400W Navitron PV with 19KWh storage

[solaluvva]

This is our system. The panels are 2 x 100W in series (Voc 40V, Imax 8A), 2 x 50W in series (Voc 40V, Imax 4A), and 3 x 20 W in series (Voc 60V, Imax 1.5A), secured to an 'A' frame made from scavenged old garden furniture. Everything is connected with 4mm dia copper multi-strand The charge current is metered by an instrument I designed and built myself (max 25A @ 24V through a 0.1 ohm 25Watt shunt) which has registered Icharge up to 12.5 or 13 A over Dec. and Jan. It gets a bit warm... The storage is provided by 20 x 160Ah, 6V batteries arranged by 4 in series and 5 of these blocks, giving 24V nominal. These feed to 20A MCBs connected to a 100A MCB which feeds a 1.8KW domestic sine-wave inverter. The banks are separated at the charge-point by diodes, so each bank receives the current it needs without draining the others and is balanced by the cable run to the MCBs in the new consumer-unit in my kitchen. It takes weeks to re-charge them under winter conditions (under 5A per bank averaged at 2-3 hrs full sun per day, max usage) but in summer, well, I'll probably boil them. Been thinking of building a flow battery for mass storage for winter, or thermal storage in a huge water tank, but both are mega engineering tasks. Any ideas anyone? The batteries were an e-bay miracle @ only £10 each, but not repeatable. The panels were the most fairly priced available ANYWHERE thanks to Ivan, Steve and all at Navitron. The system is practical, on-budget and operational, just a little rough around the edges, but, hey, so are my son and me!
 

[KenB]

Nice system solaluvva,

If you get 8 hours of sunshine in summer, then its  going to be  3.2kWh output per sunny day.   

I suspect that your household will easily consume this amount of power from the batteries/inverter on a daily basis.

If you are concerned about overcharging in the summer, then wire a  pair of 200W 12V dump load elements in series and install them in your hot water tank as a dump load.

Try these surplus people for 24V cartridge heater elements 

http://www.engsurplus.btinternet.co.uk/temperature.control.htm

A normal domestic tank (about 120 litres) will only rise in temperature by a maximum of  23 C if you dump the whole 3.2kWh solar output into the tank


Ken



 

[solaluvva]

Cheers Ken.
From your URL, I could see that 2 x 190 W elements @ 24V would absorb all ecxesse energy to heat water. How do I fit these? Do I drain the cold supply circuit of the HW bit of my GCH system and drill my main HW tank? Also, I'm thinking bigger, eg an industrial Kilo-liter tank buried in the garden in place of a ground-source heat-pump circuit, for storage on a seasonal scale rather than a weekly one. Less problem than storing the 100's of gallons of sulphuric acid I'd need for a reasonable flow battery, but with greater heat-loss to envyroment. Or does this depend on it's depth-of-incarceration?
 
The problem of renewables is the smoothing of their erratic supply.

[KenB]

Jon (Solaluvva) & List,

With only 400W peak of pV installed, I cannot see you having a huge excess of either inverter power or dumped heat.

If you look at a standard 3kW immersion heater (£15) , the heating element is soft-soldered into the brass flange - and easily removed with a blowlamp.

I suggest that you sacrifice an immersion heater (or just plain flange fitting)  to mount your solar dump heaters,  rather than drill into the tank itself.

It would be of use to know how many kwh of electricity your household typically uses on a daily basis - so we could work out the likely contribution % from the pV array.   I'm fairly frugal here, but I still use 8kWh per day. 

If you buried a 1000l IBC in your garden, it would have to be very well insulated with polyurethene insulation (Cellotex or similar) to get the heat loss down to an acceptable level. 

I would be tempted to upgrade at some point to a 250 litre tank, indoors, and a set of 20 tube solar water heater panels at some point.



Ken

[solaluvva]

Hi Ken.
A quick audit puts us to about 7 or 8KWhr of electricity per day, plus gas for heating/hot water. Projector/x-box responsable for a third of that!!!
 
proj             =             250W, 4hrs, 1kwhr
x-box           =             300w, 4hrs, 1.2kwhr
fridge           =              80w, 10% 'on' time, 0.2kwhr
cooking        =              1kw, 2hrs/day, 2kwhr
lighting (all LEDlights) = 45w, 6hrs, 0.3kwhr
GCH circulation pump  = 90w, 8hrs, 0.75kwhr
laptop/router =             60w, 16hrs, 1kwhr

It looks about right as it took about 3 days to flatten that battery with panels connected under winter conditions. I estimate a 25% reduction in electrical energy use in summer, plus we could be away from home on average 30% of the time.

8kwhr-25%=6kwhr-30%=4kwhr per day. That's very close to your estimate of 3.2kwhrs based on 8hrs sun. Around mid-summer, we can get full sun from 5am to 9pm, or 16 hours. That could produce up to 6.4kwhrs by your estimates.

Haha, at solstice we'll be heading out the door and it'll be;

"Did you leave the lights on?"
"(sigh) Yes Dad."
"And your x-box?"
"Yes Dad"
"And the fridge. Did you leave the door open?"
"Yes Dad, and my telly on, and my electric blanket. Look, I made sure we wouldn't melt the house down, OK?. Are we there yet?"

I think over next 18 months, I'll need to double my whole system; storage first, then collection, then storage again.

 

I like PV, as I can un-install it and go 'mobile' almost instantly. I want to be a C-neutral festival solar cinema for underground movies and video lectures, a 'c-none-info-nema' for short. (Kinda catchy huh?)
Plus, I've only spent £2K so far. Poverty is the strange-uncle-that-only-you-get-on-with of invention.
Is anyone working on systems for collecting solar generated Browns gas (2H2O2) as I have a molecular resonater you might be interested in...

[KenB]

Jon,

Are your electricity figures based on actual consumption measurements,  daily meter readings or just a quick tot-up of the estimated wattages of the various devices connected?

I believe that a knowledge of existing energy usage is vital to understanding the demands of the property/lifestyle and very helpful in allowing you to scale your renewable energy system to meet your actual requirements.

By chance I found that the only really effective method is to take daily meter readings at the same time each day, which I do for both my electricity and gas consumption.

I have been doing this for more than 6 years now, so I have a daily record logged in Excel, for nearly 2400 days. This has been most revealing in that I can show the long term trend of driving down my energy consumption, but also highlights the day to day and seasonal changes.

By summing the readings from the last 365 days, and recalculating this on a daily basis shows the annual consumption being reduced significantly.

It's important to get a baseline consumption figure, before you add any significant equipment, or change to the system. 

Over the last 6 years, loft insulation,  thermostatic radiator valves, new condensing boiler and better controls,  underfloor heating, solar water heating, and improved knowledge of system etc have all improved my consumption figures.  The attached XL spreadsheet shows a summary of the gas consumption figures and shows the ever decreasing trend.

This property is a 1905 built, solid 9" brick construction, and the amount of gas used in heating each day, is directly proportional to the difference between the inside temperature (19C) and the ambient outside temperature.  My XL spreadsheet helped me to prove that it is more economical to keep the heating on 24/7, than have it come on twice a day, and have to reheat the structure of the house. Sounds controversial - but proven to work for properties of this type of construction.

I wonder if during the summer, you can run the X-Box and projector, directly off the dc from the solar panels?  That would restrict it's usage somewhat. ;-)




Ken

[solaluvva]

I wonder if during the summer, you can run the X-Box and projector, directly off the dc from the solar panels?  That would restrict it's usage somewhat. ;-)

Ken

Kick the boy outside to play on his bike!!!

  Every Revolutionary is a subverted policeman.

[solaluvva]

Seriously, that sort of study takes a great deal of commitment, and so thankyou for sharing that research. I had heard that constantly-on was more efficient than on-off-on-off, but when I tried it here, my bills went through the roof.
 
There are two of us in a 15 year-old south-aspected 2 bed semi-detached bungalo with double glazing + loft insulation, but no cavity-wall ins. No desk-tops, CRTs, hair dryers or freezers. We have LED lighting throughout (max 45W) and cook on appliances I've moded for economy. I've hacked the washing machine to use only cold water and to not use it's heater, and have recently bought a "A" class fridge. I think my estimate was pretty good, even on the high side.
6.3kwhr/day over 3 days= 19kwhrs= my (second-hand) batterys' specified capacity.
The lead speaks for it's self.
 
I feel it compensates a bit for driving a hummer...

[KenB]

Jon,

The "always on"  strategy will only work for older, less well insulated houses, with solid internal walls,  9" exterior walls and lots of brickwork such as chimney breasts to heat up.

By fixing the internal temperature on the thermostat at say 19C, the gas usage is directly proportional to the temperature difference between indoors and outdoors - and since this temp difference can vary from say 6C to 25C it give an equally wide variation in gas usage.

For this reason, on a cold day (say 7th Feb when we had -6C frosts here) my gas usage was 121 kWh, whereas a week later, Feb 14th, it was only 58kWh.

If you live in a modern house or bungalow, that has very little thermal mass (stud partition plasterboard walls etc), and a good level of insulation, then the "on/off" strategy will prove to be more efficient.   There is no one strategy that works for all!


Ken
 

[solaluvva]

Ah, that explains a lot.

Thanks Ken, I know what's going on now. Yes, you were right in your original post that I should now address my gas consumption. I am, however, rather off-put by the radical shift in technology (from electricity to water) and my inexperience in the new medium. If I have a 'leaky' wire, the system would trip or I'd get a belt. A bit of insulting tape and it'd be sorted. With the hot water, it's a bit more complicated.
Have you seen ManWithTools' system? Wow! I can't do that. Working in the loft space and on the roof is difficult for me, nay, it's out of the question because of my leg. Neither can I afford to pay someone to do that. That's why I'm looking, have to look, at other forms of stand-alone technology.
If we had a co-ordinated, centralised and inclusive government policy to lever homes off fossil fuels, it wouldn't be a problem (and it'd cost less than current plans allowing for nuclear generation expansion), but we haven't. See, by centralising resources they also centralise wealth, which means they get looked after by their new friends (how many houses has Blair bought now? 5 or 6? On 100Kpa?).
Until this changes, or I find a very charitable plumber AND roofer, we're screwed. I'm the only person in my circle to have gone so far and that's because no-one else is able to perform maintenance or repairs as I can. As they can call central-heating engineer from the phone-book, or call the housing department, they feel insured of a consistent service. I can't even find "solar" in my yellow pages.

What do we do?

 

jon

[KenB]

Jon,

I agree - when plumbing goes wrong it makes a lot of mess, In the past, I have tackled gas, electricity and water installations, and I like water the least!

I agree that if the recent petition to the Government can convince them that they need to help promote (and fund) renewable energy projects, and that solar water heating, pV and wind are now mature enough technologies for risk-free investment.

I still think that it is well worth anyone taking time to understand their energy usage and its implications.


Ken

[Antman]

Jon

Aesthetics and direction permitting, there is no reason why a solar panel cannot be mounted on the ground in the garden - providing it is not unreasonably shielded from the sun by trees/fences etc. I think Ivan does a flat roof mounting kit that can be adapted for this. Obviously the nearer the house the better due to pipework losses.

Antman


PS  You would also need to avoid balls of all types - regardless of what wyleu claims 

[solaluvva]

Hahaha!

Look, I'm too old and ugly to learn proper plumbing, but how's this?
Solar PV gets hot, really hot. Not only by absorbed sunlight, but also (as any conductor) by square of the current it carries. This effect is strongest when the ambient temperature is high (ie, in full sun in summer).
What about a system to remove that heat?
It could be absorbed by a cold water circuit run by a small pump powered by the array it cools, or even a reclaimed compresser from a refridgeration unit of some sort. A pal of mine has mentioned that with an 80w compresser, I should see an energy transfer of min 4:1, eg 300w+ of heat removed from the array. If the radiation circuit of the compresser were immersed in/epoxy-ed to a cold water vessel, I'd have a safe supply of free hot water (the black pipes on the back of a fridge don't rise over 60C). Most of the heat generated by the compresser would also be transfered by the refridgerant to the heat-store.
And running at temperatures of sub 20C (how low could I actually go before I compromise the PV's materials anyone?) as oppossed to 60-80C means, from performance graphs, almost doubling the electrical energy gathered, more than enough to spare a bit for the compresser.
I have an old F/Freezer on my driveway for this very purpose. I wasn't going to mention it till I had results to show, but...
 

[solaluvva]

And stop picking on wyleu, he can't help having that avatar! ("...what? Oh ghod, can he? Oh...")
         

[Ivan]

It's definitely worth trying to keep the panels cool. It would be difficult to do it with a heatpump, though - in terms of running the various  high pressure pipes effectively along the back of the panels. Simple pumped water-cooling would seem a good idea though, even if you simply 'waste' the heat. I guess you could try two circuits, a water jacket on the back of the panels pumped around a buffer tank which is cooled by the heatpump (refrigerator). Maybe use the inside of the fridge as the buffer tank. Bear in mind that the efficiency of the compressor in pumping heat will reduce as your hot water storage warms up.

I think somewhere I did see a solar PV with water circuit built into the back of it.....but I cannot remember where.


Ivan