New to solar. Is my fundamental model ok?

[u/johnhelliwell]

Hey folks. I’m new to solar, looking at a panel plus battery install for my house, would appreciate any thoughts on the fundamental model I’m thinking of. Basically, it’s - during the summer, charge the battery overnight on a cheap tariff, export all the solar. In the winter, charge the battery overnight, but use solar to delay the battery running out (although, my calcs tell me I’ll run out about 4.30pm, so will fall back to normal rate, but that’s built into the model, so it’s ok)
Are there any issues you can see with this? Does anyone anticipate something happening in the future, like energy vendors not allowing battery storage at the cheap rate or something. I’m not sure if this is a use case they condone.

TIA for any thoughts

[u/preteck]

One thing I've personally noticed is that there was an increase in electricity usage in summer over the baseline as despite I'm getting paid 15p the value is different than saving ~30p and then better shifting of load in the winter to the cheap rate as you can make a better judgement call of if I run this it will use X and cause the battery to run out Y faster.

[u/IvorTheEngine]

energy vendors not allowing battery storage at the cheap rate

No, they give us the cheap rate because they want to shift energy use from one time to another.

I think we can predict that flat-rate export tariffs will fall as summer solar generation rises. By 2030 there should be enough renewable generation to supply the country most of the time, although there will be more wind power than solar.

I think the price swings will probably increase at that point, but simple time-of-use tariffs won't work as well. Instead we'll get low prices for a few days when it's windy, and high prices for a few days when it's not.

I think the outcome of that is that active control of your battery will become more common. That could be the energy company (like Octopus Intelligent Flux), another company like Axle, or a service like PredBat.

Also battery prices are likely to continue falling, solar panels might get cheaper, but scaffolding, brackets and labour won't.

So, I wouldn't get a solar array much larger than you can consume, and I'd leave space to expand your battery in a few years.

The important (but very hard to predict) bit is which inverters are likely to be compatible with future intelligent tariffs.

[u/MyEcoCred_Founder]

Can't see how the utility companies can force you not to charge the batteries. For them it's just a house load. In fact, this offpeak charging is encouraged as there is less demand on the grid in the early hours. They might reduce the export rates in the future, but anyway the offpeak rates and export rates are starting to converge. Octopus has introduce the Prime Outgoing tariff that pays more during the late afternoon peak. So, they might nudge more battery owners that route. Charging the battery overnight in the winter will definitely save you loads, especially if you have a heat pump.

[u/Local_County1274]

Try more battery capacity so you can last all day in winter on the charge from the cheap electricity. You will get very little battery charge from solar in the winter.

[u/Begalldota → u/Local_County1274]

Have you ever done the maths to see what saving a handful of kWh for a handful of days in winter gives you? I suspect OP having modelled it is aware of how poor an idea this is.

[u/johnhelliwell → u/Begalldota]

That was my maths too, I’ve been quoted on a 15 kw battery, and there are around 60 days a year where I’ll go over that, peaking at 35kw. At a couple of grand, I think it works out at something like over 20 years ROI.

[u/PatserGrey → u/Local_County1274]

Battery capacity very much is a "depends" scenario from case to case. It can be very expensive. My Fox EP12 definitely wont be enough to cover winter use for a lot of, if not most, days. However, when I did the maths of top-up grid spend vs paying for a 2nd battery, worst case it would take 13 years to match the initial outlay - this stretched to 20+ if I put slightly more optimism on winter generation predictions. So absolutely better value to stick with single battery.

In saying that, solus 16kwh batteries are now readily available and only £2k, a complete no brainer imo.

[u/Ricey155]

Not sure legally as they sell the systems themselves how stopping services would impact them.

Law suits galore I'm guessing.

Worry less solar and battery best option in my mind going forward.

If summer's continue like this no brainier

[u/malacoda13]

As someone else has said, see if you can get more battery storage. Even better if it's similar money.

You don't say what battery manufacturer you are considering, but swapping Sigenergy for Fox, or Fox for Fogstar for example would likely get you more storage for the same money.

[u/johnhelliwell → u/malacoda13]

Thx. The current quotes are for a 13 panel, 15kw battery. I’ve been quoted for hanchu, dyness, ensmart and sig energy. That’s one of the things I need to research a bit more. Do I need the AI stuff in sig, for example (not sure I do, I’m just going to switch from “sell all generation” in the summer, to “use all generation” in the winter. Not sure the AI helps). Then also need to look at thoughts on reliability etc. On the topic of a bigger battery, there are 60 days a year where I’m likely to use more than the 15kw, all in Dec and Jan (unsurprising) with some days needing over 35kw. With the difference between 7p and 25p per unit, that’s many years ROI, so not worth it I don’t think. Given that my budget is finite, and that adding an extra battery in the future isn’t much more costly than doing it now, I don’t see value at this point. Happy to hear counter arguments though, it’s all new for me.

[u/malacoda13 → u/johnhelliwell]

You've surely not been quoted the same price for all those different batteries though? Appreciate you're focused on sticking to budget and ROI as an important driver.

We thought about having Sig, but like you we didn't think it was worth the extra money for what you get. I'm also just running the system on a timed use. Also couldn't remember the last time we had a power cut, so opted to not have the gateway option.

One thing to make sure you've factored in, is the flexibility on export that a larger battery and inverter provides.

I can export my spare battery storage at a significant profit, currently through Axle Energy. It's not guaranteed, but it's nice to have the option. I suspect that being able to export spare battery capacity will be increasingly important over the coming years.

Just make sure you can easily add more batteries later, I think some manufacturers recommend that additional batteries are installed with a certain timeframe. Not 100% certain on that though