Can I charge my battery with a solar panel?

D

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Divide the watts of the panel by 10 to get the approximate average charge rate. say you have a 100w panel. divide that by 10 gives you 10 watts. if you have a 400wh battery it would take 40 hours to charge.

I have a 10w panel, which I wired up to a 12v 8Ah battery, that was about 50% charged already. It took about a week to go from 12.3v to 13v, so a 30w panel would move a 36v battery from 36.6v to 39v in a week. Extrapolating that, we get about 2 weeks to fully charge a 36v 8Ah one and 3 weeks for a 12Ah one. A 60w panel would do it in half the time.

I conclude that to do it in a meaningful way, you need about 300w of panels.

To go with the panels, you need an adjustable MPPT charge controller so that you can charge the battery directly from the panel for better efficiency. The MPPT controller would need to be set to 42V for a 36v battery and you'd need a panel array that would produce constantly more than 42v.
 

Danidl

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Or would it take forever?

I don't really understand electricity & batteries so, if I bought something like these https://www.sunstore.co.uk/Portable-Solar-Chargers/ would it charge the battery or would it take days? If I can which one should I buy?

Just asking as I like the idea of being a bit greener....
Sorry Kathymac, it's one of those good ideas that basically doesn't work. Unless there is a lot of input.
Those solar panels typically produce 12v DC voltage into a load . Let's say it was a 100watt panel, that means that it would under best sunshine conditions produce maybe 14 to 15 volts at a current of 8 amps. Best sunshine conditions are typically only about 3 hrs per day. There is power available at all the time the sun is shining but t can be pretty low.
Now the battery in your bike wants around 42volts from its charger to charge the battery properly. Therefore you would need a special electronic device called a DC to DC convertor to up the voltage from 12 to 15 v up to 42 and in doing this maximum current would drop to say 3 amps. So your battery could charge in 4 or 5 hrs.best case.

But those specialist devices are not usual and it is more usual to get a DC to AC invertor which would then mimic the mains supply. You would then use your mains charger with it... There has been some discussion on another thread here about possible damage to the bike charger from the output of some ac inverters.
When you add up the cost of these items, you would buy a large amount of mains electricity for the money. Now solar panel pv is great for those who need it. Boats, remote cabins etc. And led lights have made it a much more feasible option , but not a good idea when mains electricity is readily available.
A better arrangement is to go the full hog and get a full domestic 2kw peak unit fitted on your roof , and avail of whatever feed in tariff is available. Much longer life and basically a set and forget option, which will give real savings every day.
 
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anotherkiwi

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Yes you can, after you move to Vendée or the Cote d'Azur. Forget Spain they have a tax on solar panels...

As Danidl has said it works quite well if your south facing roof is covered with panels.
 

Jimod

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Danidl

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That is confusing the issue. The OP asked a valid question. Some additional information. The peak power from the sun on a very bright sunny day at noon is slightly under 1000 watts per square metre. This is broadly irrespective of summer or winter... PV panels are around 20% efficient, so with ideal orientation, upwards of 200w peak of electric power can be generated. Cloud cover or any obstruction shading the panel, reduces the power big time. So if you achieved 500whr, of energy from this square metre panel , in a day you would be doing well. .. that's 10 pence worth. At peak time rates. On a roof a square metre is about the size of a velux window. Domestic power of PV panels will be 2 m by 1m and maybe up to 6 used giving a peak power close to 2.5kw peak ( just enough to boil a kettle)
 

Katymac

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Thanks everyone - sorry for the late reply I lost all my log in details & oly just found them

It is a shame as it's a lovely idea....Especially the ones you can plug into using a normal plug

We are moving to a new house & holding off on panels as there is some new battery technology coming out soon and I'd like to fit that!
 

Danidl

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Thanks everyone - sorry for the late reply I lost all my log in details & oly just found them

It is a shame as it's a lovely idea....Especially the ones you can plug into using a normal plug

We are moving to a new house & holding off on panels as there is some new battery technology coming out soon and I'd like to fit that!

.. if you read my last posting, you will see that I am enthusiastic about mounting PV panels on a roof, having them connected via a proper inverter control system and being linked directly to your electric main supply. My son is moving to a new property and it will have 5 such panels mounted.
My objection is to a piecemeal approach, getting panels which might work for a bike, getting an inverter converter for that purpose and then actually fretting whenever you are using the bike away from this kit when the sun is shining as your kit is then lieing fallow. Much better to have it working all the time automatically as part of the house infrastructure.
You made reference to batteries?? I cannot understand the relevance unless you want to be a new age hippie and live off grid. All batteries need maintenance and have limited lifetime s, and certainly utility level ( house ) suoply will be expensive to own and consume. Much better to effectively use the national grid as your battery, by sending your excess power to it, and using their power at other times
Off-grid makes sense only if the cost of actually making an electric connection is very high. .. up a long rural valley, in an area of outstanding beauty requiring underground cables , living on an island. .. or you want to make an expensive political statement.
 
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anotherkiwi

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Off-grid makes sense only if the cost of actually making an electric connection is very high. .. up a long rural valley, in an area of outstanding beauty requiring underground cables , living on an island. .. or you want to make an expensive political statement.
You have been to Navarra Danidl! :)

I was out and about the other day and came across a new electric vehicle charging parking spot in my town. The access card costs 18 € a year. If you charge between 23:00 and 6:00 the electricity is free! I bet that setting my alarm clock to 5:40 is going to work out a whole lot cheaper than installing solar panels on my roof... ;)
 
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Flyingppg

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To go with the panels, you need an adjustable MPPT charge controller so that you can charge the battery directly from the panel for better efficiency. The MPPT controller would need to be set to 42V for a 36v battery and you'd need a panel array that would produce constantly more than 42v.
Not strictly true. Most MPPT charge controllers are dc-dc step down "buck" converters but MPPT charge controllers that are dc-dc step up do exist and not expensive such as this: https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/182671320308

This item is a configurable cccv charger, about 70% efficient. So on a really sunny uk day plugged into a 250w panel you might get 3.5 amps at 42v from it.
 
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Katymac

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I now have 12 panels on my roof - today we got 15.5 kWh and since they were installed after Christmas we have produced 399kWh

My electric bill says we use an average of 7.5kWh a day......so I reckon we are doing OK

The FIT is tiny but if we can use most of what we produce we will do OK (I hope)

& it's enough to charge 2 bikes as I bought my hubby an electric bike for Christmas!
 

Benjahmin

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Change all your house light bulbs to LEDs. A 5watt LED gives about the same light output as a 50watt halogen, so you can cut your lighting bill by a factor of about 10.
Use your dishwasher and washing machine only during daylight hours (put them on a timer if necesary) so they will be at least partially fed by your panels.
I get great pleasure from knowing that my panels are charging my bike after a sunny ride.
2 bikes, chargers use 4 amps over 4 hours. 4 amps is approx 1Kw. Doable on a sunny day.
 

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