Solar hybrid system

[Suited72]

I have a chalet and have an electrician installing an off grid solar system. He's told me to design and supply everything I want and he's going to fit. He fits grid tie but hasn't done an off grid.

I've got

2 x sharp 250w panels
1 x hybrid 4000w off grid inverter with charge controller

PIP4048HS is a 4000w continuous / 8000w surge, 48V DC input Pure Sine Wave inverter-charger featuring:

NEW - max 60A Utility Charging
NEW - total system max charging: 110A (50A solar + 60A utility)
Built-in 50A PWM solar charger
2X Surge rating up to 5 sec
Generator Starter Dry Contact

4 x 105ah batteries
1 x garage type consumer unit

There will be a small AC circuit and a DC for the lighting and a couple of cigarette skt.

I have a few questions
What fuses and or disconnects should I be buying?
Would I be able to run a single electric oven on that?
Do these hybrid inverters make any noise does anyone know?
Would there be any reason not to install all of the components in a plastic keter type shed outside the chalet?

Trying to use as little on gas as possible.. Help appreciated. [/b][/i]

 

[davelx]

What type of battery - you need the "Deep Discharge" type as normal "automotive" types have the wrong characteristics and are not going to work at all well.

12v or 24V system? Let's assume 12V. Battery bank capacity 420Ah.

What is the power consumption of the oven you have in mind?

Let's assume for now 1300W.

so 1300/12 = 108 Amps. Let's assume inverter is 80% efficient.

108/0.80 = 135A current from the batteries.

The quoted battery capacity will be given at the 10 or 20 Hour rate, i.e. they can supply 42A for 10 hours, or 21A for 20 hours. The capacity will be greatly reduced when supplying 135A - maybe to only 50%.

So effectively you have about 210Ah capacity with 135A load - so you can probably run a 1300W oven at full tilt for around 1.5hours from fully charged batteries, a bit longer if the panels are providing some of the power at time.

However, the oven won't be drawing power all the time as the thermostat will cycle once it's up to temperature. Let's say average duty cycle is 33% (I've no idea if that is realistic for the type of oven you have in mind). This will make the load on the batteries intermittent which will improve their usable capacity - maybe to around 70%. Taking this into account the idea looks feasible.

All of the above is approximate, but you get the picture?

 

[bernardgreen]

A pure sine wave invertor may be less efficient than a pseudo sine wave invertor of the same output power so unless the 230 equipment requires a pure sine wave you may have over specified the invertor.

Would there be any reason not to install all of the components in a plastic keter type shed outside the chalet?

Depends where the chalet is, theft is one reason not to have them in a shed outside the chalet.

 

[Suited72]

12v or 24V system?

What is the power consumption of the oven you have in mind?

- The inverter requires a 48v DC input.

- Haven't chosen one, but as an example:
Energy rating A
Energy consumption 0.79kwh
Logik model LBFANX14

From that I don't know you can tell the peak consumption isn't higher than the inverter Maximum? Thanks

 

[davelx]

12v or 24V system?

What is the power consumption of the oven you have in mind?

- The inverter requires a 48v DC input.

- Haven't chosen one, but as an example:
Energy rating A
Energy consumption 0.79kwh
Logik model LBFANX14

From that I don't know you can tell the peak consumption isn't higher than the inverter Maximum? Thanks

As you say, the energy consumption figure isn't that helpful - you need to know the electrical load in Watts.

You can plug your figures into the calculations I've show above. If you can get the discharge curves for the specific batteries you are looking at you can use them to determine the effective capacity at the relevant load currents - but it will still be an approximation as the real-life load is so variable.

As said above, a "modified sine wave" inverter may be more efficient if your proposed loads are happy with that type of supply (a fanless oven should be ok - synchronous motor fans may complain)

 

[Suited72]

What type of battery - you need the "Deep Discharge" type as normal "automotive" types have the wrong characteristics and are not going to work at all well.

12v or 24V system? Let's assume 12V. Battery bank capacity 420Ah.

What is the power consumption of the oven you have in mind?

Let's assume for now 1300W.

so 1300/12 = 108 Amps. Let's assume inverter is 80% efficient.

108/0.80 = 135A current from the batteries.

The quoted battery capacity will be given at the 10 or 20 Hour rate, i.e. they can supply 42A for 10 hours, or 21A for 20 hours. The capacity will be greatly reduced when supplying 135A - maybe to only 50%.

So effectively you have about 210Ah capacity with 135A load - so you can probably run a 1300W oven for around 1.5hours from fully charged batteries, a bit longer if the panels are providing some of the power at time.

All of the above is approximate, but you get the picture?

That's great and really helpful, I'm trying to get my head around the fundamentals of all you've said. The batteries are leisure type deep discharge. Ideally I want to stick to 20-50% maximum discharge range.

I guess if the drain is too high I can go for another 4 batteries. This would still be cheaper than buying a gas oven and changing 47kg propane. Also it justifies the cost of the solar add Il save on gas over time's

Should I have any fuses for safety?

 

[bernardgreen]

There are some small ELV electric ovens that operate on 24 volts DC. Using one of these would remove all the inefficiency of the invertor.

Probably to be found in suppliers of equipment to transport fleets or camping / leisure activists

For starters ( and the main meal )

http://www.roadking.co.uk/mobile-12v-and-24v-microwave-ovens.html

 

[davelx]

Should I have any fuses for safety?

On the AC side you would use the garage consumer unit as normal. Remember that you will need to fit earth stake(s) so that the RCDs on the AC can operate reliably. You can't guarantee that the AC side is totally isolated from earth, so you need to have it properly earthed.

On the DC side: I'd fit battery isolator switches so that you can totally disconnect the batteries from the inverter and other loads and the panels. Most inverters should have suitable DC fusing built in (eg Victron do). Otherwise suitably rated industrial fuses in a suitable enclosure. Similarly you should fuse all the DC circuits appropriately -suitable fuse boxes are available from Automotive or Marine suppliers, also from places like RS or CPC-Farnell.

I would think the that solar panels and control components either have fusing built in, or the installation manuals will detail what is required. They will probably also show the required isolators.

 

[davelx]

There are some small ELV electric ovens that operate on 24 volts DC. Using one of these would remove all the inefficiency of the inverter.

Probably to be found in suppliers of equipment to transport fleets or camping / leisure activists

For starters ( and the main meal )

http://www.roadking.co.uk/mobile-12v-and-24v-microwave-ovens.html[/QUOTE]

One thing to bear in mind if you go down this route is that, since you will have your 4 batteries in series to give the 48V for the inverter, putting a heavy load such as an oven across just 2 of those batteries (24v) will give uneven discharging, which will make charging them as a 48V bank problematic and may result in damage to the other two due to over-charging.

You need to try to keep the load on all four batteries balanced - eg you could have 2x24V or 4 x12V dc circuits spread across the four batteries, and then select the load supplied by each to even out the discharge rates.

If you could find a 24V oven that has two 24V elements that could be connected as 24V-0V-24V that might help you to balance the load (the elements must be fully isolated from the chassis or you could short out the battery bank!)

 

[Suited72]

I'm definitely not expecting to go with a DC oven.

I've tried to use your equation based on a 48v dc input to the inverter. Worked out the dc current loading to be 34amps- so am I right in saying that gives me 10 hours halved? So 5?

 

[JohnD]

I believe you may find a 24v wet and dry vehicle cooker on the military surplus market.

It might not be very elegant.

Have a look here
http://whitelabel.globalauctionplat...5c5-d099-4488-a509-a47500e97465?clienturl=wca

http://www.mod-sales.com/auction/

 

[JohnW2]

I'm definitely not expecting to go with a DC oven. ... I've tried to use your equation based on a 48v dc input to the inverter. Worked out the dc current loading to be 34amps- so am I right in saying that gives me 10 hours halved? So 5?

A DC oven and an AC oven with an 100% efficient inverter would, for a given oven power, require exactly the same current from the batteries. As has been said, since inverters are far from 100% efficient, you'd actually require less current from the battery (for a given oven power) if you used a DC oven.

Kind Regards, John

 

[davelx]

I'm definitely not expecting to go with a DC oven.

I've tried to use your equation based on a 48v dc input to the inverter. Worked out the dc current loading to be 34amps- so am I right in saying that gives me 10 hours halved? So 5?

Sounds about right.

 

[ericmark]

I have had problems with DC to AC inverters when using cheap types. The inverter had a row if 16A automotive blade fuses one for each FET. When all are OK it worked OK but if a fuse blows then there was no indication it had blown until the expensive blue smoke escaped. I think the main problem was load sharing and since your using 48 volt not 12 volt the problem should be reduced.

However I would say you need a battery isolator so with a fault you can turn it off quickly.

You need 24 cells likely as 4 batteries but you need to consider weight and having all cells in series is better than having some parallel cells as well so better to have 8 x 6 volt batteries than 8 x 12 volt batteries. Much again depends on what load but personally I would be looking at a standard battery rather than anything special and I expect most likely to fit the job would be a fork lift battery. These are often built from single cells so if a cell goes down you can just change one.

Although a 110AH vehicle battery may be rated 110A for traction batteries a 110AH is likely rated at 22A so your oven at 1300W will draw around 30A so it would need around 220AH of batteries. So looking at something like this

now these are very heavy in the fork lift this is an advantage without the batteries they would need to add weights but you need to physical get the batteries to where they are to be used.

In the main traction batteries are designed to be discharged in 5 hours or more. So AH/5 = planned current draw. When I set up a farm using batteries we realised the cost of the batteries was the main problem. He bought an old bus then stripped and used bus as green houses sold engines and used the NiIron batteries in the farm house. It is likely old fork lift, bus, of milk tanker batteries will be the cheap option.

Buses often do not have standard vehicle batteries the batteries are designed to allow the bus to park for some time with all lights on and heaters running without the engine so batteries are far bigger than used in a truck and are designed for deep cycle. The same applies to milk tankers the batteries are huge to allow them to suck in the milk with wagon engine off.

I have looked at solar panels for boats and quickly realised great for keeping battery topped up when not on the boat or using some lights. But for any heavy use the best was a generator. A battery in a boat should last around 7 years, but walk any tow path and you will be told lucky to get a year out of them. Milk float do get 7 years so it's not the battery at fault but the way it is used.

Flatten a battery over night and fully recharge next day and all is good. But if it waits a day before being recharged then not quite so good and remain flat for a week and battery will suffer. What happens with boats is the first 80% of charge gets banged in but never quite get that last 20% and battery gets flatter and flatter until they arrive at a huck up point when it gets fully re-charged.

Now the narrow boats with twin alternators and the sterling battery pulse charger are really pumping power into the batteries often 180A to start with but the 5 hours the engine is running is not long enough. As a result they fit solar panels and wind chargers to try and give the battery that little extra.

I would take a walk down the tow path and ask narrow boat owners. Hire boats rarely have solar panels so with solar panels it's their pocket so they have an interest in learning about them.

If it were me I would use a small solar panel to work lights but use a generator for things using any more power than a laptop.

 

[Suited72]

Should I have any fuses for safety?

On the AC side you would use the garage consumer unit as normal. Remember that you will need to fit earth stake(s) so that the RCDs on the AC can operate reliably. You can't guarantee that the AC side is totally isolated from earth, so you need to have it properly earthed.

On the DC side: I'd fit battery isolator switches so that you can totally disconnect the batteries from the inverter and other loads and the panels. Most inverters should have suitable DC fusing built in (eg Victron do). Otherwise suitably rated industrial fuses in a suitable enclosure. Similarly you should fuse all the DC circuits appropriately -suitable fuse boxes are available from Automotive or Marine suppliers, also from places like RS or CPC-Farnell.

I would think the that solar panels and control components either have fusing built in, or the installation manuals will detail what is required. They will probably also show the required isolators.

Just to update, the install went very well. Thankyou.

To give help to anyone searching info on off grid systems:

The PIP4048 range of off grid inverters are nothing short of amazing. I thought for £500 on a 4000w inverter compared to victron at £1700 I was going to end up with some flaws. A lot of people tried to put me off including the electrician, don't be.
- The 4kw inverter & batteries needs to be connected up with 25mm cable. This was difficult to get locally for me. You also need 25mm rated ring terminals to connect to the inverter,
- Test your earths. As davelx pointed out above, 1 wasn't enough for my system. The ground is terrible and I've ended up with 4.
- the inverter unit is fused

If anyone is planning similar in the future feel free to ask me how I'm getting on with it. Or any other concerns.