iBoost questions

oldskoo1

Hi all

Considering getting one of these with my new pv install in a couple of weeks.

I can't decide if it will be worth it and have a good payback.

Boiler is ideal classic about 13 years old
Around 82% efficient maybe
Use 28,000 kW of gas per year
In summer we use around £10 per month in hot water
Pay 2.99p / kW (coop fix 16)

I imagine the iBoost is most active through summer when heating is off

So quick calc if it provides half of my dhw heating saving me £5 for 7 months of the year it will take 7 years to payback, is this right?

Also say if it detects unused pv energy and diverts it to immersion how quickly does it stop heating when the panel output drops?

If I turn on the dishwasher will it immediately stop the immersion? Diverting solar energy to power dishwasher?

What happens if the panels are unused but don't produce enough to run the immersion, does it run at a lower wattage?


Ps just a general pv question. Sorry newbie question. If I set my electric car to draw 2kW from my 4kW array, it's 11am and likely to produce decent output, if the clouds come and it drops below 2kW to say 1.5kW will my car draw that 1.5kW from the panels and top up with 500 watts from the grid?

Thanks

Dave_Fowler

£10 per month is around 33p per day. Assuming the £10 excludes any standing charge, the 33p equates to around 11kWh. With a boiler efficiency of 80%, you are putting 8.8kWh into the hot water tank per day.

If you had a base-load of say 2.5 kWh per day (during daylight hours) and you were only using the PV to heat water, you would provide all your needs for hot water whenever the PV produced 11.3kWh per day. In 'O' terms this is under 3 Os.

There would be the odd unusual day between April and October when this is not achieved. Likewise there would be quite a few days during the winter months when a good proportion of the 11kWh would be produced.

Any additional load you use - dishwasher, washing machine boiling a kettle etc. - would result in the immersion controller throttling back the power to the immersion, and if the load to these devices were more than being produced by the PV, there would be some power imported to make up the difference.

Charging the car could make a big difference to the power pattern. If the car is set to use 2kW whilst charging, this would result in 2kW being unavailable to heat the water. How much this will affect your hot water will depend on how much charging the car needs. If you are charging the car and your panels are producing 2.5kW, the immersion controller would reduce the power to the immersion. If the panels were producing 1.5kW then the car would take 0.5kW of imported energy and the immersion controller would turn off.

Remember that any power from the PV panels which is used to charge the car is a saving of imported power at the electricity price rate. That used to heat the water is at the gas rate.

From my experience, my panels produce all my hot water needs between the beginning of April and the end of October (except for the odd day) and supply a good proportion of the hot water during the winter months (note I have 6kWp). I have calculated a saving of around £85 per year.

Dave F

theboylard

See Dave's answers, much better than my waffle!!!
But I was fixing a loo seat, sorting out the washing and getting dinner ready whilst I was typing below!!!

From the top then...

do you have a hot water cylinder with an immersion element?
Do you know the rating of the immersion heater element?
Do you know how long it is? Makes a big difference as it can heat more of the tank if it's longer.

Yes, but active whenever your generating a surplus, so beneficial all year round and only you know your usage patterns for hot water.

Surplus is diverted when it exceeds internal usage plus a buffer - so if your house runs on 400w during the day with no one in, and the iBoost or similar is set to kick in when there is 100w more than the house is using, then it will feed the immersion.
As soon as you draw more power in the house elsewhere, then the diverter will reduce or stop it's load accordingly - most diverters are proportional, so they'll constantly flex the power diverted so house needs are met first, buffer next then divert.

Yes

As long as the panels can see the sky, and it's daytime (sunrise to sunset obviously), then they will take whatever and use it for the house first (whatever the house demands are at the moment, so kettle on house needs jump, kettle finishes and house settles back down etc) so as long as it's criteria of house needs (which is a variable) and buffer are met, then it will throw any surplus into the immersion, so you might only send a few Wh's, or if the panels are covered in snow then nothing is going anywhere!

You won't be able to set you car to draw directly from the array - you draw from the house supply which the car is connected into and the house needs come first.
I've not looked at EV (because I've worked with them - I won't be getting one!) so others will be able to answer you better, but generally EV, Solar PV and a diverter - dosn't sound like a good mix!

nigelpm

I've written lots on this that I don't think the payback is great but the two major factors are :

1) Will smart meters that measure export and report back on this come into being in the next five years?

2) Lifespan of the diverter.


If the answer to 1) and 2) are greater than four years then it probably is worthwhile.


Also, depends on the initial cost obviously.

£15 a year benefit is probably a sensible level of value per Kw/h.


So quick calc if it provides half of my dhw heating saving me £5 for 7 months of the year it will take 7 years to payback, is this right?

Sounds about right.

JimLad

To answer your question of will the iboost turn off as soon as you turn on your dishwasher...yes it will as it monitors the export from your house constantly. If your car is charging from your house though during peak time, will there ever be excess being exported for the iboost to use?

As posters above have said....I find that my only gas usage between april and october is my gas hob and the very odd hot water boost on dull days.

nigelpm

If I turn on the dishwasher will it immediately stop the immersion? Diverting solar energy to power dishwasher?

Depends on how much is being generated and how much the dishwasher needs.

I've had tumble dryer AND washing machine on before and still some electricity is being diverted to the immersion because there was some left out of 3.5Kw/h.

oldskoo1

Thank you all, i'm very close to finalising my new solar pv install and the iBoost is the last remaining option.

I am simply 50/50. Its £300, more than i hoped and i'm writing numbers on bits of paper and pondering wether its worth it. I feel it is a nice to have, it feels like i'm doing my bit but the numbers say the pay back is a good few years.

I have a megaflo 210L tank with an immersion element (3kW) at the bottom of the tank. I believe it is an element with a thermostat built in, so no break out thermostat. I don't know the length, don't know how to check this.

Can anyone clarify for me if these are notoriously problematic due to thermal tripping... something about the thermostat being inaccurate and overheating being tied to the element etc.

My thermostats range from 1 to 5. I am assuming thats roughly 50c to 70c. My gas HW i set to 2.5 and my immersion to 4.5 to give some leeway.

I wondered if anyone knew if these things trip a lot? I read of one person saying it was continuously tripping.

thanks

Davidb4

I have a 210l Megaflo too. I think the immersion heater is 11" long.

silverwhistle

Out of curiosity I just checked my invoice and it was £210 (incl VAT) as part of my installation. You should be able to get if for less than £300.

I've saved 1800 kwh since August 2013, and I'm a (single) low user of DHW or indeed for CH (c. £80 a year for gas), so it also benefits me by not cycling the boiler for 7 months of the year and cutting down wear and tear and maintenance costs.