Solar PV system for heating water

[asdex]

Thanks, yes all this is pretty new to me even though I have had solar panels and regulators on a bus we lived in and then a yacht, it was much simpler. We still use those original Solarex panels. 83 watt and $990 each in 1996. The six 320w panels will be nearly 2kw. I have alot (40 meters) of 16 mm two core TPS I hope to use. I will prefer to site them nearer the house if I can but will have to convince the team of the benefits. (wife thinks they might not be aesthetically acceptable)
But as you say, I'll need to work out the system in total before preceding to do the install.
Cheers,

[stuman]

My neighbor uses the dump load to trip a solid state relay when battery voltage exceeds 54 (48 volt nominal system).  He has an electric water heater with 110 volt elements, which run 400 watts plus at 48 vdc.  I want to mirror that, and since my water heater just died, I'm not too far away.

I also have a summer direct type M copper heating array for water, and a wood burner for when nothing else works.  I'm going to relocate the coil next summer, as i relocate my panels for wind protection.

Hi, I'm setting up a solar PV system for heating water. We are off grid and decided we don't want a thermal hot water panel sitting idle for 7-8 months of the year when we heat our hot water with our indoor fire. I'm getting 4-6 320 watt PV panels soon to run a 24 volt system and once I have the details worked out will probibly get a Midnite 150 to gain as much power from the sun as I can then hopefully dump it all to the hot water tank. Anything left will charge the batteries but I already have panels and a wind generator for that.
I'll be following anything about configuring the Midnite Classic and if anyone is heating water with PV panels.
I'm in New Zealand.
Cheer's

[asdex]

Hi, thanks for your reply. Just waiting for my panels to arrive in a couple off weeks then will look at element voltage and get the Midnite 150 controller.
I hope do do the same as the neighbor you mentioned but in reverse so temperature will operate the relay rather than voltage.
I think I'll connect them 3x2 to give 17.22A and 111VMP and change my 12volt battery bank to 24 volts.
Cheers,

[tecnodave]

Would someone that is using low voltage water heater elements please point me to the source of these. I am using propane flash boiler heater now but would like to add small pre heater to use excess solar power.

tnx.   td

[dgd]

Missouri wind and solar amongst others with Ebay stores.
dgd

[tecnodave]

dgd,

Thanks, I will check that out. I do have excess solar power at least 9 months a year and do not like lugging propane bottles to my house.

td

[stuman]

Hi, thanks for your reply. Just waiting for my panels to arrive in a couple off weeks then will look at element voltage and get the Midnite 150 controller.
I hope do do the same as the neighbor you mentioned but in reverse so temperature will operate the relay rather than voltage.
I think I'll connect them 3x2 to give 17.22A and 111VMP and change my 12volt battery bank to 24 volts.
Cheers,

By doing it the way he does, it is only excess power that heats water.  His primary use of PV power is to charge his batteries and run his fridge/freezer/etc...just like my setup.  I'm currently just building a small wood fire when I want hot water...and I keep a pan on a small propane heater in my bathroom for quick washup warm water.

[phonetic]

Looking to use a 250 litre hot water electric heater.
using 200 litre per day and 45'c temp rise (15 to 60'c) will need 10.7kWh of energy (2.6KW array for 4 peak sun hours)
using 10 250W PVs (Vmpp 30 volts) will give 2.5kW @ 300 volts DC, water heater uses 2.4kW heating element, almost a good match.
use solid state relay & use thermostat from water heater to control.

All I need to do is wait for PVs to get under 60cents per watt, to make it cost effective with heat pump or solar thermal water heater.

Aprox cost $3k with 250 litre storage tank &  10 250W PVs ??

[asdex]

My panels will cost $3000 plus element and SSR and should be comparable with a thermal system. Probably a bit cheaper even if I need to buy a PWM controller to divert  to load. With the added advantage of being able to produce electricity if needed, I'm hoping the system will be worth the effort.
We only use about 50 to 80 lts max and I plan to supplement the hot water with some basic water heating devices like solar shower and passive heating systems (copper tubing in glass front box connected to tap)
I have gone for the standard 180 lt cylinder with a wrap to reduce loses.

[phonetic]

Looking at using a MPPT type DC circuit,  for PVs to charge a capacitor bank & dump to heater element, problems if  not using  MPPT circuit, PV array and heater element will have a very small window of max  power transfer.
Aim is to transfer kWh from PV array to heater element.
Looking to set up a system if total installed cost can be under $2.5-3k

[dgd]

Looking at using a MPPT type DC circuit,  for PVs to charge a capacitor bank & dump to heater element, problems if  not using  MPPT circuit, PV array and heater element will have a very small window of max  transfer.
Aim is to transfer kWh from PV array to heater element.
Looking to set up a system if total installed cost can be under $2.5-3k

Sounds interesting. Capacitor? what type and size?
What about just connecting PVs direct to water heating element?
dgd

[phonetic]

Good example: PV array gets 25% of nominal isolation ie 25% of Impp....as power is proportional to the square of voltage/current for resistance load..will only yield 1/8 of mpp power, but if the array charges a capacitor bank, when capacitor bank gets  charged to Vmpp.. switched to load, the power  duty cycle is approx 25% rather than 12.5%
I hope my ramblings makes sense..maybe the midnite guru's can offer a better example ?

[stuman]

One other option to consider is one I'm about to do at home.  I have swapped the 220 elements from my electric hot water heater for 2000 watt, 110 elements.  I have manually connected them directly to my 48 volt battery bank, and they each pull just over 300 watts of 48 volt DC.  Once I get the solid state relays in place, I will automate this at home and never lose another watt.