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 mapj1 over 3 years ago

The stored magnetic energy (I2 L where L is the inductance of the primary when the secondary is unloaded) may be released as a short duration transient, but the sizing of transformer cores and winding resistances is such that this transient is all over in a few 50ths of a second, or the transformer is seriously oversized… Usually enough to make a rather scary ‘pock’ at the switches, and maybe burn the contacts a bit. This is the ‘back EMF’ spike that you may have been bitten by.
There is no exact magnetic analogy of the stored electric charge , where a charge may persist across an open circuit capacitor almost for ever.
The nearest you get to magnetic energy storage that is the superconducting magnet, where a coil of superconducting alloy wire cooled to zero resistance has a current set flowing, and then the ends joined together. That gives a more or less permanent electro-magnet, but unless you make medical scanners or work at CERN it is not the sort of thing you see very often. The biggest risk there is not shock, but being struck or trapped by magnetic objects. (or being killed by a leak from the cooling system)
However, like shorting the capacitor, if the superconducting wire warms back to normal, you get your magnetic energy back, as a lot of heat in a small space, and that can be impressive.
Again, not in the more normal transformer sort of case luckily.
Mike.
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0 mapj1 over 3 years ago

The stored magnetic energy (I2 L where L is the inductance of the primary when the secondary is unloaded) may be released as a short duration transient, but the sizing of transformer cores and winding resistances is such that this transient is all over in a few 50ths of a second, or the transformer is seriously oversized… Usually enough to make a rather scary ‘pock’ at the switches, and maybe burn the contacts a bit. This is the ‘back EMF’ spike that you may have been bitten by.
There is no exact magnetic analogy of the stored electric charge , where a charge may persist across an open circuit capacitor almost for ever.
The nearest you get to magnetic energy storage that is the superconducting magnet, where a coil of superconducting alloy wire cooled to zero resistance has a current set flowing, and then the ends joined together. That gives a more or less permanent electro-magnet, but unless you make medical scanners or work at CERN it is not the sort of thing you see very often. The biggest risk there is not shock, but being struck or trapped by magnetic objects. (or being killed by a leak from the cooling system)
However, like shorting the capacitor, if the superconducting wire warms back to normal, you get your magnetic energy back, as a lot of heat in a small space, and that can be impressive.
Again, not in the more normal transformer sort of case luckily.
Mike.
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Question about Output Power of Batteries in Domestic Solar PV Installation

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