Battery Issues - Solar Power.

Main Issues Addressed:
(Note: These articles all refer to DIY 'Off Grid' options.)

1. With High Battery Prices, 'Solar Power' costs more than the 'Grid'..

2. Solar Power Without a Battery??

3. Powering your Fridge / Freezer in a blackout?

4. Battery Types and Cost?

5. Battery Life?
('Life' determines if a battery can Pay for itself before it dies!)

1. With High Battery Prices, 'Solar Power' costs more than the 'Grid'..
A small house uses a minimum of 3 kWh/day - Which, at 2017 grid prices, costs $1/day..
The Solar equipment required for 3 kWh/day costs about $2300 and so (at $1/day) will take 6 years to pay for itself.
However, the Batteries ($1000) might only last 5 years! So, including some occasional replacement costs, solar power is not cheaper than the exorbitant 'grid'!
Most Solar Power systems (from $1000 to $30,000) do NOT currently save you any money! They just give you some protection from the increasingly frequent power Blackouts.
Note: Battery prices are going to 'crash' within a few years.. Then, you WILL be saving money!
As an example, many professional installers have shown that a 'Tesla Powerwall 2' takes about 18 years to pay for itself - BUT, is only likely to last 12 years.

2. Solar Power Without a Battery?

If you just want to run small passive appliances or heat water while the sun is out, you can get by without a battery. But, if you want to power a fridge or computer, you will need a 'Deep Cycle' battery (Eg. 70 Ah; $200+).
The 'start up' current of a fridge can be 8 times the running current (eg. 60 amp @ 12V). Most Solar panels can only provide 8 to 16 amp - so you need a battery to provide that 60 Amp.
A computer needs stable power - a battery will stabilize the power even when the sun is behind a cloud for a while.
So, in most solar applications, you should include a 'Deep Cycle' battery.

 3. Powering your Fridge / Freezer in a blackout?

Many people have a considerable investment (time and money) in the content of their Freezer.. To preserve the freezer in an extended Blackout is the main reason for having minimal 'Off-Grid' Solar power.

A freezer or fridge presents special problems for Solar Power..
Their 'start up' current can be 8 times the running current (eg. 60 amp @ 12V). Most Solar panels can only provide 8 to 16 amp - so you need a battery to provide that 60 Amp. You also need a 1000w inverter to safely start the average (100watt) fridge/freezer.
Caution.. Deep Cycle batteries don't like this high startup current. Their voltage can momentarily drop to 10.5V which will trip off the Inverter. This leads to a dangerous sequence..
* Both Fridge and Freezer have now lost power and will need to stay off for a few minutes to allow the refrigerant back-pressure to leak away. Otherwise the motor will 'Stall' (Lockup) and pull 15 times normal current for 10 secs until the motors thermal overload trips out!
* But, the Solar Inverter will re-start within a few seconds and the batteries will not be able to power this '15 times' current for both the Fridge and Freezer!
* The Solar Inverter will trip off again - for a few seconds - then re-try.. This cycle can repeat endlessly (if the batteries are near the end of their day) and the Fridge/Freezer will be thawing out.
In summary.. * An Inverter that 'Trips Off' at a brief 10.5V can kill your Freezer! Try to find a quality Inverter that has a few second delay on the 'Undervoltage Trip'.
Note.. A normal 'Car Battery' does not have this problem. (they have a lower impedance than Deep Cycle batteries)


4. Battery Types and Cost?

* Normal car batteries do not suit solar projects.. Their ability to stand daily deep discharge is severely compromised in order to cheaply deliver a high Starting Current.
*. 'Lithium Ion' is currently 'best' but very expensive and they are soon to be superseded by Graphene Batteries. The mining of Lithium (rare earths) also causes enormous damage to the environment.
* Lead acid "Deep Cycle" batteries (eg. Caravan Batteries) are also soon to be superseded but currently are the best value for money. They can stand up to 6 years of being taken down to half charge every day.


5. Battery Life?
'Life' determines if a battery can Pay for itself before it dies.
(Most Battery types today do not live long enough to pay for themselves!)

Our 400Ah battery bank costs about $1000 - How soon will it pay itself off??
The sun might only be 'useable' for about 9hrs per day - so the batteries have to 'fill in' for 15 hrs/day. This takes a heavy toll on their life span.
Over their life time, 'our' average capacity will be about 180 Ah or 2kWh per day. At 30c/kWh, this is about $4/week - Or, about 4 years to 'pay back' $1000.
'Battery + Solar' is supposed to be cheaper than Grid Power! But, if your batteries don't last 4 years, then the Grid is cheaper!

Our first four Deep Cycle batteries were 'cheap' N70Ts. ($250 per 100Ah) We have demonstrated that they don't last 4 years with a 50% daily discharge. They only lasted 2 years! (The manufacturer quotes 850 days @ 50% drain.)
Even the "Expensive" Deep Cycle batteries ($550 per 100Ah) are only listed to last 5.8 years @ 50%.
That @ 50% of 100 Ah = 0.6 kWh/Night =  17 cents = 8 years to pay it off!

Our current disenchanted decision is to only drain the battery bank by 20% each day (switch to Grid Power during the night) - this will preserve the $1000 bank for maybe 6 years - and, it will then be capable of powering our Freezer during the many inevitable power blackouts.
With this limited use, our 1Kw solar array can still save 5kWh/day. ($1.50/day)

The most common destroyer of battery life is a poor quality charging controller.
The Charge Controller should be at least a 'Three Stage' charger (eg. Bulk/Boost, Constant Current, Float) plus a monthly 'Equalize' program. (see diag. 1.5 below)
With a good charger (eg. $250), you should be able to get 5 years from your batteries. With a cheap charger, you might only get 2 years!