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Posts: 25
Reply with quote  #1 
A friend wants to run his central heating circulation pumps from batteries if there is a power cut. If that is successful he will then look at charging the batteries with solar panels, but initially he will charge the batteries from the mains power supply (220V). He asked me for help sizing the system but in reality I know little more than he does so I would welcome any advice.
There are 2 or 3 pumps, depending on what space is being heated. The load is 150W to 300W and this is normally powered by the 220V mains power supply. He wants to be able to run his pumps for 2 or 3 days from the batteries, if necessary.
First question is what equipment he needs to start, using mains power to charge the batteries. I guess he needs batteries, charger, inverter. What else? What would be needed to have the battery-based supply kick in when the mains power goes off?
Second question is what does he need to do (if anything) to ensure the batteries are kept in good condition and ready for use. It is likely that the system will be unused for long periods but when it is needed (perhaps a handful of times per winter) it must be ready to go.
Third question is what solar panels would be needed to (re)charge the batteries? I think he can never have enough panels to be sure of supplying the power he could need at any time of year, but he wants an answer no matter how vague.
So what can anyone tell me? What other information is needed and what other questions should we be asking?


Posts: 139
Reply with quote  #2 

It has been a week and no response yet,  I think because there is not much going on here in DIY land for most of us.  I am not an expert by any means, but I will take a stab to see if we can get the ball rolling here.  Mostly, I have questions which may stimulate others to kick in.  You say you have a load of 150 to 300 watts for the circulation pumps, which is probably a "running draw.".  I presume that this is a hot water baseboard or radiator system...or radiant heat? You say it is a 220 volt system, but are the HVAC circulation pumps you want to power 120 volt?  Is the heating water heated by other non-electric mean...oil or gas...solar?  If so, your draws from the pumps will be determined by the start up requirements of the pumps.  Do they all fire at once or do you have a zoned system with separate thermostats to start the pumps? In any event, you should probably power them to start up all at once. That load is likely to be 3 or 4 times the running draw...some of that can be reduced with the use of starting capacitors.  

You say you want the solar power to "kick in"...automatically?  I have used automatic transfer switches that are made to automatically switch from house current to generator current whenever the house current is interrupted for more than 10-20 seconds.  These are expensive, but ideal for someone who is not able to manage a system with a manual transfer switch, such as my 90 something MIL.  If you are only using this system to run the heat circulation pumps, I would look at a simple and less expensive manual transfer switch. 

And how much do you need to build to run this system?  More than is economically feasible unless you have some other use for the power being generated, but then you are getting into a lot more than the heating system.  I would go ahead and look at someway to selectively draw and use the power otherwise wasted once the batteries are fully charged.  I think you should use and recharge the batteries more than a couple times a winter. Are there other summertime uses for the power...outside lighting or outlets, pumps for a pool or water feature, a whole house or other cooling fans?   To be honest and risk being chastised by others on this SOLAR forum, if all you want is backup power for the heat system, I would look more closely at a generator based system.  

Good luck and keep asking questions here, but give us a little more information to work with.  The is a lot of knowledge here...and lots of people who will work with you through the process when you proceed with this project.


Posts: 25
Reply with quote  #3 
Hi Bruce, and thanks for your input. I'll try to give more information but I don't actually know a lot more.

The pumps are 220 volt. This is in Europe so that is the mains voltage. I don't know how the water for the system is heated, or if it is zoned. I would guess oil, and not zoned, but those are just guesses. I could check that. It is a hot water radiator heating system.

The automatic switchover to battery power is the key to his requirement. He is currently not prepared to leave the house unattended for more than a few hours in winter. He would like the option of going away for a few days but if it were, say, -30C and the power failed there could be significant damage.

He does already have a large (16 kW I think) generator that kicks in automatically when the power fails, but that is too big just to run the heating pumps, hence the idea for a battery-based system.

It may be, as you suggest, that this system would not be viable. That is for him to decide but he can't do that until he finds out what is needed.

Posts: 16
Reply with quote  #4 
I agree with Bruce: batteries, inverters, solar panels and all associated hardware would be costly and maintenance hungry. Perhaps the addition of a smaller generator is the best option, connected via a manual change over switch such that when the house is unoccupied the smaller generator is selected for auto start.
If you already have fuel storage it is another reason to go this way.
Another consideration to support the small generator option: if the location is subject to such low temperatures solar charging, when temperatures are lowest (and days as shortest) could be quite inefficient. Also battery performance would be adversely effected with extreme low temperatures.
For reasonable performance the batteries might require a heated room, which would be another unnecessary energy draw.   
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