Sorry my wording was ambiguous; when I said "that size" I meant 2.7 kWh, which is what the hypothetical concrete blocks might provide.

Nevertheless, you can get a 16 kWh battery (which is enough for most days of a typical house) for only £2k, which is kind of insane really: https://www.fogstar.co.uk/products/fogstar-energy-16kwh-48v-...