Hi, hoping for a bit of advice. Last year, I took up a local authority (Sussex, England) offer to get a quote for a PV installation on our 1960s bungalow. An initial estimate based on info I'd supplied duly came through. In general it looked sensible enough.

Specifically, it suggested that we would be able to use 1,100kWhr of solar power if no battery was installed; or 3,200kWhr (our entire usage) if a 6.1kWhr battery was added.

However, I wondered if that allowed for specific appliances (information they didn't have, AFAIK), especially the 10kW electric shower. I asked what the maximum output (Watts or Amps) of the battery was.

They couldn't answer, unless I paid the £100 deposit to proceed, which seemed a bit unhelpful. I couldn't readily find said info online, either.

A little bit of modelling this evening:

• I assumed that high load appliances were never, ever, used at the same time.
• We have electric shower, kettle, oven, washing machine etc.
• No electric space or tap water heating, and no electric hob, no dishwasher either.
• I chose an arbitrary 2kW “limit” to the battery power, sufficient to power smaller high-power appliances, but less than kettle or shower.

Result suggests that of our roughly 3,200kWhr annual usage:

• ⅓ is low-load appliances that may be on quite a lot of the time. Readily supplied from a battery, I'd think.
• ⅓ is appliances up to 2kW that may be on occasionally. This includes the first 2kW of big wattage units like the kettle & shower, which assumes that a high load can be shared between battery and incoming supply, rather than just turning the battery off.
• ⅓  is the portion of high-load appliances that exceeds 2kW. The vast majority of this is the shower.

So, clearly, the ability of the battery to power high wattage appliances over 2kW is quite important to the overall payback, up to a maximum of 10kW at least.

Does anyone here know what the maximum instantaneous output (sustainable for say 10 minutes) of these domestic battery systems is likely to be?

Also, depending on battery technology, it strikes me that heavy use of the shower during gloomy months could run close to the batteries real capacity limit: I don't know how these systems are quoted, I do know for our camper van there are dire warnings of consequences if more than 50% of the lead-acid habitation battery nominal capacity is used.