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

Arfa__

I'm currently researching solar panel installation options. After getting a few firms out to provide info, quotes etc. I have three options:

1. Solar panels only
   
2. Solar panels only with an Eddi to feed surplus to immersion on hot water tank
3. Solar panels + ~5kW battery

I've a decent size roof, in Scotland facing SE. Quotes are offering between 5 and 6 kW systems, G99 cert etc. The main quote I'm looking at is 5.1kW of panels, 4080kWh / year yield. My estimated annual electric usage is ~8000kWh. I work from home and expect a fair daytime electric usage.

No combi boiler, standard gas boiler feeding large well-insulated hot water tank, which also has 1 3kW immersion heater for backup.

The Eddi is about £500, and seemed like a good budget option to use surplus in lieu of battery. Has anyone done sums on this option saving gas & 150W hot water pump power usage vs Octopus 15p/kWh SEG payback?

(There are 4 of us in the house who have daily showers or baths).

Or am I better off just skipping the Eddi and going for the battery? To either better use surplus across everything in the house and/or fill up at night on super cheap Octopus EV tariffs etc. 

Also, has anyone had experience with getting the 0% interest home energy loan available in Scotland? Any issues, tips?

QrizB

The general consensus over on the Green & Ethical forum, where solar is commonly discussed, is that with current electricity tariffs there's no rea economic l case for a solar diverter or a home battery. You can sell electricity to the grid for more than the cost of gas water heating, and the potential savings from storing your own electricity are unlikely to recover the cost of the battery over its life.

Now, economics aren't everything. If you live somewhere prone to power cuts, or if losing electricity is a particular danger to you (eg. you have tropical fish that will die during an outage) there may be peace of mind reasons for choosing a battery.

Slinky

I came to the conclusion that £500 buys an awful lot of gas heated water and I'd get more selling surplus electric back to the grid. 

Petriix

An Eddi or similar would only be viable if your alternative method for heating water is exceptionally expensive. I've seen many people justifying such a purchase by pointing to the amount of energy diverted as if this all equates to a saving of peak-rate electricity and ignoring two key facts:

1. They actually end up wasting much of that energy because they didn't really need that much hot water.
2. They could have heated the water they did need far cheaper than peak-rate electricity and indeed earned more through SEG payments. 

It's almost always the case (now) that any self-use of solar energy that could have otherwise been met with gas or off-peak electricity will actually cost you money compared to simply exporting it. The only self-use that's worth while is where it directly replaces unavoidable peak usage.

Even those like me on the old FIT scheme with deemed (unmetered) export payments are now better off switching to SEG payments. As soon as my Zappi is compatible with Octopus Intelligent, I'm better earning 15p per kWh exported and just charging the car at 7p per kWh overnight; any solar diverted to the car would actually *cost* me 8p per kWh more. 

Alnat1

I agree there's no point in an Eddi when heating the water by gas is so cheap. We only heat as much hot water as we need, I find 40 minutes is enough for 2 showers with some left so a mop bucket etc. can be filled, 3-4kWh of gas per day. We have the boiler temperature set at 55C for the hot water.

I do like my battery though, I can top it up overnight or early afternoon at cheaper rates on the Agile tariff and it gets me through the more expensive morning and evening peaks in winter. In summer the battery is filled by the panels and runs the house load overnight.

Maybe you could do some research on what is using 8000kWh a year and see if any savings could be made there?

Arfa__

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.

QrizB

Your base load of 600W is 4-500W higher than a "typical" property, and will be adding maybe 4000kWh/yr to your household electricity use, costing you more than £1000 a year.

Arfa__

QrizB said:

Your base load of 600W is 4-500W higher than a "typical" property, and will be adding maybe 4000kWh/yr to your household electricity use, costing you more than £1000 a year.

Yeah, I know this is fairly high. But have been struggling to bring it down.

I know approx 150W of this is a computer server, laser printer on standby, network switches, wifi access point, router, TV aerial amp etc.

I'm not sure about our fridge freezer exactly (it's hard-wired in), but docs suggest ~420kWh/yr.

The rest is probably other stuff hard-wired in - alarm, heating controller/kit, a couple of Echo devices etc.

Alnat1

If that fridge freezer is getting on a bit, perhaps it's no longer so efficient. The docs for my 14 year old overflow FF said iirc 345kWh pa but after 48 hours of monitoring I could see it was likely to use nearer 900kWh. It is now a deceased FF and has been replaced with a bit smaller one which should use under 300kWh.

chris_n

Arfa__ said:

QrizB said:

Your base load of 600W is 4-500W higher than a "typical" property, and will be adding maybe 4000kWh/yr to your household electricity use, costing you more than £1000 a year.

Yeah, I know this is fairly high. But have been struggling to bring it down.

I know approx 150W of this is a computer server, laser printer on standby, network switches, wifi access point, router, TV aerial amp etc.

I'm not sure about our fridge freezer exactly (it's hard-wired in), but docs suggest ~420kWh/yr.

The rest is probably other stuff hard-wired in - alarm, heating controller/kit, a couple of Echo devices etc.

The vivarium could easily be another 150W maybe more depending on lights and heaters.

Arfa__

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.