Chris Pearson said:

I have an older vehicle which has a 110 Ah lead acid battery. If it really can deliver 110 A for 1 hour (or 1 A for 110 h) at 12 V, that is 1.32 kWh and half a dozen would be 8 kWh.

Whilst lead-acid are great for some applications, there are quite a number of reasons why they may not be suited for domestic storage. There are also a number of differences between the VRLA used for "backup" supplies for alarms, control panels etc, to the starter battery in a car.

Plus the fact, what would we do with all of those end-of-live EV traction batteries?

But then again, can we install second-life equipment without the electrical installation designer taking full responsibility for its safety, given Regulation 511.1 ?

The biggest advantage of Lithium is weight for a given amp hour* voltage capacity - partly because lithium is quite a light metal and partly because the voltage per cell is between 3 and a half and 4 volts depending on the state of charge, and how flat you are prepared to take it. The self discharge rate is also quite low, at least when brand new, and a shelf like of many months is possible

Lead acid are only 2V- ish per cell, and in weight and volume sensitive applications, like phones and laptops, lithium wins.  It  is not clear for a situation where weight /volume may not be the last word, like a house or even for something like a boat, if in fact one of the more mature technologies would not be a better bet.

Actually when weight is no issue, then Nickel Iron has probably the longest lifespan and best resistance to being left in the flat state. Unfortunately the energy density is less than impressive. Lead acid is quite reasonable in terms of power per volume, but of course quite heavy.

Mike.

Most of the 'home made' PV/Wind storage systems I have read about have used lead acid batteries, typically leisure batterys that are designed for deep cycling rather than delivering a high current for a short period of time. 

The Centre for Alternative Technology in Wales notes:

Batteries

Batteries are essential in most off-grid wind or solar systems, but are expensive and will deteriorate. They store low voltage (up to 48V) DC electricity and need to be protected from over and under charging with a suitable controller. Lead-acid batteries were common in off-grid projects, but now lithium-ion are becoming more common. The latter have a longer lifetime but are more expensive – so lifetime costs may be similar.

Deep cycle batteries are preferable for renewable energy systems, as they are designed to have up to 80% of their charge repeatedly removed and replaced over a period of 5 to 15 years (or 1000 – 2000 times). Vehicle batteries are not suitable as they are designed to give a short burst of high current and be recharged immediately. They will perform poorly if allowed to discharge more deeply. Do make sure you follow proper safety procedures when dealing with batteries.

Photovoltaic (PV) Solar Panels - Centre for Alternative Technology (cat.org.uk)

I have come across a German made solar powered boat in the Norfolk Broads and on Lake Thun which uses lead acid batteries as the energy store. 

I would think here that the weight is not so critical and the management systems for lead acid batteries are rather simpler than those for Lithium systems.

Lithium Iron Phosphate batteries are becoming more common these days (including in many electric vehicles).  They don't hold as much charge, but have several advantages:

• Less flammable
• Can be recharged more times
• No cobalt required

It's worth looking at the data sheets batteries, as the Ah rating varies with the rate of discharge, and often assumes a discharge rate of C/20 (where 'C' is capacity) - so, for your example, you would get 110Ah when discharging at 5.5A (and less when discharging at a higher rate).

If you can run a submarine on a whole compartment of lead acid batteries, they cannot be that bad!

Indeed - a lot of older off-grid systems used to use ex-submarine batteries. I recently visited South Stack Lighthouse - they still have racks of old glass cased lead-acid batteries (no longer in service) that were used as stand-by power the light & fog horn - all inside the main building, along with a diesel generator.

+1 for the discharge level warning - as a rule of thumb the leisure battery in our caravan isn't supposed to go below 50% - so the 100Ah unit is really only useful for 50Ah.

   - Andy.

Whereas deep-discharge is ok with lithium, but it's not good keeping them above 80% for extended periods as it causes them to age faster.

Ideally, for lithium, not charged above 80% or discharged below 20%