Now that Spring is poking her head out of the clouds, it’s absolutely the best time to invest in a bit of solar. And all solar installations need a controller which, if you want MPPT technology – and you may not know it but yes, you do, can be the most expensive part of the install.
There are two types of solar controller PWM, the standard, cheap offering, around £15 from Maplins in Bath, and MPPT, of which it is usually recommended to go for a Tracer, £65 from Bimble Solar. MPPT can offer a substantial increase in power harvested by matching the panels and batteries to the best voltage for maximum power (MPPT = Maximum Power Point Tracking )*. By contrast PWM simply switches off part of the time to avoid over-voltage. Going a bit techie, this means that the greater the difference between the VOC of the panel and the voltage of your battery (12V–14.8V) the more power is wasted whereas with MPPT you can string panels in series up to the maximum input voltage of the controller without losing power. The cheapest solar panels are those used for domestic arrays and are generally around 36V which either won’t work or waste most of their power with a PWM controller.
You have to be careful when looking for an MPPT controller, there are a lot of cheap solar controllers on eBay claiming to be MPPT which are, in fact PWM, but this model checks out as a genuine MPPT at around £20 to £25:
Charge voltage is fixed at 14.7V which may be a little high for some, though not high enough to properly charge or equalise traction batts, but will give them more than a tickle. Max solar input is 50V.
A couple of links for these on Ebay:
http://www.ebay.co.uk/itm/MPPT-Solar-Charger-Controller-12V-24VDC-10A-20A-Battery-Regulator-USB-5V-Output-/142188324794
http://www.ebay.co.uk/itm/5A-10A-12V-24V-MPPT-Solar-Panel-Regulator-Charge-Controller-100V-Input-DC-USB-JS-/181861868553
Not as good as the latest Tracers and may be not as reliable, but possibly a good budget option for a small setup.
From Bimble Solar’s website
PWM vs MPPT charge controller test
We often get asked about the actual difference you get between an MPPT and a PWM controller so we setup a side by side test using our Yingli part used panels onto 2 separate 12V batteries, 1 with a PWM controller and one with our Tracer MPPT. Panels were set-up side by side angled south.
With early March sun the MPPT was giving 3.7A into the batteries while the PWM gave 2.5A which was 32% lower than the MPPT.
In cloudy conditions the MPPT was giving 1A when the PWM was giving 0.8A (20% lower with PWM)
Both charged the batteries well, but 20%-32% more power was gained by using the MPPT.
http://www.bimblesolar.com/beginnersguide#mpptpwm
(with thanks to Smiley Pete on CWDF for spotting it)