TSHE: Time for a solar battery?

It’s definitely a pretty piece of kit, but is it worth the price tag? (credit)

This post is part of an ongoing series in The Solar House Experiment where I review and investigate different options available to drag my house into the 21st century and play with some cool technology along the way. Other posts in the series are included below:
The Solar House Experiment: An Overview
TSHE: Solar Panels + 1 year review

I finally did it. I broke down and started calculating out whether I could justify a solar battery or not for the house. I wish I could say it was due to boredom or having a long weekend of little to do, but it was actually because of this picture I took of the system output:

Yep, it’s early afternoon and both the electric car and hot water are maxed out. That’s 2.6 kWh of power leaving the house, every hour…

As we head into the summer months I have an increasing ‘problem’ that my solar panels are producing way more than I can consume during the day. And then at night we fire up the oven / TV / computers / lights and none of it was saved and I have to pay (more) to buy the electricity I sold to the grid (for way less). It just seems wasteful and inefficient to me!

Doing the maths

I usually work out how much something will cost and then work out the Return On Investment (ROI) in years but I’m going to do something a bit different today and work forwards instead. Currently we use about 1500 kWh per year in the house, excluding the hot water solar diverter (which only uses excess solar) and the electric car. Currently having the solar panels reduces our usage from the grid by about ~35% meaning we’re paying to use about 975 kWh of electricity for the house and (in non-Coronavirus times) I estimated the car would need about 2,500 kWh of electricity a year for my driving patterns. However the car is charged at a much cheaper rate due to the tariff I’m on (Octopus Go).

So in summary the maximum savings I could achieve in an ideal scenario where all solar energy is produced and consumed by myself (aka pay nothing for grid electricity) is:

Usage TypePower Usage (kWh)Cost Per kWhTotal
Table showing max potential savings with a solar battery (assumes all solar power generated is consumed instead of exported)

This solar battery would need to be able to store about 4 kWh a day on average (3000 kWh produced a year, minus 500 kWh consumed by the house already, minus 1000 kWh consumed by the hot water, and then divided by 365 days a year). Or to simplify:

(3000 kWh – 1500 kWh) / 365 days = 4 kWh/day

This would probably allow me to cover 90% of the house’s needs through the year… but would barely reduce my electric car charging usage. Hmm. We’ll come back to this.

I also decided that a 12 year ROI is not a bad thing for a solar battery. I think they will easily last up to 15 years and beyond but will of course degrade over time. As electricity bills have generally been increasing by 3% each year, the total I should be prepared to spend for a battery and receive a 12 year ROI that would cover only the house usage would be about £2,000 overall.

Checking out the options

After speaking with several companies and getting some quotes I narrowed my options down to three main choices (plus a wild card!). Spoiler alert: none of them meet my above requirements, but it’s an interesting investigation into the market right now.

Moixa BatteryTesla PowerwallEnphase BatterY
Product InfoLinkLinkLink
(2x 1.2)
Usable Capacity (kWh)3.8413.52.4
(2x 1.2)
Max Sustained Output (kWh)
Warranty (Years)10 / Lifetime1010
Notes12 months 0% payment plan available
Extra £50/year for signing up to GridShare program
Mountable inside or outsideModular design allows easy expansion at later date
(with installation)
Table highlighting the different options available I would consider

Straight out of the gate you can see that even the cheapest usable option, the 2x Enphase batteries, are too expensive and don’t have enough capacity for me to make a big enough saving to justify it. It also outputs a very paltry amount of power (500 Watts an hour).

At the other end, the Tesla Powerwall has more than enough capacity but is over 4x my 12 year ROI budget. It could power a kettle / oven / dishwasher too which is nice. The problem is that the ROI greatly exceeds the potential lifetime of the battery, even if I used it to charge the car as well as power the house. This is only for people who have money to burn.

The Moixa battery is actually the most interesting to me for two reasons. One, they offer a 12 month 0% finance option which would mean the maths on the ROI changes a little and I wouldn’t have to stump up all the cash straight away. Second, they offer an ‘unlimited’ warranty on the battery and £50 a year (for 3 years) if you sign up to their GridShare scheme which basically makes money for them by using a percentage of your battery to deal with high demand on the grid, when electricity costs the most. What annoys me is that 20% of the battery capacity is locked away to, I suspect, fulfil that lifetime warranty. If there was a 6 kWh usable capacity at that price point, I think I would take the dive.

The wildcard option

This is an 8 year old electric car with a 24 kWh battery available for around £5,300.

A 2012 Nissan Leaf on the AutoTrader website

This is a Vehicle to Grid (V2G) charger that works with the Leaf’s CHAdeMO connector that is currently being tested by OVO Energy in the wild.

The prototype V2G charger by OVO Energy

V2G is where you store power in your car which is connected to your house through a charging cable, like above. When the house needs energy, the car’s battery is used to supply that energy and no power is taken from the grid. In the future it is expected that more and more of the national grid in the UK will be managed in this way, helping reduce the need for coal / oil / gas power plants which are mainly used to deal with high load on the grid (such as when everyone gets home and starts cooking dinner).

Aside from space issues (I happen to have an empty garage I could utilise), there is nothing to stop me buying an old electric car like the one above, whose battery is likely to still have about 70-80% of it’s original capacity (let’s say ~17 kWh for that Leaf above), install a V2G charger when they become more wildly available and then plug it in and never touch the thing again. I could declare the car SORN (not legal to drive on UK roads) and it then literally becomes a battery on wheels with more capacity than a Tesla Powerwall at a cheaper price.

And I can easily sell the battery (car) on at a later date. A lot harder to sell a fixed installation battery on to someone else. I could even potentially take it with me to a new property if I decide to move!

But you have an electric car already? Use that?

I do, but alas Tesla have basically said they will not allow their cars to be used as V2G batteries. The fact they have a separate product (the Powerwall) to sell you is more likely to be the reason than the car is unable to do it, but I don’t know for sure.

Current V2G chargers only work with the CHAdeMO connector, whereas my Tesla Model 3 has a CSS connector and I don’t know of any in development right now. Maybe in the future…

In summary

I am optimistic that the costs for solar batteries will be coming down over the next 5 years or so. But right now I think they either offer too little capacity for the cost or they are simply way too expensive for your average user to ever really make their money back on them. I am still interested in the Moixa battery personally and will be keeping an eye on their future offerings, but right now? I’m going back to watching someone else make use of my excess solar power. Oh well.

2020 Q1 Update: Coronavirus Quarantine Edition

The hidden danger floating around the world

Well, it certainly has been the weirdest start to a year that I can ever remember. Lock downs, food shortages, eerily quiet streets and more video conference calls than you can shake a stick at. As always, I hope you have been spared the Covid-19 disease so far or are having the mildest symptoms possible while we all try and wait out the virus and not overwhelm the incredible people working at the NHS.

I am fully expecting to be furloughed in the not too distant future as the work at my employer has been steadily dropping due to postponements and cancellations of projects but so far so action has been taken by management in this vein so fingers crossed. Fortunately, being able to survive on a rather low amount of money a month, even dropping to the £2,500 maximum payment from the government (a not insignificant pay cut), would still let me have a positive savings rate. Further proof that the FIRE lifestyle works both in the good and bad times! While my FIRE pot has certainly taken a bit of a battering, I still hold enough in cash, bonds and shares to get me through a couple of years if the shit really does hit the fan harder than it already has.

And as a nice extra bonus, when I passed my ‘bloody difficult’ exam, it turns out I was eligible for an extra ~£2,000 (after tax) bonus which I never knew about! That money has been chucked at the car loan, as per Monevator’s excellent series on debt I read recently.

Matched Betting

Encouraged by TheSavingNinja’s and weenie’s posts on Matched Betting, I thought I would take a look into it and see if it was for me. I made £504 (after costs) in late January which was nice but I’ve decided it just takes up too much time for me to bother with on the whole and I don’t enjoy being spammed by bookmakers. Based on the fact most sporting events have been cancelled recently I’m not sure it would be worth doing right now anyway. But if you want to try it out I’ll provide weenie’s OddsMonkey referral link here – I have no wish to benefit from promoting Matched Betting, for reasons I may elaborate on in a future post.

Solar House Project

The days are getting longer and the solar power is rising! Having just submitted my Feed-in-Tariff figures for Q1 of 2020 I’m happy to report that the panels managed to produce around 497 kW of power! We have been getting pretty much free hot water during the sunniest days and on an especially sunny long weekend the car gained 180 miles (~45 kW) of ‘free’ sunlight powered range which is amazing!

Due to the extended lock down though, I am running into the issue of the car’s battery being near full all the time and unable to use the excess power being generated off the panels and it is instead being sent out to the grid. This isn’t a bad thing (I’m offsetting someone else burning gas / coal) but does lower my utilisation figures(!).

Health & Fitness

This game was destroying me at the beginning of the year

I mentioned way back in early January (remember that simpler time?) that I would be progressing from my light(-ish) workout of Ring Fit Adventure to a ‘proper’ workout, such as the Insanity Workout during the summer. Well that plan was brought forward massively and my wife and I now spend 6 days a week doing the Insanity routine religiously of an evening, just before a nice hot shower and a healthy dinner.

We’re currently near the end of Week 3 and having done ~16/17 workouts now, I can say that I was absolutely not ready for this again haha. But I am improving! It also adds a bit of structure to our days and we actually look forward to it, because afterwards we’re free to relax. And having a gym buddy does make it so much easier to keep going, even when you just want to put on Netflix and eat biscuits instead…

Net Worth Updates

And finally, how is the net worth situation looking on my end? Frankly, when I did the calculations for valuations on 31st March I was bit surprised the drops were as low as they are. Certainly they may drop a lot further as the quarantines around the world drag on, but there’s a surprising amount of ‘meh’ in the markets on the whole from what I can see (ignoring specific areas such as travel which have cratered like an asteroid hitting the moon).

All in all, I am roughly down about 12% from 31st December 2019, excluding new money added during 2020 Q1. That drop was made a lot less worse by the fact I had shifted nearly 35% of my portfolio to bonds in 2019 Q4 based on trying to estimate my risk tolerance and deciding being 100% equities was perhaps not the best idea. Pure luck on my part that I preempted the stock market crash, but I’ll take it!

For the latter part of 2019 I was buying £300 of VAGP (Global Bonds ETF) every month and not much else as I was still throwing money at my car loan as much as possible. Since the crash I have shifted to buying £500 a month of VHYL (High Yield Shares ETF) and have shifted 10% of my portfolio from VAGP to VHYL. I also have a large slug of VWRL (World Index Tracker ETF) but am not currently adding to it yet. The car loan is nearly gone and then I can go full on into pushing £2,000 a month into my ISA on both VWRL and VHYL, assuming my usual employment holds out(!).

Here’s how the overall situation is looking for now:

December 2019 ended at around £210k, whereas March 2020 ended at around £220k
(Blue is non-pension stuff, Orange is pension stuff (SIPP / Company Pension))
Investment2019 Q4Contributions2020 Q1Difference
(minus Contributions)
A table showing the contributions made in the past 3 months

If you’re wondering how my pension contributions are so high, it’s because I currently sacrifice 25% of my salary into my work pension, my employer tops it up by an additional 5% and they also give me most of their employer NI savings. I also had the option to receive my bonus entirely into my pension if I wanted, which I took them up on and which saved me a large chunk of income tax! Hopefully if/when the markets recover I will have been very happy to have bought in at lower share prices as the Pension currently sits in a 25/75 bond/equities split.

Plans & Goals for Q2

I only have a few goals going forward right now:

  • Get fitter with Insanity and enjoy more time at home
  • Push as much money into my ISA as possible before being furloughed
  • Play more games with friends (online of course!) as I have more free time
  • Finish paying off the car loan (less than £3,000 to go)!
  • Keep washing my hands!

What are your own goals for the coming summer? Keep safe and have a good one!