I am new to all this and looking for feedback on my 'off grid' system

[dangermouse]

Hello everyone,

I'm new to the idea of running my home from solar power, I've been lurking on these forums for a while and I've already learnt a lot, so thanks to everyone who posts so much great information and thanks for letting me join.

I've been thinking about going solar recently, and I've come up with a design for an "semi off grid" system that I think would work for my situation.

I've got a small house (2 bedrooms) and we use about 5kWh of electricity a day. Heating is from a combi boiler so about 50% of my energy spend goes on gas, and I think the only realistic thing I can do to reduce that is buy a newer more efficient boiler.

My idea is based around the Victron EasySolar II. Basically the plan is:

- 2400W of PV panels on the roof - that's all that will fit.
- EasySolar II as the hub of the system
- 5kWh of batteries charged from PV. Haven't decided yet whether to go for AGM or Lithium batteries.
- Fit a new consumer unit alongside the existing one, and move most of the house circuits to the new unit.
- Power the new CU from the inverter.
- Leave the 2.5kW electric oven and smoke alarm circuits on the mains powered CU.
- Add another output to the existing CU with a timer switch that connects mains to the Victron overnight, to charge batteries on Economy 7.

I get the impression that feeding power back to the grid is not really worth it, especially with only 2.4kW of panels, so I'm not bothered about that. The EasySolar can apparently be programmed to disable grid feed, and it would only be connected to the grid at night anyway.

Basically the entire house, except the oven and the smoke alarms would be supplied from the inverter. I would probably plug my freezer into the 13A socket on the oven switch, at least in the short term, until I know that the batteries won't die during the day.

Obviously the most important question I have to ask is - is this a sensible idea?

More specific questions I need to consider:

24V or 48V batteries? I think that the 3kVA inverter will be enough, but there is a 5kVA version that only accepts 48V.

Is is feasible to expand the system in the future by adding more batteries and a second stand alone inverter? Probably with yet another CU, and distribute the house circuits between CUs as appropriate. Actually on reflection it's probably a better idea to buy the 5kVA inverter in the first place.

Most important detail I don't really understand - how to earth the new system? Can the inverter fed circuits share an earth with the mains? I see the EasySolar includes an earth relay but I don't really understand the use of this.

Many thanks for any advice you can offer!

Edit - It occurs to me that this is more of a "battery storage system with a bit of solar" - a fair amount of my power will be coming from Economy 7 rather than the solar panels. So apologies if I've posted in the wrong section.

[Stinsy]

You’re reinventing the wheel and have come up with an expensive and over-complicated solution!

1) Buy a hybrid inverter from: Solis/Solax/SoFar/whoever for half the price of the EasySolar.

2) There is no need for separate CUs for on grid/off-grid circuits, timer switches, or anything else you’re imagining. The hybrid inverter will charge the battery on cheap-rate or solar, will monitor power flowing to/from the grid and will adjust its charge/discharge rate in real-time to target zero import/export during peak period.

2) Lead is dead. LiFePO4 has been the standard choice for years. The lifespan, DoD, maintenance, efficiency, of Lithium just outclasses lead so very clearly.

[Tinbum]

Ditto.

If you want an off grid / power cut supply many inverts as above do EPS, just add a relay, as mentioned in many post on here.

[Oldgreybeard]

As above, there are simpler and well-proven ways to do this. I opted for pretty much the cheapest budget solution, although I already had 6kW of PV that had been on the roof for about 6 years when I opted to add batteries. I bought a Sofar ME3000SP battery inverter, (cost me about £400 as unused old stock, 2 years ago) that will work with or without solar panels. In summer we charge the batteries almost entirely from excess solar generation. From around mid-October through to about mid-March the batteries get charged from off-peak electricity, using Economy 7.

The net result is that we don't really use peak rate electricity at all. Our average peak rate electricity usage over the past year has been about 2kWh/month. We have electric heating and hot water and run an electric car. From about March to October we run the car for free as well (charged it yesterday and today for free, it's now fully charged with a couple of hundred miles of free driving stored in its battery).

In terms of batteries my system is overkill, 6 off Pylontech US3000C's rated at about 3.5kWh each. Usable capacity of these 6 batteries is a bit under 18kWh. Lead acid batteries are hopeless, you will be lucky to get a usable capacity that is more than half the the rated capacity, might drop to 1/3rd the rated capacity for high load current. To get 5kWh of usable capacity using AGM you probably need to install around 12 to 15 kWh of rated capacity.

The downside at the moment is that every man and his dog has decided that installing solar panels and batteries is a good thing, so prices haver risen a great deal over the past 12 months. Back when I bought my battery packs they were under £1,000 each, inc VAT, now they around 40% more expensive, just because demand has skyrocketed this year. Same goes with inverters, they are now selling for around 50% more than they were 18 months ago. Delivery lead times have also increased. When I bought all the bits I needed the delivery times were between 2 and 3 weeks. Now they are perhaps closer to 4 to 6 months.

[nowty]

Ditto, Ditto………………

Welcome dangermouse, I really don’t want to offend you here but,

Obviously the most important question I have to ask is - is this a sensible idea?

The answer is very much no I’m afraid. I would say you seem to want to make your life really complicated for very little benefit. You seem to have gone down the classic rabbit hole of finding a solution before understanding what you need.

Personally, I would forget any idea of going off grid or semi offgrid, especially with a small 2.4kW of solar and a small 5kWh battery. We have things called grid tie inverters which are much better and some are hybrid, so they can take both solar panels and batteries. And some even have Emergency Power Supply backup if that’s what you want.

Lithium batteries over AGM every time, I guarantee you will regret a decision into lead acid land in the long run due to longevity, efficiency and operational performance.

Read Stinsy's post if you want the short version.

Don’t run away though, we are very friendly.

[dangermouse]

This is exactly the feedback I needed, thank you all for replying.

Sometimes you get the wrong answer because you are asking the wrong question, and I think that's what I was doing.

I will investigate hybrid inverters, I had seen mention of these devices but hadn't grasped their capabilities.

Thanks again all, I will post some more once I've got a more sensible idea!

[Stinsy]

This is exactly the feedback I needed, thank you all for replying.

Sometimes you get the wrong answer because you are asking the wrong question, and I think that's what I was doing.

I will investigate hybrid inverters, I had seen mention of these devices but hadn't grasped their capabilities.

Thanks again all, I will post some more once I've got a more sensible idea!

Sorry if I, or anyone else, came across as unnecessarily blunt! I hope you've spent enough time lurking here to understand that, as a group, we have real knowledge and experience and we were not ripping your plan for the sake of it or to feel superior. You'd gone down the wrong alley, so making the post and sharing your plans has saved you a lot of: time, money and heartache!

Everyone and his dog has gotten interested in solar/battery systems in the last 6 months, so getting bits can be tough, you might have to chose equipment based on what you can get ahold of rather than on the specs. But here is what I'd suggest as a starter:

• Inverter - SOL-3.6K-RHI-48ES-5G-DC - £1200

• Batteries - 2x Pylontech US2000 @£1000 ea - £2000

[Oldgreybeard]

Well worth doing as much research as you can, and trying to add some bounds to each requirement.

For example, you mention using about 5kWh per day. If that is how much you need to be able to use from the batteries then they will need to be larger than that, both because the rated capacity is never the actual usable capacity and because batteries have a much longer cycle life if not always run from fully discharged to fully charged.

One winter option, when solar generation won't be that useful for a fair bit of the time, is to switch to a time of use electricity tariff and use the battery to run the house during the day, charging at the off-peak rate overnight. At the moment this strategy can just about halve electricity costs, so is worth looking at.

I'd also caution against being overly optimistic about the solar generation. The reality is that it tends to be patchy and there is a great deal of variability through the year. Our own PV generation (south facing 6kWp array) falls off a cliff in October each year, and we don't really start to get useful generation again until about March. The winter PV is useful, but nowhere near enough to run the house, whereas is summer there is more than enough to run the house, charge the car and have spare generation to export. The PVGIS tool is very useful: https://re.jrc.ec.europa.eu/pvg_tools/en/ and will give a reasonably good estimate if the data put in to the form is accurate. That should give you a feel for how many kWh your proposed PV system will generate each month.

Finally, there are some good suppliers around, but equally there are some who have jumped on to the bandwagon recently, as the demand for PV systems and batteries has risen, so it pays to be aware that there are one or two less than scrupulous installers around.

[dangermouse]

Sorry if I, or anyone else, came across as unnecessarily blunt! I hope you've spent enough time lurking here to understand that, as a group, we have real knowledge and experience and we were not ripping your plan for the sake of it or to feel superior. You'd gone down the wrong alley, so making the post and sharing your plans has saved you a lot of: time, money and heartache!

Don't worry, it wasn't. I made the post to get advice, and I got the advice I needed!

Everyone and his dog has gotten interested in solar/battery systems in the last 6 months, so getting bits can be tough, you might have to chose equipment based on what you can get ahold of rather than on the specs. But here is what I'd suggest as a starter:

• Inverter - SOL-3.6K-RHI-48ES-5G-DC - £1200

• Batteries - 2x Pylontech US2000 @£1000 ea - £2000

Thanks, I've been looking at those products on the Bimble web site, they do sound like what I need.

More questions, if I may:

For the inverter, the 3.6kW in the description refers to the grid output power? Why not save a few quid and get the 3kW version, if I only have 2.4kW of PV? Then again, it really is only £35 difference.

Why not buy a single Pylontech US5000, which has the same capacity but lower price compared to 2xUS2000?

Can I mix and match the batteries? For example use a US5000 and a US2000 to give a total of 7.2kWh?

Are Bimble a good place to buy from, generally?

[dangermouse]

Well worth doing as much research as you can, and trying to add some bounds to each requirement.

...

One winter option, when solar generation won't be that useful for a fair bit of the time, is to switch to a time of use electricity tariff and use the battery to run the house during the day, charging at the off-peak rate overnight. At the moment this strategy can just about halve electricity costs, so is worth looking at.

Yes, I've checked and my current energy supplier (EDF) will fit an Economy 7 meter for free. And I understand that the Solis inverter that Stinsy recommended can be programmed to only charge from the grid during certain hours (I think - I downloaded the user manual and that's what it seems to say, but it's a bit ... Chinglish).

Thanks again for everyone's feedback.