Home DC lights, is there a standard?

I have recently had PV solar installed and currently it is not economical to install a full set of batteries. So I was thinking about having a smaller battery system to operate the lights in the house as most are LED now, is there a standard for DC low voltage lights that can easily (& safely) be retrofitted?
I then plan to replace some of the lights with the "standard" low voltage LEDs and drive them from a solar powered battery system.

freddyuk

A couple of observations
Having already got LED is great and cuts your lighting loads by around 70-80% so the power load is already much lower than before. If you then want to run these off batteries you are actually going to find the expense of batteries will not be offset by the savings if that makes sense? I fully understand what you want to do but it is an expensive way to do it.
If you want to run 12 volt lighting you will need very large cable so it will not work around the house so it makes sense to plan your off grid aspirations by using a proper 48 volt system. You then run everything off 230v so it all works as normal. I know it's hard thinking you can easily edge gently into off grid but in fact it is not really that easy in the home but OK for a small building or other installations.
Most LED do run on low voltage but often via a 230v transformer in the home!


I would invest the money in a PV diverter to your immersion heater which will use your surplus PV power to heat the water rather than charge a battery to run the lights which cost virtually nothing to run. If you have payments from EI these will soon stop but if you missed out I would do it now and not be exporting free power to the network. You will need to possibly change your immersion heater for maximum benefit.
Once the electric bills start to rise with inflation we may find the solar/battery option becomes slightly more economic.

I wasn't really looking to go off grid, more to avoid giving away surplus electric to the ESB for free, I already have solar thermal but it may still help to add a PV diverter as I have a large buffer thank that the solar thermal can't heat completely.

What is a "proper 48v" system? I know that there is a PoE (power over ethernet) standard for VOIP phones that are powered by the network switches ( I work in IT) but is this standard extended into lighting as well.

In the long term I will be looking to reduce the bills as much as possible during retirement so I am less worried about spending extra now if there is a long term benefit.

freddyuk

That was my point as you are going to spend more than you save in fact by buying batteries for a very cheap load.

If you run 12v then the voltage drop will be significant so it does not work for larger installations even for lights. You would run a 24v or 48v system where the DC is 48v (4 x 12v batteries in series) going into an inverter charger giving you standard grid power at 230v.
You cannot directly integrate a battery based system with your existing grid system as this is illegal. Having a PV diverter is the best option at the moment. If you have 4kw of PV and 30 tubes of thermal then 500 litres of storage would cope. You just need to make sure the water is a usable temperature by good system design. You need immersions/coils in the correct places.
If you are not familiar with battery systems I would recommend attending a course which many manufacturers/suppliers offer as it is a completely different technology with inherent dangers.
You cannot really add to a battery system so it needs to be planned from day one.
I would build on your low energy lighting by keeping as much power on site as possible by adapting lifestyle.
Make sure all appliances are A rated as an old fridge/freezer can eat power so by investing in a modern 'A' rated unit savings are instant and long term and will be far more benefit than a battery LED system.
LED TV's and monitors etc. Turning off Routers at night all save a lot of power and thus money.

The inverter that we have has been designed to take an optional battery charger module so that option is available when batteries become cheaper. I expect there will soon be an after market for all the EV batteries that have dropped below the 80% range that the car is specified to have, these should provide a good few years of operation in a domestic setting before deteriorating too much.

We have already deployed a few energy saving (well load shifting) techniques, like always running the washing & dishwasher and other power hungry appliances near midday whenever possible. This Is where I expect to make the greatest savings.

You may find your inverter modules are for lead acid charging not an EV Ni-Cd/Li-Ion. If you know where to look you can get cheap/free batteries that aren't tippy top but can be serviceable.

For what it's worth the efficacy on mains leds seem much better than that of the low voltage. At least comparing Philips anyways. See pages 7 versus 8 here.

Extra low voltage DC distribution doesn't make much cents in a house, it's much more cost effective run it through an inverter and feed existing circuits from that on some form of changeover.

whizbang

Interesting comparison between 12v and 230v leds there. Not sure its correct to read it that way tho'.

Running your 12v through an inverter (70%?) and back to DC led drive is not any more efficient than direct DC.

Cable for 5A is cheap, and easily come by.
Whats the capital cost of a decent inverter?
If you can source some cheap batteries, a simple DC system is a whole lot more cost effective.
Doesn't take much in terms of cost. 10Ah battery will run 30W of led light for 3 hours. That's enough for a kitchen and living room for a family.

No chance of washing or ironing from 12v, so I don't see the point of an inverter. You may need to be creative about supplying a 5v USB type charging system.
Laptops could be a problem...

freddyuk

I agree that converting AC to DC and back is not cost effective.
Can you elaborate your calculations for running 30 watts of DC into living room and kitchen using "cheap" batteries? Are we talking old car batteries here?
Exactly what cable calculations did you do to come up with this solution? (bearing in mind the battery would not be in the middle of the kitchen or living room). You would not get far due to 12volt voltage drops.
How were you recharging the battery every day for this cheap system?
Would 3 hours of light be any good in winter?

whizbang

whizbang wrote: »

Interesting comparison between 12v and 230v leds there. Not sure its correct to read it that way tho'.

Modern Inverters are listed as 90% efficient in the factory under controlled climate conditions with forced air ventilation, a nice steady pure square wave input at a rated load with unity power factor, real world conditions will vary.
This inefficiency will possibly be offset by light efficacy...maybe...close though.

whizbang wrote: »

Running your 12v through an inverter (70%?) and back to DC led drive is not any more efficient than direct DC.

Correct so run "AC" Leds instead.
Use direct DC in the battery storage room if you want. Although 48V would be more sensible so I'd but the leds in series x4.

whizbang wrote: »

Cable for 5A is cheap, and easily come by.

Cheaper still use the existing cable and a switch.

whizbang wrote: »

Whats the capital cost of a decent inverter?

Second hand not a lot. About €1 - €2 per watt for a battery inverter iirc.

whizbang wrote: »

If you can source some cheap batteries, a simple DC system is a whole lot more cost effective.

After you pay to install an isolated extra low voltage system? Double up on fixtures and switches? Or commit to a 12v system that only lasts 3 hours before you get the candles out? Or use mains to charge a battery while it runs the lights...that's a 70% efficient round trip.
You can run the same circuits on optically isolated solid state relays but not according to building regs.

whizbang wrote: »

Doesn't take much in terms of cost. 10Ah battery will run 30W of led light for 3 hours.

OK realistically you want a 48V battery to reduce cable costs. Yes 12v can run tiny loads but there's no economy other than efficiency. To justify the expense you want some big returns. the battery will derate over time and temperature so you need to make an allowance for the Winter with an 8 hour lighting demand to 50% discharge or 10% if you know what you are doing not 100%. To cover a 100W base load that's 100w / 48 (volts) *24 (hours) :50 Ah let's call that 70Ah to allow for derating. So you need a 150Ah 48V battery that'll last 3ish years or an 800Ah battery that'll last 10 and so far it's just running a few leds in Winter, some light loads and some more in Summer.

Whereas with an inverter you can changeover when you want or stick it on ebay when you get fed up.

If you want to run appliances direct from battery you need to purchase a selection of regulators to protect them from voltage charge/discharge fluctuations as they all only come with mains supplies.

whizbang wrote: »

No chance of washing or ironing from 12v, so I don't see the point of an inverter. You may need to be creative about supplying a 5v USB type charging system.
Laptops could be a problem...

Possible but you have to think bigger. Laptops/USB look at the auto/marine-market.

whizbang

Nice one, Sir Liam, I haven't get the same verbosity..

My system was primarily to provide young kids with light when the mains went out. Up till about 3years ago this was a regular occurrence.

You can run the same circuits on optically isolated solid state relays but not according to building regs.

This is probably the real question (sorry op!)

OP is looking for a way to use surplus energy not charge a 120Wh battery.

Here's one I prepared earlier.

freddyuk

If OP wants to SAVE money just divert the surplus power from the PV into something useful and easy without any safety or certification issues. LED lights off your existing system are using minimal power now so savings already made and you have in fact more surplus power to use on site! There are systems that will switch loads automatically when solar is in surplus and I think this is the way forward if there is no export payments on the horizon. So save the savings for a full home management system (which is modular) so you can add new controls as and when funds are available. Check what thermal storage capacity you have and see how much you may need to offload elsewhere. Ensure you are using all the storage and not keeping half a tank of cold water at the bottom. What is spare may be minimal except on those wonderful sunny days in the typical Irish summer when everything is boiling.

Yes my primary objective is to divert surplus electricity into storage rather than giving it away, I'll look into the diverter systems and maybe attach an immersion or use it to charge garden lights and the like.

I'll just continue with the process of replacing all the lamps with LED units, still a few more to go, just wanted to investigate the option of a low voltage system first.

A large scale battery charging system is just too expensive at the moment.

Do you know if there's such a thing as an immersun device for running a well-pump Freddy?

freddyuk

At the moment they are only good for resistive loads. What we could do with "any load" diverter!!
I have been involved with a diverter unit which switches any load power when surplus PV is available but the quality was not good enough and not proportional control. However keep the faith as something will be available soon.