Grid Batteries could pay for themselves in 18 months in Ireland

I think grid batteries could pay for themselves in 18 months in Ireland. In January I calculated this as taking 3 years. 

Solar in May and June were enough here that it caused a bigger drop in wholesale price than usual during the day. You can see this as electricity prices drop below night time prices during the afternoons now.

This means that if you have a cheap enough battery it is economically feasible to buy at night and sell at 7am. And buy again at 2pm and sell at 8pm.

The recently set record-low tender price of €44 per kWh of battery storage, a one-kilowatt-hour battery following the May–June 2025 Irish spot-price spread would recoup its capital cost in  about 16 months on a gross basis, or  about 18 months after allowing for 90% round-trip efficiency. 

This is buying every night at 3am. Selling at 7am.
Buying again at 2pm and selling at 8pm. Losing 10% each time.
If you were clever and you could predict the best time that day to buy and sell for that day. Not just a do this everyday at this time strategy. These correct predictions would increase this profit. and reduces the payback time to 13 months including round trip losses. 

This wrongly assumes the all months are sunny like May and June were so spread persists year-round and excludes maintenance, inverter, and degradation costs. But also there is a lot of free electricity you would not have to buy at the wholesale price. ''2024's wind dispatch down rate is 14%'' means 14% of the time (usually winter nights) the electricity has no price and is not put onto the grid. Storing that, at your wind farm, and selling it in the morning is higher profit than our May/June calculations. Which would offset some of the lower profit from the lower solar then.

This is a rough calculation using Chinese battery prices but still it looks like a battery asset with a long lifespan is paid off in 2-3 years.

Code for this analysis is here

Solar has been doubling every 3 years for a long time. This graph might give some idea of what 2026 and 2027 will look like. The higher the peaks and troughs the higher the profit in storing the power.

An analysis of the last 365 days assuming knowing the perfect time to buy and sell electricity gives enough profit to pay for the battery at the Chinese tender prices. 

Period analysed: 2024-07-03 → 2025-07-03 (365 complete days)

Total profit: €45.01 per 1 kWh