Making the most of what you have
Over the past few months, I’ve been discussing reducing our energy footprint and especially our bill.
Really this is about achieving the best bang for your buck and is one of the reasons the world is looking to incentivise reducing our carbon and other emissions.
We were lucky and did this early enough that we get a good return on our installation from August 2014. That means our installation costing £6,000 has generation between £500 and £800 per annum which means they have covered half they’re installation costs. That’s ignoring what we’re saving in terms of reduced electricity costs (and we’re possibly not sweating the assests enough because we’re not using any spare electricity in a planned way – if we’re in excess we tend to cook bread, doing a load of washing or charge the car.
Take this month, May 2019. We’re 11 days in and we’ve charged the car once, done 10 loads of washing, cooked normally and switched lights on when it’s dark.
Let’s compare that to what we’ve generated.
| Date/Time | Energy Produced (kWh) | Energy used (kWh) | Difference |
| 01/05/19 | 14.604 | 8.000 | 6.604 |
| 02/05/19 | 11.752 | 9.000 | 2.752 |
| 03/05/19 | 3.444 | 20.000 | -16.556 |
| 04/05/19 | 15.851 | 7.000 | 8.851 |
| 05/05/19 | 9.414 | 10.000 | -0.586 |
| 06/05/19 | 7.875 | 6.000 | 1.875 |
| 07/05/19 | 10.735 | 7.000 | 3.735 |
| 08/05/19 | 4.858 | 12.000 | -7.142 |
| 09/05/19 | 7.185 | 9.000 | -1.815 |
| 10/05/19 | 11.686 | ||
| 11/05/19 | 9.544 | ||
| Total | 106.948 | 88.000 | -2.282 |
You can see from the numbers, we are generating more than we are using but because we’re not making use of our energy, we are having to pay around £40 a month for electricity. That’s the case between April and August most years.
Which makes a battery very tempting. At full utilisation, we generate 850Wh for a number of hours. If we compare that to the cooker or microwave, 3 hours charge when it’s sunny would give us free electricity for cooking during the day.
But such a battery would need to cost in. We’re paying £600 a year for our electricity. We could go down to near zero with a battery without having to go off grid: but a Tesla Powerwall 2 has a suggested cost of £7,900. That would take 13 years to pay off and that’s if it lives up to the promise and we do not charge the car at home (we’d be looking to double the money otherwise!).
It promises to cover us for a week of no sun, if the battery is fully charged but then it is assuming we use 12kWh, which means no charging the car.
We’ve gone for a system with inverters built into the solar cells which means we make electricity if only one cell is generating unlike systems with a single inverter. We’d be binning part of our solution and may risk our feed in tariff by making such a big change.
One of Tesla’s competitors in the home battery market is Nissan whose X-Storage system can use old Nissan Leaf batteries. This brings the cost for a 12kWh battery down to £6,750 (though they do not quote installation!).
Of course, it would be much cheaper to reduce our energy costs with a solar heater for the hot water and heating…
Posted: May 12th, 2019 under 42, Driving off the grid.