Solar Panel / Eddi / Battery research - help me weigh up options

Netexporter

I wouldn't have an American fridge/freezer as a gift.

chris_n

Arfa__ said:

My lad's vivarium has a 100W heating lamp and 30W UV lamp. Both on timer/thermostats and will cut out at night.

The fridge is a nice big Fisher and Paykel US style double door fridge & freezer with ice maker, water dispenser etc. Not sure on the exact age - came with the house. TBH, I'm not going to be replacing this in a hurry, it's decent quality and will be well over £2k to buy a similar new one. It would have to use considerably less electricity to make that replacement economically viable.

So there's 130W of your 600, or put another way close to 750kWh / £250 per year if on 16 hours a day i.e. not overnight.

Petriix

Looks like you would benefit from as much solar as would fit on your roof and a 13kWh battery. A bigger battery would be redundant on many days so have a longer ROI (but may still be worth while).

Arfa__

chris_n said:

Arfa__ said:

My lad's vivarium has a 100W heating lamp and 30W UV lamp. Both on timer/thermostats and will cut out at night.

The fridge is a nice big Fisher and Paykel US style double door fridge & freezer with ice maker, water dispenser etc. Not sure on the exact age - came with the house. TBH, I'm not going to be replacing this in a hurry, it's decent quality and will be well over £2k to buy a similar new one. It would have to use considerably less electricity to make that replacement economically viable.

So there's 130W of your 600, or put another way close to 750kWh / £250 per year if on 16 hours a day i.e. not overnight.

My maths was not quite as bad as that:

UV lamp = 40W (measured)

Heat lamp = 100W

On for 13hr day (7am-8pm)

Paying 26.4p/kWh (nice fixed Octopus deal)

I worked that out as 1.82kWh/day

£3.36/week or £174.89/ year.

But yes, your point still stands, it is a substantial power usage (TBF my son has offered to cover it from his pocket money). Overall, there's no two ways about it, we do just have a high energy demand and hence I'm looking at solar panels. In theory, such high usage will mean we'll break even sooner, most of the firms we've had quotes from estimate between 7-8 years.

The battery is an interesting one. The thinking here is it may be more beneficial to store cheap electricity overnight from Octopus Flux at 8p/kWh (or whatever it is), especially during the winter when the panels won't generate much. And this may still be beneficial in the summer too, as we'll still likely consume more electricity than the 5-6kW array we can fit on the roof will generate.

Scot_39

Arfa__ said:

Cool, thanks for the input. I'll scratch the Eddi from my plans and just stick with the gas boiler to heat the water tank.

I'm still a bit of a dilemma regarding a battery. I know I need to purchase it at the same time as panels (or within 12 months and put it down as a variation of contract VoC) to get 0% VAT on it.

As for my high electric usage, yes, I have been trying to track that. I'm just in a large house, loads of lights (I put over a 100 LED bulbs in when we moved in!), hoovering takes ages (now got a robot hoover), got two teenage kids, dishwasher, washing machine are running a couple of times a day, we avoid the tumble dryer, but this time of year have a heated clothes rack on 24/7 (360W). We cook most nights (electric ovens, combi/microwave), got a big fridge/freezer, air fryer and slow cookers are used for some meals too and we don't overfill the kettle. We've all got computers on most of the time, including a small server (uses 70W), I work from home every day. My son has a vivarium with lamps etc for his snake, home cinema in the loft that's used a few nights a week (<600W). etc etc. it all adds up. I've gone around with smart meter plugs and spreadsheeted what uses what, worked out what I can swap for modern stuff that'll pay for itself in a reasonable timeframe etc. Already ditched an old power-hungry TV and network switch. Already worked out what devices have high standby usage and make sure they're off at the wall or use smart plugs.

Ultimately, the main smart meter never drops below ~600W at night or 900W if the heated clothes rack is on. When the washing machine, dishwasher, oven or kettle kick in, it'll jump to 3-4kW. But then we're using them cause we need to use them! Octopus dashboard says we're averaging 25kWh / day for the last couple of weeks. A week when we were away on hols it dropped to 5.5kWh/day. So, TBH, I'm not sure how I bring usage any lower.

600W as a minimum usage - depending on what exactly you mean by night - non trivial - as that itself is 14kWh a day.

My IHD shows as little as 20-30W - 100W if fridge freezer compressor on - when I go up to bed - unless heating hot water on.

4 occupants in a large house are obviously never going to live as cheaply as one in a small one.

Even your 70W server - is nearly a kWh evenings / overnight - if not being used as a media server into wee small hours - you considered standby / possibly a wake on lan type approach to wake up ?

Your heated rack - 0.36*24 - 8.64 kWh if element really permanently on 24/7 - probably tad unrealistic - but if it was - that would probably "pay" for 2-3 reasonable sized loads in a modern tumble dryer - and lighter items (shirts etc) - probably don't need any heating anyway - just airing at ambient for a day - in a house kept at reasonable temperature / humidity level - although that may take up more space.

chris_n

Arfa__ said:

chris_n said:

Arfa__ said:

My lad's vivarium has a 100W heating lamp and 30W UV lamp. Both on timer/thermostats and will cut out at night.

The fridge is a nice big Fisher and Paykel US style double door fridge & freezer with ice maker, water dispenser etc. Not sure on the exact age - came with the house. TBH, I'm not going to be replacing this in a hurry, it's decent quality and will be well over £2k to buy a similar new one. It would have to use considerably less electricity to make that replacement economically viable.

So there's 130W of your 600, or put another way close to 750kWh / £250 per year if on 16 hours a day i.e. not overnight.

My maths was not quite as bad as that:

UV lamp = 40W (measured)

Heat lamp = 100W

On for 13hr day (7am-8pm)

Paying 26.4p/kWh (nice fixed Octopus deal)

I worked that out as 1.82kWh/day

£3.36/week or £174.89/ year.

But yes, your point still stands, it is a substantial power usage (TBF my son has offered to cover it from his pocket money). Overall, there's no two ways about it, we do just have a high energy demand and hence I'm looking at solar panels. In theory, such high usage will mean we'll break even sooner, most of the firms we've had quotes from estimate between 7-8 years.

The battery is an interesting one. The thinking here is it may be more beneficial to store cheap electricity overnight from Octopus Flux at 8p/kWh (or whatever it is), especially during the winter when the panels won't generate much. And this may still be beneficial in the summer too, as we'll still likely consume more electricity than the 5-6kW array we can fit on the roof will generate.

Your actual measured figures and costs are obviously better than my very rough rounding but importantly you get the point. I do think in your case batteries charging on a cheaper overnight tariff are the way to go. In the summer on most days you should generate more than you use in a 24 hour period but there will be days when this doesn't happen. Remember though that the cheapest kWh is the one you don't use.
FWIW I think you would be better off both financially and for the health of the house with a dehumidifier rather than a heated rack.  A heated rack is putting moisture into the air making it harder to heat and more likely to cause condensation.  A dehumidifier will also give you a small amount of 'free' heat.