Energy Storage


Note: Comparisons based on a system to supply 3kWhr daily for a minimum of 10 years. This may be sufficient for nightly use of a two person household with excess solar capacity (over 1.5kW). Check your power bill for average daily power use. Deep discharge in extended overcast periods may substantially shorten battery life. New invertor and regulator may be required.

Lead/Acid – traditional deep cycle battery storage. Cost per Kwhr increases with size and suffers from limited life under heavy discharge eg 1000 cycles at 70% discharge or 4000 cycles at 20% discharge. Around $7000 (10yr, 3kWhr daily). These systems have often been set up at 24V so converting to new battery types at 48V may require replacement of regulators, invertors etc.

Nickel/Cadmium – Highly toxic components and suffers from memory charge ie if overcharged battery life is dramatically reduced.

Lithium  – eg Powerwall, Genevo , Compact and comparatively light. Claims of long life with deep discharge (70%) not yet confirmed. High voltage in the Powerwall requires specialised invertors and regulators. Minimum of 2 Powerwalls recommended for off-grid application. Genevo operates at 48V in a less compact system. Around $9000 (10yr, 3kWhr daily, 6kWhr total with inverter )

Zinc/Bromine – RedFlow, high energy density 8kWhr 48V units claims 100% discharge with unlimited life. 10yr guarantee provided daily discharge less than 35%. Bromine is toxic. Claims fully recyclable but not currently listed by battery recyclers.

Manganese/Sodium – Aquion 7.8kWhr (3 stacks, around $6,000) 48V claims 3000cycles (8yr) at 100% discharge or 12,000cycles (24yr) at 25% discharge. Non-toxic & recyclable and less temperature sensitive. No maintenance required but the energy density is low ie 3 times more bulky than lead/acid. 5yrs Guarantee contact

Useful battery Blog –

Battery Recycling

Molten Salt

– Used by tower type solar thermal generators in the MW range. Some salt types can be toxic but may use commonly available ammonium salts. Use steam turbine generators with relatively high water demand and high minimum power output.

Super heated Water

Used by parabolic trough type solar thermal. Water stored in commercial propane tanks under 1800kPa requires minimum supervision and achieves energy storage at 20% cost of lead/acid batteries.

Power generation by uniflow steam engines do not vent to waste and so water use is much lower. Power output can be varied to demand.

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