Build a solar pv system to power this little lot??

poisondwarf · Post by **poisondwarf** » 02 May 2007, 21:59

Hi Andy,

Have a look at this

http://cgi.ebay.co.uk/Deep-Cycle-Gel-Ba ... dZViewItem

How does the price of this battery compare with what you paid for yours, (discounting the postage cost of course)

Cheers

Pete_M · Post by **Pete_M** » 02 May 2007, 22:17

Andy,
I included a battery monitor with my system (Studer smb-01). Partly because I wanted to keep a close track of the charge / discharge and partly because my system is outdoors so this gives me a monitoring display in the house. It was quite pricey though.

It displays the current (+ into the battery or -ve out), terminal voltage, amp hours down (from a rather arbitary reference). When you think the batteries are fully charged (when the controller has been float charging for a day or so), you tell the battery monitor. From then on it displays the amp hour status determined by monitoring current over time and an estimate of the time the current load can be maintained.

I was really thinking that such a device might give you the information you need to keep track of your battery life. For example - my batteries are 5 years old and have from time to time had their terminal voltage dropped to 11V. The monitor currently indicates that they really arnt holding their charge (down 10 AHrs over the last 4 weeks) even though their combined terminal voltage is about 26 volts.

Pete M

Andy Hunt · Post by **Andy Hunt** » 03 May 2007, 09:52

poisondwarf wrote:Hi Andy,

Have a look at this

http://cgi.ebay.co.uk/Deep-Cycle-Gel-Ba ... dZViewItem

How does the price of this battery compare with what you paid for yours, (discounting the postage cost of course)

Cheers

That is exactly the battery I have. I bought a pallet of 8 of them from that guy for about ?550-ish, I think it was.

Seem to be OK!

Andy Hunt · Post by **Andy Hunt** » 03 May 2007, 09:57

Pete_M wrote:Andy,
I included a battery monitor with my system (Studer smb-01). Partly because I wanted to keep a close track of the charge / discharge and partly because my system is outdoors so this gives me a monitoring display in the house. It was quite pricey though.

It displays the current (+ into the battery or -ve out), terminal voltage, amp hours down (from a rather arbitary reference). When you think the batteries are fully charged (when the controller has been float charging for a day or so), you tell the battery monitor. From then on it displays the amp hour status determined by monitoring current over time and an estimate of the time the current load can be maintained.

I was really thinking that such a device might give you the information you need to keep track of your battery life. For example - my batteries are 5 years old and have from time to time had their terminal voltage dropped to 11V. The monitor currently indicates that they really arnt holding their charge (down 10 AHrs over the last 4 weeks) even though their combined terminal voltage is about 26 volts.

Pete M

Thanks Pete, that might be useful to bear in mind, I will see how it goes. It seems to be a bit of a black art telling what is going on in the system.

I was reading some of the technical info on the Grundfos website (they make the pump in my solar hot water system). It seems that the pump can use anywhere between 60W-100W when it is running. That, combined with the other bits and pieces of electronica I have connected, will probably eat up most of the electricity my 330W panels generate, which would correlate with the system's performance at the minute.

I have to keep reminding myself that I have only about a third of the PV of the smallest 'standard' PV systems, so I can't expect too much really! It's a really good exercise in getting my energy efficiency sorted out though, that's for sure. Every little counts for a lot!!

I've pretty much made up my mind to get an additional panel, although it probably won't be until next year now. It's good to know that what I have will run all my basic stuff anyway, and my solar hot water system isn't susceptible to summer power cuts when everyone else is cranking up the aircon.

RevdTess · Post by **RevdTess** » 03 May 2007, 15:46

I have been looking at the feasibility of building out an all-solar narrowboat (eg http://www.solarboat.co.uk/)

The idea really is to avoid any requirement for diesel or gas or coal. Currently of course I do live on a narrowboat but the 12v system is only used for lighting, water pumps and engine cranking. Frankly I have about 200Ah of nice gel leisure batteries sitting around doing bugger all, especially when I'm plugged into the mains shoreline. My water heating is performed by mains power, or by the engine when on the move. Cooking is on gas. Heating is by coal or wood. Propulsion is of course a diesel engine.

If I was to switch to a completely solar electric approach the biggest draw on the system would be the propulsion motor. A 15hp system (minimum spec to move a narrowboat) uses 11KW, or 44KWh for 4 hours of travel at full power.

(transmission inefficiencies ignored in what follows)

Assuming a 48V system this is around 900Ah, which is the sort of spec solarboat recommends. 900Ah is of course huge. A typical leisure battery is 100Ah at 12V or 25Ah at 48V, so you'd need 900/25 = 36 of the monsters. My boat currently has ... 2!!

Then assuming you have all this electric ballast set up, you need to solar system to do the charging. There's probably enough room on a narrowboat to comfortably fit 1KW of panels. I'm guessing from what the cognoscenti have been saying that this will deliver conservatively 2.5KWh/day into my batteries which at 48V is around 50Ah, thus taking 900/50 = 18 days(!) to charge the batteries.

So I could travel 4 hours (* 4 mph = 16 miles) every 3 weeks... 325 miles per year... not very thrilling.

But on the other hand, I've moved my diesel boat aboat 24 miles in the past 4 months, so perhaps this is not so unreasonable.

And given the size of those batteries, I'd have little difficulty running a typical household electrics. Even when I lived in a house I averaged 3KWh consumption per day, and a boat is much more frugal, especially if I forego a washing machine and use the local laundrette.

The cost of all this of course is significant. Solarboat.co.uk quote around ?15k. This is almost as much as the steel boat shell itself, and on top of that you'd need to pay for the interior fit out. However, with the system in place, you'd never need to 'plug in' again unless you wanted a rapid charge for a trip away. No need for coal, gas, diesel. Just a few wood logs on the stove for old-times or a backup. It means enormous freedom.

Post by **clv101** » 03 May 2007, 16:01

Without doing any calculations your numbers seem reasonable - the reasonable conclusion therefore has to be that PV propelled boats are a bad idea! How about a horse to pull you along?

JohnB · Post by **JohnB** » 03 May 2007, 16:03

Tess wrote:especially if I forego a washing machine and use the local laundrette.

Surely that's like claiming that we've reduced our CO2 emissions because we now have everything manufactured in China. Unless you have a local solar powered laundrette

RevdTess · Post by **RevdTess** » 03 May 2007, 16:16

JohnB wrote:
Tess wrote:especially if I forego a washing machine and use the local laundrette.
Surely that's like claiming that we've reduced our CO2 emissions because we now have everything manufactured in China. Unless you have a local solar powered laundrette

I wouldnt claim any such thing

My total resource usage is probably higher over all - just mostly in the past rather than in the future when it's all run out! The point is really sustainability and freedom rather than minimised footprint.

Replacing all those batteries every 6-8 years wouldnt be cheap either!

Post by **clv101** » 03 May 2007, 16:23

Tess wrote:The point is really sustainability and freedom rather than minimised footprint.

In which case just buy a bigger diesel tank and mentally prepare for the remote possibility of not being able to move the boat as much as you'd like in a decade's time... your diesel requirements are so low that I can't imagine physical fuel shortages will be a problem. In an environment where you can't buy 10 litres of diesel for love(!) nor money then expect your solar panel to have been stolen long ago!

RevdTess · Post by **RevdTess** » 03 May 2007, 17:15

clv101 wrote:
Tess wrote:The point is really sustainability and freedom rather than minimised footprint.
In which case just buy a bigger diesel tank and mentally prepare for the remote possibility of not being able to move the boat as much as you'd like in a decade's time... your diesel requirements are so low that I can't imagine physical fuel shortages will be a problem. In an environment where you can't buy 10 litres of diesel for love(!) nor money then expect your solar panel to have been stolen long ago!

I guess I am trying to unplug from the dependence on other people supplying stuff like that. For some reason I like the idea of having an energy-self-sufficient living space, even if it costs a packet to set up and consumes lots of energy to create. Having to fill up with diesel every so often just breaks the spell somehow. Ideally I'd like to grow my own food and collect my own water too, but I feel no need to make my own clothes... so there are limits apparently.

Minimising the footprint is clearly important to me. It's just not the be-all-and-end-all.

Andy Hunt · Post by **Andy Hunt** » 03 May 2007, 21:22

Sorry to get back to my system again, but I'm buggered if I can understand what's going on with it.

I measured the voltage on the batteries today when the sun was on the panels, the actual charge at the battery terminals going into the inverter said 30V. According to the voltmeter.

Then after the sun went down a few minutes ago, I measured it again - 30V again.

But I have used my desktop PC in between, and the indication of charge on the inverter says the batteries have gone down from 24.6V to 24.2V.

Voltmeter still says 30V on the batteries though.

What's going on?! Help!!

Post by **mikepepler** » 03 May 2007, 21:33

Does your inverter have a MPPT (Maximum Power Point Tracker)? Refer to the graph I posted earlier - you'll see that there is a point on the graph where maximum power occurs. A MPPT tries to keep the PV array voltage at the point where it will get most power, and perhaps that was still 30V, even just after sunset?

I've got no practical experience of MPPTs, so I'm only guessing, but perhaps it's not "learning" quickly enough to respond to the sun going down, and so is still at 30V. Or, was it completely dark and still 30V?

Ultimately, you ought to be measuring the panels voltage open circuit, i.e. disconnected from the inverter and batteries, otherwise you never really know what's going on.

Post by **kenneal - lagger** » 04 May 2007, 02:16

Tess wrote

Assuming a 48V system this is around 900Ah, which is the sort of spec solarboat recommends. 900Ah is of course huge. A typical leisure battery is 100Ah at 12V or 25Ah at 48V, so you'd need 900/25 = 36 of the monsters. My boat currently has ... 2!!

You would need 72 batteries, Tess, because you shouldn't really discharge them to more than 50% Depth of Discharge (DOD), which gives you the maximum storage capacity over the lifetime of the batteries. 50% DOD would give you 4.9 years of use against 0.8 for 100% while 20% DOD would give 7.7 years. In the sort of situation we are talking about here you really should be going for maximum battery life, so I would suggest minimising your electricity usage on the boat and hiring a horse to move it occasionally.

RevdTess · Post by **RevdTess** » 04 May 2007, 07:43

kenneal wrote:
Tess wrote

Assuming a 48V system this is around 900Ah, which is the sort of spec solarboat recommends. 900Ah is of course huge. A typical leisure battery is 100Ah at 12V or 25Ah at 48V, so you'd need 900/25 = 36 of the monsters. My boat currently has ... 2!!
You would need 72 batteries, Tess, because you shouldn't really discharge them to more than 50% Depth of Discharge (DOD), which gives you the maximum storage capacity over the lifetime of the batteries. 50% DOD would give you 4.9 years of use against 0.8 for 100% while 20% DOD would give 7.7 years. In the sort of situation we are talking about here you really should be going for maximum battery life, so I would suggest minimising your electricity usage on the boat and hiring a horse to move it occasionally.

I heard it depends on the battery - that some can cope with up to 70% DOD (or maybe that's just marketing) but yes of course you're right. I erroneously assumed they could sustain 100% discharge in my calculation.

However, mitigating this is the fact that while the propulsion motor is rated at 11KW, in practice it would draw less than half that because you wouldn't typically be running it at full power while cruising and drag is proportional to the square of speed. See http://www.solarnavigator.net/solar_nar ... ompany.htm
The efficiency rises a lot if you cut speed from 4mph to 3mph...

Post by **kenneal - lagger** » 04 May 2007, 09:22

Hi! Tess

The table I've got is for gell filled, sealed, deep cycle batteries. It may vary slightly from maker to maker but the graph curve will be similar for most batteries: the deeper you cycle the shorter the life.