Valhalla

[dawsonnick]

I am perhaps looking for the impossible or, if not impossible, a system that would be too expensive to ever give a return on the investment.

I am connected to the grid and, with my 21 panels I produce more electricity over the year than I use (or I think I do based on forecasts).

I have a 3kW battery and two strings, one feeding a hybrid inverter and the second micro inverters.

My theory is that if I purchase an additional battery (perhaps 6kW which gives me 9kW) and using CT clamps and RJ45 to link the two strings and thus charge the batteries from the full 21 panels I could charge sufficiently during the day and, at night when the power is less expensive, top up.

In theory this would give me either free energy from solar or lower cost energy from off peak power and I would power the house in this fashion.

The above is my winter scenario as in the summer, I certainly generate more than required so will sell the excess to the grid and run from batteries - probably switching to a cheaper lower electricity rate with no off peak option.

In both scenarios, should the grid go down, I would like to seamlessly run from batteries.

This would include my electric heat pump in the winter.

I would also still like to be able to charge the batteries via solar.

I understand that the design of these systems is such that if the grid goes down, the system is no longer permitted to produce electricity so there would have to be some way of ensuring that the connection to the grid was physically off and controlling the inverter so that power was diverted to the batteries. This may have to be a physical switch.

Is this scenario achievable (or something along those lines) or am I daydreaming?

Thank you in anticipation

Nick

 

[dawsonnick]

Answering my own question here as I know that I can run the system from batteries and top up on cheap rate as required - cost of the battery required to do this may be too prohibitive though but we shall see.

More the point is how to seamlessly manage to switch over to battery power in the event of the grid going down and still charge the batteries during the day.

This is not a regular occurance and has only happened once in the 7 years we have lived here but, in the current political climate, I would prefer to have a working solution.

At present I have a socket by the main electricity panel from which to run a trailing cable.

In my mind, that's not a very workable solution!

 

[binky]

Have a read of the various battery threads on here, I think all the answers are in those somewhere. Seamless transission to battery is not so easy to achieve, although possible. You need some form of automatic changeover switching to isolate the grid supply. These do exist, but I'm not familiar with them, it's the sort of thing hospitals use to kick in their back up generators.

 

[dawsonnick]

Thank you

 

[Bob Smith]

Answering my own question here as I know that I can run the system from batteries and top up on cheap rate as required - cost of the battery required to do this may be too prohibitive though but we shall see.

More the point is how to seamlessly manage to switch over to battery power in the event of the grid going down and still charge the batteries during the day.

This is not a regular occurance and has only happened once in the 7 years we have lived here but, in the current political climate, I would prefer to have a working solution.

At present I have a socket by the main electricity panel from which to run a trailing cable.

In my mind, that's not a very workable solution!

Hi, you are referring to EPS (Emergency Power System), This will kick off in case of a power cut.

Be aware that they are designed to provide emergency power ie depending on your house you may have to create a circuit that includes (lights, fridge, freezer) and this is what the EPS will cover.

I have been told by installers contradicting information about EPS. One told me they can only be manual so in case of a power cut you need to manually turn a switch, while another one told me it is automated.

I am having a new system (PV; batteries etc...) installed (in addition to an existing from 2016) and I decided not to have EPS. 1) They can't cover all your need (you need to decide what you put on your emergency circuit) 2) like you, power cuts are very rare.

As Binky said, your are not alone asking these questions, I was like you too and searching the forum you will find many discussions on that topic.

 

[dawsonnick]

Thank you.

My installer told me that I had to identify what circuits I wanted should the power fail and he would pull them from the electrical cabinet and feed them them through as to a seperate board so that, in the event of a power failure, I could pull a switch and onoy these circuits would be live.

I understand that but want more.

If I have enough juice in my batteries and a big enough battery array to power the house, why not use it?

Why not also use the sun to recharge the batteries during the day?

This is what I would like to have but obviously it is not that straightforward!

 

[Bob Smith]

Letting the sun charge your batteries is, how to put it, the basics

When I looked at the EPS, I too wanted to have all my house covered (including my electrical underfloor heating), I then realise it would not help because even if some batteries will have enough discharge power this would only be for an hour or 2.
Then trying to have enough storage would be very expensive.

I personally weighted the pros and cons (including cost) and decided that for me, 1) I could not afford a system that would cover all my house needs in winter for half day (assuming no power cut last longer), and the risk to have power cut lasting more than 10min was very small, therefore not a cause of concern.

As mentioned, you need to do you own "maths" and see what important to you, what the costs and what you can technically achieve without breaking the bank

 

[michael8554]

You might not be able to find an inverter with a large enough EPS output to power your whole house.

For instance, my 5kW inverter only has a 3kW EPS output.

You can avoid extra "fuse boxes" and changeover switches by permanently connecting maintained equipment to the EPS output.

I have my two freezers permanently on the EPS output, the EPS output remains powered when the grid fails.

Assuming I have enough PV or Battery at the time of course :-<

 

[binky]

10 kw battery, will supply 1 kw for 10 hours, 2kw for 5 hours, and so on, so powering the whole house for any length of time is going to need a very big battery Indeed! The EPS is automatic on grid fail, and will supply whatever is connected to it, but output is limited to give a reasonable battery life. You can do whole house, but you need a changeover switch on the incoming supply to protect whoever is trying to fix the fault, and stop you supplying all your neighbours. There are automatic changeover switches available, but you would have to look for one as I've never fitted any. Personally I would fit a manual unit, that way you know you are on battery only, and can switch off non essential loads, like the jacuzzi.

 

[dawsonnick]

Thank you for your sound advice.

Looks like the Valhalla may be obtainable however at a price which far outweighs the risks or any ROI.

So, best to look at what I have and try to improve things by increasing battery storage and way I use the batteries along with the time of year.

I have calculated that by buying 10Kw of additional battery storage and managing things differently, Incan Dave around 500€ p.a. which gives me a ROI on the batteries of 8 years.

It will also allow me to power a number of limited devices in my house including essentials like the fridge and freezer for most of the day and longer if I get power from sunlight to top up the batteries.

All good news. Have to recheck my figures and confirm the tarriff from the electricity supplier but that won't take long to do.

Exciting stuff - than you everyone who has contributed to this thread

 

[binky]

I've looked at going off-grid for several customers over the years, the numbers just don't stack up, unless you are prepared to live like a hermit .

That was before the recent energy price hikes, but that doesn't change the reality that being self sufficient, especially in Winter is more pipe dream than achievable. For summer, spring and autumn, it's not so hard to do without massive capital outlay, so I would look at that, with a view that what you install will certainly put a big hole in winter bills.

 

[bladerunnerpv]

Hi dawsonnick, you might find this article on EPS helpful...

https://www.deegesolar.co.uk/eps_for_solar/

 

[dawsonnick]

What a well written article.

Thank you for sharing it with me

 

[johnb2713]

I've looked at going off-grid for several customers over the years, the numbers just don't stack up, unless you are prepared to live like a hermit .

That was before the recent energy price hikes, but that doesn't change the reality that being self sufficient, especially in Winter is more pipe dream than achievable. For summer, spring and autumn, it's not so hard to do without massive capital outlay, so I would look at that, with a view that what you install will certainly put a big hole in winter bills.

My next project is possibly going completely off grid, achieved with a few more panels, another 14 kWh of battery storage and the gem that makes it possible a water cooled diesel generator.
The generator I would operate as a CHP plant and that's the secret of making it cost effective. The second aspect of this is using old discarded chip oil and converting it into diesel (I did it years ago for my van using a BioBuddy, simple quick and easy process. The last generator I converted to CHP I used a marine heat exchanger and that worked really well on a 200 kW Volvo powered genny.
Then again, I may just leave it all as is and take the 12.5p kWh on the chin

 

[dawsonnick]

12.5p is a good rate!

I am 0.19€ peak power and 0.14€ off peak here in France!

Plus 19€ a month standing charge for the pleasure...

 

[Bob Smith]

If we had the same type of tariff as in France, I would probably not be investing so much in solar...
Now I do hope that once I get my second system, prices will remain high for at least 10 years (I know it is selfish but when you invest you think of your ROI )

 

[johnb2713]

If we had the same type of tariff as in France, I would probably not be investing so much in solar...
Now I do hope that once I get my second system, prices will remain high for at least 10 years (I know it is selfish but when you invest you think of your ROI )

In my experience with my system before this latest battery my break even point was 3.2 years. It should be even better now.

 

[binky]

If we had the same type of tariff as in France, I would probably not be investing so much in solar...
Now I do hope that once I get my second system, prices will remain high for at least 10 years (I know it is selfish but when you invest you think of your ROI )

The one thing you can guarantee is prices won't go down. Even if the UK suddenly installed a shed load more wind turbines, we will still have to pay for the nuclear power, and that isn't cheap because the government has offered the Chinese a lucrative deal to get them to pay for the investment.

 

[shaunuk]

I put the sort of thing in a few weeks ago that you will be aiming for. It’s inline with the grid connection not in parallel like most inverters. So the main power from the meter goes into a victron 8kw inverter and then from the inverter to the house. If I flick off the mains we can run for 24 hours and don’t need to sacrifice anything. It will even run a 9.5kw electric shower which is the highest current device we have.

We coupled it with 20kwh of batteries. But will be expanding to 32 kWh after new year.

That’s the easy bit.

The hard part is taking the worst day of the year, so that’s today. The ovens been running all day, family over, people leaving every light on all day, easily will suck 20-25kwh. And then trying to generate that much power onsite is hard. I’ve been experimenting with different pannels orientations, flat roof, ground mount and soon on the pitched roof. But you just can’t make enough from Solar on a cloudy day with out a field full of them to cover that much demand.

In the mean time we switched to edf go electric 35 a few months back which is 4.5p over night and 41p in the day I think. The victron can charge the batteries to full in the given 5 hours. Charges at about 68amps I think it’s set for. So we have shifted 90% of our usage to the 4.5p rate.

It’s a great setup but not cheep. Probably thrown 3k in for the inverter. 8k for the batteries, another 2-3 I for solar.

It’s the gold standard of off grid / on grid and backup for grid failure. But even that has me wanting more, this transition to off grid is addictive. And fun

 

[dawsonnick]

Wow. That sounds fantastic and what I am looking for too.

I have enough sunlight here to get away with the panels I have on most days although, December and January (when you probably need it most) it can be iffy.

I will have to cost the whole thing and run some forecasts as my peak and off-peak rate difference is minimal which makes a ROI harder.

Thank you for detailing what you have done.

..and a very Merry Christmas!