times of the day when grid tariff is high). I have no control over how much solar energy is generated each day, but I can control how that energy is consumed or stored for later consumption. For me, in my situation, I think it is best to try to have zero grid consumption during peak tariff periods (minimise what I have to pay) and that means starting every peak tariff period with sufficient battery charge to supply my peak tariff period consumption demand, and try to ensure all my grid consumption is during off-peak or shoulder tariff periods.

That all means that one of the most important components of a battery solution for me will the ability to control how the solar generated power and stored power is managed each day. The control software/tools/APIs is going to be very important to me.

My ideal electricity plan for battery storage would be one that has:

• low daily supply charge (I see variations from 90.0c to 136.4c)
• low off-peak and shoulder tariff rate
• not concerned about Feed in Tariff rate (I expect very little residual solar to feed in after battery storage)
• I don't care about the peak tariff rate (I plan to avoid consumption during peak tariff period)

The installation cost is less of an issue as I expect having a quality solar and battery system installed will add value to the property in excess of the installation cost.

 

[Quickstatus]

I do not have sufficient excess generation every day to charge the battery to fully cover the peak tariff consumption

This appears to be the main issue. Batteries only make sense if you have excess solar generation. Charging from grid financially does lot make sense

The calculations only show the cost of battery in c/kWh over the warranty of the battery.

 

[NM]

This appears to be the main issue. Batteries only make sense if you have excess solar generation. Charging from grid financially does lot make sense

only considering charging from the grid on low-generation days when it would not be sufficient to charge the battery sufficiently to cover peak tariff period consumption. Certainly not feasible if doing that every day. But there are days almost every month, and sometimes up to 5 consecutive days) where the "sun does not shine" to the extent needed to achieve zero peak tariff period consumption.

 

[Quickstatus]

only considering charging from the grid on low-generation days when it would not be sufficient to charge the battery sufficiently to cover peak tariff period consumption.

That only makes sense if the cost of grid power to charge battery + cost of battery in c/kWh is less than cost of peak tariff.

In most cases it is not

 

[NM]

That only makes sense if the cost of grid power to charge battery + cost of battery in c/kWh is less than cost of peak tariff.

In most cases it is not

But if you have already made the battery investment, then its really just the cost difference between off-peak and peak tariff rates (less a little for efficiency impact) on the days where solar generation is low due to environmental conditions.

Justify the battery investment cost based on say 80% of days having sufficient excess solar generation to store and cover the peak tariff period. Then on the other 20% of days that you still have the battery available but just can't charge it enough to cover the peak tariff period consumption, then I am still saving because I can buy the electricity needed for the peak time at off-peak rates.

And the other incentive, which cannot be quantified, is that with current base-load generation capability being phased out or reduced, I expect the grid supply to become less reliable over time so having battery storage to cover possible grid supply instability periods (most likely to be peak demand periods) might give me supply when others in the street are searching in the dark for a torch or candles to see their frozen dinner sitting on the kitchen bench.

 

[markis10]

NM, sounds like you need to invest in a couple of EVs with a good VTL setup, in some ways cheap batteries

 

[Quickstatus]

But if you have already made the battery investment, then its really just the cost difference between off-peak and peak tariff rates (less a little for efficiency impact) on the days where solar generation is low due to environmental conditions.

Not really, the cost is still there even if sunk costs.

You could average it out over the 10 year warranty period but with differential prices:


Let's say best case your battery costs 20c/kWh to store and release. Charging is extra. And half of your days in the year you charge from the grid. And the other half you charge from solar:

50% of battery electricity is 25c/kWh (20c + 5c charging from solar(
50% of battery electricity is 40/kWh (20c + 20c charging from grid)

So your average cost is 32.5c/kWh over the year. If this is below your prevailing tariff then good if not then reconsider

 

[DC3]

NM, sounds like you need to invest in a couple of EVs with a good VTL setup, in some ways cheap batteries

Or, move to an area that gets some sunshine.

 

[Quickstatus]

I expect the grid supply to become less reliable over time so having battery storage to cover possible grid supply instability periods (most likely to be peak demand periods)

South Australia is robust despite lots of renewables and lack of inertia

 

[DejaBrew]

If you have been with your electricity provider last winter, you should have consumption data in your online account - monthly/daily/hourly to help with estimation for July 2024

Therein lies my other problem.... I didn't have a smart meter until I got solar. So my monthly/daily/hourly consumption data is only available from October last year. So as I said, I think I'll be needing to make some assumptions.