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Calculating my energy consumption


blackrose

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Since I installed my solar panels just under 3 months ago I've generated nearly 62 kWh of electricity from the panels and I've used 98 kWh of mains from shore power. Today was exceptional and I ended up getting 2.24 kWh from the panels, the most in one day so far.

 

So is it as simple as saying that since I started 38% of my electricity consumption has come from the panels? 

 

The panels charge the batteries which are used to run mains appliances and run my 12v system, whereas mains power is used direct to run appliances direct (and also occasionally to charge my batteries with the battery charger). So I can't quite get my head around whether all the power I'm generating with the panels is actually being used or if some of it's being lost in the charging process so it doesn't all count as consumption?

 

IMG_20230206_200100.jpg

Edited by blackrose
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53 minutes ago, blackrose said:

Since I installed my solar panels just under 3 months ago I've generated nearly 62 kWh of electricity from the panels and I've used 98 kWh of mains from shore power. Today was exceptional and I ended up getting 2.24 kWh from the panels, the most in one day so far.

 

So is it as simple as saying that since I started 38% of my electricity consumption has come from the panels? 

 

The panels charge the batteries which are used to run mains appliances and run my 12v system, whereas mains power is used direct to run appliances direct (and also occasionally to charge my batteries with the battery charger). So I can't quite get my head around whether all the power I'm generating with the panels is actually being used or if some of it's being lost in the charging process so it doesn't all count as consumption?

 

I'd say not all the power generated by the panels is used. Once the charging is done, the panels, through the charge controller, will not be dumping their full capacity and will go to float. Once the domestics have been charged, on a sunny day, the amps will go right down. I might then connect the inverter batteries to the controller and see the amp rise again to what the panels can supply. I give the leisure batteries priority, and maybe top up the inverter batteries with the engine, if its a dull day. 

 

 

Edited by Higgs
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15 minutes ago, Higgs said:

 

I'd say not all the power generated by the panels is used. Once the charging is done, the panels, through the charge controller, will not be dumping their full capacity and will go to float. Once the domestics have been charged, on a sunny day, the amps will go right down. I might then connect the inverter batteries to the controller and see the amp rise again to what the panels can supply. I give the leisure batteries priority, and maybe top up the inverter batteries with the engine, if its a dull day. 

 

Yes once the batteries are full the amps will drop and solar controller will reduce the power coming from the panels, but what's shown on the display unit already accounts for that. The kWh shown is what's come though the controller.

 

My inverter is on all the time, unless I happen to be charging the batteries from shore power.

Edited by blackrose
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30 minutes ago, blackrose said:

 

My inverter is on all the time, unless I happen to be charging the batteries from shore power.

 

My panels have only recently been fitted, so I'm only used to the winter conditions. Low light levels. The inverter is switched off normally. Switched on to charge laptop and run oven fan in the evening. I imagine I use the mains a lot less than you might. I'm not attached to a shoreline. I use the solar panels, the engine, and sometimes a generator to charge the batteries. Might use the washing machine, powered by the solars, charging the inverter batteries in the summer, but in the winter, I use the generator. 

 

 

 

 

 

Edited by Higgs
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The panel monitor is likely to record energy output of the solar panels.  But insofar as some went into the batteries, there will be materially less available when you come to withdraw.  Charging and discharging batteries is not 100% efficient.

 

So unless you feel able to claim that the heating of the battery when charging and discharging is desired, allowance needs to be made for these losses.

 

Same applies to the BEV claims.  If a car does 4 miles per kwh, it will take more than 1kwh from the mains to recharge per 4 miles.

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2 hours ago, Higgs said:

. Might use the washing machine, powered by the solars, charging the inverter batteries in the summer, but in the winter, I use the generator. 

 

In this winter sun I've been running the washing machine powered by the panels. Today I was getting a maximum of 40 amps from the controller into the batteries.

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8 hours ago, blackrose said:

 

In this winter sun I've been running the washing machine powered by the panels. Today I was getting a maximum of 40 amps from the controller into the batteries.

Very good. What make and type of panels?   What area do they occupy? I see it is a fatter than narrowboat so you have more roof area.

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8 hours ago, blackrose said:

 

In this winter sun I've been running the washing machine powered by the panels. Today I was getting a maximum of 40 amps from the controller into the batteries.

 

That's looks like a pretty good figure. The best I've managed, yesterday, a sunny day, was 12Amps, measured at that point. Forgot to check the daily tally. I've got 6x100w panels, connected in parallel. The whole array is rated at a bit over 30amps. 

 

 

 

 

Edited by Higgs
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Obviously the mains kWh is correct. But the solar kWh is complicated!

Efficiency of solar power that is used instantaneously by dc appliances, very nearly 100%. But there won’t be much of that.

Solar power going directly to power ac appliances - about 85-90% (inverter losses)

But then if you bring batteries into it… about 93% charge efficiency. So for every 100Ah you put in, you get back 93Ah. But energy (kWh) is the multiple of charge (Ah) and voltage. When the solar is charging the batteries, the voltage might be up at say 14.4v. When discharging it may be down at 12.4v. And a bigger difference for faster charge and discharge. So the voltage efficiency is roughly 86% for moderate loads. So energy efficiency is around 80%. That would be the figure for dc loads.

 

For ac loads from the battery you need to add in the inverter efficiency so we are looking at around 70% efficiency. Ie 70% of solar input energy goes to operate ac loads when powered later via the battery.

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Your basic assumption is broadly correct, provided you have not used the  engine, or a generator, to charge your batteries, or run any other power consumer and also provided the batteries were at the same state of charge at the start and the end  of you counting period.

 

Your solar will have provided more power to the batteries than the batteries will have delivered to your 12V (24v ?)  loads, because of charge inefficiency, but the lost power will eventually have appeared somewhere as heat. Exactly how much went missing is very difficult to guess, because sometimes (battery  full, small load on )  the solar is driving the loads directly, sometimes it is doing part of the work, and sometimes it is doing nowt, (night)  but the battery is discharging and will need to be filled up when the sun returns.  Similarly, if you have used a mains battery charger some of the mains power will have been lost in charge inefficiency.

 

N

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25 minutes ago, BEngo said:

Your basic assumption is broadly correct, provided you have not used the  engine, or a generator, to charge your batteries, or run any other power consumer and also provided the batteries were at the same state of charge at the start and the end  of you counting period.

 

Your solar will have provided more power to the batteries than the batteries will have delivered to your 12V (24v ?)  loads, because of charge inefficiency, but the lost power will eventually have appeared somewhere as heat. Exactly how much went missing is very difficult to guess, because sometimes (battery  full, small load on )  the solar is driving the loads directly, sometimes it is doing part of the work, and sometimes it is doing nowt, (night)  but the battery is discharging and will need to be filled up when the sun returns.  Similarly, if you have used a mains battery charger some of the mains power will have been lost in charge inefficiency.

 

N


Charge efficiency on battery monitors etc is the efficiency in terms of charge (the physical thing with units of coulombs or Ah). Not the same as energy efficiency because of course charge does not have dimensions of energy. Confusion is caused when people refer to charge as the charging process and others to the physical property of coulombic charge.

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32 minutes ago, nicknorman said:

Obviously the mains kWh is correct. But the solar kWh is complicated!

Efficiency of solar power that is used instantaneously by dc appliances, very nearly 100%. But there won’t be much of that.

Solar power going directly to power ac appliances - about 85-90% (inverter losses)

But then if you bring batteries into it… about 93% charge efficiency. So for every 100Ah you put in, you get back 93Ah. But energy (kWh) is the multiple of charge (Ah) and voltage. When the solar is charging the batteries, the voltage might be up at say 14.4v. When discharging it may be down at 12.4v. And a bigger difference for faster charge and discharge. So the voltage efficiency is roughly 86% for moderate loads. So energy efficiency is around 80%. That would be the figure for dc loads.

 

For ac loads from the battery you need to add in the inverter efficiency so we are looking at around 70% efficiency. Ie 70% of solar input energy goes to operate ac loads when powered later via the battery.

All good stuff.  In terms of calculating energy proportions  both mains and solar will/might be used to charge the batteries and then some be inverted to 230v before use.  But probably not in equal proportions.

 

So not easy to arrive at a firm figure!

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28 minutes ago, Tacet said:

All good stuff.  In terms of calculating energy proportions  both mains and solar will/might be used to charge the batteries and then some be inverted to 230v before use.  But probably not in equal proportions.

 

So not easy to arrive at a firm figure!

Yes I had assumed that the batteries would exclusively be charged from solar. But as we know, assumption is the mother of …

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8 hours ago, Tracy D'arth said:

Very good. What make and type of panels?   What area do they occupy? I see it is a fatter than narrowboat so you have more roof area.

 

Canadian solar 455W. I think it's these but I bought them from Bimble. Area of my 2 panels is 4.418 m2          I paid £444 inc VAT and delivery for 2 panels so these look a lot cheaper. Edit: Just seen the delivery costs on that website so it's about the same.

 

Canadian Solar HiKu – MONO 455Wp – Heathrow Solar Systems & Supply (hsolar.co.uk)

Edited by blackrose
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7 hours ago, nicknorman said:

Obviously the mains kWh is correct. But the solar kWh is complicated!

Efficiency of solar power that is used instantaneously by dc appliances, very nearly 100%. But there won’t be much of that.

Solar power going directly to power ac appliances - about 85-90% (inverter losses)

But then if you bring batteries into it… about 93% charge efficiency. So for every 100Ah you put in, you get back 93Ah. But energy (kWh) is the multiple of charge (Ah) and voltage. When the solar is charging the batteries, the voltage might be up at say 14.4v. When discharging it may be down at 12.4v. And a bigger difference for faster charge and discharge. So the voltage efficiency is roughly 86% for moderate loads. So energy efficiency is around 80%. That would be the figure for dc loads.

 

For ac loads from the battery you need to add in the inverter efficiency so we are looking at around 70% efficiency. Ie 70% of solar input energy goes to operate ac loads when powered later via the battery.

 

Yes, I've realised it is a bit complicated, if not only for the fact that if you draw loads from the batteries while the sun is shining you'll get more out of them than if you just leave them to charge the batteries. Yesterday I ran the washing machine and topped up my batteries and ended up generating 2.25 kWh from the panels. Today was just as sunny but the panels only ended up generating 1.41 kWh because I wasn't really using much power.

6 hours ago, nicknorman said:

Yes I had assumed that the batteries would exclusively be charged from solar. But as we know, assumption is the mother of …

 

My batteries are only charged from the panels - unless I'm getting close to 50% and then I switch to shore power and switch the battery charger on. I haven't done that for about a week.

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Do you have a power meter on your incoming mains supply? 

 

You can get devices which record the consumption onboard. If you combined this with the amount of power accepted by your batteries via the solar panels then presumably you could get an accurate estimate of how much actual power you are using each day. 

 

Washing machine? 

 

I suppose you are going to say you have a shower as well. Talk about high carbon footprint. 

 

And a solid fuel appliance!

 

Shocking! 

 

;)

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4 minutes ago, magnetman said:

Do you have a power meter on your incoming mains supply? 

 

You can get devices which record the consumption onboard. If you combined this with the amount of power accepted by your batteries via the solar panels then presumably you could get an accurate estimate of how much actual power you are using each day. 

 

 

I just have one of those Owl energy monitors on the incoming shore power just to make sure I don't trip the 10 amp breaker on my boat. It's a 16 amp supply. I don't think they're very accurate. It's only set up to work on shore power and I use my 12v battery monitors if I'm off shore power.

8 hours ago, Higgs said:

 

That's looks like a pretty good figure. The best I've managed, yesterday, a sunny day, was 12Amps, measured at that point. Forgot to check the daily tally. I've got 6x100w panels, connected in parallel. The whole array is rated at a bit over 30amps. 

 

 

Tilting the panels really helps in winter - I get up to 3 times as much from the panels tilted compared to flat.

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