Electricity generated from solar is either immediately used or stored for later use, during nights or on days in times of extended cloud cover, or when appliance peak loads need to consume larger currents all at once.
Battery storage is critical to enabling energy independence and moving off grid and freedom from energy companies and their rising bills.
What’s Sucking up my Electricity?
There’s a few options for storing energy efficiently for its intended purpose. Some non-electrical. We should first minimise electricity consumption and opt for alternative more energy efficient options in the building’s Passive Home Design, energy efficient appliances and energy efficient alternatives.
To run things like a TV, WiFi, Fridge, Fans, Laptops, washing machine, electric cars etc. We can tally up the electricity consumed by these appliances against how long each is run daily/weekly, to draw up a usage profile. Which we then measure against the AH (amp hours) or WH (watt hours), we have sized in capacity storage in our Battery Bank(s).
Identifying appliances and estimating in a spreadsheet:
- Reading their device labels, for how much electricity they use in Watts, Amps and Volts. Recording at least 2 of these parameters, in order to calculate the 3rd.
- Each device is used for how many minutes, daily/weekly?
- Devices may include:-
- Lights, sensors, WiFi, security cameras, door bells, smart home devices, smart door locks, security devices, servers
- Fridges, chest freezers, wine chillers, ice makers
- Induction cooker, oven, Air fryer, microwaves, steamers, dehydraters, exhaust fan,
- Toaster, kettle, blenders, grinders, coffee machine, sandwich makers, other kitchen appliances.
- Fans, AC, electric heaters, underfloor heating/cooling pumps, radiator pumps, climate sensors, ventilation fans, dehumidifiers.
- Washing machine, dryers, irons
- Laptops, phones, screens, digital cameras, TVs, sound systems, portable speakers, projectors, entertainment systems
- Battery and mains powered tools
- Electric car, bikes or quad recharging. However their batteries can act as additional storage capacity, recharged during ample sunlight, but may be a drain during cloudy periods.
You may trend towards buying devices with rechargeable batteries inbuilt. Like Sonos portable Roam or Move sound systems, thus extending device specific energy storage for greater resiliency.
People’s Usage Profile
More people may mean more electricity for some activities. Like longer usage cycles when cooking, washing, climate control, laptop/phone recharges, TV/music time etc. To be factored into your spreadsheet. Advice can then be sought from a certified off-grid solar/battery installer.
Electrical Battery Storage
There’s a number of electricity battery storage options with varying factors in sustainability, ethics, economics, environmental, longevity, robustness, complexity, etc.
A Solar system needs solar panels, batteries, an Inverter and electrical management system etc, to power a building. An Inverter converts the battery banks Voltage and Current from 48v DC to household 240 volts AC (alternating current), as is used by most appliances that you plug into a home power socket.
Opting for a 48 volt DC (direct current) battery bank system, with as many AH (Amp Hours) as you can afford. The battery bank is made up of multiple individual batteries connected in Series together to generate the desired Voltage. In this case 48 volts, because its more efficient to convert 48v upto 240v through the inverter. Albeit a higher startup cost investing in battery storage. As opposed to a 12v or 24v solar/battery system.
To cover consecutive cloudy days, when there’s little solar, you may need multiple 48v battery banks.
Here’s some batteries I like.
Nickel Iron Batteries (NiFe)
NiFe pros/cons are:
- Pros
- Robust, almost indestructible, safe, tried & tested 100yr old technology
- Ultra-deep-cycle, as battery bank can be fully discharged and recharged without damage! Unlike lithium or lead acid.
- Longivity, 50 to 100+ yrs lifetime. Ethical ultra long term usage life cycles.
- Environmentally friendly, the depleted electrolyte can be used as fertiliser and reproduced from eco safe substances readily and cheaply available.
- Cons
- Only specific models of solar charge controllers and inverters are compatible.
- Needs 15% more solar panels to charge up. Inefficient with losses.
- Large upfront cost as the entire battery bank(s) needs to be setup from the start to ensure individual batteries voltage charge is used synchronously. Depleted and charged together.
- Maintenance: summer evaporation and overcharging results in electrolyte fluid evaporation, requiring battery fluid top-ups every 2 weeks. Unless a DIY custom auto refill system is made and used.
- Lazy in Winter, sometimes stops working in early mornings for 15mins then kicks in after 15min solar charge. Prefers long charge days of summer as opposed to short days during winter.
- Electrolyte fluid replenishment every 5 to 10 years depending on usage. However its cheap, easy and safe.
- Complexity in battery management to ensure individual battery’s charge rate and voltage is stable and the same across all batteries as they are depleted and recharged.
So how many do we need?
Each individual battery outputs ~ 1.2volts 400AH (amp hours).
So you’d need approximately 42 x 1.2volt batteries for a 48v bank. Which allows extra batteries for some minor voltage loss between connections. Each 1.2v battery would be connected in ‘Series’ to generate the desired 48 volts.
As of Feb 2023, at approximately AU$200, or UK£112 per 1.2v battery is $8,400 / £4,700 per 48 volt bank. You’d need 1 to 2 banks in Australia, or at least 2 banks in UK or more, given less sun. So 2 banks = $17k/£9k, or 3 banks = $25k/£14k. Just for battery storage, not the ret of the solar system.
Why so many 48v battery banks? Each bank of 42 x 1.2v batteries @ 400AH, (amp hours), = 16,800 AH. 2 banks = 33,600AH and 3 banks = 50,400 AH. This helps determine energy density we have stored in batteries for earlier estimated usage.