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• airgradient, Powerful Air Quality Solutions

It's not what you think... it's worse. Sky high power prices are by design. Topher Project Ep 194

Bid Stack Electric Power System

In my home jurisdiction housing with single phase power reticulation are generally limited to solar systems with 5kW of feed in capacity, so systems are limited to 6.6kW of peak solar panel capacity coupled to a inverter with 5kW maximum capacity. The requirements have developed and changed significantly over the past 15 years as features of residential solar power has significantly changed during this time, particularly renewables system cost and grid penetration.

The BESS can allow some flexibility on the installed Solar capacity, however the maximum solar feed in capacity is generally limited to 5kW on a single phase system.

I had installed upon my house circa 2013 5kW of solar panels (20 x 250W peak capacity solar panels with 10 micro inverters each with 2 x 250W rated inputs). I replaced this system with new solar cells and string inverter in April 2025.

Comments on system performance and why I replaced; tl;dr;

I installed a new solar system with a 6.6kW panels and 5kW sting inverted in April 2025. In August 2025 I had installed a 5kW/10kWhr battery system, the installer replaced the string inverter with the BESS that included an integrated dual string inverter. There were substantial government subsidies available at the time I had the BESS install that allowed an approximate 6 - 7 year pay back to be possible. Further to this the system supplier included a full 10 year warranty on parts and labour. The supplier seemed reputable, that is hopefully will be around and honour any warranty claim with in years. The BESS supplier Alpha ESS also had a 10 year warranty, which helps mitigate risk on parts warranty.

It is too early to form any conclusive comments on this system. The spring and autumn periods are traditionally thoses where I have the lowest energy demand (low heating and cooling requiremnts coupled with reasonable solar output, where as summer that has best solar output also tends to have higher associated cooling electrical power costs. Winter is the worst month with lower solar power generation coupled with high electrical power consumption for electrical heating (reverse cycle heat pump heating coupled with typical Australian pre circa 1995 poorly insulated housing.) My preliminary observations are:

• Battery capacity could easily be higher 20kWhr versus installed 10kWhrs.
• During overcast weather and winter months of lower available solar irradiation it is unlikely the extra battery capacity would be utilised. For about 8 months per year the solar power system would have the capacity to charge the 20kWhr system.
• The the installed cost of an additional of 10kWhr capacity is high. Similar to the outlay cost of the original BESS system.
• The increased battery capacity would reduce my grid power consumption.
• The increase battery capacity would possibly improve battery life by adjusting up the depth of discharge (DoD) setting in winter and reducing the current draw on the batteries (double battery capacity means each battery would see nominally half the peak current draw on charge and discharge.)
• Increasing the DoD limit would increase the amount of battery power available for backup in the event of a blackout as well as improving battery life.

The high capital cost of the additional battery capacity, coupled with the limitations on usability would probably not make this a viable option in terms of economic payback. It would certainly be nice to have though.