Very small solar power system for sleepout

Forums › Home Workshop DIY › Very small solar power system for sleepout

redfiat

57 posts

Master Geek

#233604 24-Apr-2018 11:23

I've got a sleep out with no mains connectivity.

I was thinking of using solar power for this.

Most of the solar companies I've talked to have a minimum kit that costs $6000+++

All I want to do is power 6 LED light bulbs, a laptop, a desktop fan and a few other small appliances.

I believe I need something that can supply up to 400W.

Even if I went up to 1kwh system I think I'd have more than enough.

Any recommendations on what I'd need and where I can get it from please?

(i've looked at jaycar/burnsco/supercheap - they all seem to be 12v/24v systems rather than mains 230v supply)

Thanks.

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539 posts

Ultimate Geek

#2001504 24-Apr-2018 11:33

for solar you will need, the panels, battery, to store the power, a controller for the solar panel so battery does not blow up when overcharged, and then an inverter to go from 12v dc to 240v ac - all this start to add up, best bet is to talk to your local motorhome / RV place and ask them as they do it all the time for caravan/motorhomes at the scale you want it for.

PS alot of the stuff you want it for will work with 12v dc too, just need to get the right charger etc for laptop, light are fine at 12v, again motorhome place will have heaps as there light is 12v.

redfiat

57 posts

Master Geek

#2001534 24-Apr-2018 12:05

Thanks for the reply, I got this far and was hoping someone might recommend a particular set of products :)

Spyware

3761 posts

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Lifetime subscriber

#2001539 24-Apr-2018 12:16

That cost around $6K.

wellygary

8312 posts

Uber Geek

#2001548 24-Apr-2018 12:25

laptop, a desktop fan and a few other small appliances.

its the battery and a desire to run 240V appliance that cause your biggest expense here,

12V LED lighting is no problem and can be done for not much, but what appliances are you talking about specifically?

redfiat

57 posts

Master Geek

#2001553 24-Apr-2018 12:35

I've a 85amp hour battery out of a caravan already.

Appliances are going to be a radio, a desktop die cut machine (cannot find wattage but it will be similar to a printer), sewing machine and a desktop fan.

The fan is likely to be on for 2-3 hours per day as with the radio.

Other stuff is only going to be used for minutes at a time, and never at the same time.

timmmay

20574 posts

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#2001559 24-Apr-2018 12:39

Laser printers can have a very high power draw.

redfiat

57 posts

Master Geek

#2001560 24-Apr-2018 12:41

timmmay:

Laser printers can have a very high power draw.

Probably an ink jet printer. If printer to high that can be kept in the main house.

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Ge0rge

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#2001565 24-Apr-2018 12:44

Watching with interest. Currently I'm looking to do something similar to run all my network equipment - we have frequent power outages and I've got a source of 115Ahr batteries.

Plan at this stage is to run two batteries in series to make 24v. An inverter will provide up to 600w of 230v power for devices that I can't run from dc buck converters.

I have two separate 12v battery chargers that will maintain a battery each (will get significantly longer life from the batteries this way rather than one 24v charger). Essentially it's a home made ups, but I have power in the building where the gear sits so a little different to what you are looking at. I can look to add solar to this at a later date. Rpi will monitor voltages, and be able to turn devices on/off through dc relays remotely as required for power management.

Yes, I could just buy a large ups, but where's the geek in that?

Aredwood

3885 posts

Uber Geek

#2001924 24-Apr-2018 21:21

Contact AA Solar in Silverdale, Auckland. From my limited research so far. They have good pricing and can put a package together for you.

https://aasolar.co.nz

I have only dealt with them for buying a 270W solar panel. But will probably buy more from them later.

Aredwood

3885 posts

Uber Geek

#2002003 25-Apr-2018 00:51

@Ge0rge Make sure that the dc-DC converters that you are using have over voltage protection. Otherwise add your own over voltage protection. You don't want all of your networking equipment to be destroyed by a failed buck converter.

Have made a shunt regulator for my own setup. Doesn't use any power at 12V. But starts conducting at around 12.5V and conducts lots of power at 13.2V It will quench but otherwise ride through short spikes. And if an over voltage situation happens. It will either disconnect the power itself, or blow a fuse which will also disconnect the power.

raytaylor

4014 posts

Uber Geek

Trusted

#2003703 27-Apr-2018 18:47

Load or power consumption

Assuming 4 hours per day of

- Laptop 70 watts
- Fan 50 watts
- LED light bulbs 60 watts
- Radio 10 watts

Assuming 1 hours per day of

- Printer 100 watts

========================
860 watts per day total
========================

Battery capacity
We dont want to get too fancy so we are going to use Sealed Lead Acid. (SLA)
There are other technologies such as lithium and PB-C etc but let just keep it cheap and simple for now.
Do not use unsealed batteries that require topping up with water. Its just not worth the risk and they are easy to damage.

Voltage will be 12 volts to keep it simple.

860 watts divided by 12 volts = 72 amp hours.

We also dont want to discharge the batteries more than 10% per day. A standard SLA battery should be good for about 600 cycles if they are discharged by 10% each time. If you discharge them more than 50% each time, the cycles drops to about 50 so its important to keep the discharge as shallow as possible.

So if the battery was sized at 720 amp hours, a 72 amp hour daily discharge also happens to equal 10%
======================================================
This means we should size our battery bank for 720 amp hours or higher at 12 volts.
======================================================

Solar Panels

The solar panels must capture enough power to recharge the batteries, and provide enough load.

We also tend to oversize our solar panels so if its raining, they can still capture some energy and provide at least enough for the load. A typical rate is approx 20% of their nominal capacity on a rainy or overcast day.

We are also going to assume the panels are facing north on a 45 degree angle, with no trees or shadows for any part of the day.

For small systems these rules tend to work quite well.

The load is 860 watts per 24 hour period, but we need to capture that in 8 hours on a rainy day.
So 860 watts over 8 hours is 108 watts per hour.

But we still need to capture that on a rainy day when the panels are capturing only 20% (One 5th) of their rated capacity. That means we could assume approx 540 watts of solar panels will do the job.

===============================
540 Watts of solar panels
===============================

Providing Power

You may want to use 12v DC LED bulbs for the lighting for simplicity reasons and you dont need any qualifications to wire them up. Put a switch between them and the batteries.

The inverter is what converts the 12v power from the batteries up to mains voltage so your appliances can easily use the power.
It needs to be a pure sine wave inverter so you dont get interference noise coming from your radio or laptop.
Assuming also that your appliances are not high draw such as a hair dryer or vaccuum cleaner then 1000 watts is an adequate rating for your inverter. The inverter needs to be capable of supplying the combined total amount of electricity your appliances could be drawing at any one time.
From the appliances I have listed above, that is 300 watts.

We also need to multiply the instantaneous load by 3x as inverters always advertise a claimed a higher rating than reality. So a 900 watt inverter at minimum.

================================
1000 watt pure sine wave inverter
================================

Solar Controller
You will need an MPPT solar controller rated for your total number of watts in the solar panel array (rounded up to 600 watts) divided by the voltage of the batteries (12 volts) which in this case is 50 amps.
Up until now thats been great except solar controllers over 40 amps start to get expensive.

There is something we could do by re arranging the batteries to make them 24v but im going to continue suggesting we keep it simple and instead we will drop the solar panel array down in size, and add an extra battery to make up for it. This will help prolong the life of the batteries anyway while keeping the cost slightly lower.

======================
50 amp solar controller
======================

Now the Parts List

AASolar

3x 150 watt solar panels (450 watt array)
5x C12V156 12v 156ah deep cycle battery (12v 780ah bank)
1x Tracer MPPT 40A solar controller (Get the A series, not the BN series)

Solar panel roof mounts and cables appropriate for 40 amps. This will probably mean a pair of cables for each panel.

Jaycar
So you have two options there for the inverter.
I highly recommend you get this one https://www.jaycar.co.nz/2000-watt-12vdc-to-230vac-pure-sine-wave-inverter/p/MI5710

It means you will be able to temporarily use an appliance that draws more power, and is a great price.

But you could also use this and not use the solar controller part
https://www.jaycar.co.nz/1000w-pure-sine-wave-inverter-with-30a-solar-regulator/p/MI5722

The jaycar solar controller+inveter all-in-one units are not MPPT and this means if its cloudy you wont capture much energy at all from the sun. The 30A controller portion is also not big enough for the array you need. Which would mean again dropping down by two panel sizes to 100 watts x3 and then doubling your battery bank size again to make up for it.
They are more suited for charging at a slower speed, and then only being used as an inverter maybe one day a week rather than 5 days a week because the solar controller wouldnt be able to keep up with the load you are drawing off the batteries.

So using the jaycar all-in-one unit would be a lower price and you only need to use the inverter part. The solar controller part can still be done by the Tracer 40A MPPT A Series controller I recommend from AASolar.

So my estimate is $4,200 all up.

Because we dropped the solar panel array down, it means on a cloudy or overcast day your load consumption will still slightly exceed the capture capability of the solar panels.
The good news is after 10 days of overcast, you will still be at a healthy 70% charge, and it will only take one full day of sun to top you back up to full charge. It is normal to get 10-15 days of constant cloudy weather at some times during the year - even here in sunny hawkes bay. But in reality for most of the year, you will usually get days of half sun, half cloud. But I urge you not to assume you can further undersize your panels or battery bank.

Might be cheaper to get out the shovel and dig a trench for mains.

Ray Taylor

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andrewNZ

2487 posts

Uber Geek
Inactive user

#2003709 27-Apr-2018 19:17

For the inverter, don't skimp on size. Many mains voltage devices need significantly more power than their wattage to start.

A 300W inverter will not start a 300W motor it probably won't start a 100W motor.

Other things like fluro light fittings and chargers often draw loads of current at startup. Inverters hate that and just shut down.

redfiat

57 posts

Master Geek

#2003754 27-Apr-2018 20:53

raytaylor:

Load or power consumption

Assuming 4 hours per day of

- Laptop 70 watts
- Fan 50 watts
- LED light bulbs 60 watts
- Radio 10 watts

Assuming 1 hours per day of

- Printer 100 watts

========================
860 watts per day total
========================

.....

So my estimate is $4,200 all up.

Because we dropped the solar panel array down, it means on a cloudy or overcast day your load consumption will still slightly exceed the capture capability of the solar panels.
The good news is after 10 days of overcast, you will still be at a healthy 70% charge, and it will only take one full day of sun to top you back up to full charge. It is normal to get 10-15 days of constant cloudy weather at some times during the year - even here in sunny hawkes bay. But in reality for most of the year, you will usually get days of half sun, half cloud. But I urge you not to assume you can further undersize your panels or battery bank.

Might be cheaper to get out the shovel and dig a trench for mains.

Thanks so much, this is exactly what I'm after.

Cheers

Aredwood

3885 posts

Uber Geek

#2003827 27-Apr-2018 23:22

andrewNZ: For the inverter, don't skimp on size. Many mains voltage devices need significantly more power than their wattage to start.

A 300W inverter will not start a 300W motor it probably won't start a 100W motor.

Other things like fluro light fittings and chargers often draw loads of current at startup. Inverters hate that and just shut down.

Don't ever connect older magnetic ballast fluro lights to an inverter. As those fluros typically have power factor correction capacitors wired across their input terminals. The capacitive load destroys the output MOSFETS in the inverter.

And don't ever connect power supplies that have active power factor correction to a modified sine wave inverter. In this case, you will destroy the power supply.

Aredwood

3885 posts

Uber Geek

#2003835 27-Apr-2018 23:46

More thoughts. Consider going with a 24V or even a 48V system. As a 2000W inverter on 12V will draw around 180A fully loaded. Which means big expensive cables and extreme attention to detail around making the connections is needed. As just 0.025 Ohm resistance in your connections will cause 4.5V of volt drop. Which in a 12V system is massive losses.

Go to 24V, and you are down to 90A, which although is still quite big, it is far easier to manage. And you can still get away with using simple mechanical switches. Or even re purposed mains rated switches with 24V.

And if you want to reduce the current further, go with 48V. As then you only need 45A to run your 2000W inverter. But you then have to use HRC fuses and DC rated switches.

Although using 48V also means that you can often design a battery bank with all of the batteries in series. Or at least a low number of parallel strings.

I'm also of the opinion that it is better to buy more solar panels. As a means of reducing the amount of battery capacity needed. As solar panels are often warranted for around 20 years. But you will have gone through at least 4 sets of batteries in that time.

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