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.

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Question about Output Power of Batteries in Domestic Solar PV Installation

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.

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0 Simon Barker over 2 years ago
I'll assume it's a typical system with panels on the roof, and the battery connected to the same inverter as the panels.
My system has
3.4kWp of panels. They are old, and nowhere near the power output of modern ones.
a 3.6kW inverter.
a 3.3kWh battery, of which 3kWh is usable. The best ways to wreck a LiIon battery are to run it flat, or to rapid charge it all the way to 100%, so the inverter will not let me use that last 0.3kWh.

Lead acid batteries really shouldn't be discharged on a regular basis more than about 50%. But LiIons can go down to 20% if you're cautious, or 10% if you want to get more out of them, and can live with a slightly shorter life. Mine is supposed to be good for 10 years.
3.6kW inverters are very common, as it's the maximum you can export without asking permission from your DNO first. It works out at 16A single phase.
The output of the system is capped by the maximum rating of the inverter. So it will happily run a kettle on solar, battery, or a mix of the two. But there's no way it will power the electric shower. My typical steady load, working from home or watching TV is in the order of 250W. It's saying only 146W as I write this - modern inverters are clever and internet-enabled.
Luckily long-duration loads over 3kW are pretty rare in a home. So I can boil a kettle or even bake a cake in the oven without relying on the grid. That said, I don't have an electric vehicle to plug in yet. That will change things entirely, and I may see if it's practical to upgrade the battery.
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0 Simon Barker over 2 years ago
I'll assume it's a typical system with panels on the roof, and the battery connected to the same inverter as the panels.
My system has
3.4kWp of panels. They are old, and nowhere near the power output of modern ones.
a 3.6kW inverter.
a 3.3kWh battery, of which 3kWh is usable. The best ways to wreck a LiIon battery are to run it flat, or to rapid charge it all the way to 100%, so the inverter will not let me use that last 0.3kWh.

Lead acid batteries really shouldn't be discharged on a regular basis more than about 50%. But LiIons can go down to 20% if you're cautious, or 10% if you want to get more out of them, and can live with a slightly shorter life. Mine is supposed to be good for 10 years.
3.6kW inverters are very common, as it's the maximum you can export without asking permission from your DNO first. It works out at 16A single phase.
The output of the system is capped by the maximum rating of the inverter. So it will happily run a kettle on solar, battery, or a mix of the two. But there's no way it will power the electric shower. My typical steady load, working from home or watching TV is in the order of 250W. It's saying only 146W as I write this - modern inverters are clever and internet-enabled.
Luckily long-duration loads over 3kW are pretty rare in a home. So I can boil a kettle or even bake a cake in the oven without relying on the grid. That said, I don't have an electric vehicle to plug in yet. That will change things entirely, and I may see if it's practical to upgrade the battery.
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Question about Output Power of Batteries in Domestic Solar PV Installation

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