Solar

by **daveiron** Sun Aug 14, 2022 10:19 pm

Finished installing a solar system this week,so far i've been pleasantly
suprised. The object of the excersise was to try to keep my chest freezer
going during power cuts.
I have at present 2x 100 watt panels,2x90 ah leisure batteries and a good
quality pure sine wave inverter rated at 1500watts continuous output.
Started off with 100% battery and that never droped all day, night was my
concern so i got up at dawn to check battery level,i could not believe it, 96 %
Seriously considering adding to the system now as its clear i can run a lot more
than expected.
Cost so far £500 as its decent quality gear. I recon its going to pay for itself
soon given the price rises they have in store for us.

The gauling thing is i live in a HA house that has 9 large solar panels on the
roof which feeds straight into the grid.

by **assassin** Mon Aug 15, 2022 3:04 am

Currently solar is running well due to the heatwave and long periods of sun and the real test comes in winter with little to no sun and little available energy and you have to remember that a freezer is on and off and not running constantly.

by **daveiron** Mon Aug 15, 2022 8:36 am

Yes i am aware we have optimum sun levels at the moment ,also took
into account that in this heat the freezer is running more often than usual.
Its early days ,next i will see if it will also power the PC which is on all day.
I seem to have got into the habit now of instead of just running things like
blenders & vac packers in the kitchen,i now plug them into the solar system.
Every little helps as they say.

by flyingfish Mon Aug 15, 2022 3:09 pm

Just for reference our freezer which is a modern(ish) upright uses around 0.7 kWh per day. Your chest freezer may use less as they're supposed to be more efficient. It's quite interesting using one of those plug in energy monitors to check appliances for a few days at a time.

How are you measuring battery state of charge? It can be a bit of a black art with lead acid batteries.

by **LionsShare** Mon Aug 15, 2022 8:57 pm

flyingfish wrote:How are you measuring battery state of charge? .

when general state provided electric is free why would 1 care?

by flyingfish Tue Aug 16, 2022 11:47 am

LionsShare wrote:
flyingfish wrote:How are you measuring battery state of charge? .
when general state provided electric is free why would 1 care?

Couple of reasons, firstly dave wants to confirm the batteries have enough juice to run his freezer while the sun isn't shining. Secondly and sort of related if you discharge a lead acid battery below 50% then you start seriously shortening its life.

by **daveiron** Tue Aug 16, 2022 2:14 pm

Clearly that small device i bought to measure battery level is not fit for
purpose. Yesterday the inverter shut down as batteries reached 50%.
So from 2 x 90 ah batteries i got 4 days of running whilst connected
to solar charging.
I have an additional battery coming tomorrow & may get another 100watt
panel next week.
Trial and error at the momnent.

by flyingfish Tue Aug 16, 2022 4:42 pm

To see what I mean about it being a black art, have a look at this doc and see the way the battery voltage can mean wildly different things depending on how much current is going in or out of the battery. To make it worse the voltage remains artificially high even after disconnecting from charge ..
https://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

One option is a device measures current in or out, for example. But I don't know how accurate these are ..
https://www.foxschandlery.com/nasa-bm1-battery-monitor-for-12v-system

It's good that your invertor cuts out rather than running the battery into the ground.

by **daveiron** Tue Aug 16, 2022 7:26 pm

Like you say its a bit of a black art. there are readouts on both the charge
controller and the inverter.
However its been my experience through life thats its best to over engineer
things,so i will add where necessary until i achive what i require & build in some
redundency.

by **assassin** Wed Aug 17, 2022 3:56 am

flyingfish wrote:To see what I mean about it being a black art, have a look at this doc and see the way the battery voltage can mean wildly different things depending on how much current is going in or out of the battery. To make it worse the voltage remains artificially high even after disconnecting from charge ..
https://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

One option is a device measures current in or out, for example. But I don't know how accurate these are ..
https://www.foxschandlery.com/nasa-bm1-battery-monitor-for-12v-system

It's good that your invertor cuts out rather than running the battery into the ground.

There is no black art as there are over exagerated theoretical claims from manufacturers and people who dont know how batteries work and are measured and most are measured on the 20 hour cycle. On the 20 hour cycle this is the battery output is divided by 20 to give a figure which should not be exceeded and for a 90 A/H battery this would be 90amps divided by 20 hours which equals 4.5 which is the figure which must not be exceeded for current draw.

In simple terms if you stay at, or below this figure of 4.5 amp current draw you will get this for 20 hours or get the full 90 amps from the battery. Connect a 90 amp load to the battery and theoretically you should get this for 1 hour but in reality you wouldn't achieve it for 3 minutes.

by flyingfish Wed Aug 17, 2022 8:25 am

There is no black art as there are over exagerated theoretical claims from manufacturers and people who dont know how batteries work

What's your preferred way of measuring state of charge?

assassin wrote:In simple terms if you stay at, or below this figure of 4.5 amp current draw you will get this for 20 hours or get the full 90 amps from the battery. Connect a 90 amp load to the battery and theoretically you should get this for 1 hour but in reality you wouldn't achieve it for 3 minutes.

If you want the battery to last then for a typical leisure battery these figures need to be halved. Discharge it below 50% on a regular basis and it will soon be toast. So in dave's case, with two 90AH batteries he has a total of 90AH usable, 45 from each battery.

However that's a good point about heavy load. My freezer draws 1200W peak load, I have no idea for how long because the average is much much less, something like 150W while the compressor is running. However to power it from an inverter that short term 1200W needs to be supplied, and even if the inverter is 100% efficient that means 50A from each battery.

by **Mrblue2015** Fri Aug 19, 2022 6:42 am

Good work DaveIron!

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