As a Software Engineer at Expand Energy, you play a crucial role in developing and maintaining the software systems that power our energy solutions. This position is integral not only to the technical foundation of our products but also to enhancing user experience and operational efficiency across the organization. You will work closely with cross-functional teams, including product management, operations, and data analysis, to create innovative software solutions that meet the evolving needs of the energy sector. The impact of your work extends beyond coding; you will be at the forefront of solving complex challenges that involve optimizing energy distribution and improving sustainability practices. You will contribute to products that are pivotal in transitioning to cleaner energy sources, making your role both significant and rewarding. This is an opportunity to influence strategic decisions and engage in projects that have real-world implications, positioning Expand Energy as a leader in the industry.
Initial Phone Screen
reportedFirst contact to evaluate candidate's background and fit for the role.
What to demonstrate
- First contact to evaluate candidate's background and fit for the role
- Depth in Behavioral Interviewing
How to prepare
- Be able to walk your CV end to end in two minutes, and say why this company specifically.
- Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.
In-Person Interviews
reportedMultiple interviews that may include technical assessments and behavioral evaluations.
What to demonstrate
- Multiple interviews that may include technical assessments and behavioral evaluations
- Depth in Behavioral Interviewing
How to prepare
- Answer aloud and timed: Describe your experience with Object-Oriented Design and its benefits.
- Answer aloud and timed: What are design patterns you are familiar with?
Technical Questions
reportedCandidates are asked technical questions to assess their skills and knowledge.
What to demonstrate
- Candidates are asked technical questions to assess their skills and knowledge
- Depth in Behavioral Interviewing
How to prepare
- Answer aloud and timed: How would you implement dependency injection in your projects?
- Answer aloud and timed: How would you approach optimizing a software application for better performance?
Case Studies
reportedDiscussion of case studies to evaluate problem-solving abilities and thought processes.
What to demonstrate
- Discussion of case studies to evaluate problem-solving abilities and thought processes
- Depth in Behavioral Interviewing
How to prepare
- Answer aloud and timed: Describe a challenging technical problem you faced and how you resolved it.
- Answer aloud and timed: If you were given a project with a tight deadline, how would you prioritize tasks?
Behavioral Evaluations
reportedAssessment of past experiences and collaboration skills within team dynamics.
What to demonstrate
- Assessment of past experiences and collaboration skills within team dynamics
- Depth in Behavioral Interviewing
How to prepare
- Prepare three examples from your own work, each with a decision you made and an outcome you can quantify.
- Re-read the description of the behavioral evaluations above and write down what you would ask to confirm before it.
PracHub editorial advice for the preparation topics above.
Understand the Industry
Familiarize yourself with current trends in energy technology and sustainability practices. This knowledge will enhance your conversations during the interview.
Practice Behavioral Questions
Prepare for scenario-based questions that assess your teamwork, problem-solving, and conflict resolution skills.
Engage with Your Interviewers
Be ready to ask insightful questions about the team dynamics and project priorities. This demonstrates your interest and engagement.
Showcase Your Projects
Be prepared to discuss past projects in detail, highlighting your contributions and the impact of your work.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Write a function to implement FizzBuzz. Explain your approach.
Write a function to implement FizzBuzz. Explain your approach.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Can you provide an example of a situation where you had to use recursion?
Can you provide an example of a situation where you had to use recursion?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Discuss the trade-offs between using an array versus a linked list.
Discuss the trade-offs between using an array versus a linked list.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Write the update path that detects a concurrent edit
resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.
Approach
- One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
- Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
- State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
- Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.
Follow-up
- A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
- Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?
Explain why the owner filter ignores the listing index
The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.
Approach
- Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
- For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
- Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
- Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.
Follow-up
- 90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
- A dashboard runs this for 40 owners in one page load. What changes about the design?
What is.NET, and how is it relevant to your work?
What is.NET, and how is it relevant to your work?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Can you explain the Model-View-Controller (MVC) pattern?
Can you explain the Model-View-Controller (MVC) pattern?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What are design patterns you are familiar with?
What are design patterns you are familiar with?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How would you implement dependency injection in your projects?
How would you implement dependency injection in your projects?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How would you approach optimizing a software application for better performance?
How would you approach optimizing a software application for better performance?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Describe a challenging technical problem you faced and how you resolved it.
Describe a challenging technical problem you faced and how you resolved it.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
If you were given a project with a tight deadline, how would you prioritize tasks?
If you were given a project with a tight deadline, how would you prioritize tasks?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How would you architect a system for real-time data processing?
How would you architect a system for real-time data processing?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
What considerations do you take into account when designing APIs?
What considerations do you take into account when designing APIs?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Can you explain the importance of microservices in modern software development?
Can you explain the importance of microservices in modern software development?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Every query on one table stalls for forty seconds mid-deploy
During a release on PostgreSQL, every query touching resource times out for about 40 seconds and then recovers with no intervention. The release ran one migration, ALTER TABLE resource ADD COLUMN archived_reason TEXT, and the migration log shows it completing in 6 ms. Unrelated tables showed no change in error rate. Explain how a 6 ms statement caused a 40-second stall, give the ordered checks you would run on a live system to confirm it, and give the migration procedure that prevents a repeat.
Approach
- Separate the statement's duration from the lock's duration. ADD COLUMN with no default is a catalogue-only change and genuinely runs in milliseconds, but it requires ACCESS EXCLUSIVE, and it cannot acquire that until every transaction already touching the table has finished.
- Account for the queueing, which is the part that surprises people. A lock request that is waiting blocks later requests for conflicting modes behind it rather than letting them overtake, so one long-open transaction holds the DDL and the DDL holds all the traffic. The stall length is set by the longest open transaction, not by the size of the change.
- Confirm on a live system in this order: pg_stat_activity for that table ordered by xact_start, looking for the oldest transaction and specifically for state = idle in transaction; then pg_locks where granted = false to find the waiter; then join them on pid to name blocker and blocked. pg_blocking_pids() does that join for you and is the fastest single call.
- Prevent rather than merely time it better. Set lock_timeout to a second or two on the migration session so the DDL abandons the queue after a bounded wait and is retried, instead of holding it for as long as the oldest transaction lives. Be exact about what that buys: queries arriving during the wait still queue behind the pending ACCESS EXCLUSIVE request, so each attempt costs them up to one lock_timeout of added latency. The outage goes from 40 seconds to about one second per attempt, not to zero. Also run migrations away from deploy-time peaks, and put a statement timeout and an idle-in-transaction timeout on the analytics role that opens the long transactions.
Follow-up
- The same release also wants NOT NULL on that column. What is the sequence that gets there without a long lock?
- Your lock_timeout retry fails ten times in a row because the analytics transaction is always open. What do you change?
Built from the rounds and topics Expand Energy candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Expand Energy loop
- Write out the reported sequence: Initial Phone Screen, In-Person Interviews, Technical Questions, Case Studies, Behavioral Evaluations.
- For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.
Deliverable: A one-page map of the 5 reported rounds, with the weakest marked.
02Work Behavioral Interviewing
- Spend the session on Behavioral Interviewing, which Expand Energy candidates report being tested on.
- Write one worked example in Behavioral Interviewing and time yourself on it.
Deliverable: One timed worked example in Behavioral Interviewing.
03Work Object-Oriented Design (OOD)
- Spend the session on Object-Oriented Design (OOD), which Expand Energy candidates report being tested on.
- Write one worked example in Object-Oriented Design (OOD) and time yourself on it.
Deliverable: One timed worked example in Object-Oriented Design (OOD).
04Work Dependency Injection
- Spend the session on Dependency Injection, which Expand Energy candidates report being tested on.
- Write one worked example in Dependency Injection and time yourself on it.
Deliverable: One timed worked example in Dependency Injection.
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: What is.NET, and how is it relevant to your work?
- Answer aloud, timed: Can you explain the Model-View-Controller (MVC) pattern?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: Problem-Solving / Case Studies
- Answer aloud, timed: How would you approach optimizing a software application for better performance?
- Answer aloud, timed: Describe a challenging technical problem you faced and how you resolved it.
Deliverable: Spoken answers to 2 reported Problem-Solving / Case Studies question(s), under time.
07Answer out loud: Behavioral / Leadership
- Answer aloud, timed: Describe a time when you had to work with a difficult colleague. How did you handle it?
- Answer aloud, timed: What motivates you as a software engineer, and how do you maintain your passion for technology?
Deliverable: Spoken answers to 2 reported Behavioral / Leadership question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Describe your experience with Object-Oriented Design and its benefits.
Describe your experience with Object-Oriented Design and its benefits.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Describe a time when you had to work with a difficult colleague. How did you handle it?
Describe a time when you had to work with a difficult colleague. How did you handle it?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
What motivates you as a software engineer, and how do you maintain your passion for technology?
What motivates you as a software engineer, and how do you maintain your passion for technology?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Share an example of a project where you took the lead. What was the outcome?
Share an example of a project where you took the lead. What was the outcome?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
- 01
Describe your experience with Object-Oriented Design and its benefits.
- 02
Describe a time when you had to work with a difficult colleague. How did you handle it?
- 03
What motivates you as a software engineer, and how do you maintain your passion for technology?
- 04
Share an example of a project where you took the lead. What was the outcome?
How difficult are the interviews, and how much preparation time should I expect?
The interviews are generally considered to be of average difficulty. A preparation period of 2-4 weeks is typical for candidates to review technical concepts and practice behavioral questions.
Expand Energy Software Engineer candidate reports ↗What differentiates successful candidates?
Successful candidates demonstrate a strong alignment with Expand Energy's values, showcase technical expertise, and exhibit clear communication skills.
Expand Energy Software Engineer candidate reports ↗What is the company culture like at Expand Energy?
The culture at Expand Energy is collaborative and innovative, with a strong focus on sustainability and teamwork. Employees are encouraged to share ideas and contribute to projects that align with the company’s mission.
Expand Energy Software Engineer candidate reports ↗What is the typical timeline from initial screen to offer?
The entire interview process can take anywhere from 3 to 6 weeks, depending on scheduling and the specific teams involved.
Expand Energy Software Engineer candidate reports ↗What topics does Expand Energy test in interviews?
Expand Energy interviews most often cover Behavioral Interviewing, Communication Skills, Data Warehousing Concepts, Problem Solving, and Financial Analysis. The exact emphasis depends on the specific role you apply for.
Expand Energy Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.
- 01Expand Energy Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
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