Can I power an electric shower from my solar batteries?

[petercoupe]

Hello all,
I got my gas bill today, and it’s over £1000 for the first time ever.
I‘m looking at ways of saving energy- no surprise- so I wonder if I can get some advice on this question…
I have roof mounted solar panels, and 7.2 kW batteries.
During the summer, the batteries regularly fill to 100% by lunchtime.
Could I power an electric shower from my solar batteries?
This would certainly help me save on the cost of gas.
Thanks.
Peter

 

[mikeyd]

kW is a unit of power and doesn't describe the capacity of your batteries.

If you actually have a battery pack of 7.2kWh, then that would run a shower with a power rating of 7.2kW for an hour. (in theory, excluding losses etc.)

 

[ericmark]

Using the excess energy for electric solar panels can heat water that has been an option for a long time, my father-in-law had hot water solar panels fitted and they were a flop, but daughter has them in Turkey and they work well.

The problem is the combi boiler, so many people no longer have storage for the domestic hot water, and direct depends how much power you can get from your batteries, it is confusing, a watt is a Joule per second, so a watt hour is 60 x 60 Joules = 3600 Joules.

So kWh = 3.6 MJ and has nothing to do with time, even when it has time in the name. Why we have kWh no idea.

But the battery will have a amount it stores be it in Joules, kWh or Amp hour, and also the amount it can supply in amps, or watt or kW. In theory you can use the battery, in practice it depends on its rating.

 

[JohnD]

Have you got a hot water cylinder?

The cost of HW from gas is ludicrously low, so much so that it is not worth spending on complex alternatives. Your solar electricity will be better used for things that are only electric, such as a tumble drier.

If you are spending £1k a year on heating, concentrate on draughtproofing and insulation.

 

[robinbanks]

3.6 MJ and has nothing to do with time, even when it has time in the name

Joules have time implicit. In electrical terms, the joule equals one watt-second; the energy released in one second by a current of one ampere through a resistance of one ohm.

We have kWh when the SI unit is J for similar reasons as we have litres and gallons when the SI unit of volume is the cubic metre. Putting the price of petrol on a road sign as 0.001999/m3 is impractical and humans struggle to visualise very small and very large quantities. A Jaguar I-Pace having a 70kWh battery instead of a 100 litre fuel tank is talking about things in a numeric range that most humans can easily grasp. Telling them it has a 252,000,000 joule battery and a joule of electricity costs 0.0000125 pence means nothing

 

[ericmark]

Joules have time implicit. In electrical terms, the joule equals one watt-second; the energy released in one second by a current of one ampere through a resistance of one ohm.

Wrong way around a watt = Joule per second.

 

[RandomGrinch]

Wrong way around a watt = Joule per second.

Watt = J / s

J = Watt X s

the joule equals one watt-second

 

[ericmark]

Joule = the SI unit of work or energy, equal to the work done by a force of one newton when its point of application moves one metre in the direction of action of the force, equivalent to one 3600th of a watt-hour.

 

[OvertonPlumber]

my father-in-law had hot water solar panels fitted and they were a flop, but daughter has them in Turkey and they work well.

Why our solar thermal provides all our hot water needs for most of the year.
On the 6th December outside temp was only 6c although I got a full tank of hot and my panels hit 135c!!

 

[ericmark]

Why our solar thermal provides all our hot water needs for most of the year.

My father-in-law said how much money the solar panels were saving him, and we did consider some ourselves, however when he had the smart meter fitted the truth came out. He had no DHW, middle of summer and it was cold, when I came to investigate found supply to pumps etc was marked immersion heater, which had been removed, so he had turned it off, but on turning on still no hot water, it transpired all his hot water was coming from the central heating boiler, and when the smart meter was fitted, they never re-lit the pilot flame, re-lighting boiler did get him hot water, and we assumed the problem was due to him turning the system off, however after the expert came to reactivate the system, best it did was remove chill off the water.

When I died the new owners fitted a new central heating boiler and did a lot of work on the house so the system was disconnected, but it seems his electric bill had gone down, but gas bill went up, solar panels were a complete flop. We did however live in the most North/East corner of Wales, had we lived further south the outcome may had been different.

 

[RandomGrinch]

When I died the new owners

Blimey, I didn't know this forum was a portal to a different realm!

Joule = the SI unit of work or energy, equal to the work done by a force of one newton when its point of application moves one metre in the direction of action of the force, equivalent to one 3600th of a watt-hour.

Yes we know, but...

One Watt = One Joule / One Second
Is equivalent to
One Joule = One Watt x One Second

Just as...
I = V / R or V = I x R

@robinbanks didn't have it the wrong way around - it's called maths!

 

[flameport]

Could I power an electric shower from my solar batteries?

Only if the inverter can supply the power required for the shower and whatever else is in use at the time.

This would certainly help me save on the cost of gas.

A 30kW gas combi boiler at full power would use 5kWh of gas for a 10 minute shower, cost about 50p.
Entirely irrelevant in the context of a £1000 gas bill.

 

[petercoupe]

Only if the inverter can supply the power required for the shower and whatever else is in use at the time.


A 30kW gas combi boiler at full power would use 5kWh of gas for a 10 minute shower, cost about 50p.
Entirely irrelevant in the context of a £1000 gas bill.

Family of four, showering 3 times a week is £6 a week at 50p. That said I think we take longer than 10 minutes to be honest, more like 20.
We have full batteries for over half the year, 26 weeks, makes that a potential cost saving of £156.
In reality it would be almost double that, so more like £250 to £312 a year.
That’s not a bad saving ?

 

[big-all]

if you water is heated by gas its 1/3 the cost for the same energy input
i think your battery output will be far better aimed at electrical use
you must also consider perhaps 20-30% percent off assumed stored energy or possible energy input as not actually being there as inefficiency being well below your expected levels it could be far less a failing battery will show its 100% charge but if its old it may be as low as say 20% capacity so dont assume 100% means maximum when it can infact mean perhaps 15-25% capacity

in fact old phone batteries would reach 100% charge in 10 - 15% off required time so no real capacity

 

[JohnW2]

Joule = the SI unit of work or energy, equal to the work done by a force of one newton when its point of application moves one metre in the direction of action of the force, equivalent to one 3600th of a watt-hour.

Exactly - and "one 3600th of a watt-hour" is 1 watt-second - which is exactly what robinbanks wrote, but about which you appeear to be arguing

Kind Regards, John