Solar Panels

scarletjim

Another couple of questions on batteries, one simple one and one perhaps more difficult:

How easy would it be to add a battery to a system later?
  -  Would adding it later have significant installation costs?
  -  Could it just be bolted to a wall and plugged into something (what? the fuse box?) by a non-DIY person, or would it need a qualified electrician?
  -  Does anyone need to go back up on the roof for any reason when installing the battery, or is that work all done 'on the ground'
  -  Are there precautions that can be taken with the initial install to make adding a battery later easier?
  -  Anything else to consider in relation to adding a battery at a later date?

Why is there a general consensus here that the cost of batteries will fall reasonably soon?
  -  Is there that consensus, or have I gleaned it inappropriately?
  -  What is it based on?
  -  What sort of timeframes and reductions are people expecting?

With regard to that second question, when I look at tech prices, it seems that whilst the techie bits come down over time, the hardware itself doesn't always, because the components still use the same raw materials. Take a mixing desk or an amp for example - their prices don't seem to have really come down significantly in the last 20-30 years do they? (I'm only going on hearsay there).

Spies

Couple of things to mention, if you go with a hybrid inverter with the intention of adding a battery later, the inverter will cost more due to its hybrid nature and they typically last 10-15 years so by the time you add batteries, potentially a third of its life has gone.

Adding a second AC connected inverter would be my preference but there are losses from going from DC to AC, then AC to DC to charge the batteries but it give you more options, it doesn't have to be placed anywhere specifically but does need its own circuit. It would have to be installed by a qualified electrician.

Battery prices are likely to stay high due to demand unless cheaper sodium-ion batteries are produce in large quantities, sodium is a lot easier to source than lithium and there is a plentiful supply.

Alnat1

Costs of batteries are actually rising quite a lot at the moment, simple supply and demand.

So many installations ongoing/wanted that it's difficult to get hold of the inverters and batteries in the UK.

[Deleted User]

scarletjim said:

I'm back again! Two questions this time - firstly for @[Deleted User] - you say above:

"I have a solar diverter (EDDI) which uses excess solar to heat my water. On an average day, this is saving me about 6kWh of gas OR about 3.5kWh of Grid electricity from March through until October. Break even - I doubt it."

Is EDDI basically the same thing as iBoost that others here have spoken of? And are you saying that it saves you about £107 a year? (6kwh of gas per day, say 30 days pm for 8 months at 7.4p per unit = £107)

If so then at a cost of just a few hundred pounds, it would break even in about 4 years? Am I missing something?

You have to do the maths. An EDDI is similar to an IBoost. The cost is £435 plus fitting. The device is warranted for 3 years (up to 5 years with an extra premium). There also is very little energy to boost with from November to February. It also depends on how much you pay for your offpeak electricity. Mine went up this week to 8.5p/kWh (it was 5.5p last Winter). 

It follows that if I heated my HW off the Grid at night it would cost 25.5p/day. However, the loss of solar export payments also have to be taken into account. On Agile Outgoing during the spring; summer, autumn period it can average 20p/kWh. So it follows that my 25.5p/day saving could have cost me 70p/day in lost SEG income or 12.3/day if on Agile Fixed. Assuming Agile Fixed, my daily saving using the EDDI is 25.5 - 12.3p/day: 13p/day equates to about £3.90 a month less than Grid heating. One needs to save a lot of £3.90s to pay for an EDDI.

Clearly, if you are using SVT rates, then solar diversion is a good thing to do and there should be a return on investment.

FWiW, my personal list of priorities would be a solar array as large as possible; a battery twice the size of the array (ie, 6.5kWp = a 13.5kW Powerwall), and then a solar diverter. I also have a very large solar diverter in the garage called an EV.

Alnat1

I had solar installed in March and still heat the tank using gas. We don't use a lot of hot water, mainly it's for 2 showers a day, so we only heat for 40 minutes and the boiler is set to only heat the water to 50C. Uses 3-4kWh a day (11p a unit on Octopus Tracker) so average 30p

For me, it works out better, as Dolor mentioned, to export the excess solar. Outgoing Agile rates are between 29-54p/kWh today and have been at decent rates since my system was installed.

scarletjim

Aha, between you I see two (at least) 'flaws' in my assumptions:

1. I forgot that of course the iBoost (or similar) will have a useful life that will be far less than the solar panels themselves.
2. I also forgot that some people are on non-standard tariffs. I will have to check out Octopus - though if it is the only one of its kind, I'd be reluctant to base my calculations on it as it could go out of business, the market seems so unpredictable at the moment, and lots of providers disappeared last year, so I'd want to base my calcs on whatever is most likely to still be around in 3-5 years' time (though I appreciate that with the current state of the market, god only knows where we'll be in 3-5 years time!)

The problem with adding a battery as 2nd priority (after maximum size array - which I think will be 6kw for me) is the cost - my calcs so far have suggested that a battery for my system (was looking at 6.5kwh) will take 9 years to pay for itself, which is almost its useful life, so not much point in that. I suppose I now need to investigate the payback time and also lifespan of iBoost, and also that of a bigger battery (though I suspect the cost will make that almost as pointless as a smaller battery).

As for inverters and hybrid inverters, I need to learn about those so I can properly understand comments above on those in relation to adding a battery later.

Thanks to everyone helping by the way - once I understand the basics and have refined all my calcs accordingly, I'll start a new thread with all my calcs, assumptions and plans, and see what feedback people have. I'd rather do that than talk to any installers yet, as you guys have nothing to gain by selling me something I don't need - I'd rather be at least somewhat informed before requesting any quotes etc.

Spies

Highly unlikely Octopus are going anywhere, they've weathered the storm so far and they're a global entity. 

Alnat1

Octopus are in it for the long run, they aren't going under anytime soon. They are always looking to a future of sustainable energy and have the best options for customers who are doing the same.

So good rates for those with EVs, cheap overnight charging, really good (best in market?) rates for solar export (not available together with cheap overnight rates, that would be too good) decent TOU (time of use) rates.

I'll just add, battery fitted with PV system would be VAT free, added later would incur VAT. The system needs to be installed by an MCS registered company and you received a certificate from them which is needed to obtain SEG payments. For an larger array (over 4-5kWh) you'll need DNO approval or you'll be unable to export more than 3.68kWh and the output will be capped. The solar company will sort this but it is an extra expense and there's no guarantee permission will be granted.

[Deleted User]

Alnat1 said:

Octopus are in it for the long run, they aren't going under anytime soon. They are always looking to a future of sustainable energy and have the best options for customers who are doing the same.

So good rates for those with EVs, cheap overnight charging, really good (best in market?) rates for solar export (not available together with cheap overnight rates, that would be too good) decent TOU (time of use) rates.

I'll just add, battery fitted with PV system would be VAT free, added later would incur VAT. The system needs to be installed by an MCS registered company and you received a certificate from them which is needed to obtain SEG payments. For an larger array (over 4-5kWh) you'll need DNO approval or you'll be unable to export more than 3.68kWh and the output will be capped. The solar company will sort this but it is an extra expense and there's no guarantee permission will be granted.

DNO sign off on the completed installation is also required before the supplier will apply to the DNO for an export MPAN. My sign off was a short email from SPEN confirming that it had received and was content with the commissioning and testing paperwork.

xeny

A question about the iBoost and similar diverters. How much power does the array need to have surplus to household demand for a 3KW immersion heater to heat a tank usefully. Is say 1KW enough, or realistically do you need 2 KW or more?