Solar and battery power system

[eniacs]

Thought I would share this to the MMM group as this is slightly money saving orientated.

I've built myself a battery/inverter/solar power system which enables my house to prioritise the solar and battery supplies befor using the grid power. Essentially, its been installed now for 2 months and I havent used any power from the grid. I still pay the connection fee every month (£8) which is annoying, but gives me the back up of grid power if required.

Attached to this post are the battery build pics.

[eniacs]

Finished inverter and battery combination.

Components:
Battery switch/fuse to the left
Inverter - Solis 5G 6Kw
Battery - Made from EVE 280ah cells lifepo4 and a seplos BMS.
Solar isolator
AC isolator

[eniacs]

And solar panels fitted to the roof.

All parts installed by me. The battery is in the garage for safety and convenience... Better for the garage to burn down than the house!

Panels are trina 380w, there are 16, giving about 6kw peak power.

[middo]

Wow.  Looks great.  Was there any particular reason for going with Lithium cells rather than a cheaper option such as lead acid?  I'm curious.

[uniwelder]

Could you give a price breakdown for the various components?

[nereo]

Thanks for sharing
£8/mo sounds like a great deal on a ‘subscription service’ to have the grid as your backup. Over the course of a decade it’s still less than what a fixed backup generator would cost.

[bill1827]

Wow.  Looks great.  Was there any particular reason for going with Lithium cells rather than a cheaper option such as lead acid?  I'm curious.

I'm not the OP, but I have an off-grid system which I designed several years ago. Originally I was looking at lead-acid, but a closer look at characteristics made me change my mind and use LiFePO4.

The issues are efficiency and longevity. In order to get acceptable life span out of lead acid batteries you can't regularly discharge them below 50% SoC, LiFE batteries can be discharged to less than 20% SoC regularly and close to 0% occasionally - that would likely kill a lead acid battery. That means you need only half the nominal Ah capacity in a lithium battery than a lead acid battery - that made the capital cost about the same when I designed my system. Lithium batteries are cheaper now.

Lithium batteries are over 90% efficient, lead acid batteries have much higher losses.

Good lithium batteries are likely to have a life of 5000 cycles or more, lead acid batteries aren't.

Lead acid batteries need to be looked after; ensure that they're not overcharged, not over discharged, the electrolyte level needs to be maintained, they produce hydrogen so good ventilation is essential, they're very heavy, so difficult to install.

Lithium batteries also have some constraints about over charging and over discharging and use in extreme temperatures, but a good BMS (which is essential) will look after those considerations automatically.

[eniacs]

Price breakdown as requested:

Panels - £120ea x 16 = £1920
Mounting - £500 (estimate, already had some and just added to it so real cost probably very little)
Inverter - £1000 (wholesale price paid)
Cells - £112 each x 32 = £3584
Battery management system - £200
Battery housing and various small items - £500 (likely an overestimate)
Cabling from garage to house - £500

Total: £8204


Lithium vs lead acid has been nicely covered by Bill. In my experience, lead acid cannot be discharged less than 50% of its rated capacity. Cycle lifetime is usually 1000 cycles or less. The cells I have are 6000 cycles. Lithium simply works out cheaper.

[middo]

@bill1827  and @eniacs .  Thank you.  I was genuinely interested.  Looks like lithium is a much better prospect now.

[uniwelder]

Price breakdown as requested:

Panels - £120ea x 16 = £1920
Mounting - £500 (estimate, already had some and just added to it so real cost probably very little)
Inverter - £1000 (wholesale price paid)
Cells - £112 each x 32 = £3584
Battery management system - £200
Battery housing and various small items - £500 (likely an overestimate)
Cabling from garage to house - £500

Total: £8204


Lithium vs lead acid has been nicely covered by Bill. In my experience, lead acid can be discharged less than 50% of its rated capacity. Cycle lifetime is usually 1000 cycles or less. The cells I have are 6000 cycles. Lithium simply works out cheaper.

Thanks for the pricing.  From your other posts, it sounds like you're in England. I guess if the US didn't have tariffs on chinese panels, our cost would be closer to yours.  Converting currency, yours comes out to US $0.39/watt, while I think we're somewhere around $0.60/watt right now.

What's the payback like for a solar system there?  How much does electricity cost from the grid per kWh?  Even if your not using power from the grid now, I assume it'll be a lot different in the winter.  Does the power company buy surplus production during the summer?  What made you decide to install batteries?

[eniacs]

Welder we pay £0.30/kwh on a good tariff so $0.37/kwh. With the energy crisis these figures have more than doubled. I am still on an old tariff at £0.13/kwh, however it does run out soon.

I am on a tariff where we get very cheap night rate electric (£0.05/kwh) so will charge the battery from the grid in the winter and use the cheap stuff during the day. I doubt the solar will put much in for about 4 months of the year. Charging the battery every night will probably be 5-6 months. Not sure yet and will depend on weather.

Power companys can buy the excess but mine isnt setup for that, the payback for this is minimal. I had a solar setup prior to the battery, it made very little difference to my energy bill. Now with the battery, i pay nothing, and will have severely reduced bills in the winter.

[zolotiyeruki]

Your (future) higher electricity rates definitely will improve the economics of your system.

I'm not so lucky.  At work, we have several thousand surplus-but-brand-new high-capacity (3Ah) 18650 cells, which I could buy for $2 apiece.  Each stores 11.1Wh of electricity.  Our electricity rates are about $0.15/kWh.  So, if electricity were free, each cell would have to store/release 13kWh ($2/cell divided by $0.15/kWh) in order to break even.  That comes out to about 1200 cycles.  That assumes charging the cells is free, that the cells are fully charged and discharged each time, and ignores all conversion and efficiency losses, plus the cost of other equipment and permitting and installation, etc.

1200 full depletion cycles is a LOT.  Reduce it so that it only goes from 20% to 80% (in order to get more cycles), and the number of cycles required to break even goes up to almost 2,000.

[eniacs]

Zolo those cells sound a terrible deal. The work involved with turning 18650 cells into a battery is much more than the prismatic cells i used. The lithium in 18650 also only does around 1000 cycles as you say. I would go for the prismatic lifepo4 cells, 6000 cycles to 80% and 80% discharge so payback is still long term, but they last long enough that it is possible.