How many solar panels do you need in Massachusetts?
Put in what your house uses a month and add panels until the year turns green. The honest answer is not a single number, it is which months you are covered and which you are not.
An average American home uses about 900 kWh a month, which is roughly 29,605 watt-hours a day. Covering that with solar in Massachusetts takes about 7 kW of panel in midsummer and about 21.9 kW in midwinter, because the northeast delivers roughly 5.6 peak sun hours a day at its best and 1.8 at its worst. That gap is what most solar calculators hide inside an annual average: the array that carries you through July can leave you short in December, which is the month the power is most likely to go out.
It is on your power bill. The US average is about 900 kWh a month.
Panels
Watts per panel
Covered 4 months. Short 8.
breaks evenfalls shortAt 900 kWh a month your house burns about 29,605 Wh a day. In Massachusetts, Jul delivers roughly 5.6 peak sun hours and Dec delivers about 1.8, which is why the same array can carry you through summer and leave you short in winter.
To cover all twelve
55 panels · 22,000 W
35 more than you have selected. The worst month sets the whole bar, which is why the last few months of coverage cost as much as the first several.
What that is, to buy
55 × 400 W · about 1257 sq ft
Plus a charge controller rated to at least 250 A, and somewhere to put the power.
Do you have somewhere to store it?
Good. The chart above assumes you can bank the daytime surplus and spend it overnight. Without that, the green months are only green while the sun is up.
The other half of the answer
Power you can make. Now see how long your family would last.
Provision Planner tracks your power alongside your water, food and heat, and turns all four into one number: days covered for the people in your house.
About 2 minutes.
What this assumes
- Peak sun hours are regional averages for Massachusetts, in the style of the NREL resource maps. They are good enough to tell you whether December works where you live, and no substitute for a site survey.
- A 25% derate for the inverter, wiring, heat, dust and a panel that is never perfectly aimed.
- Shade, roof pitch and which way the panels face will move this more than anything on this page. A north face in winter can halve it again.
Read this before you rely on it
Rooftop solar usually shuts off when the power goes out.
This surprises almost everyone who owns panels. A standard grid-tied system is required to shut itself down the moment the grid fails. It is called anti-islanding, and it exists so that your panels cannot push power back down a line that a utility crew is working on. It is a safety feature and it is not optional.
So on a bright afternoon in a blackout, a house with ten thousand dollars of panels on the roof sits in the dark alongside the neighbours. What changes that is storage plus an inverter that can island, which is to say a battery system and a transfer switch. Without those two things, solar is an electricity bill strategy, not a backup plan.
Before the next outage
Panels are one line in a much shorter list than people expect.
Provision Planner counts the power, water, food and heat already in your house and tells you how many days each one covers for the people living there, what runs out first, and what to buy next.
About 2 minutes. Nothing to install.
Grid-tied, off-grid, or both
Grid-tied sells your surplus back and needs no battery, and it goes dark in an outage. Off-grid never touches the utility, which means you carry every cloudy week yourself and you size for the worst month rather than the average one. Hybrid is grid-tied with a battery and an islanding inverter: the expensive option, and the only one of the three that keeps the lights on when the street does not. For a household thinking about outages rather than bills, hybrid is usually the honest answer, and a small off-grid setup for a fridge and a few circuits is usually the cheap one.
Why the last two months cost so much
Sizing solar is set by your worst month, not your average one. In the northeast the darkest month delivers roughly 32% of what the brightest one does, so an array that covers you from spring to autumn can need to be two or three times larger to carry December as well. That is the real decision hiding in this page: cover most of the year cheaply and accept a gap, or pay a lot more for the months when you would actually need it.
Sunlight by state
Provision Planner
See exactly where your household stands.
Power, water, food and heat, counted against the people who actually live in your house and turned into days covered, with what expires next and what to buy this month.
See how long my preps will lastAbout 2 minutes. Nothing to install.
Peak sun hours are regional averages in the style of the NREL resource maps, applied at state level with a 25% system derate. They tell you whether a month works where you live; they are not a site survey, and shade, roof pitch and orientation will move the answer more than anything on this page. Already own a battery? Work out how long it runs your fridge. Power out right now? The live outage map shows what is reported near you.