Why We Chose The Batteries That We Use
There are two battery types commonly used with solar: lead-acid and lithium-ion. Each type has its pros and cons.
The standard battery for solar applications is lead-acid, however, with the advent of low cost wall mounted lithium packs, we’re seeing more of a mix of both chemistries.
Lead acid has a lower cost per kWh, excellent surge capability, can withstand cold temperatures, and are readily available. However they are very heavy, somewhat large and have a lower cycle life compared to lithium.
Lithium has a very high energy density and extremely long cycle life, however they have a higher cost per kWh, often lower surge capability and suffer substantial capacity loss in below freezing temperatures, therefore we want to install them in conditioned space.
At Mountain View Solar, we will choose the battery type that makes the most sense from a technical standpoint for a given application. We consider space, power requirements, operating temperature, cost and equipment availability amongst a few important design considerations.
About our lithium batteries:
For compact wall mounted batteries we use the LG Chem RESU10. It is a DC coupled battery which performs better in a backup scenario as compared to an AC coupled battery such as the Tesla Powerwall. The AC coupled Tesla unit is best for time of use and peak load shaving applications, more common out west. In our area backup power is most important, so we utilize the LG unit (time of use metering doesn’t apply in our area). For more information on AC vs DC coupling, click here.
For small lithium backup systems, we use the SolarEdge “StorEdge” with the LG Chem wall mounted battery. This turnkey 9.8kWh backup solution can handle most small appliances with ease. The LG battery is rated for 27.4MWh of energy throughput and warrantied for 10 years.
For large lithium backup systems, we use Schneider XW series of equipment combined with either the Iron Edison lithium bank, or soon the LG RESU10 48v version, expected to become available sometime in 2018. The Iron Edison lithium batteries are American-made but cost around 3 times a comparable lead acid solution. Therefore, for backup situations where the battery sits on stand-by most of its life and space or weight isn’t an issue, lead-acid is a better choice.
About our lead-acid batteries:
When it comes to lead-acid, quality matters. Mountain View Solar uses DEKA/East Penn lead acid batteries, which are American Made using a sustainable manufacturing process. Most of the lead in DEKA’s new lead batteries is recycled from old lead batteries.
The lead batteries that we use are of the deep cycle variety, meaning they are built with thicker plates to withstand heavier use. Compared to a typical starting battery, they are much more robust and capable when drawn down repeatedly. Additionally, they are sealed or SLA type lead-acid. We do not install flooded batteries which emit dangerous gases and can leak acid.
For most lead systems we use the DEKA Unigy II line, an industrial AGM bank consisting of a single string of 2v cells. This battery bank is rated at 1800 cycles at 50% DOD, and can sit on stand-by for a decade or more!
Mountain View Solar has the most off-grid and battery backup experience in the mid-atlantic area. Our systems are clean and compact, built to last over twice as long as competitor’s designs.