Discussion elsewhere prompted me to look into what I spent on what you might term my energy smart systems relating to electricity consumption, so I thought I’d document it here.
| Item | Description | Cost | Comment |
| 1 | Solar photovoltaic system (4kW) | £5,500 | Bundled with ImmerSUN. |
| 2 | Powervault battery storage (4kWh) | £2,000 | Free installation as part of UKPN trial. |
| 3 | ImmerSUN management system with monitoring. | £600 | Estimate based on today’s pricing. |
| 4 | Remote-controlled car charger. | £300 | Modified used charger from eBay. My own software. |
| 5 | Raspberry Pi items to make HEMS | £200 | My own software. |
| 6 | Wet goods automation (WIFIPLUG x 2) | £70 | |
| TOTAL | £8,670 |
Prior analysis of items #1-#4 in pre-Agile days has suggested a total of 9 years to achieve payback on this investment through use of around 85% of the generated energy. Solar panels are potentially good for over 20 years operation, although I doubt the lead-acid batteries will still be operating for anything like that long.
The combination of item #5 with my Octopus Agile dynamic smart electricity tariff has resulted in my average bought electricity price being 7.75 p/kWh in 2019, about half the UK average. I suppose that I could make the same judgements and program items manually each day, but the HEMS significantly reduces my time commitment to achieve that.
Item #6 is my most recent addition. The sophistication of the algorithm combining the Agile tariff with a simple model of the cycle of each device is such that I would never achieve such a high quality result manually. However the saving is perhaps only a three pence each day so maybe £10 per year on my Agile tariff and thus 7 years to pay for the two smart plugs.
Much of this content is thus around 7 years to payback. The HEMS is potentially much quicker, but relies on having smart systems to control such as battery storage and car charger.
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Subsequently over the winter of 2022/3 I’ve enhanced my Powervault battery storage as the working capacity had dropped significantly over six-and-a-half years. That’s cost me about £700, mostly for the batteries themselves but also for other parts like cables, fuses etc. That’ makes my total investment £9,370 over 8 years.
The crazy energy prices over the last year have however likely improved my payback as the value of my solar output is much higher, high inflation is driving up my FiT revenue (it’s index-linked), and I continue to buy most of my electricity from the grid for as little as 7.5 p/kWh.