solar self consumption device..... 30 June 2021 at 8:02PM in Green & ethical MoneySaving 13 replies 319 views

nologo

I am considering  solar for my large south east facing roof, I know Im not going to save the planet on my own but every little helps.

I have mains gas heating, & a large hot water tank with two immersion heaters installed.(economy 7 style) 

As fits are low my main objective is self consumption, so to this end a solar diverter to hot water is a good start, someone working from home three days a week(office/ computer) is also useful, but I think I recall  device that could divert excess  to another device ( resistance heater/oil filled rad) but cant for the life of me remember what its called, can any body help?  also any other ways to self consume?   we have delay timers on our dishwasher & washing machine so thats another idea 

TIA. nologo

ABrass

Electric storage radiators?

Dolor

There there are no longer any FITs paid for new solar installations. You can claim SEG payments for all exported energy. This requires a smart meter and an export MPAN. There is only so much energy that you can use in the home. For example, I have a solar diverter (an EDDI) and average consumption to reheat a cylinder is about 3kWhs a day.

To put all this into context, I have a 7kWp array and a 13.5kWh Powerwall 2. In December last year, my daily output varied from 350Whs to 10kWhs. I would be hard pressed to meet home needs; reheat a HW cylinder and power a radiator with an output of 350Whs.

silverwhistle

I luckily get FITs but what has made a difference to my exporting is getting an EV to add to the hot water.diverter. In the shoulder months I also use an oil-filled radiator which has 800/1200/2000w settings which I adjust manually if I'm at home. I take cooking/baking/washing for granted in terms of watching the weather and using solar. As a single occupancy household I can't really justify the cost of a battery.

Grumpy_chap

What about air conditioning?

Reed_Richards

This thing, https://www.marlec.co.uk/specifications/ "two cascading load connection" ?

QrizB

If you're interested in SEG, do keep in mind that a kWh sold to the grid is potentially worth 5p (or more) while a kWh used to replace gas is only worth 3p.

If you have a large roof you can probably fit much more than the 4kW or so of panels that suit a capped 3.68kW export. To export more than that you'll need DNO permission and they may charge a fee. If you don't fancy the fee, a DC-coupled battery might be worth considering (@Reed_Richards has one) but the economics of batteries are still marginal.

As @Grumpy_chap says air-air heat pumps can also make good use of surplus electricity in the shoulder months when there is decent sun but also need for space heating, and they give the option of aircon in the summer months if needed. @Martyn1981 is a fan and he can give pointers.

nologo

Thanks for all your replies, I know Im not going to use all of the generated power, but Reed_Richards has identified the blighter I was unable to recall, I know gas may be cheaper to heat water than electricity, but my point is to not use as much gas, as its not renewable & I am trying to do my bit to save the planet.

Hexane

Also worth considering this device: https://myenergi.com/product/eddi/

Some argue that exporting your surplus locally generated solar energy to the grid, and using your gas boiler to heat domestic hot water, is more environmentally sound than using that locally generated solar energy to heat your domestic hot water through an immersion heater. I carefully avoid having any opinion on the environmental merits, because I am on deemed export therefore it saves me money.

Petriix

nologo said:

Thanks for all your replies, I know Im not going to use all of the generated power, but Reed_Richards has identified the blighter I was unable to recall, I know gas may be cheaper to heat water than electricity, but my point is to not use as much gas, as its not renewable & I am trying to do my bit to save the planet.

I'm fairly certain that all immediate electricity demand in the UK is met by gas power stations with a round trip efficiency of around 60%. It's objectively better for the planet for you to export the surplus and burn gas to heat your water at 80% efficiency. 

Reed_Richards

Petriix said:
I'm fairly certain that all immediate electricity demand in the UK is met by gas power stations with a round trip efficiency of around 60%. It's objectively better for the planet for you to export the surplus and burn gas to heat your water at 80% efficiency. 

I disagree.  Whilst this may be true at times of peak ("immediate") demand, the time when you have spare solar power is not when there is peak demand, most likely gas power stations are off or in idle mode.  The whole point of a tank of hot water is that it stores energy.  So the choice is not between burning gas in a power station or in your house, it's between burning gas somewhere or not at all.

Edit:  The other thing to consider is that if you run your immersion heater around the middle of the day you may well be generating more spare electricity than the 3.68 kW most of us are allowed to export so you are being payed 0p per kWh for that even if you can get 5p per kWh for what you can export.  Can you set the iBoost or the eddi to siphon off spare electricity once the export gets to 3.68 kW I wonder?  That's the economic logic of what @QrizB is saying.