mikefitz
Solar Wizard
- Joined
- May 28, 2020
- Messages
- 2,977
Thats a low budget for a system so some compromise will need to be made.
Its possible that after living with your system for a period more power will be needed so a system that allows upgrade is advisable. The service life of lead acid batteries with a daily cycle is difficult to predict, my guess, for the batteries you are considering, is 2 years.
The 450 watt panel wont deliver 450 watts, conversion losses and the fact that the panel will lose efficiency when it gets hot, results in practice to around 80% of panel rating. To get a daily yield assume 5 to 6 effective sun hours in summer and around 1/3 of that in mid winter. Thus on average about 2000 watts per day in summer and 600 watt per day in mid winter. Your fridge will be the major power consumer , with other appliances my estimate is 1000 to 1500 watts per day. I don't think there will be any significant problem over summer but in winter its possible you could have several days of poor weather with insufficient solar to keep up with the demand. The most cost effective is to add an extra solar panel.
Lead acid batteries will initially charge at a high rate but there is a recommended limit, for the GEL batteries you are considering this is 30 amps. However due to the chemical process once the SOC exceeds approximately 80% the battery accepts less and less current, thus full charge may take perhaps several hours for a GEL battery. If not fully charged there is a gradual 'walk down' of battery capacity reducing service life. For a GEL 3GL6E the quoted cycle life with optimum charging is 500 cycles. In general it is considered best practice not to discharge LA below 50 % to extend service life. LA battery voltage falls with reducing SOC and voltage drop with high currents, practical current limit will compromise a large inverter.
A lithium battery has a number of advantages, almost constant voltage over usable SOC, high current delivery, (subject to battery management system), does not need to be fully charged, will accept full power from the solar charger until almost fully charged, can use all the capacity without reducing service life of typically 2000 ( at full rated current) charge/discharge cycles, has a higher charge efficiency ( power out to power in) of 99% compared to GEL of 85%. If discharged to less than full capacity at modest currents, cycle life is extended considerably, and natural ageing will be determine service life. Expect in excess of several years. Depending on battery type and capacity there will be a maximum current output, this will impact on the inverter power used in the system.
example,
consider a poor solar day with only 10 amps average from our solar system available for charging.
assume the battery has been discharged by 50 amp hours overnight from a full charge.
260 Ah GEL battery discharged 20%, charge time is, 0.38 x battery capacity / charge current, = 0.38 x 260/ 10 = 9.88 hours, ( formula taken from Rolls Battery User Manual v7.3)
100 Ah Lithium battery discharged 50%, charge time is, lost capacity / charge current , = 50/10 = 5 hours
note other sources have different formula for calculating charge time,
example from Mastervolt, GEL charge time =( lost capacity x efficiency factor / available charge current ) + 4 hours
lithium charge time = lost capacity x efficiency factor / available current
thus GEL = (50 x 1.15 / 10 ) +4 = 9.75 hours
lithium = 50 x 1 / 10 = 5 hours.
for a single 450 panel yes, a 100/50 would support an additional panel.
the GEL 3GL6E have a recommended maximum charge current of 30 amps, exceeding this with more solar is possible but the issue is perhaps not too serious because, the controller 100/50 cannot exceed 50 amps, the battery will self limit to some extent, solar yield will be low sometimes in winter, the Victron controller can be adjusted for maximum current output, charging at 50 amps is not going to significantly damage the GEL batteries.
Of course alternative batteries may have a higher recommended charge limit.
laptop charger example, charger
phone ,phone USB
adjustable step up converter, converter
Some small devices may run direct from 12 volts via a fuse, example 12v LED lights
You connect everything to the battery via a suitable fuse/breaker and use suitable cable that is safe for the expected current. Additional hardware is needed, a fuse box for small consumers and larger fuses/breakers for high power items like solar charge and inverter.
example,
many AC fridges use the side panels has heat exchangers, thus adding external insulation is a no no. Where there is an obvious heat exchanger at the rear its a possibility.
Fridge power.
AC fridge daily power use will be in the the range of 500 to 1200 watts/day depending on ambient temperature, size and use, use a working power consumption of 800 watts/day for a modest fridge, add inverter efficiency of 90% and inverter standby consumption of 10 watts, 800 + 80 + 240 = 1120 watts/ day
DC fridge , assume same cooling power, 800 watts per day
Its very possible a 800 VA inverter will not start a AC fridge reliably. I suggest a Victron 1600VA or a 2000 VA to ensure a reliable start without and possibility of fridge damage. The 1600 VA has a peak power of 3000 VA,
Of course the battery must be able to supply this power short term.
Freezers & Fridges on Batteries: Inverter Sizing – workshoppist.com
workshoppist.com
The 800 VA Victron may start the fridge but you wont know for sure until its installed. Having the option to return for a larger unit would be useful. Because the compressor starting current is high and somewhat variable, an undersized inverter may not get startup every time, several days may be needed for full evaluation.
Mike
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